Clinical Evaluation of Horizontal Pediatric Strabismus and the Management Challenges

*Lawan Abdu*

## **Abstract**

 Pediatric strabismus is not uncommon. Poor knowledge and religious and cultural practices result in inattention to the child's need and stigmatization. Horizontal strabismus consisting of esotropia and exotropia constitutes the common types presenting. Childhood ocular deviations are associated with uncorrected refractive errors, diseases causing obstruction of the visual axis such as cataract, and intra ocular tumors commonly retinoblastoma. In parts of the developing world, there is poor documentation and recollection of medical events at family and community levels. Squint in a child is not a painful dramatic condition that can prompt quick action from the parents or caregiver. There is generalized inequity in access to health care. Pediatric ophthalmic services are at best in developmental stage, and purpose design service centers are quite few. Neglect of the causes and timely treatment of amblyopia can retard child's development resulting in dependency and aggravation of poverty circle. A comprehensive approach to management of childhood eye diseases including strabismus is desirable in the low income developing countries. Provision of health insurance as a citizen's right will reduce most of the health challenges.

**Keywords:** horizontal, strabismus, challenges, management, low income

## **1. Introduction**

 Strabismus is defined as deviation from normal position of alignment resulting in the eyes pointing in different directions [1]. From the historical perspective existed, the concept that there is spasm of the bodies which move the eye balls and there is oblique tendency of the muscles [2]. Ocular movement is controlled by six muscles comprising the four recti muscles (superior, inferior, medial, and lateral) which arises from the annulus of Zinn [3]—a fibrous structure which is fused to the optic nerve and foramen and the two oblique muscles [4]. The medial rectus takes a course close to the medial orbital wall, while the lateral rectus course is close to the lateral orbital wall before they reach their respective points of insertion. Primary action of medial rectus is adduction and lateral rectus abduction. The two are called the horizontal recti muscles. The superior and inferior recti muscles are called vertical muscles. The superior rectus muscle ran a course anteriorly above the eye ball, over the insertion of the superior oblique forming an angle of 23° with the visual axis. The primary function of superior rectus is

 elevation, secondary action is intorsion, and tertiary action is abduction. The inferior rectus passes anteriorly above the orbital floor and below the eye ball to which it is inserted at 23° to the visual axis. In the primary position, the main action of inferior rectus is depression, secondary action is extortion, and tertiary action is adduction. Superior oblique arises from the orbital apex above the annulus of Zinn, courses anteriorly close to the superior medial orbital wall. It becomes tendinous as it passes through the trochlear—a cartilage-like structure attached to the superior nasal orbital part of the frontal bone. The muscle tendon turns backward and inserted in the posterior medial quadrant of the eye ball under the superior rectus muscle forming a 51° angle with the visual axis [5]. In primary position, the action of superior oblique is intorsion, secondary action is depression, and tertiary action is abduction. Inferior oblique muscle originates from the periosteum of the maxillary bone behind the orbital rim and lateral to the entrance of the lacrimal fossa. It then passes laterally, superiorly, and posteriorly below the inferior rectus, under the lateral rectus and inserted into the posterior lateral quadrant of the eye ball. In the primary position, its primary action is extortion, secondary action is elevation, and tertiary action is abduction. The spiral of Tillaux describes the distance in millimeters from limbus to the insertion point of the four recti muscle: superior rectus (7.7 mm), lateral (96.9 mm), inferior (6.5 mm), and medial (5.5 mm). The lateral rectus is supplied by the abducent nerve, superior oblique by trochlear nerve, and the oculomotor nerve supplies all the rest (superior/medial/ inferior recti and inferior oblique). Extra ocular muscles are supplied by muscular branches of the ophthalmic artery. The larger medial muscular branch supplies the inferior/medial recti and inferior oblique, while the lateral muscular branch supplies the lateral/superior recti, superior oblique, and the levator palpebrae superioris muscle. Eye movements can be uniocular (ductions) or binocular (versions). Movement of the eye nasally is called adduction, temporally abduction, downward infraduction, and upward supraduction. Nasal rotation of the superior corneal meridian is called intorsion or incycloduction, while temporal rotation is termed extortion or excycloduction. An agonist is the primary muscle involved in moving the eye in a given direction. A synergist is the muscle in the same eye that acts with the agonist to produce a given movement. An antagonist is a muscle in the same eye that produces action opposite that of the agonist. According to Sherrington's law [6] of reciprocal innervation, increased innervation and contraction of a given extra ocular muscle is associated with decrease innervation and contraction of its antagonist. Conjugate binocular eye movements which ensure the eyes move in the same direction are called versions; disconjugate movements which make the eyes move in opposite directions are called vergences. By this notation, right gaze is dextroversion, left levoversion, upward sursumversion, and downward deorsumversion. Rotating the eyes such that such that the superior pole of both corneal meridians is turned to the right is called dextrocycloversion, when to the left levocycloversion. Yoke muscles are two muscles in separate eyes that are prime movers for any given position [7]. All the muscles have respective partners that they work simultaneously to produce binocular movement. According to Hering's law [8] of motor correspondence, equal and simultaneous innervation goes to yoke muscles to produce binocular movement in desired direction. Convergence arises when the two eyes move nasally from any initial position, and divergence is when they move temporally from relative initial position. Nasal rotation of the vertical pole of both corneal meridians is incyclovergence, while temporal rotation is excyclovergence. The relative position of the eyes at rest is that of divergence, hence tonic convergence maintains the position of the eyes during wake period. The synkinetic near reflex consists of accommodation, convergence, and miosis. There is consistent increase in accommodative convergence (AC) for each diopter

#### *Clinical Evaluation of Horizontal Pediatric Strabismus and the Management Challenges DOI: http://dx.doi.org/10.5772/intechopen.82547*

 of accommodation (A) [9]. When the accommodative convergence/accommodation (AC/A) ratio is high, excess convergence could result in esotropia when viewing near objects. Voluntary convergence can consciously be induced as part of the near synkinesis. Proximal convergence can be produced based on the psychological awareness of nearness of the object. Bitemporal retinal image disparity stimulates fusional convergence which insures the image of an object is projected on corresponding retinal points. Conversely, fusional divergence could occur as an optomotor reflex to align the eyes so that images fall on corresponding retinal points. Retina stimulation is perceived as light coming from a specific visual direction in space. Retinal correspondence is said to occur when light stimulates two points in both eyes which share a common visual direction. Corresponding retinal points share a common relationship with the fovea in both eyes, and such relationship is described as normal retinal correspondence (NRC) [10]. Anomalous retinal correspondence (ARC) occurs when two points in the retina of both eyes do not share similar relationship with the fovea. Normal fovea and extra foveal NRC result in binocular single vision. Similarly, points in both eyes with similar fixation/orientation appear singly so far as they fall on a point that passes through the optical center of each eye and fixation point (Vieth-Muller circle). The process of cortical image unification of objects that fall on corresponding retinal points is called fusion. Retinal images are fused in the cortex when they are similar in shape, size, and clarity. Fusion has sensory, motor, and stereopsis components. The sensory part deals with relationship of the retinal points in the two eyes, while motor fusion is vergence movement that ensures retinal image fall and is maintained on corresponding points. Stereopsis is said to occur when disparity in image size is big enough not to permit cortical fusion but not enough to cause diplopia. Stereopsis is a binocular perception of depth that adds to quality of vision and three dimensions.

## **2. Visual assessment in children**

 The techniques of assessing vision in children are tailored to fit the patient's age. It is often challenging and tasking irrespective of the age and requires gaining the trust of the child and the parent. The clinic environment should to some extent fit ideal setting to do so. This is frequently not available in some low income countries as few pediatric ophthalmic clinics are purposefully designed. Frequently, the same make soft clinic area is used for all purposes. The CSM (Central, Steady, and Maintained) criterion can be used for preverbal children. This involves determining the location of the corneal reflex which should be central in a normal child while mono-fixating with the contra lateral eye occluded. The location of the reflex should be central in both eyes as uncentral position is abnormal. The fixation should be steadily (S) maintained with the light in stationary position and when moved in other directions. Fixation should be (M) maintained in both eyes, and failure in one eye may indicate the presence of amblyopia. A child would elicit avoidance movement when the seeing eye is occluded and can be indifferent when occlusion involves an amblyopic eye. Illiterate "E" chart "game" can be used to assess vision in preschool children. HOTV test can be used as it employs matching of objects placed on the distant display and a hand held version that enables the child to indicate similar images. Children of school age can have vision tested with Snellen's chart which has the drawback of crowding of letters that make its use limited in those with amblyopia. Various picture charts are developed showing objects that are commonly seen in the locality instead of trains and busses that may be unfamiliar to children in the developing world.

## **2.1 Light reflex test**

Light reflex tests consist of the Hirschberg and Karimsky. The Hirschberg test measures the extent of decentration of the corneal reflex, and 1 mm of decentration is equivalent to 7° or 15 prism diopters. When the light reflex is at pupillary margin, there is (15°), mid iris is (30°), and at limbus (45°) of deviation, respectively. The Krimsky test uses corneal reflex from both eyes and a prism is placed before the fixating eye and adjusted till alignment is achieved. The test is ideally performed at near gaze position. To a lesser extent, Bruckner's test [11] can be used to detect (without quantifying) the presence of a squint. Light from an ophthalmoscope is shone directly into both eyes, and the reflection from the deviating eye is brighter than in the fixating eye. The light reflex tests can be affected by angle kappa (the angle between the anatomical and visual axis of the eye). In normal situations, the fovea is usually temporal to the pupillary center making the corneal reflex slightly nasal (the resulting positive angle Kappa that appears like an exodeviation), and this can affect the light reflex test though it has no impact on cover tests.

#### **2.2 Cover tests**

Cover tests are employed to assess misalignment. Monoocular test such as cover-uncover is used to distinguish heterophoria from heterotropia. When one eye is covered, the uncovered eye moves to take up aligned position, and the movement is reversed when the cover is removed. The test is based on the principle that breaking up of binocular vision during the test leads to adjustment in alignment in those with phorias. In the presence of manifest squint, the test is started with a deviated eye, and at the end, it is noted that the deviation is maintained by the index or contra lateral eye. Alternate cover test is done to determine and quantify the extent of deviation whether latent or manifest by the placement of a prism is in front of the eye. The base of the prism is placed opposite the direction of the deviation. The amount of deviation is measured with prisms as the cover is moved from one eye to another till alignment is achieved. Simultaneous prism and cover test can be employed to determine extend of manifest deviation when both eyes are uncovered [12].

#### **2.3 Dissimilar image test**

Dissimilar image tests involve making the images appear dissimilar in both eyes. The principle is that in the normal eye, the image falls on the fovea, while in the deviating eye, it falls elsewhere in the retina. A patient sees the images appearing somewhat homonymously in esotropia and crossed in exotropia. The Maddox rod consists of parallel cylinders that convert a point source of light into a straight line that is at right angle to the arranged cylinders. In normal situation of orthophoria, a person looking at a distant pointed light source with the rod placed before one eye would see a straight line (with the eye wearing the Maddox rod) and a point source of light (with the other eye). The light spot will appear to be at the center of the line. Maddox rod can be used to measure horizontal and vertical deviations. The relationship of the line relative to the spot of light determines the type of deviation. To quantify the deviation, a prism can be placed before the deviating eye till the state or orthophoria is achieved with the spot of light superimposed on the middle of the line. Cyclo deviations can also be measured with double Maddox road [13].

*Clinical Evaluation of Horizontal Pediatric Strabismus and the Management Challenges DOI: http://dx.doi.org/10.5772/intechopen.82547* 

#### **2.4 Dissimilar target test**

 This test involves making the eyes to be exposed to different targets at the same time and measuring the extent of deviation with one eye fixating then the other. Patients with esotropia will have crossed fixation and exotropes homonymous diplopia. The Lancaster red-green test consists of red-green goggles that can be reversed, red/green slit projector, and a ruled screen with many small squares. With red lens on the right, the patient is requested to superimpose the green slit, and the goggles are reversed to run the test again. This test is done in patients with diplopia from incomitant squint and may not apply to children who rarely present with this type. The mayor amblyoscope is calibrated to measure the extent of vertical, horizontal, and torsional deviations when the patient look through and superimpose dissimilar targets.

#### **2.5 Historical perspective**

 Children require an adult who may be a parent, sibling, or other relations to accompany them to the hospital. The mother is the person closest to the child and in better position to offer more reliable information on the ocular condition of the patient. However due to religious and socio cultural practices, it is not unusual to see grandmothers and other relations who have minimal knowledge are made to accompany the children to the clinic. In vast rural communities, there is virtually no documentation of medical illness and recollection of what happens in the past is quite vague. Coverage of antenatal care by orthodox methods is largely poor with cost, distance, and attitude of healthcare providers constituting a barrier. Squint and other ocular conditions that are not associated with dramatic pain or debility may not attract attention warranting prompt medical care. There is varied individual and community perception of squint based on cultural and religious beliefs resulting in poor awareness of the cause and availability of treatment often leading to social stigmatization [14]. There is poor perception of strabismus in community that could partly be due to poor knowledge of the condition [15]. Deviating eye may be considered as an act of creation by God. In some communities, there is taboo and superstition attached to it resulting in stigmatization and ostracism. In the United States, an estimated 4% of children have strabismus [1]. In sub-Saharan Africa, population prevalence statistics are at best scarce, and the exact extent is likely to be known. A study involving thousands of elementary school children showed that esotropia and exotropia occurred in 0.14% of the population [16]. The prevalence varies between countries and the type of study conducted ranging from 0 to 2% in Ghana [17], 1.1% in Ethiopia [18], 0.5% in Tanzania [19], and 1.22% in Cameroons [20]. As much as is realizable, it is important to determine the onset, description of the type, laterality, variation with time, and duration of the deviation. Key knowledge includes determining whether it affects one eye or alternates. Any associated ocular features such as leucocoria to suggest secondary causes like cataract and retinoblastoma [21]. The clinician should obtain the history of previous spectacle prescriptions or ocular surgery performed. There may be a positive family history of similar symptoms and where available photographs could provide further clues in the patient's evaluation.

#### **2.6 Definition and classification**

Strabismus is a Greek term which simply means ocular misalignment. Manifest deviations that are detectable when both eyes are opened are called tropia and

may present as a constant or intermittent deviation involving one eye or both eyes. Latent deviations are termed phorias and detectable only when one eye is covered so that the vision is monocular. In phorias, the misalignment is minor and corrected by cortical adjustment of the extra ocular muscles. Deviations are said to be comitant when they are the same in amplitude and degree of misalignment in all directions of gaze. Incomitant deviations vary in degree and amplitude with direction of gaze. Horizontal deviations could be nasal termed as esotropia or temporal exotropia. Other less common deviations in childhood include vertical (hyper deviation or hypo deviation) and torsional (incyclodeviation or excyclodeviation). Deviation could also manifest as a combination of the above. Pediatric strabismus can be infantile or acquired. Risk factors for infantile strabismus include a positive family history among first and second degree relatives, maternal alcohol ingestion in pregnancy, maternal smoking [22], genetic disorders (such as Crouzon's and Down's syndromes), prematurity and or, low birth weight, congenital ocular defects, and cerebral palsy. Causes of acquired strabismus include refractive error (particularly hyperopia), head injury that could include birth trauma, and neurological conditions (such as cranial nerve palsy involving nerves 3, 4, 6, and spina bifida).

## **2.7 Infantile esotropia**

 Esodeviations can be described as a latent or manifest convergent ocular misalignment. The latent type (esophoria) is negated by the fusional mechanism of the brain. Intermittent esotropia is the type that is to some extent controlled by fusional mechanism, and deviations manifest under conditions of stress or fatigue when the fusional mechanism becomes obviated. Esotropia noted within the first 6 months of life is termed infantile (or congenital) and in most instances is present in an otherwise normal child. Although the etiology is unclear, Worth's concept postulates a deficiency in cortical in the brain, while Chavasse postulates a possible mechanical cause [23], and thus cure can be achieved by eliminating the deviation in infancy. In developed countries where health documentation is the norm, a positive family is often present, while in sub Saharan Africa, such information is rarely obtained. Children with esotropia elicit alternate fixation, those with large angle deviation uses the adducted eye to fixate on objects in the contra lateral visual field (crossed fixation). The deviation is large and often greater than 30 prism diopters. Quite frequently the patients tend to have demonstrable inferior oblique overreaction in over 50% [24].

### *2.7.1 Management of infantile esotropia*

 The assessment of degree and extend of deviation are important in addition to cycloplegic fundal examination to rule out other secondary causes of misalignment such as a cataract or retinoblastoma. There may be a need to examine and refract the child under anesthesia. This warrants clinical examination by a pediatrician in addition to laboratory tests such as electrolytes and urea, and hemogram and hemoglobin electrophoresis as sickle cell disorder is frequent in SSA. Cycloplegic refraction often reveals a hyperopia of not more than two diopters, though in some instances, patients may be myopic or have astigmatism. It is necessary to correct any detected refractive error fully and promptly. In most instances, surgical correction is required preferably within the first 24 months of life. Early surgery is aimed at reducing deviation as much as could be achieved and obtaining orthotropia. This would enable better alignment and achieving fusion [25], characterized by favorable cosmetic appearance, improved peripheral fusion, and central suppression.

*Clinical Evaluation of Horizontal Pediatric Strabismus and the Management Challenges DOI: http://dx.doi.org/10.5772/intechopen.82547* 

### **2.8 Acquired esotropia**

This includes accommodative [26], nonaccommodative, and nystagmus associated esotropia. Accommodative esotropia presents between second and third year of life and is associated with activation of the accommodation reflex. It is characteristically intermittent at onset and later becomes constant and there may be associated amblyopia. In aged children, diplopia may be elicited before the onset of facultative suppressive scotoma. This type of esotropia has a hereditary component and could be precipitated by illness or trauma. Refractive accommodative esotropia is associated with hypermetropia, accommodative convergence, and insufficient fusional divergence. The esotropia is equal for both far and near fixation. Treatment involves cycloplegic refraction and dispensing of full correction to ensure good outcome [27]. Parental counseling to ensure constant use of spectacle correction is important in achieving compliance. Children who manifest non-accommodative component or fail to regain fusion with glasses may require surgery.

### **2.9 Accommodative esotropia**

The accommodative synkinetic reflex consists of accommodative esotropia, convergence, and miosis. The age of onset range ages between 6 months and 7 years; it is intermittent at onset, and later becomes constant; symptoms may be precipitated by trauma or illness; and often there is associated amblyopia and is of hereditary nature.

#### **2.10 Refractive accommodative esotropia**

This type of esotropia is associated with uncorrected hyperopia, accommodative convergence, and fusional divergence insufficiency. Accommodation is stimulated due to existing hyperopia to obtain better retinal focus. Accommodative esotropia accounted for 18% of 7000 school children is examined [16]. Esotropia could manifest early [28], and the extent of deviation is the same for far and near. The amount of hyperopia is about +4 diopters, and the degree of deviation is in the range of 30–40 prism diopters. The aim is to do a cycloplegic refraction and offer full correction to be worn at all times. Counseling of the parents is important as treatment may not completely eliminate the deviation. Indication for surgical correction includes failure to attain fusion and presence of nonaccommodative component of the deviation.

#### **2.11 Esotropia with high accommodative convergence/accommodative ratio**

This type of esotropia can be refractive or nonrefractive. In hyperopia, excess convergence can result with accommodation for near objects. The degree of esotropia is more for near than distance vision. There is a detectable difference in extent with varied distance of accommodation. Nonrefractive accommodative esotropia can occur with normal levels of hyperopia, astigmatism, and myopia. Refractive esotropia with high AC/A can occur with hyperopia, and when associated with myopia or emmetropia, it is described as nonrefractive accommodative esotropia. Partially, accommodative esotropia could arise from decompensation of fully accommodative esotropia or an esotropia that develop subsequent accommodative component.

#### **2.12 Management of esotropia with high AC/A**

Bifocals are prescribed for treatment of nonrefractive accommodative esotropia. Flat top executive types of bifocal are preferred with power of +3.00 diopter sphere. The caregiver needs to be advised on consistent use and patient monitored

 to achieve restoration of fusion and stereopsis. The goal is to attain fusion with less than 10 prism diopters of residual esotropia for near vision with patient wearing the correction. Relative high AC/A has been observed even with bifocals use over time period [29]. Other measures include use of long-acting anticholinesterases such as 0.125% ecothiopate iodide drops. The treatment should commence with maximum dose and tailored based on response. Anticholinesterases have complications arising from depletion of pseudocholinesterases leading to increased susceptibility to depolarizing muscle blockers such as succinylcholine. Surgery can be performed to correct the esotropia instead of the earlier listed modalities. The normal trend with hyperopia is that it increases about the age of 5–7 years. Partially, accommodative esotropia is treated with full cycloplegic refraction and prescription of full correction. There is often a need for concurrent treatment of associated amblyopia.

## **2.13 Nonaccommodative acquired esotropia**

 This type of esotropia presents between the ages of 1 and 5 years. It may acutely present the following disruption of binocular vision from amblyopia treatment or after ocular injury. There may be associated underlying neurological disease or malignancy [30]. When clinical neurological assessment is normal, binocular vision is restored with prisms or surgery.

## **2.14 Sensory deprivation esotropia**

This arises from occlusion of the visual axis from other ocular condition such as cataract [31], corneal opacity, glaucoma [32], and retinoblastoma [21]. This requires prompt removal of the underline cause wherever possible and treatment of any resulting amblyopia.

## **2.15 Surgical esotropia**

Surgical esotropia is also referred to as consecutive esotropia. This form of esotropia arises as a result of surgical correction of exotropia (perhaps due to overcorrection). The deviation may improve spontaneously and when it this doesn't happen, prisms are used to correct it. The presence of abduction deficiency should raise suspicion of a slipped lateral rectus muscle [33], and patient may require transposition procedure.

#### **2.16 Near synkinetic reflex spasm**

The near reflex has accommodative, convergence, and miosis components. There may be a manifest cycle of esotropia and orthotropia. The cause may not necessarily be organic and could be due to psychological factors. The patient has no demonstrable abduction paralysis. Cycloplegic refraction and prompt correction lead to improvement, and in the presence of hyperopia, the patient may require bifocal correction.

#### **2.17 Incomitant esotropia**

This deviation varies in severity with the position of gaze and is due to abducent nerve paralysis. Cross fixation can be mistaken for this type of esotropia. In the absence of strabismic amblyopia, the vision in both eyes is comparably normal. Sixth nerve paralysis is rare at infancy, and its presence in childhood should raise the suspicion of an intracranial mass. Therefore, full neurological screening including brain CT scan and MRI is needed. Infectious causes such as meningococcal and tuberculous meningitis are more common causes in SSA. Treatment involves

correction of any associated hyperopia, patch therapy for amblyopia, and use of membrane (Fresnel-press on) prism. Those with underlying medical condition should be treated in collaboration with respective specialists.

## **2.18 Exotropia**

Divergent squints can be latent (exophoria-negated by the fusional mechanism) or manifest (exotropia). Exophorias can be demonstrated by breaking the fusional mechanism (uniocular occlusion as in cover test). Exophoria is often small, and there may not be a need for treatment unless an exotropia develops.

## **2.19 Intermittent exotropia**

 This is the most common type of exodeviation and can be latent or intermittent and usually present before the age of 5 years. The deviation is associated with fatigue, stress, and periods of relative inattention. Initially, the deviation tends to be greater for distance (intermittent distant exotropia—IDEX) than near, and later, the extent is similar irrespective of relative object's position. The disparity could be due to high AC/A ratio or tenacious proximal fusion which arises from slow relaxation of the fusional mechanism, thus limiting conversion of exophoria to exotropia. Progression to constant exotropia is common though there is usually no associated amblyopia. Management involves assessment using the Newcastle control score [34]. Good control is defined when exotropia manifests only with cover test with resumption of vision without blink/refixation. Fair control is defined when exotropia manifests after cover test and fusion resumes with blinking or refixation. Poor control is defined as spontaneous manifestation of exotropia and remaining for extended period. The degree of deviation is assessed at a distance using prism and cover test. Patients' with high AC/A will have less deviation with +3.00 diopters. Intermittent esotropia can be classified based on observed differences in prism and alternate cover tests for near and distance. In the basic type, the deviation is the same for distance and near. In divergence excess, the deviation is greater for distance than near, and convergence insufficiency is present when the deviation is greater for near than distance. Nonsurgical management involves providing appropriate refractive correction in patients with myopia, astigmatism, or hyperopia. Minus lenses of 2–4 diopter sphere can be used to stimulate accommodative convergence and delay surgery. Part time patching (4–6 h daily) and alternate day patching can produce some improvement which can be used before surgery. Some clinicians advocate orthoptic treatment consisting of training for diplopia awareness and fusional convergence. Base in can be used as short-term treatment as their long-term use is associated with reduced fusional convergence amplitude. Surgery should be considered when deviation is present more than half of the time and consists of bilateral recession of lateral rectus muscle, or recession of one lateral rectus with ipsilateral medial rectus resection. Bilateral lateral rectus recession could result in postsurgical (consecutive) esotropia usually of less than 15 prism diopters and may require treatment with press-on prism if persistent beyond 4 weeks of postoperative period. Without evidence of slipped muscle, observation over a few months of period is advocated as spontaneous resolution is common. A review has shown that despite the absence of natural history data of IDEX, unilateral surgery appears to be more effective than bilateral surgery [35].

## **2.20 Other types of exotropia**

This includes constant exotropia that could arise from decompensated intermittent or sensory manifest exotropia and can be treated with similar surgical

 procedure as intermittent exotropia. Infantile exotropia typically present within the first 6 months of life is usually associated with neurological anomalies. Sensory exotropia could arise from disease causing uniocular visual deprivation such as cataract, corneal opacity, gross retinal anomalies, and optic nerve atrophy. Convergence insufficiency esotropia is not common in children.

## **2.21 Amblyopia**

 Amblyopia is defined as the reduction of best-corrected visual acuity of one or both eyes that cannot be attributed exclusively to a structural abnormality of the eye. It develops during childhood and results in the interruption of normal cortical visual pathway development and is characterized by a difference in best-corrected visual acuity of two or more lines between the eyes [36]. A study in Asia, Latin America, and Africa indicated a prevalence of 1.52 per 1000 children [37]. In amblyopia, there is reduced visual acuity and contrast sensitivity due to the abnormal processes in the visual cortex [38]. The causes of amblyopia include uncorrected refractive error, strabismus, and obstruction of the visual axis. There is the traditional view that treatment should commence before the age of 8–9 years, and a study suggests that the treatment can extend into early adulthood as the ability of the brain to adjust (plasticity) extends to such period [39]. Treatment involves correction of refractive errors with guidance on consistent use of the prescribed glasses. Children with conditions giving rise to occlusion of the visual axis (cataract, corneal opacity) should have the cause removed without delay. The patients with strabismus should be accessed, and appropriate treatment measures should be instituted. Patching therapy is indicated to encourage the weaker eye take up fixation and realign with the visual cortex. There are various regimes based on hours per day or, alternate days. It is of importance to monitor the child by both clinician and caregiver to assess progress. Penalization can be employed as alternative to patching, and it involves the use of atropine eye drops to blur images in the better eye, thus encouraging the child to use the so-called weaker eye [40].

## **3. Conclusion**

Childhood strabismus strabismus, presenting unit challenges, is evaluation and management. There is poor recollection of medical history and often children are not accompanied to the hospital by their biological parents. Poor knowledge results in misconception and stigmatization of children with squint. Religious and cultural practices coupled with inequity in access to health care could result in amblyopia, thus retarding the child's development.

## **Acknowledgements**

Appreciation to the management of Bayero University Kano—Nigeria for providing an enabling academic environment.

## **Conflict of interest**

None.

*Clinical Evaluation of Horizontal Pediatric Strabismus and the Management Challenges DOI: http://dx.doi.org/10.5772/intechopen.82547* 

## **Author details**

Lawan Abdu Department of Ophthalmology, Faculty of Clinical Sciences, College of Health Sciences, Bayero University Kano, Nigeria

\*Address all correspondence to: lawal1966@yahoo.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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[15] Bodunde O, Runsewe-Abiodun T, Alabi A, et al. Awareness and perception of strabismus among the youths and women of child-bearing age in a local government in South Western Nigeria: A qualitative study. International Quarterly of Community Health Education. 22 Jul 2016. DOI: 10.1177/0272684X16660025

[16] Azonobi IR, Olatunji FO, Addo J. Prevalence and pattern of strabismus in Ilorin. West African Journal of Medicine. 2009;**28**(4):253-256

[17] Ntim-Amponsah CT, Ofosu-Amaah S. Prevalence of refractive error and other eye diseases in schoolchildren in the Greater Accra region of Ghana. Journal of Pediatric Ophthalmology and Strabismus. 2007;**44**(5):294-297

[18] Mehari ZA, Yimer AW. Prevalence of refractive errors among schoolchildren in rural Central Ethiopia. Clinical and Experimental Optometry. 2013;**96**(1):65-69

[19] Wedner SH1, Ross DA, Balira R, Kaji L, Foster A. Prevalence of eye diseases in primary school children in a rural area of Tanzania. The British Journal of Ophthalmology. 2000;**84**(11):1291-1297

*Clinical Evaluation of Horizontal Pediatric Strabismus and the Management Challenges DOI: http://dx.doi.org/10.5772/intechopen.82547* 

[20] Ebana MC, Bella-Hiag AL, Epesse M. Strabismus in Cameroon. Journal Français D'ophtalmologie. 1996;**19**(11):705-709

 [21] Lawan A, Sani M. Clinicopathological pattern and management of retinoblastoma in Kano-Nigeria. Annals of African Medicine. 2011;**10**(3):214-219

 [22] Susan C, Rohit V, Kristina T. The joint writing committee for the multi-ethnic pediatric eye disease study and the Baltimore pediatric eye disease study groups. Ophthalmology. Nov;**118**(11):2251-2261

[23] Robert JB, George SE, Sprague EH. At the crossing: Pediatric ophthalmology and strabismus. In: Proceedings of the 52nd Annual Symposium of the New Orleans Academy of Ophthalmology; New Orleans, LA, USA. The Hague, Netherlands: Kugler Publications; 2004. pp. 99-110

[24] Eustis HS, Nussdorf JD. Inferior oblique overaction in infantile esotropia: Fundus extorsion as a predictive sign. Journal of Pediatric Ophthalmology and Strabismus. 1996;**33**(2):85-88

[25] Shirabe H, Mori Y, Dogru M, et al. Early surgery for infantile esotropia. British Journal of Ophthalmology. 2000;**84**:536-538

[26] Robert PR. Update on accommodative esotropia. Optometry. 2008;**79**(8):422-431

[27] Mulvihill A, MacCann A, Flitcroft I, et al. Outcome in refractive accommodative esotropia. The British Journal of Ophthalmology. 2000;**84**(7):746-749

[28] Davis KC, Cynthis WA, Evelyn AP, et al. Early onset refractive accommodative esotropia. JAAPOS. 1992;**2**(5):275-278

[29] Wook KK, Sung YK, Soolienah R, et al. The analysis of AC/A ratio in nonrefractive accommodative esotropia treated with bifocal glasses. Korean Journal of Ophthalmology. 2012;**26**(1):39-44

[30] Mohney BG. Acquired nonaccommodative esotropia in childhood. Journal of AAPOS. 2001;**5**(2):85-89

[31] Paul C. Childhood cataract in sub-Saharan Africa. Saudi Journal of Ophthalmology. 2012;**26**(1):3-6

[32] Lawan A. Primary congenital glaucoma in Kano, northern Nigeria. African Journal of Paediatric Surgery. 2007;**4**(2):75-78

[33] Lenart TD, Lambert SR. Slipped and lost extraocular muscles. Ophthalmology Clinics of North America. 2001;**14**(3):433-442

[34] Haggerty H, Richardson S, Hrisos S, et al. The Newcastle Control Score: A new method of grading the severity of intermittent distance exotropia. British Journal of Ophthalmology. 2004;**88**(2):233-235

[35] Sarah RH, Lawrence G. Interventions for intermittent exotropia. Cochrane Database of Systematic Reviews. 2013;**5**:CD003737

[36] https://www.aao.org/ disease-review/amblyopia-introduction

[37] Gilbert CE, Ellwein LB. Refractive Error Study in Children Study Group. Prevalence and causes of functional low vision in school-age children: Results from standardized population surveys in Asia, Africa, and Latin America. Investigative Ophthalmology & Visual Science. 2008;**49**(3):877-881

[38] Levi DM. Linking assumptions in amblyopia. Visual Neuroscience. 2013;**30**(5-6):277-287

[39] Levi DM. Visual processing in amblyopia: Human studies. Strabismus. 2006;**14**(1):11-19

[40] Osborne DC, Greenhalgh KM, Evans MJE, et al. Atropine penalization versus occlusion therapies for unilateral amblyopia after the critical period of visual development: A systematic review. Ophthalmology and Therapy. 2018;**7**(2):323-332

## **Chapter 6**

## Congenital Nasolacrimal Duct Obstruction and the Visual System

*Adnan Aslam Saleem* 

## **Abstract**

 Congenital nasolacrimal duct obstruction (CNLDO), previously considered a benign disease, affects 20% of the children globally. It is described by a collection of symptoms in which continuous epiphora and intermittent discharge are present in either one or both the eyes. CNLDO usually resolves in most healthy infants in the first few couple of months; however, it may persist for a number of years in some children. There has been a lot of recent deliberation on how a constant watery eye affects the visual development during the phase of emmetropization in children. A connection between CNLDO and anisometropia has been hypothesized. Multiple factors which include developmental and environmental aspects are thought to play a contributory role in the development of anisometropia by and large; particularly hypermetropic anisometropia, raising the chances of developing amblyopia in children with CNLDO. Published literature on CNLDO had shown inconclusive evidence on this anecdotal propinquity. This chapter discusses CNLDO; etiology, pathogenesis, treatment modalities, surgical intervention, and its role in inducing refractive errors; and its propensity to cause amblyopia.

**Keywords:** congenital nasolacrimal duct obstruction, anisometropia, refractive status, amblyopia

## **1. Introduction**

 Tears are words that need to be written (*Paulo Coelho*). Tears physiology and fluid dynamic are intricate and multifaceted. Tears are produced by the main and accessory lacrimal glands and drain medially into the puncta, then flow through the canaliculi to the lacrimal sac, and then through the nasolacrimal duct (NLD) into the nose. Contraction of the orbicularis muscles creates a pumping action that facilitates the flow of tears through the lacrimal system. Congenital nasolacrimal duct obstructions (CNLDO) are one of the most common cases seen in pediatric ophthalmology clinics. CNLDO occurs in 5–15% of full-term newborns [1]. CNLDO is characterized by epiphora and intermittent discharge. CNLDO remains the most common cause of epiphora in infants. It is usually unilateral or asymmetric and is largely due to a persistent membrane at the level of Hasner valve. The valve of Hasner is located at the distal end of the nasolacrimal duct where it enters the inferior meatus lateral to the inferior turbinate.

 The valve of Hasner obstruction occurs due to unfinished canalization, a process that begins in the 12th week of gestation and is completed by the 24th week. An incidence of 35–73% has been reported for imperforate NLDs in full-term infants,

 with a preponderance opening up spontaneously during the first couple of weeks of life [2]. The nasolacrimal duct normally canalizes from proximal to distal, so the distal portion is often last to open up. Therefore, premature infants conceivably have higher rates of CNLDO. However, because tear production does not take place almost near term, these infants mostly do not exhibit the symptoms of epiphora. Infants with CNLDO present with excessive tearing or mucoid discharge from the eyes due to blockage of the nasolacrimal duct system, which can result in maceration of the of the eyelid skin and local infections. On examination, there is an increased tear meniscus and there may be stickiness or crusting on the lashes. Secondary infection is common in CNLDO due to the stasis of lacrimal sac contents, proximity of the sinuses, and a rich lymphatic and vascular system within the submucosa of the lacrimal sac.

## **2. Initial assessment**

It is important to note that typically, CNLDO does not usually cause much discomfort to children. Affected infants are otherwise well and act normally despite the presence of noteworthy overflow of tears and mucopurulent discharge. If infants have photophobia or other signs of chronic irritation, they should be checked carefully for signs of glaucoma, keratopathy, or epiblepharon, i.e., other factors of pediatric epiphora must be ruled out. The absence of corneal and conjunctival abnormalities is an important factor in establishing a diagnosis of CNLDO. Other causes of epiphora such as acute conjunctivitis, congenital anomalies of the upper lacrimal drainage system (punctal or canalicular atresia or agenesis), entropion, and triachiasis also must be evaluated. The most important entity in the differential diagnosis of CNLDO/epiphora would be infantile glaucoma. NLDO may be confused with glaucoma by primary care physicians due to the presence of epiphora. It is important to check intraocular pressure, corneal diameters, and cup to disk ratio to rule out this condition.

It is recommended to do a fluorescein disappearance test (FDT) on all children with epiphora as it provides evidence to support a diagnosis of lacrimal outflow obstruction. Fluorescein 1% is instilled into each lower conjunctival fornix. The child sits on the parent's lap while the cobalt blue light of a slit lamp is used to illuminates the eyes. Cobalt blue light of an ophthalmoscope can be alternatively used. The tear meniscus is evaluated at 2, 5, and 10 minutes. Each eye is graded at 0, 1, 2, or 3 (0 = fluorescein completely gone, 3 = no fluorescein gone). Normally, the fluorescein disappears by 5 minutes but the dye remains in the conjunctival cul-de-sac in children with obstruction. Mild pressure on the lacrimal sac produces regurgitation of fluorescein-stained tears, particularly in those with a mucocele. This test visibly demonstrates the nature of the problem to the parents and provides practical time to discuss the cause and management of CNLDO. The fluorescein dye disappearance test can reliably confirm lacrimal duct obstruction noninvasively, with a sensitivity of 90% and a specificity of 100% [3]. In most centers, FDT has become the preferred tool for diagnosis of CNLDO.

Approximately 90% infants with CNLDO experience spontaneous resolution before the age of 1 year. It becomes symptomatic in merely 5–6% of infants [4]. Probabilities of spontaneous resolution by 12 months of age are 80–90%, at 3 months of age, 68–75%, at 6 months of age, and 36–57% at 9 months of age [5]. Bilateral symptoms are present in 14.0–33.8% of patients with CNLDO, all of which either spontaneously resolve simultaneously or within 3 months of contralateral resolutions. In cases of bilateral CNLDO, when epiphora in one eye settles spontaneously during 10–12 months of ages, it is rational to monitor the

#### *Congenital Nasolacrimal Duct Obstruction and the Visual System DOI: http://dx.doi.org/10.5772/intechopen.82546*

child for further 3 months as spontaneous resolution can occur in a substantial percentage of children after 1 year of age [6].

Congenital dacryocystoceles are an uncommon variant of CNLDO, typically seen at birth or shortly after birth as a blue-colored cystic mass over the lacrimal sac. The valve of Hasner again is the most frequent site obstruction due to incomplete canalization. A congenital dacryocystocele accompanies CNLDO in approximately 0.1% of infants. Children with Down syndrome, craniosynostosis, Goldenhar sequence, clefting syndromes, hemifacial microsomia, and midline facial anomalies are at an increased risk for CNLDOs. Although most cases of CNLDO are diagnosed clinically, some conditions especially craniofacial malformations or Down syndrome, the bony obstruction at the CNLDO can be confirmed with computed tomography (CT Scans). Dacryocystocele (where both proximal and distal lacrimal system are obstructed) commonly results in dacryocystitis (or, rarely, neonatal respiratory obstruction) at birth, it necessitates surgical intervention following diagnostic imaging.

## **3. Initial Management**

 The treatment of CNLDO is, at first, conservative. Conservative treatment consists of nasolacrimal massage, warm compresses, and topical antibiotics for secondary infections. Massage of the lacrimal sac increases the hydrostatic pressure within the sac thereby breaking open the distal membrane. The most important aspect of conservative treatment is educating the parents, providing reassurance and information about the etiology, and natural history of CNLDO. Printed leaflets that provide information for the parent are very useful. Parents should be encouraged to clean the lids and lashes with cooled boiled water or normal saline and to lightly express the contents of the lacrimal sac. This maintains flow in the system and prevents stagnation, reducing any sticky discharge. Method of the massage should be explained to the parents. Parents find this difficult and need clear instructions. They should press on the sac below the medial canthus with their little finger multiple times per day if possible. Vaseline or liquid paraffin should be applied to the periocular skin to protect and treat any areas of redness or broken skin.

Antibiotic eye drops in CNLDO should only be used when it is accompanied by signs of conjunctivitis. It is somewhat common practice in some centers that topical antibiotics are used in combination with conservative therapy for CNLDO. However, there is no evidence indicative of the fact that antibiotic eye drops appreciably facilitates the resolution of CNLDO. Conjunctival bacterial flora in CNLDO patients is almost identical to those in the normal pediatric population and the use of antibiotic eye drops may cause normal bacterial flora to be substituted with a drug resistant flora. As infants have immune system that is in flux and is not geared-up to remove resistant bacteria they may possibly become carriers of resistant bacteria. Thus, antibiotic eye drops are completely unnecessary in conservative therapy for simple CNLDO [7].

#### **3.1 Surgical management**

Intervention is usually done when CNLDO becomes persistent and/or once the child is older than 1 year of age. Probing the nasolacrimal duct to open the membranous obstruction at the distal nasolacrimal duct is the preferred initial management. Probing can be performed without anesthesia in the office setting, but it is usually preferred to do the procedure under general anesthesia (GA) in the operating room. The benefit of GA is less discomfort and the ability to perform

additional procedures if other abnormalities are found while the child is under GA. Probing aims to solve the symptoms of epiphora/discharge by clearing up the membranous obstruction; however, it may not be able to relieve the obstruction if it is due to protrusion of the bone of inferior turbinate into the NLD or when the NLD is swollen due to inflammatory processes such as dacryocystitis. Moreover, probable complications with probing are; false passage formation, injury to the NLD, puncta, canaliculi, bleeding, laryngospasm, and rarely aspiration.

While obstruction is mostly located at the valve of Hasner, obstruction may be anywhere along the route. Surgical intervention consists of the introduction of a flexible metal probe into the nasolacrimal duct to open it. A probe is placed into the nasolacrimal duct and passed into the nose. Following probing the nasolacrimal system is irrigated to assess its patency. This is usually done with normal saline tagged with fluorescein dye. If fluorescein dye can be picked-up by suction from the pharynx, probing can be considered successful. Postoperative tobramycindexamethasone eye drops are used four times a day for 2–3 weeks. If after 6 weeks, there is no improvement in signs or symptoms, probing and syringing (P&S) can be repeated. Endoscopic inspection with a nasal scope during P&S is recommended; especially if it is being done the second time, to identify anatomical anomalies and to ensure accurate probe configuration. Various studies show a success rate of 90–95% after initial probing [8–11].

 The timing of initial probing is debatable and varies between surgeons and centers. Some surgeons recommend early intervention. Their concern is that prolonged epiphora is annoying to both child and parents. More importantly, a delay in treatment may increase the risk of infections and long-term damage to the system resulting in inferior success rates of simple probing. In countries where pediatric ophthalmic care is limited to a few urban centers; where children present late with complex CNLDO and where there is a high probability the child will not show up for a follow-up, an early probing can be justified to some extent.

Typically, it is thought that the older the child at the time of probing, the less successful the probing will be. Studies have reported variable success rates of probing and syringing when done in older children. A success rate of 94% was reported by Havins and Wilkins for probing done in children less than 8 months compared to 56% in children age 18 months and older [12]. Sturrock reported 86% success when probing was done in children less than 1 year compared to 72% between 1 and 2 years of age and 42% for more than 2 years of age [13]. Katowitz and Welsh reported success rates of 76.4% in 13–18 month old children; however, the cure rates fall to 33.3% in children over 2 years [9].

 Mannor et al. found a negative association between the age and success rates of P & S. Contrary to this, Robb, Zwaan, and El-Mansoury found more than 90% success rate in late as well as very late probing [10, 14, 15]. Robb found no difference in cure rate with increasing age and noted an overall success rate of 92% varying from 88.9 to 96.8% at different age intervals up to and beyond 3 years of age [16]. Honavar reported a success rate of 75.0% up to 4 years of age, after which it fell to 42.9% in children older than 4 years [17]. Casady reported success rates of 85% for probing in children more than 18 months of age [18].

Factors besides increasing patient age that are associated with decreased success rates for probing are severe symptoms, bilateral symptoms, canalicular stenosis, atonic sac, and non-membranous CNLDO. A recent Cochrane review assessing the effects of probing for CNLDO showed that the effects and cost of immediate versus deferred P & S for CNLDO are uncertain. Patients with unilateral CNLDO may have improved success from immediate P & S in the clinic. Limiting factors in these studies were; sample sizes of participated children in these trials were small and researchers examined outcomes at different points in

#### *Congenital Nasolacrimal Duct Obstruction and the Visual System DOI: http://dx.doi.org/10.5772/intechopen.82546*

time. They conclude that deciding whether to perform the procedure and its best possible timing will entail well-run clinical trials [19].

If the preliminary probing and syringing fails, one may perform; as discussed before, a secondary probing or an additional procedure. Second probing can be repeated four to six after the initial procedure. Cure rates of second probing are greatly decreased because unsuccessful first probing can result in cicatricial strictures or a false passage [20]. The two main secondary procedures are balloon dacryoplasty and silicone tube intubation.

During balloon dacryoplasty, a stent with a balloon at its distal end is passed into the distal nares, the balloon is inflated (usually couple of times), then deflated and removed. The aim is to widen the distal duct and decrease obstruction. The primary advantage of balloon dacryoplasty is that no stent material is left in the lacrimal system and therefore stent removal is not required. Balloon dacryoplasty is particularly useful for patients with diffuse stenosis of the distal NLD. Success rates for balloon dacryoplasty as a primary procedure are as high as 94%; however, the procedure is costly; nevertheless it may have its benefit in intractable cases [21, 22]. Furthermore, the role of balloon dacryoplasty in the management of CNLDO needs further evaluation and assessment.

 Intubation is necessary in cases with lacrimal canalicular stenosis after probing. The silicone tube prevents the formation of granulation-related obstruction around the newly patent tract. Bicanalicular or monocanalicular silicone intubation of the nasolacrimal duct can be used as a primary or secondary procedure. Intubation should take place under GA after the nose has been prepared with decongestant. It is recommended that a nasal endoscopic guidance system is used to view the inferior meatus [23]. The lacrimal system should be probed first to ensure that the tubes have an anatomical passage. Tubes come with a metal introducer and one end should be placed through the system via the upper canaliculus, into the sac and down the nasolacrimal duct into the inferior meatus from where it should be retrieved under endoscopic view. The other end of the tube is inserted in exactly the same way through the lower canaliculus. The ends are tied securely with multiple square knots inside the nose and trimmed. Postoperative treatment consists of a topical antibiotic and steroid preparation for 2–3 weeks.

Possible complications of intubation include canalicular cheese-wiring, superiorly/inferiorly dislocation, infection, and scarring of any part of the nasolacrimal drainage system. Silicone tube stents if removed too early may result in the recurrence of obstruction. Breakage or prolapse of the tube may cause corneal abrasions [24]. Retrieval of the probe is sometimes difficult during intubation and during instrumental manipulation required during it may damage the nasal mucosa and turbinate [25]. The timing of removing the tube is contentious, but the suggested time is anywhere between 6 weeks and 18 months [26]. Leaving a tube in situ for about 6 months may attain better success rates compared to removing it earlier [27]. A study reports that early removal of tube in children younger than 2 years did not reduce the success rates of intubation [28]. Long-term intubation is associated with a higher occurrence of breakage, dislodgement, migration, dislocation, or prolapse. Tubes in almost all the cases are removed under GA through the nose. The tube is cut at the medial canthus and removed under direct vision to prevent aspiration of the tube. This system is then irrigated to remove any debris and to verify patency.

 Its success rate of intubation range from 62 to 100% but in general, they decrease with increasing age [29, 30]. A study reported success rates for intubation stratified by patient age. The success rate for intubation in children aged 12–24 months was 91.3%, which reduced to 85.5% in those aged 24–36 months and to 79.6% in those aged 36–48 months [31]. Several studies have explored the effectiveness of intubation as a main treatment modality in older subgroup of children because of the

decrease in success rates for late probing. Although the success rate was high; none of the studies included a control group.

The bicanalicular device has a silicone tube with a flexible metal probe on each end. Each separate end is introduced into the upper or lower punctum and then retrieved from the nose. Bicanalicular stents pass through both the upper and lower canaliculus and typically create a closed circuit. Bicanacular system intubates the upper and lower canaliculi connecting via the common canaliculus or the lacrimal sac thereby intubating the entire nasolacrimal drainage system with the circuit being open or closed in the nose. Examples of Bicanacular stent include Crawford stent, Ritleng stent, Pigtail/Donut stent, and Kaneka Lacriflow stent.

Monocanalicular stents do not provide a closed loop system, but only intubates either the upper or lower canaliculus. Examples of monocanalicular stents include Monoka Stent and Jones Tube. Both monocanalicular and bicanalicular intubations are effective methods for treating CNLDO. Monocanalicular intubation has the advantage of a lower incidence of canalicular slit formation, technical ease of insertion, and easier tube removal. Moreover, the tubing does not threaten the unprobed part of the lacrimal drainage system [32]. Bicanalicular intubations may be a better treatment for the patients with incomplete complex CNLDO [33].

A met-analysis in 2016 showed that the results of immediate and deferred P & S did not vary in their success rates. There was no difference in between the success rates of balloon dilation and intubation. Monocanalicular and bicanalicular intubation had similar success and dislocation rates. Therefore, the preference of a particular procedure on the treatment of CNLDO should be discussed in detail with parents by the concerned surgeon to achieve the best possible results [34].

In cases where all above measures fail or in complex CNLDO, some surgeons perform additional procedures such as turbinate fracture or dacryocystorhinostomy (DCR). DCR is done provided the obstruction is distal to the lacrimal sac. DCR represents a last resort for patients in whom; multiple procedures have failed, complex CNLDO, or in whom there is obstruction secondary to bony obstruction, dacryocystitis, dacryocystocele, older children, or craniofacial dysmorphism. Infracture of the inferior turbinate, usually done with a periosteal elevator or a hemostat, is used to decrease the resistance of drainage in the distal nasolacrimal duct. It is mostly useful for patients who have an exceedingly tight space between the inferior turbinate and nasal wall. It also allows for better visualization of the inferior meatus during endoscopic surgery. The success rate of inferior turbinate fracture alone is 83% [35]. Although a combination of probing with intubation results in good cure rates of 88–100%, the success rate for a combined inferior turbinate fracture and probing is no different to that for simple probing [36].

 Conventional/external DCR is carried out through skin incision, the lacrimal sacs are exposed, an osteotomy is made through the nasal bone, flaps are created between the lacrimal sac and the nasal mucosa and then tube is placed which serves as a stent. Laser DCR is a substitute; the ostium is created by means of a laser which is placed through the canaliculus just adjacent to the nasal bone. An endoscope is mostly used during laser DCR. Nasolacrimal stents are placed at the end of the procedure. External and endoscopic DCR have excellent success rates, comparable to those of adult DCRs [37]. Endoscopic DCR can avoid a cutaneous scar and disruption of the medial canthal anatomy, but a pediatric endoscopic DCR is technically more demanding because of the poor visualization afforded by small nostrils and closer proximity of the operative field to the base of the skull [38].

Pediatric DCR has high success rates of 88–96% for external DCR and 82–92% for endoscopic DCR [39]. Rapidly altering anatomy, ill-defined anatomical landmarks, and aggravated growth of scar tissue have been suggested as possible factors that could influence surgical outcomes in pediatric DCR. On top, because of a

narrowed nasal cavity there is a propensity toward development of postoperative adhesions between the rhinostomy site and the nasal septum; the use of a silicone tubes in pediatric DCR may avert this obstruction and consequently ensure better surgical outcomes [40].

## **4. CNLDO and its effect on the visual system**

CNLDO has long been considered as a benign condition that does not influence visual development. CNLDO has been at the hub of current debate on its proposed relationship with anisometropia, strabismus, and amblyopia. The persistent tearing caused by CNLDO distorts retinal images by producing a blur, thus defocusing the retinal image thereby adversely influencing the process of physiological emmetropization. This interference with the physiological emmetropization has possibly led to frequent findings of anisometropia in various studies.

 The role of focused retinal images in the physiological emmetropization has been discussed by Wright [41]. Newborns are hyperopic having a short axial length relative to the refractive power of the cornea and lens. During the first few months of life rapid growth in axial length (AL) occurs with subsequently decreases the hypermetropia. The retinal image comes in clear focus through "emmetropization." Various studies have shown that growth of the eye after birth and the development of its refractive capabilities are dependent on vision-dependent retinal mechanisms. A basic observation is that a continuous image blur on the retinal cells in a new born can result in lengthening of the axial length thus inducing myopia. The axiom is that when we are born the AL of the eye is short; therefore, the eye is hypermetropic and image blur on the retinal tissue in early life kindles AL elongation until image clarity is achieved by proper focusing of light rays. Raviola and Wiesel concluded that when visual input is deprived, as seen in cases where there is a dense corneal opacity or ptotic/closed eyelids, the eye has a tendency toward myopia [42]. Even if the eyelids are completely closed, more than 20% of light is still passed on to the retina [43]. The influence of a blur images is so immense that (in a study done on chicks) if only half the retinal image is blurred, then only that half of the globe will lengthen [44].

In comparison to blurred images, if there is no stimulation of light, studies show that it slows down the progress of blurred induced myopia and AL elongation. In theory, clearing up the image blur would abolish the stimulus of image blur on AL elongation, thereby retarding AL growth and the process of emmetropization, thereby causing hypermetropia [45]. In addition to the influence of AL elongation by blurred image stimulation of the retina, it seems that intrinsic growth of the eye is disengaged from visual input. AL elongation and thickness of the choroid alterations occur in diurnal pattern. In general, AL elongates and choroid thickens during the day and dawdle downs at night signifying a circadian rhythm. This suggests that the eye has an intrinsic growth rate that will occur in the absence of visual input [46].

No cause-effect relationship linking CNLDO and anisometropia has been studied and the precise method by which CNLDO might cause refractive error, anisometropia, and amblyopia is indistinct. As discussed, the proper focusing of images on the retina early in life is vital for emmetropization. It is indefinite what part, if any; persistent tearing has on visual development, refractive status, and amblyopia. Several authors have recently described an association between CNLDO and the development of amblyopia and strabismus secondary to anisometropia [47–49]. The major visual concern in CNLDO is the presence of significant anisometropia during vital period of visual development in these infants.

CNLDO rarely, if ever, results in complete visual obstruction. Besides, early unilateral visual deprivation as discussed before has been linked with myopia not hypermetropia [42, 50]. It is postulated that accumulation of discharge, excessive tears, and antibiotic ointments may result in deformation of retinal images. This image disparity may lead to a lack of appropriate emmetropization process and as a result the repeated finding of anisometropia in the affected eye. It is also proposed that this anisometropia is refractory. However, recent studies reveal that this is not necessarily true [51], which will be discussed in a while.

#### **4.1 Visual system, anisometropia, and amblyopia**

 An estimated 285 million people around the world are visually impaired; 19 million are children below the age of 14 years. Childhood visual impairment is estimated to be the second leading cause of the burden due to blindness [52]. Forty percent of childhood blindness is preventable; 12 million children are visually impaired merely because of refractive errors. Uncorrected refractive errors lead to amblyopia and strabismus [53, 54]. Anisometropia is one of the major causes of amblyopia. Visual disabilities in children are also more intricate compared to adults thus preventing visual impairment in children in resource-poor countries is one of the key components of VISION 2020 the Right to Sight.

The significance of anisometropia as a source of amblyopia is well documented. Amblyopia risk factors based on *American Association for Pediatric Ophthalmology and Strabismus* (AAPOS) criteria include: anisometropia (spherical or cylindrical) >1.5 diopters; any manifest strabismus; hypermetropia >3.5 diopters in any meridian: myopia magnitude >3.0 diopters in any meridian: any media opacity >1 mm; astigmatism >1.5 diopters at 90 or 180° >1.0 diopters in oblique axis (more than 10° from 90 or 180°) and ptosis ≤1 mm margin reflex distance (MRD) [55]. Although binocular single vision (BSV) develops at the age of 2 years, the fixation reflex is not fully established until the age of 9 years. Visual acuity remains in a state of flux prior to this age predisposing the child to anisometropia, strabismus, and amblyopia. In a population-based study on 961 children with amblyopia, the author found the cause to be strabismus in 57%, anisometropia in 17%, and combination of two in 27% patients [56].

 Donahue suggests that 1D of anisometropia can be considered as clinically significant anisometropia [57]. Nevertheless due to individual physiologic variability's, amblyopia can even be seen with milder degree of anisometropia. The prevalence of anisometropia in the general pediatric population ranges from 2.3 to 3.4%, based on literature review [58]. Amblyopia has been reported to occur in approximately 1.6–3.6% of the normal population [51, 58]. The prevalence is even higher in medically underserved populations with reported rate as high as 22.7% [59]. The population-based Multi-ethnic Pediatric Eye Disease Study found that 78% of African American and Hispanic children had amblyopia which was traced back to be due to anisometropia [60]. A population-based Baltimore Pediatric Eye Disease Study was conducted on the White and African-American Children. This study concluded that 32% of cases of amblyopia were attributed to anisometropia [61].

Studies on the prevalence of anisometropia (greater and equal to 1D between two eyes) reveal that 2.3–3.4% of pediatric population aged 5–11 years is affected [62, 63]. Drover et al. showed the prevalence of anisometropia to be at 1.4% in the studied pediatric population (mean age 4.2 years) [64]. Huynh et al. study conducted in Sydney, concluded an anisometropic prevalence of 1.6–2.4% (mean age 6.7 years) [65]. Shih and colleagues conducted a population survey in Taiwan and found an anisometropic prevalence ranging from 7.2 to 9.3% in older children (age, 7–18 years) [66]. Studies show that anisometropia is an identifiable amblyogenic

#### *Congenital Nasolacrimal Duct Obstruction and the Visual System DOI: http://dx.doi.org/10.5772/intechopen.82546*

factor in 37% of cases and present concurrently with strabismus in an additional 24% of clinical populations [67].

Apart from refractive errors, a variety of risk factors increase the likelihood of amblyopia. A study showed that 28.7% of children whose parents had known strabismus were also found to have strabismus, a known amblyopia risk factor; this suggests a hereditary risk factor [68]. Low birth weight (<2499 g) and severe mental handicap are established risk for developing amblyopia [69]. Further risk factors include capillary hemangiomas of the eyelids, ptosis, blepharophimosis, craniosynostosis, and hydrocephalus. Socioeconomic factors also increase the risk of developing amblyopia. Children from underprivileged background, such as homeless kids and those coming from homes where either parents smoke, have a high prevalence of amblyopia [70, 71].

 Amblyopia is clinically significant because it is one of the main causes of visual loss in children. Amblyopia is also of central interest because it suggestive of diminished neuronal activity that occurs when normal visual growth is interrupted. Amblyopia affords an idyllic template for understanding when and how a plastic brain may be used for functional recovery. Impaired stereoscopic depth perception is the most common deficit associated with amblyopia under ordinary binocular viewing conditions. This impairment may have a substantial impact on visuomotor tasks and difficulties in playing sports in children. Furthermore, impaired stereopsis may also limit career options for amblyopes. Stereopsis is more affected in strabismic than in anisometropic amblyopia. Recovery of stereoacuity may require more vigorous treatment protocols in strabismic than in anisometropic amblyopia. Individuals with strabismic amblyopia have a very low probability of improvement with monocular training; however, they get on well with dichoptic training (promising new therapeutic approach to amblyopia, which employs simultaneous and separate stimulation of both eyes) than with monocular training and much better with direct stereo-training [72, 73].

 Thus, Anisometropia primarily disturbs binocularity thereby causing reduced stereoacuity. Development of stereoacuity is interrelated to similarity in the refractive status of the fellow eyes; fine motor skills which require swiftness and precision of movements are defective in amblyopic children. Therefore, management of anisometropic amblyopia is more prolonged and complex, especially if it is accompanied with strabismus [74]. In distinction to strabismic and deprivational amblyopia, anisometropic amblyopia is more frequently asymptomatic and detected at an older age; only 15% of affected children are diagnosed before they are 5 years of age [75].

Studies demonstrate that the most important factors in treatment results are age and depth of amblyopia that are directly related to the degree of anisometropia [76]. Therefore, as the child gets older, management becomes more complex and time consuming particularly in hypermetropic anisometropes in whom a less encouraging treatment results are seen, in contrast to myopes. It is suggested that in anisometropic subjects, amblyopia is less severe in children younger than 3 years of age and improvement in visual and stereoacuity is more probable if treatment is initiated prior to this age [77, 78]. Based on repeated finding of anisometropia in CNLDO particularly in unilateral anisometropia it is vital to check refractive status of children with CNLDO to assess visually significant anisometropia at an early age to prevent these children from amblyopia and visual morbidity.

#### **4.2 CNLDO, anisometropia, and amblyogenic potential**

First Chalmers and later Ellis questioned the relationship between CNLDO and visual maturation. Chalmers found anisometropia in 3.8%, in eyes with CNLDO; all

 their subjects were hypermetropic in the affected eye [79]. Ellis found no appreciable increased incidence of amblyopia (1.6%) in a large series of 2249 patients with NLDO compared with controls. They also found no correlation between refractive error and NLDO, including no significant increase in the incidence of anisometropia [80].

In our study, the prevalence of anisometropia (greater than 1.5 D) in NLDO patients of 13.7% is approximately thrice that of the general population [81]. It is also higher than reported studies on this subject matter [47, 48, 79–81]. Similarly, a study of around 1200 CNLDO patients found twice the rate of anisometropia in the unilateral CNLDO patients (7.6%) compared with bilateral NLDO patients (3.6%) that the rate of anisometropia and amblyopia is greater in NLDO patients. Anisometropia occurred at a greater rate in unilateral NLDO patients compared with bilateral NLDO patients and occurred at a greater rate in this CNLDO cohort than expected in the general pediatric population. Several patients with anisometropia went on to develop clinical amblyopia [47].

 Matta et al. reviewed 375 patients with CNLDO and reported that 22% of the children with CNLDO had amblyopia risk factors [48]. Piotrowski and colleagues described a high prevalence (9.8%) of anisometropia with or without amblyopia in an 8-year consecutive case series which included 305 children with CNLDO [49]. Furthermore, Eshraghi and colleagues studied 433 cases with CNLDO that underwent probing. They reported that 5.5% had anisometropia and 9.46% had amblyopia risk factors. They also found more anisometropia in failed probing cases and theorized that structural abnormality may have a part to play in the development of anisometropia [82].

Bagheri et al. evaluated refractive state in children with unilateral CNLDO; they reported that in children aged 4 years and older, the interocular difference between spherical error and spherical equivalent was considerable as compared to children younger than 4 years [83]. Contrary to this, in our study, we found no significant association between the age (in months) of the patients and the interocular difference in sphere, cylinder, and SE of affected and non-affected eyes. However, when we observed the refractive status of children with CNLDO, we found that as the children age increased the prevalence and severity of refractive error and anisometropia increased. We also observed that difference between the affected and fellow eyes was significant in terms of spherical refractive error and spherical equivalent and that hypermetropia was more common in the eye with CNLDO. These findings illustrate that when unilateral CNLDO becomes chronic, the likelihood and severity of hypermetropia increases which as detailed, is a risk factor for amblyopia [81, 84]. This finding is clinically significant, as management and prognosis of amblyopia becomes intricate in older children.

The published literature proposes that the prevalence of anisometropia increases as the nature of the CNLDO becomes more chronic. Our study on bilateral CNLDO shows that the interocular difference in the mean spherical equivalent of children with unilateral CNLDO increases with the age of the patients. This was not the case in the patients with bilateral CNLDO. Therefore, children with chronic obstruction are more prone to be amblyogenic [85]. Hence, timely resolution of the problem is recommended to avoid visual morbidity, i.e., anisometropia and amblyogenicity.

If the anticipated association between CNLDO and anisometropia is refractory and the persistent epiphora, discharge, and topical medication in the conjunctival cul-de-sac is being held responsible in hampering the physiological emmetropization, then early resolution of CNLDO should retard the development of anisometropia and thus save the child from developing anisometropic amblyopia. However, a study found results contrary to this. Recently, Pyi Son studied 244 cases and found that early and spontaneous resolution of CNLDO is more likely

#### *Congenital Nasolacrimal Duct Obstruction and the Visual System DOI: http://dx.doi.org/10.5772/intechopen.82546*

 to have a higher (not lower) rate of anisometropia compared to spontaneous or surgical resolution [86]. They proposed that the eye with CNLDO proceeds to emmetropization differently than the unaffected eye. Early resolution can hinder the process of emmetropization in the affected eye, making it lag behind the normal eye in achieving emmetropization. These findings negate the fact that anisometropia in CNLDO is transient and refractory. Further studies need to be done to determine the timing of resolution of CNLDO and its effect on the development, progression, and resolution of anisometropia and if present amblyopia. In most studies, including the one we conducted, they did not determine whether anisometropia persisted or not after surgical intervention or in later life. Simon reported that even after CNLDO has improved, anisometropic hypermetropia is a regular finding in patients with a history of unilateral CNLDO [87]. Nevertheless, results of all these studies consistently report high rates of anisometropia which concomitantly has amblyogenic effect.

 Even though studies suggest that correction of the refractive error in anisometropia alone results in enhances quality of vision in anisometropic amblyopia, it is usually contemplated that most of cases will need added treatment because refractive error adjustment alone will not be adequate to completely manage the depth of amblyopia. Therefore, patching or pharmacological treatment is often prescribed at the same time or soon after the refractive spectacle correction is given. Concrete evidence, generally from the Pediatric Eye Disease Investigator Group, has established both number of hours per day of patching (according to age) and days per week of atropine use as good penalization technique to improve vision and stereoacuity in amblyopia [88]. The use of glasses alone has also been recognized as an excellent first-line treatment for both anisometropic and strabismic amblyopia. IPad-based dichoptic training has shown promising data for vision rehabilitation in amblyopes. Use of pharmaceutical augmentation of traditional therapies has also been investigated. Several different drugs with unique mechanisms of action are thought to improve the receptiveness to amblyopia therapy. However, no data on new treatment options from evidence-based research has surfaced which proves as being better to conventional therapies in regular clinical practice. Continued research into the use of new technology and comprehending the neuronal basis of amblyopia promises alternate or perhaps improved cures in the near future [89].

 Studies mention that emmetropia is achievable in anisometropes with appropriate management [90]. However, the precise cause why studies find high prevalence of anisometropia in subjects even after CNLDO has resolved is still contentious. Nevertheless, the results endorse the fact that patients of CNLDO should be regularly reviewed for refractory status. Furthermore, as shown in our results, in older subjects, the interocular difference becomes more significant compared to younger children; this places them at high risk for developing amblyopia. They are also inclined to poor prognosis in terms of visual recovery. These facts support the benefit of early intervention in CNLDO. However, further studies with larger sample size longer follow-up time is required to establish this effect.

## **5. Conclusion**

CNLDO should be observed and treated conservatively till the child is 1 year old. If CNLDO does not respond to conservative treatment, then they should be promptly treated with probing and syringing. In cases remission two cycles of syringing and probing, intubation is a reasonable treatment option. Surgical procedures should be reserved for complicated cases. Unilateral CNLDO is a

 risk factor for anisometropia particularly hypermetropic anisometropia with amblyogenic potential. Keeping in view that CNLDO is a common presentation in pediatric ophthalmology clinics, we recommend that all children with CNLDO should be regularly followed, even after the obstruction has anatomically and functionally resolved. These children should undergo cycloplegic refraction on each visit and should be monitored for the development of amblyopia and other ocular abnormalities.

## **Author details**

Adnan Aslam Saleem Amanat Eye Hospital, Islamabad, Pakistan

\*Address all correspondence to: doctoradnansaleem@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Congenital Nasolacrimal Duct Obstruction and the Visual System DOI: http://dx.doi.org/10.5772/intechopen.82546* 

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[89] Kraus CL, Culican SM. New advances in amblyopia therapy II: Refractive therapies. The British Journal of Ophthalmology. 2018 [Epub ahead of print]

[90] Atilla H, Kaya E, Erkam N. Emmetropization in anisometropic amblyopia. Strabismus. 2009;**17**:16-19

## **Chapter 7**  Advances in Vitreoretinal Surgery

*Baris Komur*

## **Abstract**

Vitreoretinal surgery has been radically changed over the past 10 years by the development of new techniques, smaller gauge instrumentation, and improvements in vitrectomy machines. The indications for vitrectomy have expanded dramatically, and inoperable conditions have become amenable to surgical treatment. In addition to improvements in intraocular instruments, various dyes become available and enable better visualization and a more complete removal of vitreous and membranes. In this chapter, we issued latest developments in the surgical field of retina that enable improved surgical outcomes and less complications.

**Keywords:** vitrectomy, 23 gauge, 25 gauge, 27 gauge, sutureless, retinal detachment, epiretinal membrane, macular hole, silicone oil, c3f8, sf6

## **1. Introduction**

 The introduction of pars plana vitreous surgery in the early 1970s, by Dr. Robert Machemer which was a single-port 17 gauge (1.14 mm) system with a cut rate of less than 400 cuts per minute (cpm), is considered as an important step in surgical treatment of vitreoretinal diseases [1]. For the first time, patients with dense vitreous hemorrhage could achieve some visual improvement. Vitreoretinal surgery has changed a lot from that time, firstly by technological improvements in vitrectomy machines. Three-port vitrectomy, better fluidic controls, faster cut rates, better light sources, and smaller gauges are made available to vitreoretinal surgeons [2]. Secondly new techniques and devices like automated fluid-air exchange, endolaser [3], internal tamponades, and dyes make possible to treat different retinal pathologies with less complications. The advent of 23 and 25 gauge vitrectomy made sutureless surgery possible. Improvements in viewing systems and digital image software processing enable good visualization in difficult situations. These advances have enabled vitreoretinal surgeons to more effectively address different serious sight-threatening retinal conditions, including retinal detachments, epiretinal membranes, macular holes, vitreous hemorrhages, phacoemulsification complications, and subluxated intraocular lenses. In this chapter we will discuss latest developments in vitreoretinal surgery that enables improved surgical outcomes and less complications.

## **2. Improvements in vitrectomy machines**

## **2.1 New probes**

The main vitrectomy probe, during the 1990s and 2000s, is made with springdriven pneumatic cutting mechanism up to 2500 cpm [4]. In these systems,

 pneumatic pulses push the cutter to one direction, and the passive recoil of a spring returns the blade to its original position. The limitation of this design is in higher cutting rates; the speed of the spring recoil is not enough to return the blade. For these cutters, when cutting rates approach 2500 cpm, the blade could not fully return to the initial position that the vitrector port is open, so a higher proportion of a cutting cycle is spent with the port closed. Duty cycle of vitrectomy cutter refers to proportion of one cutting cycle in which the vitrectomy port is open. This is important because active removal of vitreous only occurs only when the port is open. Current-generation vitrectomy systems can achieve at least 5000–7500 cpm, but with a traditional spring-driven pneumatic cutter, vitreous removal efficiency may not necessarily proportionally increase with higher cut rates. There are currently two strategies to improve this limitation. A dual-pneumatic-driven cutting mechanism uses separate air lines to control opening and closing of the cutter. In this system, duty cycle is not dependent on the passive recoil of springs and also can be set individually. The other strategy is using a two-dimensional cutter (TDC) approach in which a double-sided blade cuts in both the forward and reverse directions to achieve an effective cut rate of 16,000 cpm with higher duty cycle [5]. The high duty cycle is achieved because the port is nearly always open as the blade moves back and forth. In dual-pneumatic systems, however, duty cycle can be controlled independent of the cut rate. Studies comparing 7500 cpm dual-pneumatic and 16,000 cpm TDC cutters against their traditional counterparts (5000 cpm spring-driven probes) have demonstrated the new technology to significantly decrease the core vitrectomy time with TDC cutters reducing surgery time by 34–50% [6, 7]. Recently, a new mechanism using ultrasound to liquefy vitreous has been developed. The ultrasound harmonic vitrector liquefies the vitreous before being aspirated and has been shown to be safe on cadaveric eyes. These vitrectomy probes have the potential advantage of creating almost no traction during vitrectomy [8, 9].

### **2.2 Endoillumination and chandelier systems**

 Endoillumination utilizes an optic fiber inserted into the vitreous cavity through one of the vitrectomy ports. The first generation of endoilluminators utilized halogen, mercury vapor, and metal halide light bulb [10]. However, halogen illuminators required more power as 50% of the luminance was lost [11]. Present vitrectomy platforms utilize xenon or light-emitting diode (LED) light sources. Both have significant luminance through small-gauge light probes and considerably longer bulb life. With increased illumination and spectral distribution, concerns about possible retinal phototoxicity with xenon light sources from wavelengths below 450 nm have been raised. For this reason, most manufacturers have incorporated low-wavelength filters to block the blue and ultraviolet light most toxic to the retina [11]. LED light sources appear to be less phototoxic in animal models at the same intensity [12].

 Chandelier lighting system is a stationary, wide-angle endoillumination developed for retinal surgery. It allows the surgeon to use the second hand for bimanual surgical manipulations. Chandelier lighting systems can be placed as single or double fibers and are available in 23, 25, 27, and even 29 gauge sizes. Apart from being used in complicated tractional retinal detachments, chandeliers have been used for primary scleral buckles for better identification of retinal breaks with wide-angle viewing systems [13]. Chandelier-guided scleral buckling is an effective alternative technique to the traditional scleral buckling. Another use of chandelier illumination system is utilizing retroillumination to enhance the poor red reflex that is typical in cases of combined cataract surgery and vitrectomy for vitreous hemorrhage [14]. Details of chandelier lighting system uses in surgery are discussed in "Surgical techniques" of this chapter.

## **3. Smaller gauges and cannulas**

## **3.1 Smaller incision sizes**

 In the past two decades, following similar trends of smaller instrumentation in phacoemulsification surgery in the anterior segment, the evolution of vitrectomy surgical techniques that had an exciting advance with vitrectomy scleral incision size has gradually decreased from 20 gauge to 23 gauge and eventually to 25 gauge and 27 gauge through transconjunctival incisions [15].

 The smaller gauges have some disadvantages at first. Instrumentation was originally so impractical that many experienced surgeons encounter a learning curve transition from 20 gauge to smaller gauge. Like every new innovation, restrictions in instrumentation and refinement of surgical techniques are needed. Some early difficulties were instruments were too flexible, small-gauge endoilluminations were weak, and speed of vitreous removal was slow. Improvements in trocar insertion techniques, vitrectomy machine fluidics, stiffer surgical instruments, and valved cannula systems have largely eliminated these issues. Wide range of different stiffer vitreoretinal microsurgical instruments has now been designed for 23 gauge and 25 gauge vitrectomy systems. These include vitreous cutters, trocars, illumination probes, intraocular forceps, micro vitreoretinal blades, tissue manipulators, aspirating picks, aspirators, soft-tip cannulas, curved scissors, extendable curved picks, extendable curved intraocular laser probes, and diathermy probes [16, 17].

Recent introduction of the 25 gauge and 27 gauge vitrectomy systems has some benefits in terms of surgical technique. The cutting port of these probes is closer to the distal end of the tip which gives access to tighter tissue planes during an epiretinal membrane dissection like in diabetic tractional membranes. This manipulation is better than bimanual approach because no instrument change is needed. Combined with the improvements in surgical techniques and better visualization with wide-angle systems, the vitrectomy probe may be used as forceps, scissor, and delamination spatula when necessary without exit from the eye. When a bimanual approach is necessary, chandeliers usually provide an optimal amount of light even the smaller gauges. In these situations, forceps can delaminate any membrane without the need of scissors.

At present, the smallest sclera incision available is 27 gauge. One factor that may lead to a learning curve for 27 gauge is the relative lack of rigidity in the instruments compared to 25 gauge, particularly the intraocular microforceps. Although the main goal of 27 gauge vitrectomy is to create less traumatic wounds, intraoperative surgical times and complications will likely be reduced with this new technology.

## **3.2 Valved cannulas**

Valved cannula systems permit closed system fluidics by limiting exit of fluid which brings various advantages. Maybe the most critical advantage is the exact intraocular pressure (IOP) control that can be kept up consistently during manipulations in trocars, particularly with new IOP stabilization capabilities of current vitrectomy machines.

With reduced flow and turbulence, valved cannulas offer a potential for decreased vitreous incarceration and fewer intraoperative iatrogenic retinal tears, which has been shown in postmortem rabbit eyes [18].

Valved cannulas have few disadvantages also. First it is more difficult to insert soft-tip instruments trough the trocar. Instruments with shorter and more rigid soft extensions and retractable soft tips are useful for insertion. Secondly extra

 care must be practiced while injecting extra fluid into system with valved trocars. In particular, injection of perfluorocarbon (PFC) liquid, silicone oil, or gas may require one of the trocars to be open, either by a backflush or another instrument to open the valve, by putting a "chimney" vent or by expelling the valve. A dual-bore injection cannula might be useful to permit departure of liquid trough the other bore during injection. In addition, perfusion at the optic nerve must be persistently observed to prevent excessive IOP rise, during every stage of the surgery.

### **4. Wide-angle viewing systems**

Wide-angle viewing systems (WAVs) are useful fundus observation devices for vitreous surgery, which have been continually developed from the late 1980s based on the indirect ophthalmoscopic principles [19, 20].

 Visualization during vitreoretinal surgery is the most important part of the surgery particularly while working on complicated cases. Current WAVs comprise of an indirect ophthalmoscopic lens system for panoramic fundus view. In contact type of WAV, the lens is put on the cornea as a contact lens. In noncontact type of WAV, the lens is placed above the cornea. There is also a prismatic reinverter in the system, which is mounted on microscope or the lens system itself for inverting the fundus view. Contact type of WAVs has a predetermined field angle of view which is dependent on the magnification power of the lens, while noncontact type of WAV angle of view can be adjusted by changing the distance between the lens and cornea. The surgeon can increase magnification of fundus view with two types of WAVs by using zooming function of microscope. The image quality is hypothetically prevalent with the contact type of WAV because of the fact that the aberration and reflection from the cornea can be compensated by putting the contact lens directly on the corneal surface without an interphase [21]. Then again, contact type of WAV frequently needs an accomplished assistant to hold the lens during the surgery.

 The WAVs enhance the safety and proficiency of the vitreoretinal surgeries by providing a panoramic view of the retina [21]. Vitreoretinal surgeon can undoubtedly assess the fundus status and the area of retinal pathologies through the panoramic view and evaluating peripheral retina without requiring extreme rotation of the glob as was generally needed when using prismatic lenses [22]. While working in one membrane, visualization of remote traction with possible advancement of retinal tears or hemorrhage is very important in complex surgeries. Complicated surgeries like dissection of anterior proliferative vitreoretinopathy, air-fluid exchanges, and silicone oil injection both an air-silicone oil exchange and direct PFC-silicone oil exchange can be performed with same system without changing settings.

The WAVs developed in recent years additionally encouraged the utilization of microincisional approaches for plana vitrectomy. Utilizing WAVs, the full-degree dissection of the vitreous base, where remaining vitreous frequently causes failure, can be performed with precise control. The modern WAVs improve the vitreoretinal surgeons' manipulative capacities by giving not just a wide-field perspective of the fundus yet additionally provides good-quality video recording of difficult maneuvers. Sharing these videos in meetings or online platforms with other surgeons helps adding to safety and facilitating the technical troubles.

#### **5. Tamponading agents**

Tamponade by medical definition is the utilization of a tampon, which itself is characterized as a plug or tent embedded firmly into a wound to arrest hemorrhage.

#### *Advances in Vitreoretinal Surgery DOI: http://dx.doi.org/10.5772/intechopen.83019*

With regard to vitreoretinal surgery, tamponade agents are utilized to give surface tension over retinal breaks, which counteracts further liquid stream into the subretinal space until the retinopexy (photocoagulation or cryopexy) gives a lasting chorioretinal attachment. Gases and silicone oils are the most commonly used classes of tamponade agents. Silicone oil was initially used without vitrectomy more as an instrument rather than tamponading agent [23].

 In addition to the availability of different viscosities of silicone oil (1000 and 5000 centistokes), heavy silicone oil (Densiron) is also available that sinks in water and hence can be used to tamponade inferior retina [24].

PFC liquids are an important contribution made by Stanley Chang to vitreoretinal surgery [25]. These heavier-than-water liquids are used intraoperatively to facilitate various procedures like inverting the flap of giant retinal tear, performing relaxing retinectomies, displacement of subretinal fluid and blood, floating dislocated intraocular lens, and stabilizing posterior pole for peripheral dissection. PFC liquids are mostly used as intraoperative agents and also sometimes used for long term in spite of its toxicity to retina. Silicone oil is still the best long-term tamponading agent available although the search is going on for a better substitute.

Partially fluorinated alkanes combined with silicone oil and two-staged surgeries that involve removing PFC liquid as a second surgery are discussed in "Surgical techniques" section of this chapter.

## **6. Intraoperative technologies**

#### **6.1 Intraoperative optical coherence tomography**

 In clinical setting, the noncontact method of cross-sectional imaging of the retina with optical coherence tomography (OCT) became an integral part of evaluation, management, and monitoring of wide range of retinal pathologies since the 2000s. [26]. Development of spectral-domain OCT (SD-OCT) provided improvement in resolution and speed of acquisition, which allowed for more detailed visualization [27]. In addition to its role in clinical management, OCT imaging plays an important role in preoperative surgical planning and postoperative evaluation, especially with epiretinal membranes, macular holes, and rhegmatogenous and tractional retinal detachments. Requirement of upright patient positioning and patient cooperation with the conventional tabletop OCT unit precluded its use in supine patients in the operation room. In 2007 a portable and handheld SD-OCT scanner was developed, which allowed imaging of supine patients. It is mainly used for exams under anesthesia for pediatric patients with various conditions, such as retinopathy of prematurity, albinism, and shaken baby syndrome [28–30].

Development of microscope-mounted OCT devices led to a decrease in image capture time and improvement of reproducibility [31–33]. Although this allowed an easier alignment of the system, but real-time visualization of the tissue and tissue-instrument interactions were not possible until the development of microscope-integrated intraoperative OCT (MiOCT) devices [34, 35]. MiOCT systems incorporate the OCT optical path into the common optical pathway of the surgical microscope, allowing improved targeting and tracking of the scan beam and achieving parfocal and coaxial OCT imaging with the surgical view.

The first publication of MiOCT use in vitreoretinal surgery was in 2010, describing a custom prototype system with a research OCT integrated with a commercially available operating microscope [36]. Several prototypes were developed to be used in clinical vitreoretinal surgery, and some have become commercially available [37, 38]. Currently, three systems are approved by the US Food and Drug

Administration for vitreoretinal surgery in clinical setting (viz., Leica EnFocus, Haag-Streit iOCT, Zeiss RESCAN 700).

Better understanding of the vitreoretinal interface disease and intraoperative changes occurred with different surgical techniques, and tissue manipulation can influence surgical decision-making and possibly lead to improved surgical outcomes. Significant advances in software and hardware of MiOCT systems led to examination of their use for different conditions. In vitreomacular traction repair procedures, MiOCT provides real-time assessment of the strength of vitreomacular adhesions and allows visualization of unroofed cysts, subclinical full-thickness macular hole development, and incomplete peeling of membranes. Intraoperative identification of these subclinical changes may alter the immediate surgical approach, such as prompting the use of gas tamponade and potentially preventing the need for reoperation [39]. In retinal detachment surgery, MiOCT aids in detection of residual subretinal fluid, small retinal breaks, and proliferative vitreoretinopathy membranes and can assist in completion of fluid-air exchange. In tractional retinal detachment surgeries, real-time visualization of the planes may also help achieve more precise delamination and segmentation. MiOCT may also offer benefits to regenerative and gene therapies in the future, improving precision of delivery of a therapeutic agent in subretinal space.

 Further software and hardware changes will be necessary to address the current MiOCT systems limitations. Known limitations are related to visualization of OCT data on external screens versus surgical oculars, difficulties with imaging peripheral retina, and light scattering and shadowing from surgical instruments. In systems with inocular heads-up display systems, the size of OCT images and the visual field are limited by the size of the surgical oculars. The use of an external monitor for viewing OCT images provides a larger image, but it requires the surgeon to look away from the surgical field. Additionally, MiOCT systems can cause deterioration of image while evaluating peripheral retina, limiting its use in evaluating peripheral regions. Surgical instruments may lead to light scattering and shadowing, limiting to some degree the realtime visualization of retina manipulation. The amount of shadowing varies depending on instrument material, configuration, thickness, and relative orientation to the optical axis of the OCT [40]. Development of instruments that minimize scatter and shadowing may allow for more precise tissue manipulation. The use of semitransparent rigid plastic material instruments may allow decreased light scatter and improved visibility of adjacent tissue as well as the tissue immediately underlying the instruments [41]. Furthermore, development of new software algorithms may assist in software-based processing of the image to minimize shadowing as well as focusing the OCT image to the area of interest.

#### **6.2 Heads-up surgery**

Recent developments in three-dimensional (3D) heads-up vitreoretinal surgery viewing are also gaining popularity. New digitally assisted vitreoretinal surgery systems allow surgeons to maintain a heads-up position instead of having to look down through the microscope oculars. 3D high-dynamic-range cameras mounted in place of the microscope oculars, which are connected to a central processing unit, finally project live feed onto screen.

Reported advantages of this system include high magnification; improved ergonomics for the surgeon; a decrease in required endoillumination through enhanced digital signal processing; improved depth of field; ability to overlay diagnostic

#### *Advances in Vitreoretinal Surgery DOI: http://dx.doi.org/10.5772/intechopen.83019*

studies, including intraoperative OCT data; and enhanced teaching and observation capabilities [42, 43].

Improved ergonomics is the most important advantage of this system. Without the need to lean forward and look into microscope oculars, the surgeon can sit back in the chair and use the backrest for back support. This setup can reduce back and neck strains, especially for long surgeries in complicated cases. Image quality depends on specific conditions, such as distance of the display from the surgeon, angle of the display relative to the surgeon, and minimization of glare. The monitor positioning must be as straight as possible to achieve optimal image quality. Because an assistant sits perpendicular to the patient's head, there is a need for a head turn toward the screen, which may require more time for the assistant to adapt.

With the surgery displayed on the screen, anyone in the room wearing 3D glasses is able to see the details of surgery. This provides an important educational benefit, allowing trainees to observe exactly what the surgeon is doing.

One of the important benefits of digital image processing is being able to use lower endoillumination levels by increasing the camera aperture settings, potentially decreasing phototoxicity, especially for macular cases. Another benefit includes real-time image processing and color manipulation, which can allow better visualization of the vitreous and decreased glare. The increase in depth of field and wider field of view also helps in complex cases, such as proliferative vitreoretinopathy involved in complex retinal detachment, intraocular foreign body, and scleralfixated intraocular lens cases. Further developments in real-time digital signal processing area also could enhance this technology more.

In summary, new developments in MiOCT systems offer immediate imageguidance for vitreoretinal surgeons; they may improve our understanding of effects of surgical manipulation on tissues and possibly allow us to explain and predict variations in postoperative visual outcomes. Heads-up digitally assisted surgical viewing systems change the ergonomics as well as enhance the viewing and teaching capabilities in the operating rooms.

## **7. Dyes**

For vitreoretinal surgery, vital dyes enable easier identification of the semitransparent preretinal membranes. Current recommendations for the application of dyes during vitreoretinal surgery indicate that indocyanine green, infracyanine green, brilliant blue, and bromophenol blue may be the best stains for the internal limiting membrane (ILM), while trypan blue may be preferred for staining the glial tissues like epiretinal membrane [44].

In regard to the toxicity issues in chromovitrectomy, a large number of experimental and clinical investigations in this challenging field with vital dyes have yielded some controversial results, but preliminary conclusions may be drawn at this time. Indocyanine green has been proven to be toxic to the retina, and brilliant blue showed a better safety profile and could protect against apoptosis, at least in vitro [44, 45].

Each vital dye injected intravitreally poses a rather dose-dependent toxicity to the retinal tissue. Furthermore, there is solid proof that light exposure, osmolarity, and existence of ions, for example, Na + and iodine, may apply further harm to the retina. Along these lines, general proposals for all vital dyes incorporate injection of a very low amount onto the retina, staying away from long macular exposure to endoillumination and expulsion of sodium and iodine from dye solutions.

## **8. Endoscopic vitrectomy**

Endoscopic vitrectomy provides direct visualization of the posterior segment with a directional camera, allowing surgeons to bypass compromised anterior segments, opacified corneas, and media opacities. Additionally, the ability to direct the visualization from the pars plana allows surgeons a method to visualize the anterior retina, ciliary body, and posterior iris surface in their natural anatomic configuration. New techniques are continually being described that demonstrate how endoscopic vitrectomy is beneficial to the retinal surgeon. The most obvious advantage of endoscopic vitrectomy is the ability to provide excellent visualization in eyes with the opacified cornea and lens. It may also allow extreme peripheral panretinal photocoagulation in the patients with peripheral ischemic retinopathies. It allows endoscopic cyclophotocoagulation in patients with glaucoma, either at the time of cataract surgery or as a stand-alone procedure [46].

 There are limitations to utilization of an endoscope, such as limited field of view, which requires some adjustment given the familiarity with wide-field viewing systems. Additionally, the view is monocular, so the surgeon must utilize other cues, such as focus, size, and light intensity, to compensate [47]. The free rotation ability of the endoscope probe creates difficulty with orientation, making movements within the eye challenging, especially in the learning period of surgeon. Despite these limitations, endoscopic vitrectomy is a useful addition to the retinal surgeon's armamentarium. The ability to bypass media opacities and to visualize structures otherwise not visible creates opportunities for unique surgical interventions in complicated and even inoperable surgical situations.

## **9. Surgical techniques**

#### **9.1 Scleral buckle**

 There are variable techniques used for vitreoretinal surgeries, and they are all being continuously refined. Scleral buckle is an example originated in the 1950s but is still developing. Some modifications are still being reported on scleral buckle; as mentioned earlier in this chapter, using chandelier lightning and WAV systems, instead of indirect ophthalmoscopy, becomes the preferred method of choice in many retina clinics. Chandelier assistance obviates the need for indirect ophthalmoscopy and capitalizes on the advantages provided by the operating microscope and modern wide-angle viewing systems such as an improved view of the peripheral retina with oblique lighting to perhaps improve identification of peripheral breaks. Wide-field viewing may also make subretinal fluid needle drainage safer as it may decrease the risk of losing the view of the needle, which may occur with indirect ophthalmoscopy. Moreover, chandelier buckling allows trainers to view same with the surgeon and is better for teaching purposes. In addition, chandelierassisted scleral buckling permits standard microscope-facilitated recording of the important surgical steps of this procedure, which also facilitates dissemination of scleral buckling techniques. Many authors of the published literature regarding this technique also mention the improved ergonomics of using the operating microscope to perform examination and treatment of retinal breaks instead of indirect ophthalmoscopy [13].

Classic scleral buckle surgery normally incorporates a substantial or 360-degree peritomy. A recent report detailed a method for segmental buckle through a small conjunctival opening, which was utilized in uncomplicated rhegmatogenous retinal detachments [48]. This surgical technique incorporates performing 5 to 6 mm radial conjunctival cut in close to the retinal break without cutting the limbal conjunctiva and Tenon's layer, followed by cryopexy and implantation of a small segmental buckle that was sutured through the conjunctival opening. Cosmetic and functional results were reported as quick and superb.

## **9.2 Suprachoroidal buckle**

Another imaginative method has been depicted for suprachoroidal buckle surgery. In this method, a lighted catheter is inserted into the suprachoroidal space and placed to any desired area over the breaks; there, an enduring hyaluronic acid filler can be injected to create choroidal indentation. This can be performed with or without pars plana vitrectomy and has been reported effective for the treatment of patients with retinal detachment [49, 50].

## **9.3 Macular surgeries**

Inverted internal limiting membrane (ILM) flap technique has been reported to improve the closure rates of large and persistent macular holes [51]. This technique has recently been suggested for the treatment of macular retinal detachment due to macular holes in highly myopic eyes in which macular holes are relatively difficult to close [52]. Higher rates of macular hole closure and retinal attachment, and additionally a little yet noteworthy improvement in visual acuity, were accomplished with this procedure [53]. It has been recommended that the inverted ILM flap stimulates the multiplication of glial cells that helps in closing the macular hole.

 Another interesting new technique has been reported for the treatment of macular folds. Detachment of macula performed by subretinal injection of balanced salt solution and minimal amount of filtered air. Under these conditions, the action of gravity of the PFC liquid and with an active globe rotation has been reported to achieve successful flattening of the macula [54].

## **9.4 Pars plana vitrectomy for retinal detachment**

Development of improved retinopexy methods which could produce immediate chorioretinal adhesion of sufficient strength may obviate the need for long-term tamponade. Recent studies have evaluated the potential of high-frequency electric welding was able to create an immediate retinopexy equal in strength to mature laser retinopexy, which takes about 2 weeks to achieve maximum adhesion [55]. Previously reported methods to achieve adhesion include the development of biocompatible glues, analogous to fibrin [56, 57]. The elimination of long-term gas tamponade and elimination of the need for patient positioning may be the next major advance in retinal detachment surgery.

An interesting technique has been suggested to prevent passage of PFC liquid into the subretinal space. After performing vitrectomy, viscoelastic material was injected over areas where confluent retinal folds were formed with possible retinal breaks. This protective layer still prevents PFC liquid from entering the subretinal space [58].

Pneumatic retinopexy is also an option for retinal detachments caused by within one-clock hour of the retinal arc in the upper two-thirds of the retina and sufficiently clears media to rule out the presence of other retinal breaks. In cases when cryopexy is not performed, it may be difficult to visualize and localize the retinal breaks after the intravitreal gas injection. A recent report of preoperative laser marking of the ora serrata at the meridians of the break made it easy to find after pneumatic retinopexy has been performed [59]. The gas used for pneumatic retinopexy is usually C3F8 or SF6 at 100% expansile concentration, which allows for injection of a relatively small volume of gas that later expands and can cover a greater area of the retinal surface [60]. The advantage of using air is its faster rate of elimination, which allows the patients to regain good visual acuity sooner (5 days versus 2–4 weeks with the gases).

A recent study reported on proliferative vitreoretinopathy retinal detachment cases, intravitreal conbercept administrated a week prior to surgery. Administration of conbercept, a recombinant fusion protein with antivascular endothelial growth factor (VEGF) activity, was found to reduce the rate of intraoperative bleeding, which can facilitate the management of these difficult cases.

Partially fluorinated alkanes that were introduced as long-term heavy tamponades, which are heavier than water, may be of benefit especially in the treatment of inferior retinal detachment cases. One of these is F6H8, which is not routinely used due to its early dispersion and emulsification with consequent inflammatory response. A study investigated its use in combination with silicone oil, in a series of eyes with inferior retinal detachment, where F6H8 was used to flatten the retina and was later partially mixed with silicone oil for long-term tamponade. This combination resulted in a clear tamponade allowing postoperative visualization of the retina, with no emulsification, inflammation, or other complications [61].

 Another option is planning a stage two procedure; after the initial vitrectomy was performed, PFC liquid is infused overlying the optic nerve head until a complete fill of the vitreous cavity was achieved. Patients were instructed to avoid facedown positioning. The staged second procedure was performed 16 to 21 days after all laser scars were noted to be pigmented, with a silicone soft-tip extrusion cannula to remove PFC liquid. Repeated fluid-air/air-fluid exchange was used to remove all PFC from the vitreous cavity. When present anterior chamber PFC also has to be removed [62].

### **10. Conclusion**

 The new developments in surgical instruments, machines, trocars, viewing systems, and surgical techniques played significant role in decreasing complications and improving outcomes of modern vitreoretinal surgeries. There are still some problems to solve in modern vitreoretinal surgeries, like finding a better tamponade that does not have necessity to remove from the eye yet also stabilize the retinal breaks better with good visual recovery from the first postoperative day. Also better drugs needed to be discovered to prevent proliferative vitreoretinopathy and hypotony. In addition there are new achievements in stem cell therapies and artificial retinal implants. The progress in vitreoretinal surgery area is ongoing faster than ever before. In the near future, surgery will be an option for a variety of different vitreoretinal pathologies, including cases we classify as inoperable today.

## **Conflict of interest**

The author did not have a conflict of interest for any products mentioned in the above text.

*Advances in Vitreoretinal Surgery DOI: http://dx.doi.org/10.5772/intechopen.83019* 

## **Author details**

Baris Komur Istanbul Haseki Education and Research Hospital, Turkey

\*Address all correspondence to: bkomur@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## *Edited by Alireza Ziaei*

 Imagination is the key to any discovery, and its presence in the science to improve vision is no exception. Vision science is racing forward, spurred on by a host of exciting novel research discoveries and the eforts of scientists. Tis book, a collection of reviewed and relevant research chapters, intends to provide readers with a comprehensive overview of the latest and most advanced fndings in several aspects of ophthalmology, ophthalmic pathology, ocular imaging, and certain treatments and surgical strategies. It is an excellent, well-integrated review of treatment options in eye disease that aims to provide a thorough overview of the recent developments writen by international authors. "Frontiers in Ophthalmology and Ocular Imaging" can be used as an important reference for clinically oriented ophthalmologists and scientists.

Published in London, UK © 2019 IntechOpen © brunorbs / iStock