Normal Functions of the Eye Motility System

Chapter 2

Abstract

and amblyopia.

1. Introduction

9

attention on an object of regard.

and Anushree Naidu

Binocular Functions

Keywords: accommodation, binocular vision, stereopsis

Arvind Kumar Morya, Kanchan Solanki, Sahil Bhandari

Binocular single vision is the ability to use both eyes simultaneously so that each

Binocular single vision is the ability of both eyes to contribute to simultaneous perception by contemporaneous use of each of them. Normal binocular single vision results due to the presence of bifoveal fixation and normal retinal correspondence and vice versa. Romano and Romano described binocular vision as—state of simultaneous vision with two seeing eyes that occurs when an individual fixes his visual

Historically, there are two schools of thought with regard to the origin and

1. Theory of empiricism: This theory describes that binocular vision depends on ontogenetic development. One describes that humans are born without binocularity or spatial orientation and these functions are acquired as a result of experiences from everyday life. This acquisition of this function is aided by

development of normal binocular vision and spatial orientation.

all other sensations especially kinesthetic sense.

eye contributes to a common single perception. Normal binocular single vision occurs with bifoveal fixation and normal retinal correspondence in everyday sight. There are various anatomical and physiological factors concerned in the development of Binocular vision. The development of binocular function starts at 6 weeks and is completed by 6 months. Any obstacles, sensory, motor, or central, in the flex pathway is likely to hamper the development of binocular vision. The presence of these obstacles gives rise to various sensory adaptations to binocular dysfunction. Clinically the tests used can be based on either of the two principles: (A) assessment of relationship between the fovea of the fixing eye and the retinal area stimulated in the squinting eye, viz. Bagolini striated glasses test, red filter test, synoptophore using SMP slides for measuring the objective and subjective angles, and Worth 4-dot test; and (B) Assessment of the visual directions of the two foveae, viz. after image test (Hering Bielschowsky); and Cuppers binocular visuoscopy test (foveofoveal test of Cuppers). Anomalies of binocular vision results in confusion, diplopia, which leads to suppression, eccentric fixation, anomalous retinal correspondence,

## Chapter 2 Binocular Functions

Arvind Kumar Morya, Kanchan Solanki, Sahil Bhandari and Anushree Naidu

### Abstract

Binocular single vision is the ability to use both eyes simultaneously so that each eye contributes to a common single perception. Normal binocular single vision occurs with bifoveal fixation and normal retinal correspondence in everyday sight. There are various anatomical and physiological factors concerned in the development of Binocular vision. The development of binocular function starts at 6 weeks and is completed by 6 months. Any obstacles, sensory, motor, or central, in the flex pathway is likely to hamper the development of binocular vision. The presence of these obstacles gives rise to various sensory adaptations to binocular dysfunction. Clinically the tests used can be based on either of the two principles: (A) assessment of relationship between the fovea of the fixing eye and the retinal area stimulated in the squinting eye, viz. Bagolini striated glasses test, red filter test, synoptophore using SMP slides for measuring the objective and subjective angles, and Worth 4-dot test; and (B) Assessment of the visual directions of the two foveae, viz. after image test (Hering Bielschowsky); and Cuppers binocular visuoscopy test (foveofoveal test of Cuppers). Anomalies of binocular vision results in confusion, diplopia, which leads to suppression, eccentric fixation, anomalous retinal correspondence, and amblyopia.

Keywords: accommodation, binocular vision, stereopsis

#### 1. Introduction

Binocular single vision is the ability of both eyes to contribute to simultaneous perception by contemporaneous use of each of them. Normal binocular single vision results due to the presence of bifoveal fixation and normal retinal correspondence and vice versa. Romano and Romano described binocular vision as—state of simultaneous vision with two seeing eyes that occurs when an individual fixes his visual attention on an object of regard.

Historically, there are two schools of thought with regard to the origin and development of normal binocular vision and spatial orientation.

1. Theory of empiricism: This theory describes that binocular vision depends on ontogenetic development. One describes that humans are born without binocularity or spatial orientation and these functions are acquired as a result of experiences from everyday life. This acquisition of this function is aided by all other sensations especially kinesthetic sense.

2. Theory of nativistic teaching: This theory states that simultaneous perception and binocular vision occur asresult of innate process viz. anatomicophysiological arrangement of components of visual system. This describes that binocular vision is acquired phylogenetically and not ontogenetically [1]. In simple words empiricism states that binocular function develop due to self- learning with trial and error and nativistic theory states that binocular function develops due to coordinated effort of the visual pathway.

### 2. Binocular vision and its development

During the initial few years of life certain normal anatomical and physiological conditions are required for the development of binocular vision [2]. The factors required for the development of Binocular vision and which enable the eyes to function in a coordinated manner are as follows [3, 4]

	- i. Architecture of the orbit
	- ii. Ligaments, muscles and connective tissues, i.e., adjacent ocular structures.

The extra-ocular muscles play an important role as they provide motor correspondence because of the reciprocal innervation of the extra-ocular muscles [4].

Following are the aims of motor correspondence:


#### i. Fixation reflexes


#### iv. The pupillary reflex

#### 3. Fusion reflex, i.e., psycho-optical reflex and its development

Cerebral activity maintains the fusional reflex which are either conditioned or acquired. They develop as a result of experience gained from environmental stimulus. Once these reflexes are formed as a result of continuous reinforcement they transform into unconditioned reflexes. Aimed to form binocular single vision, it consists of all the activities generated from the retina through the brain to maintain the images received on the fovea of both the eyes.

The elements of fusion mechanism are:


At birth, the child has random, nonconjugate and aimless ocular movements and the fixation reflex is very poorly developed. During the first few weeks of life there are no pursuit movements. The optomotor reflex is essentially a postnatal event, and it follows the following time schedule:

• First 2–3 weeks—follows light uniocularly


Various electrophysiological studies have been done in infants, which be proved to be promising in detection of stereoacuity between the age of 2–5 months. But from the age of 6 months to 3 years when the child can sufficiently comprehend to subjects the knowledge about the development of stereoacuity is miniscule. However, it was found that there stereoacuity improves gradually up to the age of 9 years. From the above literature, it is noticed that the sensitive period of development of binocular vision in human beings begins at about 4 months of age, peaks at 2 years, it is well developed by 4 years of age and slowly stops by 9 years of age. Hence it was found that the first 2 years of life is very critical for the development of binocular single vision and any obstacle during the first 2 years can hamper the development of binocular vision. The obstacle in the reflex pathway is likely to hamper the development of binocular vision can be due to the following reasons.

There can be many forms of obstacle in the development of binocular vision viz.

#### 1. Central obstacles

	- Dioptric obstacles—e.g., opacities in the media, refractive errors that are uncorrected.
	- Prolonged uniocular activity—e.g., severe ptosis, anisometropia
	- Retinoneural obstacles—lesions of retina, optic nerve
	- Proprioceptive obstacle
	- Congenital craniofacial malformations
	- CNS lesions—involving the nerve trunks, root of nuclei

The presence of any of these obstacles gives rise to various sensory adaptations to binocular dysfunction disruptive factor is present in the sensitive period. This can be in the form of:


### 4. Theories of binocular vision


#### 4.1 Projection theory of binocular vision

This is an obsolete theory. According to this theory Visual stimuli are exteriorized along the lines of direction. If a person fixates binocularly, a "bicentric" projection is supposed to occur that places the impression of each eye at the point of intersection of the lines of projection [5, 6].

This theory fails to explain certain fundamental observations such as


The basic reason for the failure of the projection theory is that the distinction between physical and subjective space is disregarded and it does not explain the localization to a dioptic-geometric scheme.

#### 4.2 Theory of isomorphism

This theory of binocular vision was developed by Linksz based on a rigid retinocortical relationship [7]. He believed that fusion is based on neuroanatomical connections in the cerebral cortex. The retinas of both the eyes are excited into close proximity within the visual cortex. The corresponding elements are consummated in Gennari's stripe, which he considered to be the anatomical counterpart of the horopter plane in objective space and of the nuclear plane in subjective space. But till date there is no evidence for the physiologic rigidity of the retinocortical relationship or the convergence of the pathways on which it is based.

#### 4.3 Correspondence and disparity theory

According to this theory sensory binocular cooperation is based on system of correspondence and disparity [8]. It assumes the presence of one to one retinocortical relationship between the two eyes. They transmit single visual impression with no depth quality when stimulated simultaneously by one object point. Binocular rivalry occurs when stimulated simultaneously by two object points that differ in character. Diplopia occurs when disparate elements are stimulated by one object point. However, a single visual impression is elicited with depth perception, if horizontal disparity remains within limits of Panum's area. With the increasing disparity the perceived depth increases. However, quality of stereopsis decreases with increasing disparity which may eventually lead to diplopia.

#### 4.4 Neurophysiological theory of binocular vision and stereopsis

Approximately [9] 80% of the neurons in the striate cortex can be stimulated from either eye in response to a visual stimulus, assuming there is a precise and orderly arrangement of connections along the retino-geniculate striate pathway. Of these 75% represented graded response from either left or right eye while 25% are binocularly driven cells and are equally stimulated from each eye. These 75% cells that could be driven by stimulation of either eye had receptive fields of nearly equal size and in corresponding positions of visual field. In normal binocular single vision, optical stimulus will excite a cortical cell only. Only one object feature is detected by each cortical cell and assigned by it to a single locus in space although two receptive fields are involved. Anatomically identical regions in the two retinas are not always occupied by the two receptive fields. There are cells whose fields have exactly corresponding points in the two retina and cells whose fields have slightly different position in the two eyes is seen at a given locus in the retino-optic cortical map. This retinal field disparity is detected by sensitive binocular neurons giving rise to binocular vision and stereopsis which occurs as a result of the difference in direction or distance of the fields in each retina forms the basis of Panum's fusion area.

#### 5. Review of literature


#### 6. Fusion, diplopia, and the law of sensory correspondence

An object is positioned at a convenient distance in front of an observer at eye level and in the midplane of the head. An image will be received on matching areas of the two retinas if the eyes are properly aligned and if the object is fixated binocularly. The two images will be the same in size, illuminance, and color if both eyes are functioning normally and equally. Though two separate physical (retinal) images are formed, only one visual object is perceived by the observer. This phenomenon is so natural to us that the naive observer believes it to be normal, he is surprised only if he sees double. Yet the opposite—single binocular vision from two distinct retinal images—is the truly remarkable phenomenon that needs an explanation.

Binocular single vision occurs when the image formed in the retina from each eye contributes to a single, common perception. It is considered in three grades:


#### 7. Prerequisites for binocular vision


Binocular single vision can be classified into three stages according to Worth's classification (Figure 1)

#### Figure 1.

The classical model of binocular visual function is composed of three hierarchical degrees.


#### 7.1 Simultaneous perception and superimposition

The ability of both the eyes to perceive simultaneously two images, one formed on each retina is defined as simultaneous perception. Simultaneous perception of the two images formed on corresponding areas, with the projection of these images to the same position in space is superimposition. This occurs based on the correspondence whether it is normal or abnormal. If fusion does not occur then two similar images are seen as separate but superimposed and no fusion range can be demonstrated.

Binocular Functions DOI: http://dx.doi.org/10.5772/intechopen.84162

Image 2. Simultaneous perception—image for second eye.

Image 3. Simultaneous perception—binocular vision image.

Exemplary on Image 1 there is element visible for one eye and on Image 2 visible for second eye. Patient with ability to simultaneous perception should perceive image similar to Image 3.

#### 7.2 Fusion

Fusion is defined as the unification of visual excitations from the corresponding retinal images into a single visual perception. Fusion can be either sensory or motor.

#### 7.2.1 Sensory fusion

The hallmark of retinal correspondence is the sensory fusion which is defined as is the ability of both the eyes to perceive two similar images, one formed on each retina, when interpreted as one single visual image. The images not only must be

located on corresponding retinal areas but also should be sufficiently similar with respect to size, brightness and sharpness to permit sensory are the prerequisites for sensory fusion. A severe obstacle to fusion are unequal images.

#### 7.2.2 Motor fusion

The ability to align both the eyes in such a way that sensory fusion can be maintained is termed as Motor fusion. Retinal disparity formed outside Panum's area and the eyes moving in opposite direction which may be horizontal, vertical or cyclovergence is the stimulus for these fusional eye movements. Unlike sensory fusion, motor fusion is a function of the extrafoveal retinal periphery. Fusion, whether sensory or motor, is always a central process, i.e., it takes place in the visual cortex.

#### 7.3 Stereopsis

The fused image will be perceived in vivid depth nearer or farther to the point of fixation within some range of limiting conditions, when two similar images are presented to both the eyes with a binocular disparity that has a horizontal component. The objects give rise to the stereoscopic depth from Horizontal binocular disparities, e.g., arrow at different distances and it gives rise to stereoscopic depth perception. Here the arrowhead has a lesser eccentricity on the nasal retina of the right eye than on the temporal retina of the left eye. The fovea is the site of fixation. The observer is aware alternately of the image to one eye and the image to the other if such dichoptic image formed is of high contrast, due to binocular rivalry that forms between the two monocular images. As a result of interocular suppression if one eye is strongly dominant as a result of either stimulus characteristics or organismic variables, perception of the image in the other eye may be entirely absent. Prolonged periods of dichoptic summation may be obtained, during which the different stimuli in the two eyes appear to be summed together as if their contrasts were added linearly throughout the dichoptic field. If however, the stimulus contrast is low for dichoptic stimuli. When the presentation time is brief (150 ms) dichoptic summation also is obtained for high contrast stimuli.

Where the image appears doubled but clearly at a different depth from zerodisparity targets stereoscopic depth from horizontal disparities is perceived both in the region of binocular fusion of the monocular targets into a single image and also in the region of diplopia, the smallest disparity interval that produces reliable depth discrimination under particular conditions is stereo acuity.

#### 8. Sensory adaptations in binocular vision

#### 8.1 Suppression

Suppression is a neuro-physiological phenomenon of the eye to prevent diplopia and confusion by suppressing the non-dominant image at the cortical level. Diplopia occurs when fovea of one eye and extra foveal point of the other eye is stimulated simultaneously. Confusion occurs when dissimilar image is projected on fovea of both the eyes.

#### 8.1.1 Types of suppression

Facultative suppression: In Facultative suppression visual acuity is not affected under monocular conditions. Facultative suppression occurs only under binocular conditions.

Obligatory suppression: It occurs even under monocular conditions resulting in diminished visual acuity which further leads to amblyopia.

Central and peripheral suppression: To avoid confusion foveal image of the deviating eye is suppressed which is known as central suppression. Similarly to avoid diplopia extra foveal image of the deviating eye is suppressed resulting in peripheral suppression.

Monocular or alternating: Monocular suppression occurs when the image from the dominant eye always predominates over the image from the deviating eye, so that the image from the latter is constantly suppressed. This leads to amblyopia. When suppression alternates between the two eyes amblyopia is less likely to occur.

#### 8.2 Anamolous retinal correspondence

Anamolous retinal correspondence is a type of sensory adaptation in which fovea of one eye shares a common visual direction with the extra foveal point of the other eye. This is an adaptation in manifest squint resulting in binocular single vision. It is known as anomalous because extra foveal point of one eye corresponds to foveal point of the other eye. But in contrast to eccentric fixation under monocular conditions, fovea of deviating eye takes the fixation which forms the basis for cover test.

Prerequisites for anomalous retinal correspondence:


#### 8.3 Motor adaptations to strabismus

Motor adaptation is in the form of abnormal head posture and occurs primarily in children with congenitally abnormal eye movements who use the abnormal head posture to maintain the binocular single vision.

#### 9. Retinal correspondence

Retinal correspondence occurs when the retinal points of both the eyes share a common visual direction. Non corresponding retinal points will never have a common visual direction.

#### 9.1 Types of retinal correspondence

#### 9.1.1 Normal retinal correspondence

Normal retinal correspondence is defined when fovea of one eye corresponds to the fovea of the other eye and they both share a common visual direction. In NRC,

points located nasal to the fovea in one eye correspond to the points located temporal to the fovea of the other eye.

#### 9.1.2 Abnormal retinal correspondence

Anamolous retinal correspondence is a type of sensory adaptation in which fovea of one eye shares a common visual direction with the extra foveal point of the other eye. This is an adaptation in manifest squint resulting in binocular single vision. It is known as anomalous because extra foveal point of one eye corresponds to foveal point of the other eye. But in contrast to eccentric fixation under monocular conditions, fovea of deviating eye takes the fixation which forms the basis for cover test.

Prerequisites for anomalous retinal correspondence:


#### Figure 2.

Empirical horopter. F, fixation point; FL and FR, left and right foveae, respectively. Point 2, falling within Panum's area, is seen singly and stereoscopically. Point 3 falls outside Panum's area and is therefore seen doubly.

#### 10. Concept of a Horopter

The term Horopter (Figure 2) is derived from Greek words, horos-boundary, opter-observer, was first introduced in 1613 by Aguilonius [5]. The horopter is a curved line formed when all the corresponding points are projected in space at a particular distance from the observer. Hence it is the locus of all points in the space that stimulates the corresponding points of the retina leading to a binocular single vision.

Geometric Vieth Muller horopter is a theoretical horopter. It is a geometrically constructed circle which passes through the corresponding points of the two eyes. But actually it is not spherical, it is flatter. The actual—Empirical horopter curve also known as the longitudinal horopter is slightly flatter than Vieth Muller Geometric horopter. It is formed by using longitudinal bars positioned such that they appear equidistant. The difference between the geometric and the empirical horopter is known as the Hering-Hillebrand deviation. Very small areas around the corresponding points can be binocularly fused to see singly. This is known as Panum's area of binocular fusion. Diplopia elicited by an object point off the horopter but within Panum's fusional area is known as physiological diplopia. Panum's area is narrowest at fovea (6–10° of arc) and broader in periphery (30–40° of arc). Objects lying outside the Panum's area will be perceived double when viewed binocularly. Even though the fusion occurs, a perceptual effort is made which is appreciated by the cortex as depth perception. So Panum's area is physiological basis for our depth perception.

#### 11. Stereopsis (Figure 3)

It is the ability of both the eyes to fuse images that lie within Panum's fusional area resulting in three dimensional perception of the object. Diplopia elicited by an object point off the horopter but within Panum's fusional area is known as physiological diplopia. Images of a single object that do not stimulate corresponding retinal points in both eyes are said to be disparate; binocular disparity is defined as the difference in position of corresponding points between images in the two eyes.

#### Figure 3.

Crossed and uncrossed disparities result when objects produce images that are formed on closely separated retinal points. Any point within Panum's area yields a percept of a single image, while points outside Panum's area produces diplopia.

Binocular disparity or Physiological diplopia can be of two types crossed (temporal or heteronymous) and uncrossed (nasal or homonymous). Crossed diplopia occurs when objects lie in front of the horopter. In crossed diplopia the monocular image of the object perceived by the right eye is displaced to left and the image perceived by the left eye is displaced to the right. Uncrossed diplopia occurs when objects lie behind the horopter. Hence in uncrossed diplopia the monocular image of the object perceived by the right eye is displaced to the right and the image perceived by the left eye is displaced to the left (Figure 3).

#### 12. Stereoscopic acuity

It can be defined as the disparity beyond which no stereoscopic effect can be produced. A threshold of 15–30 arc seconds is considered excellent; however, there is no standardization for the same. There is a critical distance calculated to be 150–200 m beyond which the stereopsis does not work as there is a threshold for stereopsis. The threshold of stereoscopic acuity also depends on the motion of both eye as well as the target object. For static targets the stereoacuity ranges from 2 to 10 arc sec which increases to 40 arc sec for objects in motion. Stereoacuity is maximal about 0.25° off dead center in the foveola. As we move along the x axis the stereoacuity decreases exponentially. Stereopsis is not present beyond 15° from the center. There is a similar exponential decline in the stereoacuity when the target is moved in front or behind the horopter along the y-axis. Stereopsis although is very essential for spatial orientation, it is not the only means of it. The various monocular clues to spatial orientation can be:

Apparent size: It depends on the size of the object as well as the distance of the object from the retina. The objects that are closer to the retina appear larger in size and those farther away appear smaller. Similarly as the object move towards the retina it appears to be increased in size.

Interposition: The objects that are relatively near conceal the objects that are far.

Aerial perspective: Environmental factors like water vapor, dust and smoke cause scattering of the light and hence cause decrease in the color saturation as well as visibility of the distance object.

Shading: Whenever light falls on a solid object it casts shadow and when it falls on the concave surface the shadow is cast in a graded manner.

Geometric perspective: The line that is parallel pragmatically appears to join together near the horizon, e.g., railroad tracks.

Relative velocity: The velocity of image of a moving target that is at a distance is slower that the velocity of image of a moving target that is near.

Motion parallax: If the fixation point is at an intermediate distance the objects that are nearer to it move in the opposite direction when the head is moved and those that are farther away from the fixation point move along with the head.

#### 13. Fusion

Fusion is defined as the amalgamation of visual impulses from the corresponding retinal images into a single visual percept.

#### 13.1 Sensory fusion

When two similar images are formed on the corresponding areas of each eye, the ability to interpret them as one is termed as sensory fusion. Retinal correspondence can be certified from the fact that a single image is formed. Size, brightness and sharpness of similar degree are equally essential components required for sensory fusion to occur as is the retinal correspondence images of unequal size are a severe obstacle to fusion.

#### 13.2 Motor fusion

For the sensory fusion to be maintained it is essential that the eyes are aligned and the ability to do so is termed as motor fusion. Retinal disparity outside Panum's area and the eyes moving in opposite direction (vergence) are the stimuli for the fusional movements. Motor fusion is the exclusive function of the extrafoveal retinal periphery, unlike sensory fusion which is dependent on fovea. However both sensory and motor fusion are central processes the control of which lies in the visual cortex.

#### 13.3 Diplopia

When there is a simultaneous stimulation of two disparate retinal points by a point object, there occurs perception of the object in two different subjective visual directions. An object point seen simultaneously in two directions appears double. Double vision is the hallmark of retinal disparity.

#### 13.4 Binocular rivalry

Retinal rivalry may be observed when dissimilar contours are presented to corresponding retinal areas and fusion becomes impossible. When areas of retinal correspondence are stimulated by dissimilar object, fusion fails to occur and leads to confusion. To surpass this confusion, image from one of the eyes is suppressed. The constant foveal suppression of one eye leads to complete sensory dominance of the other eye with cessation of rivalry, which is a major obstacle to binocular vision. For binocular vision to be functional presence of retinal rivalry is must.

### 14. Grades of binocular vision

Worth's classification of binocular vision:

Grade I: Simultaneous perception is the most basic essential prerequisite for binocular single vision. It is the power to see two dissimilar objects simultaneously.

Grade II: It represents true fusion with some amplitude. The two images are not only fused, but some effort is made to maintain this fusion in spite of difficulties. Addition of motor component to the sensory fusion represents second grade of binocular vision.

Grade III: This is the highest grade of binocular vision in which the images are not only fused but also a stereoscopic view of the image is produced. It is the ability to obtain an impression of depth by the superimposition of two pictures of the same object taken from slightly different angles.

Binocular vision assessment: All the tests are aimed at assessing the presence or absence of:


It is essential to assess the visual acuity, fixation in the deviating eye and direction and amount of deviation in every case.

Test for retinal correspondence:

Clinically the tests used can be based on either of the two principles:

1. Bagolini striated glasses test: The patient is asked to fixate a small light, after being provided

With plano lenses with narrow fine striations across one meridian (micro Maddox cylinders) a source of light is seen as a line at right angles to the striations. The axis of striations of the eyes is kept at right angles to each other. The interpretation of this test is as follows:

	- i. In the absence of a manifest squint, a cross response indicates a normal bifoveal correspondence (NRC).
	- ii. In the presence of a manifest squint, a cross response indicates an anomalous retinal correspondence (ARC) of harmonious type (subjective angle of deviation of zero).

Results can be interpreted as:

	- i. In cases of homonymus (uncrossed) diplopia, patient reports red light to the right of white light when right eye is tested.
	- ii. In cases of heterogeneous (crossed) diplopia, patient reports red light to the left of white light when right eye is tested.

b.Abnormal retinal correspondence: It can be of two types:


Measurement of angle of anomaly: It is the difference between objective and subjective angle of deviation seen in cases of abnormal retinal correspondence. The angle of anomaly is a measure of the degree of shift in visual direction.

Procedure of estimating the angle of anomaly: This test is done with the help of synaptophore. The SMP slides are used in this test. The position of synaptophore arms is kept at zero. The examiner flashes light behind each slide and keeps on moving the arm till the time there is no further movement (alternate cover test). When there is no further movement the angle of each arm is noted. The sum total of the angles recorded of both the arms is the objective angle of anomaly. The angle at which the visual targets are superimposed is the subjective angle of anomaly.

Objective angle (D): Angle by which the visual axis of eye fails to intersect the target of regard.

Subjective angle (S): Angle between the zero measure of the deviating eye and point in that eye corresponding to the fovea of other eye.

Interpretation:

	- a.If BSV is present all four lights are seen

b. If the green and red lights alternate, alternating suppression is present.

4.Hering Bielschowsky after-image test: This is a highly dissociating orthoptic test in which fovea of the two eyes is flashed with linear afterimage horizontal in right eye and vertical in left eye since each eye is individually stimulated, only the fovea are at the center of the after images.

Procedure: Subject is asked to concentrate on the central black spot of the glowing filament with alternate eye occluding the other eye. The stimulus is first presented to the better eye and then vertically to the opposite eye. This stimulus is presented for 20 s to each eye and then subject is asked to tell the distance between gaps of two images.

a.If central fixation is present, the gaps correspond to the visual direction of each fovea.

Results are as follows:

1. Foveo-foveal test of cuppers: This test is done to analyze the angle of anamoly in the presence of eccentric fixation. It determines whether the two foveae have same or different visual directions.

### 15. Suppression

Suppression involves active inhibition at the visual cortex level when the blurred image from one eye is inhibited under binocular condition. Pre requisite for suppression is large angle deviation, constant deviation and deviation that occurs in early childhood.

#### 15.1 Testing extent of suppression

The extent or the area of suppression can be charted under binocular conditions (fixating with one eye while the field of other eye is charted). This may be done by different methods:

The various responses that can be observed are:

More the dissociation larger is the single scotoma in prism's, Lee's.

Lesser the dissociation, 2–3 discrete scotomas are seen, one is foveal scotoma about 2–3° in size and diplopia point scotoma, e.g., Aulhorn phase difference haploscope and Polaroid scotometer.

Depth/intensity of scotoma: Depth of scotoma is determined by Graded Density Filter Bar of Bagolini. In it as the denser filter is applied over dominant eye, the scotoma in amblyopic eye becomes small.

#### 15.2 4 Δ base out prism test

This test is used for diagnosing a small facultative scotoma in a patient with monofixation syndrome and no manifest small deviation. In this test, <sup>a</sup> <sup>4</sup>▲ Base out Prism is placed before one eye and then other under binocular viewing condition

Patient with bifixation show a bilateral version movement away from the eye covered by the Prism followed by unilateral fusional convergence movement of the eye not under the Prism.

In Monofixation no movement is seen when Prism is placed over the nonfixating eye. A refixation version is seen when Prism is placed over fixating eye but then fusional convergence does not occur.

#### 16. Simultaneous macular perception

Simultaneous macular perception occurs when visual signals transferred from the two eyes to the cortex are perceived at the same time. It is the ability to see two dissimilar objects simultaneously. Commonly used synaptophore contain slides such as Bird and Cage, Lion and Cage. The interpretation is as follows:


The term simultaneous perception does not necessarily mean bifoveal fixation as it can also occur in Anamolous retinal correspondence. It just indicates the presence or absence of suppression.

Normal range of amplitudes of fusion:


#### Binocular Functions DOI: http://dx.doi.org/10.5772/intechopen.84162

It is necessary to assess fusion for both viz. determining the prognosis and outlining the management of the patients of strabismus.

To restore binocular single vision fusion is essential.

Following are the tests used to determine the presence of fusion are:


Following tests can be used to determine stereopsis: Tests to determine stereopsis are based on two principles viz.

	- Concentric rings, i.e., circular perspective diagrams
	- Titmus fly test
	- TNO test
	- Random dot stereograms
	- Polaroid test
	- Lang's stereo test
	- Stereoscopic targets presented haploscopically in major amblyoscope

Tests used to determine stereopsis can be qualitative or quantitative. The unit for measurement of stereopsis is seconds of an arc.

	- Lang's 2 pencil test
	- Synaptophore
	- Random dot test
	- TNO Test
	- Lang's stereo test

Polarization can also be used to determine stereopsis: Vectographs and images, used as targets seen by one eye are polarized at 90° using polarized glasses.

#### Eye Motility


#### 16.1 Stereograms

There are two stereograms

	- a. Patient sees concentric circles: Stereopsis is present.
	- b.Patient sees eccentric circles: Should be asked whether the inner circles are towards right or left. This will help us determine whether the disparate elements are suppressed in right or left eye.
	- c. Vectographs: Consists of two targets imprinted on a Polaroid material in such a manner that each target is polarized at 90° with respect to the other. A polarized spectacle is provided to the patient so that each target is seen separately with the two eyes.
	- a. Advantage: Young children can also perform the test.
	- b.Disadvantage: Stereopsis using this test is only near stereopsis.
	- a. With animals printed: It consists of three rows of animals. There one animal in each row which is imaged disparately (threshold 100, 200 and 400 s of arc, respectively). There is also one animal in each row that is printed heavily black which forms the misleading clue. The child is then asked to point out which one of the animals stands out. A child without stereopsis will name the heavily printed animal as the one that stands out.
	- b.With circles: It consists of nine sets of four circles arranged in the form of a diamond. In this test there are nine sets of four circles which are arranged to form a diamond. One of these circles is imaged dispared in each set randomly. The threshold ranges from 800 to 40 s of arc. The child is asked to push down the circle that stands out. If the stereopsis is limited the child makes mistakes.

#### Binocular Functions DOI: http://dx.doi.org/10.5772/intechopen.84162


#### 16.2 Binocular vision anomalies

In anamolies of binocular vision there occurs in confusion, diplopia that results in suppression, eccentric fixation, anomalous retinal correspondence and amblyopia.

#### 16.2.1 Classification

Duane's classification forms the basis of classification of anomalies of binocular vision in the field of optometry. This classification system evolved from a four category system to a nine-category system that was developed by Wick. Following parameters are used for classification: (a) distance phoria and (b) AC/A ratio. The accommodative classification system was developed by Donders3 and modified by Duke-Elder and Abrams. Ocular motor dysfunction is a distinct clinical entity in which fixation, pursuit and saccadic anomalies are included. Table 1 is a summary of the classification system for binocular, accommodative and ocular motor anomalies.


#### Table 1.

Summary of the classification system for binocular, accommodative and ocular motor anomalies.

Eye Motility

#### Author details

Arvind Kumar Morya<sup>1</sup> \*, Kanchan Solanki<sup>2</sup> , Sahil Bhandari<sup>2</sup> and Anushree Naidu<sup>2</sup>

1 Department of Ophthalmology, All India Institute of Medical Sciences, Jodhpur, Rajasthan, India

2 Consultant Ophthalmologist and Vitreoretinal Surgeon Guru Hasti Chikitsalya, Jodhpur, Rajasthan, India

\*Address all correspondence to: moryaak@aiimsjodhpur.edu.in

© 2019 The Author(s). Licensee IntechOpen. This chapteris distributed underthe terms oftheCreative 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.

Binocular Functions DOI: http://dx.doi.org/10.5772/intechopen.84162

#### References

[1] Von Noorden GK. In: von Noorden GK, Campos EC, editors. Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th ed. United State of America: Mosby Inc.; 1928

[2] Tyler CW. Chap. 24: Binocular vision. In: 0331—Foundations of Clinical Ophthalmology. New York: Lipincott Williams and Wilkins; Vol. 15. pp. 35-55. R2-05-21-04

[3] Kaufman FL, Alm A, Adler FH. Adler's Physiology of Eye: Clinical Application. 10th ed. St Louis: Mosby; 2003

[4] Duane TD, Tasman W, Jaeger EA. Duane's Clinical Ophthalmology. New York: Lippincott Williams & Wilkins; 2005

[5] von Helmholtz H. In: Southhall PC, editor. Helmholtz's Treatise on Physiological Optics. New York: Dover Publications; 1962. English Translation from 3rd German ed.; Ithaca, NY: Optical Society of America; 1924. Quoted from Reprint

[6] Duane A. Binocular vision and projection. Archives of Ophthalmology. 1931;5:734

[7] Linksz A. Physiology of the eye. In: Linksz A, editor. Vision. Vol. 2. New York: Grune & Stratton; 1952

[8] Burian HM. Studien u berzweia ugigesTiefensehenbeio rtlicherAbblendung. Graefe's Archive for Clinical and Experimental Ophthalmology. 1936;136:172

[9] Hubel DH, Wiesel TN. Receptive fields of single neurons in the cat's striate cortex. Journal of Physiology (London). 1959;148:574

**35**

**Chapter 3**

**Abstract**

the Child

*and Ana Didović Pavičić*

benefit in the interpretation of the results.

ophthalmological assessment

**1. Introduction**

1. Anamnesis

2. Clinical examination

Ophthalmologic Examination of

The ophthalmologic examination of the child consists of an assessment of the physiological function, anatomic eye, and visual system status. A comprehensive eye examination of the child should include history of presenting problem, patient's and family's medical histories, estimation of fixation and measurement of visual acuity, assessment of binocular vision, Bruckner test, assessment of ocular motility, Hirschberg's test, cover/uncover test, and assessment of anterior and posterior segments. The order of examination may vary depending on the child's cooperation. The record of the child's level of cooperation during the examination is of great

**Keywords:** examination, strabismus, child, visual acuity, binocular vision,

and bulbomotor examination before using cycloplegic [1]. Examination should include the following elements:

we examine the child, we can skip some of the following steps:

• Estimation of fixation and measurement of visual acuity

• Testing of binocularity/stereovision

The ophthalmologic examination of the child consists of anamnesis or, in this case, heteroanamnesis, physiological function evaluation, and anatomic eye and visual system status. The record of the level of cooperation of the child with the examination is of great benefit in the interpretation of the results. The order of the examination may vary depending on the level of child's collaboration. The visual acuity test should be done before the fusion break test, as well as the visual acuity

The following tests are of particular importance when examining a child but are indispensable when there is a strabism. If we do not set suspicion of strabism when

*Suzana Konjevoda, Neda Striber, Samir Čanović*

#### **Chapter 3**

## Ophthalmologic Examination of the Child

 *Suzana Konjevoda, Neda Striber, Samir Čanović and Ana Didović Pavičić*

#### **Abstract**

The ophthalmologic examination of the child consists of an assessment of the physiological function, anatomic eye, and visual system status. A comprehensive eye examination of the child should include history of presenting problem, patient's and family's medical histories, estimation of fixation and measurement of visual acuity, assessment of binocular vision, Bruckner test, assessment of ocular motility, Hirschberg's test, cover/uncover test, and assessment of anterior and posterior segments. The order of examination may vary depending on the child's cooperation. The record of the child's level of cooperation during the examination is of great benefit in the interpretation of the results.

 **Keywords:** examination, strabismus, child, visual acuity, binocular vision, ophthalmological assessment

#### **1. Introduction**

 The ophthalmologic examination of the child consists of anamnesis or, in this case, heteroanamnesis, physiological function evaluation, and anatomic eye and visual system status. The record of the level of cooperation of the child with the examination is of great benefit in the interpretation of the results. The order of the examination may vary depending on the level of child's collaboration. The visual acuity test should be done before the fusion break test, as well as the visual acuity and bulbomotor examination before using cycloplegic [1].

Examination should include the following elements:


 The following tests are of particular importance when examining a child but are indispensable when there is a strabism. If we do not set suspicion of strabism when we examine the child, we can skip some of the following steps:


There are numerous divisions of strabismus—according to the time of occurrence, presumed etiology, direction of visual axes, that is, clinical manifestation, frequency, affected eye—only to name some [2]. The simplest is the one dividing the strabismus on congenital and acquired forms. In the former, in the vast majority of cases, the etiology is unknown. Actually, it is not present from the birth on but usually occurs and develops in the first months of life. Therefore it might be better to name them early onset strabismus than congenital [3].

On the contrary, acquired strabismus occurs later, and usually the cause of the disorder is discovered.

Sometimes early onset strabismus is also named primary, in which case the eyes are healthy. Secondary strabismus is a consequence of an eye disease.

 The strabismus terminology also includes consecutive forms, describing the cases that in time, spontaneously or as a consequence of extraocular muscle surgery, and changes the visual axes direction, from convergent to divergent or vice versa.

Primary importance of strabismus is that it can lead to amblyopia. The risk for it is much higher in unilateral forms—only one eye is constantly deviating. Consequently, due to asymmetric input, active suppression of the impulses from the deviating eye occurs, later leading to amblyopia. In alternating strabismus, the child switches fixation between the two eyes, and the risk of amblyopia is much lower. Nevertheless, in both forms, due to different visual axes direction, stereopsis is lost. Another possible consequence of strabismus is anomalous head posture. By turning or tilting the head, the patient seeks the position in which he or she still can maintain both eyes directed to the fixation point—this state is named orthotropia. Sometimes patients have manifest strabismus even in anomalous head position, but that position gives them better vision. The underlying cause can be nystagmus or the different tonus in antagonistic muscles.

#### **2. Ophthalmologic examination of the child**

#### **2.1 Anamnesis**

 The ophthalmological examination begins with an anamnesis; when we talk about the examination of a child, it is actually about heteroanamnesis. The information is usually obtained from a parent or guardian of a child. There are general anamnesis (past illnesses), ophthalmic history, family history, drug taking, and

#### *Ophthalmologic Examination of the Child DOI: http://dx.doi.org/10.5772/intechopen.82338*

drug allergy. Attention should be paid to premature birth, family history, and hereditary diseases in the family [4].

The general (hetero)anamnesis should also be very detailed. Important data are also about prenatal development—risk factors and possible complications in pregnancy. Intrauterine growth failure, the presence of other anomalies, or premature labor is associated with a higher frequency of strabismus. Even 35% of premature infants develop strabismus, often associated with higher refractive anomalies. Therefore, an ophthalmologic examination of each premature child is recommended, certainly within the first year of life, preferably at the age of 6 months.

 Family anamnesis often reveals the existence of other family members who have strabism or refractive anomalies. If one parent squints, the risk of a child having strabism is 15%, and if both parents have strabismus, that risk is as high as 45%. If the family history is positive to strabismus, refractive errors, and weakness, an ophthalmic examination is required before the age of 3.

 Ophthalmological anamnesis: It is important to find out when the strabismus occurred—in the first months of life or later, whether the occurrence is sudden, "overnight," or whether it was gradual, in the beginning only intermittent, becoming constant with time. It is important to know when the child is tired or sick and whether it changes during the day. Sometimes the eye is deviating only when the child is looking in the far distance or while "daydreaming" and at near fixation and with attention eyes that are straight. Some squints are manifest only under certain circumstances—for example, when exposed to the bright light (intermittent exotropia) or when the child wants to see some tiny details at near (accommodative esotropia). It is also important to know whether the strabismic angle is stable—increasing, decreasing, or constant through the follow-up. Sometimes parents are not sure about the direction of deviation. Photos or drawings of convergent and divergent forms of strabismus help parents to show what they see in their child. It is always necessary to ask whether the deviation changed the direction—sometimes early convergent strabismus with time changes to divergent type. Therefore the parents should be asked whether in the beginning there was an inward turn of the eye, toward the nose, only later to change to outward turn. Very important question is which eye is deviating—always the same or the child switches fixation between the eyes, while the other eye is deviating. Often the parents of the child with divergent squint say that they never know what the child is looking at. In vertical forms, parents usually say that in some gaze direction, child's eyes are looking strange or weird. Parents can also share the information about some unusual head position and whether that is present all the time awake or only when the child is trying to see something better. Sometimes the anomalous head position occurs only during prolonged looking in the same direction. The information about anomalous head position is also important in view of strabismus treatment prognosis. If there was a period in life when the patient constantly held the head in the same anomalous position, it might be presumed that it was for maintaining the learned binocularity that could return after surgical correction of strabismus. In sudden occurrence of strabismus, somewhat older child can tell it's parents that it sees double. Younger children are not able to tell that, but it can be noticed that the child squeezes one eye to avoid diplopia. The younger the child, the period of double vision will be shorter, because suppression will develop sooner, so sometimes parents forget about this information if not specifically asked.

#### **2.2 Clinical examination**

 Inspection is the first part of the clinical examination of the patient with strabismus. Even when we talk to parents, we can observe the child—whether there is an

impression of the wrong orientation of the sight axes and where the sight axes are oriented (convergent, divergent, and vertical strabismus) [5].

#### **3. Evaluation of fixation and visual acuity**

The visual function test methods depend on the age of the child.

By the age of 2 of the child, a subjective reflection may be used to examine the reflection of blinking on a very light pupil reflex, fixation, and the monitoring of the colorful objects that are offered to the child for looking at [6].

The first examination is binocular and then monocular: is the fixation of child's view on the object, is fixation maintained, and is the object of fixation followed. Fixation reflex can be examined at the 3–4 months of age.

Objective methods can cause optokinetic nystagmus (OKN), examine cortical visual evoked potentials (VEP), and evaluate visual acuity with a preferential looking test.

#### **3.1 Determination of fixation type**

Occlusion of one eye is made.


#### **3.2 Preferential looking test**

The method of visual acuity that is based on the observation of the child's eyes, to which of the two offered fields will the child first look at (homogeneous gray and striped black and white). Children prefer to look at more interesting, striped objects. As the width of the black and white stripes becomes more and more like a gray homogeneous field, it is harder to spot the difference, and if the child is aware of the slightest difference between the stripes, the visual acuity is neat.

This method is suitable for using from the 4 months of age.

#### **3.3 Examination of visual acuity in children 2: 4 years of age**

After the child starts to speak, the visual acuity is examined by standardized tests with close-range and distance-based image optotypes. These are the first tests that examine the visual acuity quantitatively [7].

The most commonly used standardized tests are Lohnlein's tables and Lea symbols.

Lea test table consists of four symbols (circle, square, house, and heart) that are shown in each of the following order in a smaller size. Tested at 3 meters distance

and not at 5 or 6 meters as well as other tests and less environment distracts the child. The same symbols can be used to examine visual acuity at close. The test is standardized according to Snellen's table.

#### **3.4 Examination of visual acuity in children older than 4 years**

The gold standard for testing is Snellen's tables. Snellen's board consists of rows of optotypes (letters, numbers, and hooks). Each part of Snellen's optotype corresponds to a visual angle of 1 minute, unlike the image optotypes that do not hold that rule, such as the smallest pictures of image optotypes that should match the visual acuity of 1.0, that actually correspond to the visual acuity of 0.66.

Landolt's rings are also based on the Snellen's principle (the width of the ring opening is 1 angular minute). The flaw is that it can only be used with the children who learned how to tell time.

#### **3.5 Visual acuity test weaker than 0.1**

It can be done with individual Snellen's optotypes. We approach the child gradually, and at the distance at which the optotype is properly recognized, we note the visual acuity in the form of a break. If a child from 1 meter of distance detects the direction of Snellen's largest optotype, then the visual acuity is 1/60. If the child does not reveal it, we ask him to count the fingers on our hand and write down where the child is at a distance (30 cm, right in front of the eye).

If we doubt the weaker eyesight, we are examining the sensation of light and the projection in the dark room. It is tested with a lamp at a distance of 1 meter and by turning on the light from the upper, lower, left, and right sides. We write down neat sense of light and projection as L+ P+.

#### **4. Binocular vision tests/stereo vision tests**

Binocular single vision is simultaneous viewing of both eyes at the same point of fixation, which realizes a single image of the object [8].

#### **4.1 Binocular vision elements by worth**

Simultaneous perception (at the same time, at the two corresponding retinal points of both eyes, a likeness of approximately the same size is created.)

Fusion reflex (a psycho-optical reflex that connects two figures to one if they are formed at corresponding points).

Stereovision (stereopsis—disparate characters merge with a sense of space and depth) or depth perception can be characterized as the highest degree of binocular vision.

#### **4.2 Motor binocular vision component**

Motility and ocular motor balance make the motor component of binocular vision. The muscular system of eye mobility has enabled the image of the fixation object to be held in the fovea in each eye individually, and that fusion segment is called the motor fusion.

Sensory component will at the level of the visual cortex of two visible impressions merge into one. The sensory component consists of a retinal correspondence

 and a reflection of binocular vision. Its basis is normal retinal correspondence thanks to which we see single using two eyes, because the characters formed centrally merge creating a single perception.

#### **4.3 Tests for stereopsis examination**

 Testing with Bagolini's striated glasses is the most important test of simultaneous perception, because of its minimal dissociation results which are the most similar to the natural viewing of the patient [9]. The glass slides used in the test are longitudinally twisted and turn the small lamp into a luminous line vertical to the glass' striation. The straps are oriented right and left in front of the eye so that the lines are at right angles. The orientation of the line as the patient sees it is usually marked on the edge of the glass slide itself with dots. It is very important to know how the slides are oriented, because our interpretation of the test result depends on it. Usually they are set to have a right eye line at 135° and left at 45°. In the state of orthotropy and proper binocular vision, the patient sees two lines passing through the light itself, like the letter X. If there is strabismus and simultaneous perception, the patient will see both lines, but they will not cross in the light itself. If Bagolini's slides are oriented as indicated above (right line at 135°, left at 45°), the patient with esotropia sees two lines and one light on each one, and the lines will be crossed over the light (non-crossed double images). If it is a case of exotropy, the lines are crossed under the light (crossed double images). If there is a central scotoma on a stray eye, the line of the eye in the middle of the light will not be visible but only the ends of the line. Depending on their position, we can also find out whether they are associated with normal or anomalous retinal correspondence. Finally, in the case of suppressing a stray eye, the patient will see only one line—the one of the eye which is fixing the light.

 This test can be performed not only in the straightforward but in different directions of view. It is advisable to examine the direction of view where the smallest, or visible, axis of the eye is the closest (e.g., in the V exotypically downward model) to assess whether a functional case with potential binocularity or only esthetic case (constant exclusion of one eye with Bagolini's). This test can also be performed after the prism adaptation test, whereby both sight axes are directed to the fixation object. Bagolini's striated glass is placed in front of the lenses, and the patient's responses are evaluated.

With the fusion test using the prisms, we can examine whether there is bifunctional fixation and what is the potential of motor and sensory fusion. In the test, we use a prism of strength of 14 or 15 diopters because the induced fusion motor displacement is large enough to be perceived. It is very good for small children within the first year of life; in older children the cooperation in this test is somewhat weaker.

The test is carried out by drawing the child's attention to the fixing object of fixation of the appropriate size and placing the base of the prism temporally.

 Titmus test is tested with polarizing glasses. After the spectacles are placed, the respondents are given cards with different characters displayed in different depth positions. The first test is a test of the rough Fly-fly test. The person with stereo vision sees the fly in three dimensions, and the baby catches the wings of the fly with its fingers. The following is examined for the finer stereopsis: the characters are placed in rows, and in each row one character rises above the others. The last test is circle test, four circles within nine groups; one circle of each group rises. Titmus test quantifies the level of stereopsis in the angle seconds.

Lang test card is a screening test designed for early detection of problems with stereoscopic vision in children. Two versions of the test plates are available, which differ

only according to the 3D objects to be recognized. The Lang test 1 displays a star, a cat, and a car, while the Land test 2 displays a moon, a truck, and an elephant, each of them appearing on a different level. No glasses are necessary for the Lang Stereo Test.

#### **5. Hirschberg's test**

Using the Hirschberg's test, we determine the size of the squinting angle depending on the position of the reflex position on the cornea when simultaneously illuminating both eyes.

The patient is said to look at the top of the lamp. The position of the light reflex in relation to the center of the cornea of one eye and the position of the reflex light of one in relation to the other eye are compared.

The difference in the position of reflection on the cornea of the right and left eye raises the suspicion of strabismus. If the reflex is shifted from the center of the eye nasally, the impression of divergent strabismus of that eye is obtained, if shifted temporally—convergent. Reflex shift upward points to hypotrophy and downward to hypertrophy of that eye. It is important to note that it is always necessary to compare the position of reflexes on the right and left eye, since sometimes it is seen that reflexes of both eyes are slightly decentralized. Only the difference in position indicates the existence of strabismus. In small children where measurement of the strabic angle is not yet possible by other methods, the deviation can be semiquantitatively determined by the reflex position. In this case 1 mm difference in the reflex position corresponds to the angle of about 7°. With this test we can easily examine the existence of angle difference in different directions of view. The child follows the source of light as we look at the change in the position of the reflex on the corneas.

The reflex shift for 1 mm is equal to the displacement of 7°, which is 15 DP.

According to the reflex position, the angle is determined according to the following anatomic determinations: if the reflex at the periphery of the pupil is 15° or 30 DP, the reflex in the center of the iris determines the angle of 30° or 60 PD; the limbus position determines the angle of 45° or 90PD.

Hirschberg test is fast and simple, but unfortunately not accurate enough. Both the specificity and the sensitivity are rather low.

There are cases of eccentric fixation where one could, based on corneal reflex position, presume the presence of strabismus that actually is not there (false positive, low specificity). Eccentric fixation is common in ectopia of macula lutea due to retinopathy of prematurity. Strabismus associated with eccentric fixation might be operated on only if the eccentric viewing eye is not the better, fixating eye. The angle formed by visual axis and central pupillary axis is called angle kappa, and it is present in most people. Positive angle kappa (nasal shift of the corneal reflex) gives the impression of divergent strabismus, whereas negative angle kappa (temporal shift of the corneal reflex) resembles convergent strabismus. The asymmetry of angle kappa between the eyes can arouse the suspicion of strabismus that actually is not present (false positive, low specificity). In small strabismic angles—microstrabismus—the difference in corneal light reflex position is too small to be detected (false negative, low sensitivity).

#### **6. Brückner's test**

A very fast, equally simple, but more sensitive test is a test of observation of red eye reflection of the bottom of the eye or the Brückner's test. It is easy to perform

 and is very accurate right in the first year of life; from about 4–5 months when foveal fixation is already developed, it has its value in small angles of squinting, anisometropia and amblyopia, high hypermometry and myopia, and cataracts in young, noncooperative children.

With simultaneous enlightenment of both eyes with ophthalmoscope light, through the ophthalmoscope, we see whether there are differences in intensity between the light of reflex of the right and left eye fundus. It is best to use a direct ophthalmoscope, where illumination and observation are coaxial. We sit on about 70 cm from the patient and several times briefly illuminate both eyes, to prevent narrowing of the pupils to the light.

Reflexes in the eye opening of the child facing the straight line will be dark, while the reflection of the eye in deflection will be significantly brighter.

The phenomenon arises because of the anatomical structure of the fovea itself, that is, the recesses, causing all the light that vertically falls on the fovea, that is, the foveola does not return to the ophthalmoscope but is reflected in the other direction in the eye of the patient—that is why the reflex of the eye fixed by the fovea is darker. With this test we can detect very small deviations of the position of the axes—but the deviation of 1–2° gives a difference in the light of the reflex. In addition to the detection of strabismus, this test also reveals the existence of refractive anomalies (amethropy and less anisometropia) by the analysis of light distribution in the pupil. Significant hypermetropia will be shown as inferiorly positioned bright semiprecious red reflection, while significant myopia will be shown as a super bright light half-moon in a red reflex.

The absence of a reflection from the eye bottom points to the blur of optical eye media (cornea, lens, or glass body). White or very bright reflexes (leukocytes) cause pathological changes in the eyelid, such as coloboma or retinoblastoma. It is important to note that even at this test, the accuracy of the detection of strabismus is not complete, because the difference in reflex can be caused by even greater anisometropies. From a highly amethropic eye, the beam of light is divergently reflected, so the reflex from such eye is dark, although the eye may be in deflection (falsely negative result).

#### **7. Motility**

When examining the eye movement, we first look at each eye separately (the other eye is folded by the hand) from the primary eye position in the direction of the action of each muscle in particular (movements of duction). The movements of one eye are called duction. The upward movement is elevation or supraduction and downward depression or infraduction. The inward move, toward the nose, is adduction and outward abduction. Torsional or rotational movements can be examined by head tilt—head tilt to the shoulder on the same side as the eye under investigation will cause incycloduction and to the opposite shoulder excycloduction. The movements of both eyes in the same direction are called versions. Right gaze is called dextroversion and left levoversion, upgaze supraversion, and downgaze infraversion. Oblique gaze directions are called supra-dextro/−levoversion and infra-dextro/−levoversion. Torsional movements can be examined here as well—right head tilt will cause levocycloversion (rotation to the left) and left head tilt dextrocycloversion (rotation to the right) [10].

 The movements of both eyes in the opposite direction are called vergencies. If the eyes simultaneously move toward the nose, it is called convergence and outward—divergence. Simultaneous incyclorotation of both eyes usually accompanies convergence—this is called incyclovergence and with excyclorotation with divergence, excyclovergence.

#### *Ophthalmologic Examination of the Child DOI: http://dx.doi.org/10.5772/intechopen.82338*

Due to relative position of the extraocular muscles and eye globe, isolated action of vertical muscles—superior and inferior rectus muscles—should be examined in slight abduction (cca 20–25°) and superior and inferior oblique muscles in more accentuated adduction (cca 50°), because in the middle there is a combination of rectus and oblique muscle actions in the sense of elevation and depression.

The primary eye position exists when eyes fix an object that is at their height straight in front of them or in infinity (beyond 6 meters). All other positions in the eye that come up with the action of certain muscles are the diagnostic (secondary) positions of the eyes that are in the direction of the action.

There are nine viewpoints—the primary (straightforward), the central vertical position (straight and up, straight and down), and cardinal (up and left, left, down and left, up and right, right, down and right).

 When there is a case of very young children, who still have no developed attention, eye movements are tested with a doll's head maneuver. Turning the head to one side causes a reflex eye shift to the opposite side, unless there is a mechanical restriction of movement or a myogenic weakness.

#### **8. Cover/uncover test**

The most accurate test for the detection of manifest strabismus is the eye cover test or the cover test [11].

The patient fixes the object in front of him. Penlight could be used for fixation, but it is better to use a target with shape (picture or an optotype), especially at near, because it stimulates accommodation, and the influence of accommodation on the deviation could be assessed in the same time.

The examiner alternately covers and uncovers only one eye. Coverage and uncoverage are performed several times, and we analyze eye positioning movements.

Cover test–test of coverage, the occluder covers the fixing eye. It follows the action of the other, uncovered eye.

Uncover test—detection test, the occluder uncovers-detects the fixing eye. When detecting, we follow the movement setting of the recently uncovered eye.

In the orthophoria, the eyes are not moving, no adjustment movement is present, and the cover test is negative.

Cover test is always tested with and without correction and in different directions of looking.

The test is very sensitive—it can reveal deviations as small as 1°. There are motoric and sensoric prerequisites that have to be fulfilled to make the test meaningful and valid—patient's fovea must be healthy, the eye must not be blind, and the eye must be able to move to take up fixation.

If the deviating eye is deeply amblyopic, it is hard for the patient to take up the fixation. Such eye often makes wondering movements trying to fixate the object, and sometimes it is hard to detect the direction of the first movement. In patients with nystagmus, it is also hard to detect the direction of the uncovered eye. Another disadvantage of the test is that it is not suitable and reliable in very small children (first year of life).

Cover test is followed by alternating cover test that can reveal latent strabismus (heterophoria) or additional latent component of manifest strabismus. The cover is alternated between the eyes and relatively fast, so the patient is fixating only monocularly—either by the right or the left eye. To relax the fusional mechanisms, the cover is held in front of the eye a little bit longer. The eye under cover could be observed from the side to see the slow slide of the eye into the anomalous position

of muscular tone balance. When it stops, we quickly shift the cover on the other eye and observe now uncovered eye—what kind of movement and in what direction it makes. The magnitude of latent deviation indicates the amount of necessary effort to keep orthotropia—if the latent deviation is large, the demand on the central nervous system for keeping binocularity is substantial and can cause asthenopic symptoms. The direction of movement, just like in cover test, tells us what kind of heterophoria is present. In esophoria the eye shift is outward and in exophoria in the opposite direction—inward. In vertical phorias, if the right eye comes from above, and the left from below, we designate the movement as right over left (R/L) or plus vertical difference (+VD). If the movement is in the opposite direction—the left eye comes from above and the right from below—it is left over right deviation (L/R) or minus vertical difference (−VD).

Alternating cover test is followed by uncover test. After a few seconds of occlusion of one eye, the eye is uncovered and observed to see is there a fusional movement in order to regain binocularity. This test is very important because it give us information about the capacity of central fusional mechanisms that maintain binocularity. If the stress of dissociation under cover is too much for the system, the uncovered eye will stay in deviated position. Sometimes at near the fusional movement regains orthotropia, and at distance testing the uncovered eye does not move and stays in tropia. This is often the case in intermittent exotropia. Sometimes the uncovered eye does not reach the position of orthotropia; the deviation is decreased only for its latent component to the level of manifest deviation. If that manifest strabismic angle is small enough, visual system can even in this position preserve some level of binocularity, albeit anomalous. Uncover test can also be utilized in another important aspect. It can qualitatively determine the strength of eye dominance in patients with strabismus. The straight-looking eye is covered in order to shift the fixation to the strabismic eye. After a few seconds of stabilizing fixation on the accommodative object, the cover is removed. The speed of fixation shift to the uncovered eye indicates the strength of dominance but also the presence and level of amblyopia of the strabismic eye [12]. This could be semi-quantified, according to the length of holding fixation by the uncovered eye in bi-ocular viewing conditions. Based on this quantification, the length of dominant eye occlusion for treating amblyopia can be recommended even in preverbal children.

#### **9. Strabismic angle measurement**

 There are objective and subjective methods for strabismic angle measurement. Objective methods include prism cover test (PCT) and Hirschberg test. The latter has already been described, together with its drawbacks, but usually it is the first test used for orientation about the direction and magnitude of deviation to shorten the measurement with PCT. Subjective methods are based on patient's response and therefore are suitable for older children and adults. They include Maddox cross method, Hess-Lancaster test, and tangent screen. They are based on diplopia recognition, and the dissociation is elicited by colored (red/green) or stripped glasses (Maddox rod) through which the patient looks. Dissociation could be also by physical separation of images, like in classic Maddox wing that is used for near deviation measurement or in major haploscope (synoptophore) with separate projection of images in the right and the left eye. In Hess-Lancaster or tangent screen method, the deviation is measured on calibrated screen in front of the patient on which the colored lights are projected. In Maddox cross method, calibrated cross with numbers representing degrees of deviation related to the distance on which the patient is seated and point light in the center is used for measurement. The dissociation is

#### *Ophthalmologic Examination of the Child DOI: http://dx.doi.org/10.5772/intechopen.82338*

 elicited by dark red glass in front of one eye, while the patient fixates the light in the center of the cross with the other eye. The patient is asked if he/she sees one or both lights—red and white. If the patient sees only one light, either orthophoria is present (both visual axes are directed toward the light) or there is suppression of one eye. If there are two lights—red and white—heterophoria is present. According to the relative position of the red and white light, the direction of deviation of the eye with the red glass is determined. If the red glass is in front of the right eye (the patient fixates the white light with the left eye), and the red light is on the right side of the white light, there is uncrossed diplopia, indicating esophoria. If the red light is on the left side of the white, crossed diplopia is present indicating exophoria. Similar is with vertical deviations—red over white light speaks for hypophoria of the eye with the red glass and red below white for hyperphoria of the same eye. The position of the red light on the Maddox cross determine strabismic angle in degrees.

 The most accurate method for strabismic angle measurement is prism cover test (PCT). Similar to cover test, there are subtypes of this test—one that measures manifest deviation called simultaneous prism cover test (SPCT) and the one measuring the whole deviation (manifest and latent) called alternating prism cover test (APCT). This enables the determination of heterophoria component in the whole strabismic angle.

In SPCT, the prism with apex directed toward the direction of deviation is placed in front of the strabismic eye simultaneously with placing the occluder in front of the straight-looking eye. We observe the residual eye movement and change the prism strength as long as the eye under prism does not move anymore. This is the way to measure the manifest part of strabismic angle.

 SPCT is followed by APCT in which we leave the found strength of prism in front of the eye, but now we shift the occluder between the eyes and observe possible movements. If there is a residual movement, we increase the strength of the prism to the point when eyes are still. The found prism strength equals the whole strabismic angle—added manifest and latent deviation. It is important to know that sometimes in measuring esotropia with very weak or no binocular potential, it is impossible to achieve the state without eyes' movements—there is always the same small outward movement from eso position. One should decrease the strength of the prism to the value when the movement increases and again increase the strength to the point of smallest outward movement—state of small microstrabismus—and this is the true value of measured angle.

Both tests are performed at near and far distance fixations, but in small children sometimes this is not possible. Some entertaining distance fixation objects (animated feature or dancing mechanical toy giving attractive sounds) significantly improve child's cooperation.

#### **10. Skiascopy/retinoscopy**

The retinoscope is an instrument used to objectively determine the refractive strength of the eye. It works on the principle that the retinoscopic probe projects a beam of light into the eye and then observes the light reflecting on the retina. Depending on the refractive strength of the eye, the beam of the light coming out of the eye will be of different character, with the myopia of the radiating ray converging, at the hypermetropia the output rays diverge, and in the emetropy the radiating rays leaving the eye are parallel.

During examination, the examiner performs small movements with the retinoscope up/down and left/right, and in the pupil observes the movement of the "shadow of light," and then uses different lenses in the eye to neutralize the reflex.

In the miope, the light reflex moves in the opposite direction to the retinoscope movement, and in the hypermetropic light, reflexion moves in the same direction.

Skiascopy is performed only when cycloplegic accommodations are pharmacologically excluded. To achieve cycloplegia in newborns and infants, tropicamide in 0.5% concentration is used. In older children 1% tropicamide is used. The drops should be instilled twice, 10 minutes apart, and the maximal cycloplegia is reached in 35–40 minutes. In this age, 1% cyclopentolate, minimally stronger acting cycloplegic, could also be used. Maximal cycloplegia is reached in 40–50 minutes. Atropine in 1% concentration is due to prolonged cycloplegia rarely used, but sometimes in children with limited cooperation or if variable result of refraction is found with shorter acting medications, this cycloplegic could also be used. The skiascopy is useful in prescribing corrective lenses to patients who cannot undergo subjective examination of visual acuity (adults with limited intellectual ability and children with a high accommodative eye power that must be excluded because it can mask an objective refraction error).

#### **11. Fundoscopy**

 In children with strabismus, inspection of the eye fundus is unavoidable part of the examination. Organic disease as the cause of the eye deviation must be excluded. Posterior pole scars, coloboma, but also malignancies such as retinoblastoma can lead to instability or loss of fixation and strabismus. Unfortunately, peripherally situated tumors do not have to give signs of the disease in the beginning. Therefore, ophthalmoscopy in mydriasis is recommended even within usual, routine ophthalmological examination in children. Indirect binocular ophthalmoscope is the instrument of choice, due to its simplicity, speed, and the possibility to examine peripheral parts of the retina. It is recommended to use the least light intensity that still gives reliable picture to encourage child's cooperation. The attention and gaze direction change could be achieved by sound toys, like in motility exam, in order to get a glimpse on peripheral retina. Loupe of 20 diopter is usually used, as it gives optimal relation between field of vision and image magnification. If some pathological change is found, other loupes with less dioptric power (e.g., 16 d), giving bigger image, can be used, but the field of vision is less here. They are also suitable for posterior pole examination.

#### **Author details**

Suzana Konjevoda1 , Neda Striber2 \*, Samir Čanović 1 and Ana Didović Pavičić 1


\*Address all correspondence to: striber.neda@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.

*Ophthalmologic Examination of the Child DOI: http://dx.doi.org/10.5772/intechopen.82338* 

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Section 3

Disorders of the Eye

Motility System

49

Section 3
