**10. Refractive disorders**

#### **10.1 Definitions**

Ametropia, which is defined as the presence of any of the refractive disorders, is the most commonly diagnosed disorder of the human eye. Ametropia includes the hyperopia, myopia and astigmatism. The most common refractive error in the pediatric population is myopia. The World Health Organisation estimates refractive disorders to be 2-10% worldwide. The prevalence is found to be much higher in the Far East. The prevalence of astigmatism of 1 diopter or more is 50% in infancy. The prevalence decreases rapidly during the process of emmetropization. Only few children develop astigmatism greater than 1 diopter by 6 years of age (Maida et al., 2008).

#### **10.2 Etiology**

12 Complementary Pediatrics

of the infant can be checked. An infant should be able to fix and follow faces within 2-3 weeks of age (Allen, 2000). The ability of the young children to fixate and follow a small target is an important gross evaluation of vision. Consistent objection from the child to having one eye occluded suggests that the un-occluded eye is amblyopic. Refraction examination and the red reflex test should be performed. The red reflex test is a screening test for retinal abnormalities and opacities in the visual axis such as congenital cataract and corneal opacities. It is performed by focusing an ophthalmoscope light from 30 cm away from the child's eyes. If the red reflex of the 2 eyes is symmetrical, the test is normal. Dark spots in the red reflex or leukocoria (white reflex instead of red reflex) are indications for

Special tests to confirm that, an infant sees, may be performed. Optokinetic drum test and the spinning test are the most popular simple methods to confirm visual response in an infant. Forced choice preferential looking is a popular way of quantifying infant vision. Portable cards; namely Teller or Keeler cards are used to quantify infant vision. Optotype tests to quantify visual acuity may be used in children between 1-3 years of age. Cardiff acuity cards at 1-2 years of age and Sheridan Gardner optotypes at 2-3 years of age are the most commonly preferred ones. In children over 3 years of age, Snellen acuity charts may be used. Eye movements and the position of the eyes should be simply observed. Hirschberg test, which is a light reflex test, is used to exclude manifest eye deviations. If an infant with manifest deviation fixates the penlight, the corneal reflex will be eccentric in the deviating eye. The reflex will be displaced nasally in the exotropia, and temporally in the esotropia.

Pupils are smaller and poorly reacting in the newborns. Normal pupillary reactions should be documented by 3 months of age. Iris colour is permanent at 1 year of age. Colour vision assessment can be performed by the Hardy-Rand- Rittler plates in children as young as 3 years of age (Mollon et al., 1991). If the child cannot tolerate ophthalmic examination and detailed examination is indicated, sedation can be required. Routine intraocular pressure

Eye examinations after 3 years of age are more informative and more easily performed. Visual acuity assessment and the fundamental parts of eye examinations are similar with the adult patients. However, the physicians should keep in mind that, refractive status of the eye is very dynamic in preschool and school children, and preschool vision screening is

Ametropia, which is defined as the presence of any of the refractive disorders, is the most commonly diagnosed disorder of the human eye. Ametropia includes the hyperopia, myopia and astigmatism. The most common refractive error in the pediatric population is myopia. The World Health Organisation estimates refractive disorders to be 2-10% worldwide. The prevalence is found to be much higher in the Far East. The prevalence of astigmatism of 1 diopter or more is 50% in infancy. The prevalence decreases rapidly during the process of emmetropization. Only few children develop astigmatism greater than 1

measurement in cases with congenital glaucoma is an example for such conditions.

referral to an ophthalmologist.

recommended for all children.

**10. Refractive disorders** 

diopter by 6 years of age (Maida et al., 2008).

**10.1 Definitions** 

The total refractive power of the human eye is approximately 60 diopters (D). The cornea provides two thirds of this total power and the lens provides the remaining 20 D. The normal eye creates clear images by focusing the images on the retina. If the unaccommodated eye focuses the images behind the retina, hperopia (farsightedness) develops. On the other hand myopia (nearsightedness) is the state in which the unaccommodated eye focuses the images in front of the retina. The hyperopia and myopia may be due to altered total refractive power of the eye, but the axial length changes instead of that is the most common reason in most of the cases. Reduced axial length results in hyerpopia and the reverse in myopia (Riordan-Eva, 2004).

The parental history of myopia, genetic predisposition and various environmental factors are associated with the development of myopia in a child. Familial predisposition also exists in hyperopia, which is much less common in the pediatric population. The children can tolerate low amounts of hyperopia by accommodation, so most of the low amounts of hyperopia are unrecognized in this population. However, higher degrees may result in amblyopia and should be corrected promptly.

A healthy eye is able to focus all the light rays from a point source to a single point. In the presence of astigmatism, this focusing process to a single point is disrupted due to variations in the curvature of the cornea or lens at different meridians. Most of the astigmatisms are the consequences of alterations in corneal curvatures. In other words, the refractive power of some part of the cornea is higher or lower than the rest of the cornea, so the astigmatism results. If these regions of the cornea with different refractive power capacity are 90 degrees apart, the astigmatism is regular. If these regions are not 90 degrees apart, it is called irregular. Keratoconus is an important reason for irregular astigmatism.

#### **10.3 Management**

Spectacles, contact lenses, refractive surgery, intraocular lenses and clear lens extraction are the current methods of refractive correction. Refractive disorders place a significant economic and social burden on society. In USA, \$4.6 billion was spent for treatment of myopia in 1990. Spectacles continue to be the safest method of correction, whereas the interventional procedures are very rarely preferred in the pediatric population. Anisometropia refers to a difference in the refractive status of the 2 eyes. If the difference is 2 diopters or more, either spherical or astigmatic, it is clinically significant. Anisometropia should be managed with caution, since it is the most important risk factor for amblyopia.

### **11. Amblyopia**

#### **11.1 Definition**

A physician must be aware of the definition of amblyopia properly to understand the importance of early diagnosis and management of amblyopia. Amblyopia is the combination of two Greek words; amblyos – blunt and opia –vision. The parents commonly

Pediatric Ophthalmology / Eye and Disorders 15

cortex which receives the inputs from the bad eye. This is possible if the neurological plasticity of the visual cortex remains. The best outcomes are achieved if the management starts before 5 years of age, but the patching may be tried up to 22 years of age (Matta et al., 2010). If children cannot tolerate patching, the penalization, which is the impairment of vision in the sound eye by eye drops, can be preferred. There is no consensus on the duration of patching per day and the total duration of the treatment. However, it is known that, it is long treatment frequently lasting more than years. Well cooperation with the parents is crucial to obtain successful outcomes. It is commonly accepted that amblyopia cannot be treated beyond a certain age. However, some trials to manage amblyopia in adults gave promising results. Perceptual visual learning and levodepo are the possible new treatment modalities for amblyopia in the elderly. These may also be tried in elder children,

Under normal physiological conditions, the image of an object falls simultaneously on the fovea of each. This is possible if the eyes are properly aligned. This straight position of the eyes is called orthophoria. Any misalignment of the either eye is called strabismus or eye deviation in other words. There are 2 benefits of treating strabismus. The initial one is functional gain including the improvement of visual acuity and stereopsis. The second one

Tropia defines manifest deviation of eyes and phoria implies latent deviation. Phoria is detected by the simple cover-uncover test. The test is performed while the patient fixates a distant object. The physician covers one eye for 2-3 seconds and then the other eye. If orthophoria is present, no movement is detected. If latent deviation exists movement of eyes towards the opposite of the deviation is observed. For example in a patient with inward latent deviation, the uncovered eye move from inwards to outwards. Latent deviations may become manifest temporarily, when the child is tired or ill. It can also become permanently

Horizontal deviations are the most commonly observed types of strabismus. Esotropia is the manifest inward deviation of eyes, while esophoria is the latent inward deviation of eyes. Exotropia is the manifest outward deviation of eyes, while exophoria is the latent outward deviation of eyes. Esotropia is by far the most common form of strabismus. Infantile esotropia constitutes almost half of all cases of esotropia. Infantile esotropia is the inward deviation of eyes, which is diagnosed at 6 months of age. The angle of deviation is usually large and surgery is usually indicated. Pseudo-strabismus is the illusion of deviation in a child with orthophoria. It is most commonly in the form of pseudo-esotropia. The most common reason for this false appearance of inward deviation is broad nasal bridge with prominent epicanthal folds. This appearance usually resolves spontaneously and requires

Paralytic strabismus in children may be in form of third, fourth or sixth cranial nerve palsy.

if conventional treatments fail (Astle et al., 2011).

**12. Pediatric eye deviations** 

is the cosmetic improvement.

**12.1 Types of eye deviations** 

manifest during the follow-up.

no treatment (Fredrick, & Asbury, 2004).

use the lazy eye terminology instead of ambloypia. Due to the suppression of the blurred vision from the diseased eye, the risk of development of unilateral amblyopia is much higher than the risk of bilateral amblyopia. However, it may also develop bilaterally, if severe visual deprivation occurs in both eyes. A same ocular pathology that develops in a child may be an important etiology for a severe amblyopia, while the same pathology in the elderly decreases the visual acuity, but does not result in an amblyopia. This is very typical for the lens pathologies. Congenital cataracts are one of the important etiologies for amblyopia, while senile cataracts are the most common treatable cause of vision loss among the elderly. Any pathology that results in abnormal visual experience in one or two eyes before the critical period of visual development may result in amblyopia. The critical period usually ends at 6-8 years of age (Morishita, & Hensch, 2008). The amblyopia is the disease of the visual cortex and it only develops in children younger than 6-8 years old. The critical period is the time of maximum neurological plasticity of the visual cortex cells. The visual acuity and binocular vision improves depending on the visual inputs until the end of the critical period. There is no consensus on which visual acuity should be adopted for the clinical definition of amblyopia. The cut-off level varies between 20/40 and 20/30 and the prevalence also varies accordingly. The prevalence of the disease may be considered approximately 2% in the general population (Webber & Wood, 2005).

#### **11.2 Etiology**

There are many treatable and untreatable causes of amblyopia. The most common etiologies are eye deviations and refractive errors. Anisometropia is a significant difference in the refractive status between the two eyes. The eye with more hypermetropia or more astigmatism is chronically blurred, so the risk of the development of amblyopia is high in that eye. Congenital cataracts, retinoblastoma, nystagmus, corneal opacities and any ocular media opacities including vitreous hemorrhages may end up with amblyopia, if they occur before the critical period of visual development (Carlton & Kaltenthaler, 2011).

#### **11.3 Management**

The severity of the amblyopia depends on the severity of the blur, the duration of the abnormal vision and the age of onset of the visual impairment. The pediatrician plays a crucial role in the early diagnosis of possible causes of amblyopia. The major determinants of success in amblyopia treatment are early recognition by the pediatrician, early referral to the pediatric ophthalmologist and prompt treatment.

The initial step in the management is the correction of the underlying etiology, if possible. Surgical treatment of the strabismus, or the congenital cataract, correction of the refractive errors by glasses or contact lenses are the main treatment modalities for the correction of the most common causes of amblyopia. In some pathologies, such as nystagmus, retinoblastoma, it is not possible to eliminate the underlying cause of blurred vision totally. Therefore, the management of amblyopia due to such untreatable diseases is very difficult.

After the correction of the underlying organic pathology, the most difficult aspect of the management starts; the occlusion of the sound eye in most cases or the alternate occlusion if the condition is bilateral. The aim of the patching the diseased eye is to improve the visual

use the lazy eye terminology instead of ambloypia. Due to the suppression of the blurred vision from the diseased eye, the risk of development of unilateral amblyopia is much higher than the risk of bilateral amblyopia. However, it may also develop bilaterally, if severe visual deprivation occurs in both eyes. A same ocular pathology that develops in a child may be an important etiology for a severe amblyopia, while the same pathology in the elderly decreases the visual acuity, but does not result in an amblyopia. This is very typical for the lens pathologies. Congenital cataracts are one of the important etiologies for amblyopia, while senile cataracts are the most common treatable cause of vision loss among the elderly. Any pathology that results in abnormal visual experience in one or two eyes before the critical period of visual development may result in amblyopia. The critical period usually ends at 6-8 years of age (Morishita, & Hensch, 2008). The amblyopia is the disease of the visual cortex and it only develops in children younger than 6-8 years old. The critical period is the time of maximum neurological plasticity of the visual cortex cells. The visual acuity and binocular vision improves depending on the visual inputs until the end of the critical period. There is no consensus on which visual acuity should be adopted for the clinical definition of amblyopia. The cut-off level varies between 20/40 and 20/30 and the prevalence also varies accordingly. The prevalence of the disease may be considered

There are many treatable and untreatable causes of amblyopia. The most common etiologies are eye deviations and refractive errors. Anisometropia is a significant difference in the refractive status between the two eyes. The eye with more hypermetropia or more astigmatism is chronically blurred, so the risk of the development of amblyopia is high in that eye. Congenital cataracts, retinoblastoma, nystagmus, corneal opacities and any ocular media opacities including vitreous hemorrhages may end up with amblyopia, if they occur

The severity of the amblyopia depends on the severity of the blur, the duration of the abnormal vision and the age of onset of the visual impairment. The pediatrician plays a crucial role in the early diagnosis of possible causes of amblyopia. The major determinants of success in amblyopia treatment are early recognition by the pediatrician, early referral to

The initial step in the management is the correction of the underlying etiology, if possible. Surgical treatment of the strabismus, or the congenital cataract, correction of the refractive errors by glasses or contact lenses are the main treatment modalities for the correction of the most common causes of amblyopia. In some pathologies, such as nystagmus, retinoblastoma, it is not possible to eliminate the underlying cause of blurred vision totally. Therefore, the management of amblyopia due to such untreatable diseases is very difficult. After the correction of the underlying organic pathology, the most difficult aspect of the management starts; the occlusion of the sound eye in most cases or the alternate occlusion if the condition is bilateral. The aim of the patching the diseased eye is to improve the visual

approximately 2% in the general population (Webber & Wood, 2005).

before the critical period of visual development (Carlton & Kaltenthaler, 2011).

the pediatric ophthalmologist and prompt treatment.

**11.2 Etiology** 

**11.3 Management** 

cortex which receives the inputs from the bad eye. This is possible if the neurological plasticity of the visual cortex remains. The best outcomes are achieved if the management starts before 5 years of age, but the patching may be tried up to 22 years of age (Matta et al., 2010). If children cannot tolerate patching, the penalization, which is the impairment of vision in the sound eye by eye drops, can be preferred. There is no consensus on the duration of patching per day and the total duration of the treatment. However, it is known that, it is long treatment frequently lasting more than years. Well cooperation with the parents is crucial to obtain successful outcomes. It is commonly accepted that amblyopia cannot be treated beyond a certain age. However, some trials to manage amblyopia in adults gave promising results. Perceptual visual learning and levodepo are the possible new treatment modalities for amblyopia in the elderly. These may also be tried in elder children, if conventional treatments fail (Astle et al., 2011).
