Diagnostic and Correction of Heterophoria

MASARYK UNIVERSITY

FACULTY OF MEDICINE

Diagnostic and correction of heterophoria

DIPLOMA THESIS

Masters thesis facilitator: Name of autor: doc. MUDr. Svatopluk Synek,CSc. Bc. Sonja Drugović

Brno, June 2017

MASARYK UNIVERSITY

FACULTY OF MEDICINE

Department of Optometry and Orthoptics

ANNOTATION:

NAME: Bc. Sonja Drugović

SPECIALIZATION: Optometry

THEME OF THE WORK: Diagnostic and correction of heterophoria

LEADER OF THE WORK: doc. MUDr. Svatopluk Synek,CSc.

YEAR: 2017

The presented master`s thesis describes the methods and principles of diagnostic and correction of heterophoria. In theoretical part I focus on metods examinating and measuring of heterophoria in optometry practice. There are show their possible solutions with prismatic correction. In practical part I meassuaring of heterophoria with using Madox teching and Von Grafee tests. The last chapter is focused on full correction of the measured heterophoria and treatment of heterophoria.

Key words: heterophoria, mesurement of heterophoria, orthophoria, prism correction

Statutory Declaration

I declare that I have developed and written the enclosed Master Thesis completely by myself, and have not used sources or means without declaration in the text. Any thoughts from others or literal quotations are clearly marked. The Master Thesis was not used in the same or in a similar version to achieve an academic grading or is being published elsewhere.

I agree with archiving of this thesis in the library of the Medical Faculty in Masaryk University.

………………………. 15.04.2017. Zagreb Bc. Sonja Drugović

Acknowledgment:

I would like to thank doc. MUDr. Svatopluk Synek, CSc. leader my thesis whose help and encouragement was unwavering throughout the study. Its support and expertise is invaluable. I would like to also thank Mgr.Beneš and Mgr.Veselý for their assistence. Finally, I want to thank all my colleagues at the Department of Optometry on University of Applied Sciences Velika Gorica for general help and encouragement.

Content:

1. BINOCULAR SINGLE VISION ...... 1

1.1. Grades of Binocular Vision...... 1 1.2. Anatomy and the physiology of ocular movements ...... 2 1.3. Fusional reserves ...... 5 1.4. Accommodative Convergence/Accommodation AC/A ...... 5 1.4.1. Gradient method ...... 6 1.4.2. Heterophoria method ...... 6

2. DISORDES OF BINOCULAR VISION ...... 7

2.1. Heterotropia (manifest strabismus) ...... 7 2.2. Pseudostrabismus ...... 9 2.3. Eccentric fixation ...... 9 2.4. Abnormal retinal corespodence ...... 10 2.5. Heterophoria (latent strabismus) ...... 10

3. THE USE OF PRISMS IN THE DIAGNOSIS OF OPTOMETRY - SUBJECTIVE METODES ...... 13

3.1. Maddox rod ...... 13 3.2. Maddox wing ...... 14 3.3. Modified Thorington test ...... 14 3.4. Von Graefe technique ...... 15 3.5. Polarized cross test ...... 16 3.6. Shober test...... 16 3.7. Synoptophore ...... 17 3.8. Worth test ...... 18 3.9. Bagolini test ...... 19

4. THE USE OF PRISMS IN THE DIAGNOSIS OF OPTOMETRY - OBJECTIVE METODES ...... 20

4.1. The Hirschberg test ...... 20 4.2. The Krimsky Method ...... 21 4.3. Angle kappa ...... 22 4.4. Cover test ...... 23

5. GRAFICAL ANALYSIS OF NORMAL AC/A RATIO ...... 25

5.1. Donders diagram ...... 25 5.2. Sheard's criterion ...... 25 5.3. Percivals criterion ...... 26

5.4. MHK ...... 27

6. PRISM ...... 28

7. EXAMINATION ...... 32

7.1. Patient History ...... 32 7.2. Direct observation ...... 33 7.3. Measuring Pupillary Distance (PD) ...... 33 7.4. Symptoms of decompensation ...... 34

8. THE TREATMENT OF OCULOMOTOR ANOMALIES ...... 36

8.1. Correct the refractive error ...... 36 8.2. Modification of refractive error ...... 36 8.3. Orthoptic exercises ...... 36 8.4. Therapeutic prisms ...... 38 8.5. Surgery ...... 39 8.6. Botulinum Toxin A ...... 39

9. EXPERIMENTAL SECTION ...... 40

9.1. Hypothesis ...... 41 9.1.1. Hypothesis 1 ...... 41 9.1.2. Hypothesis 2 ...... 43 9.1.3. Hypothesis 3 ...... 45 9.2. Results ...... 46

10. DISCUSSION ...... 54

11. SUMMARY ...... 57

LIST OF CHARTS ...... 58

LIST OF ABBREVIATIONS ...... 59

LIST OF TABLES ...... 60

LIST OF FIGURES ...... 61

Introduction:

Anomalies of binocular vision is often subject to Optometry congresses. Binocular vision disorders including heterophorias cause unpleasant astenopeic interference or other subjective symptoms, so people with these symptoms often have to seek the help of experts. Optometrist is able to set aside enough time. Suitable individual solutions we are able to greatly facilitate the client. The goal is to reduce the difficulties and achieve greater patient satisfaction. The amount of prismatic correction, there are several ideas in accordance with the selected methodology and approach. MKH methodology is characterized by the application of a full correction of the measured heterophorie. For part correcting prism can be used Maddox, Sheard and Percival rule. All methods have their supporters and opponents, and are recognized in different geographical locations. Eye misalignments, such as phoria (latent deviation) and tropia (manifest deviation), are common disorders. Phoria exists in most individuals when their binocular fusion is disrupted. The alignment is retained through motor fusion but can voluntarily manifest as a result of fatigue or illness. Eye alignment assessment is important in decompensated phoria as it could lead to problems such as reading difficulties, headache and diplopia. Phoria measurements are important during eye examination assessment as the findings help in diagnosing binocular vision disorders that could arise due to the decompensated phoria. Phoria measurements, together with other binocular vision assessments are important as they provide a basis for differential diagnosis of eye conditions given that a variety of other defects can lead to similar asthenopic symptoms.

1. Binocular single vision

Binocular single vision may be defined as the state of simultaneous vision, which is achieved by the coordinated use of both eyes, so that separate and slightly dissimilar images arising in each eye are appreciated as a single image by the process of fusion. Binocular vision implies fusion, the blending of sight from the two eyes to form a single percept. Binocular single vision may be defined as normal, when it is bifoveal and there is no manifest deviation and abnormal when the image of the fixated object is projected from the fovea of one eye and an extrafoveal area of the other eye. Development of binocular single vision in infancy requires similar image clarity in both eyes, overlapping visual field, correct neuromuscular development (both visual axes can be aligned with the object to allow motor fusion), correct central development capable of image interpretation to allow sensory fusion and corresponding retinal areas [23].

1.1. Grades of Binocular Vision

There are three grades of binocular vision as given by Worth's classification:

Grade I: First type of binocularity is simultaneous macular perception. It occurs when the visual cortex perceives separate stimuli to the two eyes at the same time and concerns itself essentially with the absence of suppression. Simultaneous macular perception represents simple sensory fusion.

Grade II: It represents true fusion with some amplitude. Not only are the two images fused, but some effort is made to maintain this fusion in spite of difficulties.Thus the second grade implies a motor response added to simple sensory fusion.

Grade III: In the highest type of binocularity, not only are the images of the two eyes fused, but they are blended to produce a stereoscopic effect. This involves a perceptual synthesis at a higher level.

These three grades are not necessarily mutually exclusive, since fusion in the periphery, even showing motor responses, may exist coincidentally with the total absence of simultaneous foveal perception. [3]

1.2. Anatomy and the physiology of ocular movements

Each eyeball is suspended in its bony orbit by the extraocular muscles (EOM), the fascia and the fibrous septa. Of the seven extrinsic muscles located outside the eye, six of these are the EOM: the lateral rectus, the medial rectus, the superior rectus, the inferior rectus, the superior oblique and the inferior oblique. Table 1.1 sets out the actions of the EOM from the primary, secundary and tertiary position. All four recti muscles arise from the tendinous ring, more commonly known as the annulus of Zinn, which is inserted in the orbital vertex bones. The superior oblique muscle originates from the sphenoid bone, while the inferior oblique muscle has its origin from the maxilla, at the floor of the orbit.

Muscle Primary Secondary Tertiary Medial rectus Adduction Lateral rectus Abduction Superior rectus Elevation Intorsion Adduction Inferior rectus Depression Extorsion Adduction Superior oblique Intorsion Depression Abduction Inferior oblique Extorsion Elevation Abduction

Table 1. Actions of the extraocular muscles

Ocular movements in various directions are referred to be the ones initiating from the primary position. In primary position the eyes are looking straight ahead, the visual axes are parallel, the vertical meridians of corneas are vertical and parallel, and the head is vertical. In secondary position eyes assumed when the eyes are moved around the transverse, vertical or anteroposterior axis. In tertiary position eyes are moved along an oblique axis. All extraocular muscles receive innervations from cranial nerve III (oculomotor) except the lateral rectus and superior oblique muscles, which are innervated by cranial nerve VI (abducens) and cranial nerve IV (trochlear). The innervation is important in controlling each eye muscle whereby contraction of any of the muscles leads to inhibition of the antagonistic muscle in each eye, which results in muscle relaxation (Sherrington’s Law), and co-excitation of the synergistic (yoked) muscle in the other eye (Hering’s Law), which ensures conjugate movement of the two eyes.

Fig. 1. Extraocular muscles of the left eye

Sensory fusion is ability of the retino-cortical elements to function in association with each other to promote the fusion of two slightly dissimilar images. For normal binocular single vision, there is a point to point correlation between the eyes in which the fovea of one eye corresponds with a small foveal area of the fellow eye in higher cortical processing. Panum’s area is horizontally oval group of retinal elements and occurs for every point of the retina, increasing in size with eccentricity from the fovea where it measures 5-10 minutes of arc. For fusion to take place between the eyes, images must either fall exactly on the same points, or slightly disparate elements provided they are located within Panum’s area. This misalignment of one or both visual axes is called fixation disparity (FD), and is evaluated clinically to provide a measure for the degree of compensation in heterophoria. When the visual system is subjected to such undue stress, the axes slip closer to the limit of Panum’s area – if the misalignment is large enough to fall beyond, the patient will appreciate physiological double vision (diplopia) in the absence of suppression [15]

Fig. 2. Sensory fusion: Each eye views the target, AB, from a different angle. The fovea of the left eye views the “A” side of the target; the fovea of the right eye views the “B” side of the target. The occipital cortex integrates the disparate images so that a three-dimensional image (AB) of the target is perceived.

1.3. Fusional reserves

Fusional reserves present the horizontal vergence and vertical vergence required to overcome a heterophoria. When measuring the fusional vergence we encounter blur, break and recovery points. The blur point defined as the amount of vergence when no accommodation is used. The break point defined as the total fusional vergence when the individual declines diplopia and the recovery point defined as the amount of vergence when the individual regains single vision after diplopia.

Base direction Fusional reserve (Δ) Fusional reserve (Δ) in near fixation (30cm) in distance fixation (6m)

Out (convergent) 25-35 15-20

In (divergent) 12-14 6-10

Up (infravergence) 2-4 2-4

Down (supravergence) 2-4 2-4

Table 3. Amplitudes of fusional reserves at near and distance with prism orientations required for assessment

1.4. Accommodative Convergence/Accommodation AC/A

To determine the change in accomodative convergence that occurs when the patient accommodates or relaxes accomodation by a given amount. In a perfect physiological system, accommodative convergence supplies all the necessary convergence for near viewing. The normal AC/A ratio is 4:1. High and low AC/A ratios have been implicated in binocular vision problems. This ratio is use din classifying esodeviations and exodeviations and can influence managment desicions. When measuring the AC/A ratio, it is important that the targe used for measurements has a detail that requires the subject to accommodate appropriately to maintain clarity. There are two methods for measuring the AC/A ratio: the heterophoria method and the gradient method. [21]

1.4.1. Gradient method

The gradient method of calculating the AC/A ratio uses the change in vergence angle at a given distance in association with a change in the stimulus to accommodation produced by lenses. Either plus +1.00 D or minus -1.00 D lenses are placed in front of each eye. The heterophoria is measured again while the patient views the same target through the lens. The change in deviation divided by the power of lenses. The AC/A is thought to be innate and stable until the beginning of presbyopia.

1.4.2. Heterophoria method

Heterophoria method consists of comparing the measurement of the latent deviation of eyes. The client wears full correction. Using prisms & alternate cover test at a point of distance fixation (6 m) with refractive correction. At a point of near fixation (33 cm) with refractive correction. PD should be measured. Esodeviation is positive number, exodeviation a negative number. AC/A ratio is calculated from this following formula: AC/A = PD + (∆n - ∆d/D).

2. Disordes of binocular vision

Normal binocular single vision is the ability of the brain and visual cortex to fuse and integrate the image from each eye into a single perception. It implies bifoveal fusion and a high degree of stereopsis (40 seconds of arc). Normal binocular vision develops after birth from early infancy and is completed with fusion and stereopsis by the age of 8–10 years. Its maturation is associated with a maturation of visual functions in both sensory and motor systems [3]

2.1. Heterotropia (manifest strabismus)

Strabismus, or squint, or crossed eyes is defined as a misalignment of the visual axes when both eyes are viewing a single target. As a result the retinal image is not in corresponding areas of both eyes, which may result in diplopia in adult patients and can lead to amblyopia in childhood. Some strabismus results from abnormalities of the neuromuscular control of eye movement, although the cause may be disorder of the external ocular muscles. Strabismus is most commonly described by the direction of the eye misalignment.The prefixes 'exo' and 'eso' refer to an outward and intward ocular deviation. The prefixes 'hypo' and 'hyper' refer to a downward or upward deviation.This form of squint is less common. Some horizontal squints vary in severity with up/down gaze. If it is significant horizontal deviation diference between upward gaze than the downward gaze and it is said to follow a 'V' pattern. If it is significant horizontal deviation diference between downward gaze than the upward gaze, it is said to follow an 'A' pattern. These terms can be applied to both esotropias and exotropias. A manifest squint is referred to as heterotropia. Misalignment of the eyes in strabismus can be classified in a number of ways:direction (horizontal, vertical, or cyclotorsional), comitant or incomitant (deviation equal in all positions of gaze or varying with the direction of gaze), frequency (constant or intermittent), involvement of accommodative system (accommodative or nonaccommodative), state of vergence 7

system, comparing the magnitude of the distance and the near deviation (convergence- insufficiency or divergenceexcess exotropia; divergence-insufficiency or convergence- excess esotropia; basic esotropia or basic exotropia), laterality (unilateral or alternating), time of onset (congenital or acquired) or size (small, moderate, or large). [16]

Fig. 11. Classification of tropia/strabismus

2.2. Pseudostrabismus

Pseudostrabismus is a condition, which only simulates squint. The eyes are straight; however, they appear to be crossed. Often, we observed the abnormality of the eyeballs structure or its placement in the orbits. Asian children may retain a broad nasal bridge into adulthood. Another form of pseudostrabismus is a Positive Angle Kappa. This occurs when the light reflection is not centered over the pupil when the eye is looking at the light. Instead the light reflection is nasal to the center.

Fig. 10. Pseudostrabismus, wide interpupilary distance simulating exotropia

2.3. Eccentric fixation

Eccentric fixation (EF) is a monocular phenomenon when function fovea has another location. Eccentric fixation, which is more distant from the fovea, you can expect even worse visual acuity. According to the site, which took over the function of the fovea, distinguish parafoveolar, paramacular and peripheral fixation.

2.4. Abnormal retinal corespodence

Retinal correspondence is called normal when both the fovea have a common visual direction and the retinal elements nasal to the fovea in one eye corresponds to the retinal elements temporal to the fovea in the other eye. Abnormal Retinal Correspondence is when the fovea of one eye has a common visual direction with an extrafoveal area in the other eye. Angle of squint is small and the extrafoveal point is close to the fovea to regain the binocular advantage, although anomalous. This results in the eyes seeing binocularly single inspite of a manifest squint. Under binocular conditions the fovea and the extafoveal point share the common subjective visual direction. When the normal eye is closed the extrafoveal element loses any advantage over the fovea of that eye, which retains its primary visual direction. [2]

2.5. Heterophoria (latent strabismus)

The term heterophoria is derived from the Greek words, heteros, meaning different from; and phora, meaning bringing or carrying. Heterophorias may be described as ocular deviations kept latent by the fusion mechanism. If sensory fusion is suspended, or in some patients confused then a deviation in the visual axes will appear. This deviation is called a heterophoria or phoria. These are main type of causes of heterophoria like anatomical causes, refractive causes, monocular activity and trauma. Anatomical causes include an abnormal interpupillary distance. For example, hypertelorism, an abnormally wide interpupillary distance, might predispose a patient to a tendency for divergence. Orbital asymmetry may also give rise to heterophoria. Relative exophthalmos or enophthalmos may produce an exo or esophoric tendency respectively. An abnormality of orbital fascia or ligaments may be a cause of an imbalance. Refractive causes relate to the relationship between accommodation and convergence with, for example, uncorrected hypermetropia having a tendency to

induce a shift towards esophoria. The repeated and prolonged use of one eye, is also suggested as being a possible cause of heterophoria.[26]

2.5.1. Classification of Heterophoria

Types of heterophoria, dependent on the direction of eye misalignment are esophoria, exophoria, hyperphoria/hypophoria and incyclophoria/excyclophoria. Esophoria is tendency to converge. Most esophoria is accommodative. Convergence excess type where is esophoria greater for near than distance. It may be caused by uncorrected hypermetropia, latent hypermetropia, early presbyopia, spasm of the near triad or of accommodation or pseudomyopia. The AC/A ratio is often a factor in producing convergence excess type. Divergence weakness type where is esophoria greater for distance than near. This is most common cause for uncorrected hypermetropa. Nonspecific or basic or mixed type where esophoria does not vary significantly in degree for any distance. Exophoria is tendency to diverge. There are several potential explanation for this: the position of anatomical rest is relatively divergent, divergence has been thought to be relaxation of convergence associated with a relaxation of accommodation, and the eyes do not diverge beyond the parallel in normal vision. High tonic impulses to the abductors do not seem to consider such a major factor in most exophoria in the way that high muscle tonus of the adductorc contriute to esophoria. For near vision, factors that produce excessive convergence in children can even mask a basic exophoric deviation. [10] It may be: Convergence weakness type where is exophoria greatrer for near than distance which is compensated.

Divergence excess type where is exophoria greater on distant fixation than the near. The causes are uncertain, there has been a good deal of speculation as to the relative importance of the tonic and anatomical factor. Nonspecific or basic or mixed is type where exophoria does not vary significantly in degree for any distance. Convergence insufficiency is an inability to sustain sufficient convergence for comfortable near vision. The condition can be conceptualized as a permanently decompensated exophoria at an unusually close working distance, which can result in a transient decompensation at normal working distance when the patient is tired or binocular vision is under stress. Hyperphoria is tendency to deviate upwards. Primary hyperphoria is usually considered to be largely due to slight anatomical misaligments of the eyes or orbits or muscle insertions. Hyperphoria one eye is hypophoria another eye where is a tendency to deviate downwards. It is often present as a secondary condition and primary causes should be considered before treating the hyperphoria. High degree of comitant esophoria or exophoria are often related by small vertical component. Cyclophoria is tendency to rotate around the anteroposterior axis. When the twelve oclock meridian of cornea rotates nasally, it is incyclophoria, but it rotates temporally it is excyclophoria. The most common cyclovertical incomitancy is a superior oblique underaction.

3. The use of prisms in the diagnosis of Optometry - subjective metodes

3.1. Maddox rod

The Maddox rod is a series of plano-convex cylinders about 3 mm in diameter in plastic. The Maddox rod is often colored usually red. The Maddox rod convets the point of light image into a line. The patient will see a point of light with one eye and red line with another eye. Measurement of horizontal deviation involves placing the Maddox rod horizontally, in which the subject will see a vertical streak, and vice versa for vertical measurement. The subject has a phoria if the streak of light does not intersect with the spot. Measurement of the magnitude of the deviation can be performed by placing prisms in front of subject’s eye until the subject reports seeing the line crossing the spot of light. The Maddox rod test is considered a dissociative test as there are two different images viewed by the subject. One disadvantage of this test is the need to control the accommodation as this technique uses a light source as the fixation target. The Madox rod test is easy for patient to understand, easy to administer and very useful for vertical deviation.

Fig. 3. Madox rod test

3.2. Maddox wing

The Maddox wing is an instrument by which the amount of heterophoria for near can be measured. It consists of a septum and two slit apertures that will produce two dissimilar images when viewed binocularly. The patient will see only the white and red arrows with the right eye whilst the left eye will see the horizontal and vertical rows of figures. The measurement can be read directly using the horizontal and vertical scales seen by the subject’s left eye, which is calibrated in prism dioptre units. The arrow pointing to the horizontal row of figures and the arrow pointing to the vertical row are both zero in the absence of a squint ori n the presence of squint with a harmonious ARC. [1]

3.3. Modified Thorington test

This is a subjective method. The modified Thorington test is used to measure direction and the amount of heterophoria at distance and near. The technique used a vertical prism to produce dissociation. The Thorington card consists of rows of targets, horizontal and vertical, for measuring horizontal or vertical phoria. Each card has a hole in the middle where the light source is being held. The Maddox rod is placed in front of the right eye and oriented according to either the horizontal or the vertical phoria that is going to be measured. The subject is instructed to look at the ‘zero’ target at the centre of the card and report the location of the streak of light relative to the zero. The measurement of the phoria is taken as the closest target where the streak of light passes through the Thorington card.

3.4. Von Graefe technique

This technique uses dissociating prisms to create diplopic image. Often a vertical Risley prism (oriented base up) is used to dissociate the image of the fixation target on one eye and a horizontal base in Risley prism is placed in front of the other eye as the measuring prism. (6 PD base up in front of OD). Controlling accommodation is important when evaluating phoria using von Graefe procedure. The patient should see something like Fig. 12.

Fig. 12. Start point in Von graefe test (left figure) and the end point in Von graefe test (right figure)

Often, we must ask the patient to look at one image and report when the other is right above or below. Move the Risley prism wheel slowly in one direction and ask the patient if the images are getting closer or farther apart horizontally. It is very important that patient look at the lower image and to keep it clear at all time and tell when the upper image moves directly above the lower image. [17] We need to confirm that the patient sees double. If not, the patient may be suppressing, or not understand. Another stepi s record the prism power and base direction on the Risley prism at that is endpoint. This is the measure of the horizontal deviation. The end point should look like Fig. 12. (right Figure) A more precise measurement can be made by moving past the endpoint to horizontal separation again and coming back from the other direction to the endpoint once more. Record this second reading and average the two.

3.5. Polarized cross test

For this test, we need polarized glases and distance polarized test. This test helps us to evaluate phoria. Depending on the test conditions (type of dissociation) the phoria will be said to be associated or dissociated. Whether the test used involves an element of fusion, perceived in common by both eyes or not. He left and right horizontal bars are seen monocularly by the right and left eyes. Usually right eye seen vertical and left eye seen horinzontal. Any horizontal or vertical displacement can be neutralized using prisms. This is not directly equivalent to dissociated phoria.

3.6. Shober test

Schober test, is based on red-green filter to break binocular vision so to evaluate phoria. The patient uses red-green glass, and is invited to observe a target, a paticular target which is composed by usually a red cross placed centrally of two green concentric circles. When the anagliphyc filter has broken binocular vision, the target perception by the patient will be show the phoria status. If the cross will move toward left we have an exo-phoria, if it will move toward right we will have an eso-phoria, toward up an hypo-phoria, toward down a hyper-phoria. We could ask to the patient if the cross movement is slow or fast, or if the cross moves continuosly in a progressive way toward the same side in a only direction, or if it moves in a interval, so we could evaluate quantitatively both vertical and horizontal phoria in a short time.

Fig.15. Shober test 16

3.7. Synoptophore

It is an ophthalmic instrument which is used for diagnosing the imbalance of the eye muscle and treating them by orthoptic methods. The instrument consists of two cylindar tubes to present different images for each eye. The angle of deviation can be measured subjectively and objectively using a range of foveal, macular and paramacular simultaneous perception slides. Specifically used in young children from 3 years of age, also used to detect suppression and abnormal retinal correspondance. The main advantage of a synoptophore is the ability to measure eye misalignment in the cardinal position of the gaze, especially in the case of hyperphoria and cyclophoria. Simultaneous perception tested by two such as a rabbit with and without tail and ears. Fusion is ability of the two eyes to produce a composite picture from two similar pictures, each of which is incomplete in one small different detail. For example, one picture is a rabbit without a tail and the other of a rabbit withaut ears. If the patient sees both the ears and tail, fusion is present. Stereopsis is ability to obtain an impression of depth by the superimposition of two pictures of the same object which have been taken from slightly different angles.

Fig. 14. Synopthore

3.8. Worth test

This test can detect tropia or suppression by asking the patient to report the number and colour of dots they can see when looking through red–green glasses at four dots of different colours. Two of the dots are green in colour and there is one red and one white dot. The transmission characteristics of the red–green glasses are such that the eye wearing the red filter, usually the right eye, views the red dot and the eye viewing through the green filter, usually the left eye, will see the two green dots. Both eyes see the white dot. The Worth 4-dot test is easy to use and can be used to assess fusion at distance and near. A positive test result does not therefore guarantee the presence of normal binocular vision. When will ask the patient how many spots of light do you see, there are four possible responses. If patients 4 dots sees, this indicates that the patient has normal fusion, normal binocular vision without suppresion and diplopia.If patients 2 dots sees, this indicates suppression of the eye with the green filter, usually in front of the left eye. If patients 3 dots sees, all green, this indicate suppression of the right eye. If patients 5 dots sees, first will determine where the red dots are located in reference to the green dots. If is red dots to the right of green dots, eso deviation (uncrossed diplopia) is present. If is red dots to the left of green dots exo deviation (crossed diplopia) is present. If is red dots above the green dots L hyper deviation or if is red dots below the green dots is R hyper deviation is present. In Fig.7., we can see a different impression of the patient's interpretation.

Fig. 7. Examples of the appearance of the Worth 4 Dot test as seen by the patient. The red lens is over the right eye and the green lens is over the patients left eye. 18

3.9. Bagolini test

A test to detect binocular sensory and motor anomalies such as suppression, normal retinal correspondence or abnormal retinal correspondence, particularly in cases of manifest strabismus. Two Bagolini lenses, one in front of each eye with their striations oriented 90° apart usually 135° for one eye, 45° for the other are used. The patient fixates a punctate light source at distance and near. Each eye sees a diagonal line perpendicular to that seen by the fellow eye. If patient see one line, or part of one line, is missing there is suppression. If the two diagonal lines cross at the source the patient is orthophoric or if strabismic, as indicated by the cover test, the patient has harmonious abnormal retinal correspondence. In a patient with microtropia, the patient may see one light and two lines, with one of the lines having a small break in it. This is due to foveal suppression. In a patient with normal binocular functions, the expected results would be a cross with the light where the two lines intersect.

Fig. 9. Possible results found with Bagolini test. A, either orthophoria, or harmonious ARC if strabismic; B, convergent strabismus (homonymous diplopia); C, suppression of the right eye; D, central suppression in the left eye. R, view of the left eye. L, view of the left eye

4. The use of prisms in the diagnosis of Optometry - objective metodes

4.1. The Hirschberg test

The Hirschberg test is one of the objective methods for determing the presence of strabismus at near in young or uncooperative patients. A small light source is viewed by the patient at 40 cm and the examiner estimates the location of the patient’s corneal reflections. The corneal reflections should be symmetrical between both eyes, although it is normal to have slight nasal displacement of corneal reflexes due to physiological positive angle kappa. Displacement of the corneal reflection relative to the point of the other eye indicates an eye deviation. If the location of the corneal reflection is nasally displaced relative to the reflex in the fellow eye, the patient has an exotropia. Esotropia is diagnosed if the corneal reflection is temporally displaced. The smallest displacement that can be reliably detected is 0.25mm. Displacement of the corneal light reflex of the deviating eye varies with the amount od ocular misaligment. One mm of decentration is equivalent approximately 7 degrees of ocular deviation and one degress is equals approximately 2 prism diopters. [8] Corneal reflex is near the temporal border of the pupil indicating an angle of about 15°, the corneal reflex is near the limbus indicating an angle of close to 45°. [4]

Fig. 5. The Hirschberg methods for estimating amount of ocular deviation. A no deviation, B left esotropia, C. left exotropia 20

4.2. The Krimsky Method

The Krimsky test works similarly to the Hirschberg test but use a prism to neutralise the deviation of the eye. A prism is held before one eye until the light reflexes appear in the same location in each eye. A prism placed before the fixating eyes will result in a version movement of both eyes in the direction of the apex. Following insertion of the prism, the fixating eye sees a displaced image and reflex it. Because of Herings Law, the deviating eye moves in the same direction. Prism is inserted until the light reflex in the deviating eye matches that of the fixating eye before prism insertion. [9] This test can be conducted with prisms over the fixing eye. Herring’s law will cause the deviated eye to move centrally as prism is added to the fixating eye. The amount of prism needed to center the light reflex in the deviated eye corressponds to the size of the deviation. This method, with prisms over the fixating eye is modified Krimsky test. [13]

Fig. 6. Modified Krimsky test. (a) Temporal displacement of corneal light reflex indicates esotropia. (b) Left eye shifts to the right when viewing light through base out prism. Herrings law causes right eye to also shift to the right with the corneal light reflex becoming more central

4.3. Angle kappa

Angle kappa is the angle between the the line of sight and the anatomic orientation of the eye or corneal axis. Normal the pupillary axis touches the posterior pole of the globe slightly nasal and inferior to the fovea. If the fovea is slightly temporal to the pupillary axis the corneal light reflection will be slightly nasal to the center of the cornea and this is positive angle kappa. A large positive angle kappa can simulate exotropia. If the position of the fovea is nasal to the pupillary axis, the corneal light reflection will be temporal to the center of the cornea. This is negative angle kappa and it simulates esotropia. Most normal patient have a physiologic positive angle kappa. Pathologic positive angle kappa occurs when the macula is pulled or displaced temporally in disease like retinopaty of premanturity. A negative angle kappa is due to nasal macular displacement secondary to a retinal scar between the optic nerve and fovea. [6]

Fig. 4. Angle kappa

4.4. Cover test

These tests are based on the patient’s ability to fixate and both eyes should have central fixation. Cover test evaluate ocular aligment by occluding one eye. Varieties of cover testing include the cover-uncover test and the alternate cover test (prism and cover test). All can be performed with fixation at distance or near. The monocular cover-uncover test is one of the important test for detecting the presence of manifest strabismus and for differentiating a heterotropia from a heterophoria. One eye is covered and then is uncovered. When one eye is covered, the examiner observes for movement in the opposite, not occluded eye. Such movement indicates the presence of a heterotropia. If there is not tropia, each eye will maintain fixation on the target before, during, and after the fellow eye is occluded. If a tropia present the strabismic eye will turn inward, exotropia, or outward, esotropia to take up fixation while the fellow eye is occluded. The strabismic eye fixates the target only when the normal eye is occluded. In Fig.17 below we can see what is possibility when placing a cover over an eye with a phoria causes a breakdown of fixation of that eye, which allows it to move to a misaligned position.

Fig. 17. Cover and Cover-Uncover tests for detection of tropias and phorias 23

Uncovering the covered eye will allow it to return to a normal central position, but covered eye moves inward on removing cover. Covered eye moves outward on removing cover . The alternate cover test (prism and cover test) measures the total ocular deviation, regardless of whether it is tropia or phoria. This test is performed after the cover- uncover test. With alternate cover testing visual fixation is broken and therefore both heterotropia and heterophoria are detected. To do alternate cover testing, the examiner alternately occludes the eyes, looking for movement of the uncovered eye. If a refixating movement is discovered, then a phoria is diagnosed. In some patients, it can take up to a minute before refixation movements are seen or the movements can build in amplitude over time. The alternative cover test is especially helpful in evalueting patients with convergence insufficiency and those who complain of diplopia intermittently or when fatigued, when the fusional mechanism may break down. [13]

Fig.18. Cover test Fig.27 . Maddox lens

5. Grafical analysis of normal AC/A ratio

Prism value can be adjusted in accordance with different approaches and schools. In German-speaking countries, there are measurements according MKH and recommended to correct 100% of the measured value. The US approach favors visual training first, then prism applied in such an amount that the client is no longer able to compensate for their efforts. The third approach is the correct prism completely and do any kind of training. Graphical analysis can be used for the vast majority of optometric patients. It cannot be used for uniocular patients or from patients for whom testing of accomodation or convergence is not possible or practical. [11]

5.1. Donders diagram

Donders diagram is graphical representation of total convergence as a function of accomodation for any fixation distance. This graph used clinically to establish the zone of clear normal binocular single vision and evalueting the patientc visual discomfort at any distance. This is area enclosed by the total amounts of positive and negative. The positive fusional resrve is plotted on the right side of the graph and negative fusional reserve is plotted similarly on the left side of the graph. The Donders line show is the plot of the amount of convergence induced by each dioptre of accomodation utilised. [19]

5.2. Sheard's criterion

The vergence reserve should be twice the vergence demand. The vergence demand is the dissociated heterophoria position of the lines of sight (visual axis) expressed usually in prism dioptres. The dissociated heterophoria is the angle bethween the lines of sight in heterophoria when the eyes are dissociated e.g. occluding one eye: the

passive position for distance or for near fixation. The vergence reserve is the opposing limit of the zone of clear normal binocular single vision. The fusional reserve to the blur point in the opposite direction to the direction of the heterophoria. Sheards criterion is sommetime expressed as the fusional reserve should be twice that amount of the heterophoria [20]. Sheards criterion is an equation as follows: Prism needed=2/3(Phoria) – 1/3 (Compensating fusional vergence).

5.3. Percivals criterion

Percival criterion is establish whether a client is going to experience discomfort in binocular vision. The zone of comfort is the middle third of the range of positive and negative relative convergence and if Donders line lies within zone of comfort, Percival criterion of comfortable binocular vision is fulfilled.

Fig. 20. Percival's and Sheard's zones of comfort. Accommodative distance in diopters is plotted as a function of vergence distance in diopters. Percival's criterion is represented by the green-shaded region. It encompasses the iddle third of the ZCSBV. Sheard's criterion is represented by the red-shaded region. It extends on both sides of the phoria line one-third of the way to the boundary of the zone of clear single binocular vision.

5.4. MHK

The test charts included in the Polatest (a systematic set of tests for evaluating binocular vision), designed by H.-J. Haase and manufactured by Zeiss, is more commonly used in Germany, Switzerland and Scandinavia for prism correction of associated phoria and stereoacuity at near and distance using a variety of different targets for each test. From clinical experience with the Polatest Haase developed a motor and sensory theory of the different stages of decompensation of associated phoria and a strategy for its prismatic correction - the MKH (Measuring and Correcting Methodology after H.-J. Haase). The MKH-Haase method has been considered a reliable method for prescribing prisms to symptomatic binocular vision patients.

Fig. 19. MKH test chart

6. Prism

Ophthalmic prisms have been use din the treatment of binocular desorders for more than 100 years. Prisms have many clinical uses in ophtalmology and optometry. Corrective prism can be ground or Fresnel. The direction of displacement of light depends on whether the lens is of plus or minus power. Fresnel prisms as a series of very narrow adjacent prisms on a thin sheet of plastic. Fresnel prism is flexible, and can be applied to an existing spectacle lens. Iti s a very thin and can be cut to any shape with scissors or a razor blade. Desadvantege is that cause a slight loss of visual acuity caused by reflections for prisms greater than ten. Fresnel prisms used when patients have high amount of prism, for use and reuse, for sectorial application of slowing nystagmus. If patient requires a prismatic correction in both vertical and horizontal directions, we must calculate by vector addition, either graphically or mathematically. Risley prism or rotary prism is an application of obliquely crossed prisms thah is used on a regular basis in optometric practic. This is combination of two prisms. Forms of prism use din diagnosis can be single unmounted prisms, the prisms from the trial set or prism bar. We can measurements of muscle imbalances. Prisms displace the real image, moving it on the fovea of the deviated eye, thus producing fusion and eliminating corrective eye movements on cover testing.

Fig. 22. Prisms displace the real image

A prism determined by covet testing is incorporated into spectacle lenses to eliminate fusion difficulties and diplopia. Base out prism for eye exercises to correct convergence insufficiency. We use prisms in ophtalmic instrument like as Goldman applanation tonometer or exophalmometer or keratometer or Risley prism on the phoroptor or optical instrument such as binoculars, Fresnel prisms to affix on spectacle lenc. Prisms refract light. An optical prism is made of transparent material (like glass or plastic) that has a higher refractive index than air. The traditional geometrical shape is a triangular. One side of this triangle is the base of the prism, and the corner opposite the baseis called the apex. The angle of the apex is called the apical angle and its size will affect how much the prism will bend light. At the point where the light ray hits the refracting surface, we can draw a dotted line perpendicular (at an angle of 90°) to the refracting surface. When a light ray travels through the new medium, it will change the angle between the normal line and the refracted ray. The angle of refraction is smaller than the angle of incidence, if a light ray travels into a medium with a higher refractive index. The angle of refraction is greater than the angle of incidence if a light ray travels into a medium with a lower refractive indeks. A glass or plastic prism has a higher refractive index than air. When an incident light ray enters a prism, the light ray will be bent towards the normal inside the prism and away from the normal when it leaves the prism. Light entering a prism will always bend away from the apex of the prism.

Fig. 26. A prism will bend all light rays by the same amount, no matter where the light ray enters the prism. All parallel light rays that enter a prism will exit the prism travelling in the same new direction.

A prism does not focus light. If parallel light goes in to the prism, then parallel light will come out the other side. When we look at an object through a prism, the object will look like it is closer to the apex of the prism than it really is. This is called the apparent deviation of the object. When prescribing prisms, the correction is split between the two eyes. The apex of the prism must always be placed towards the deviation of the eye. One prism diopter will bend a ray of light one centimeter at a distance one meter. Light bends toward the base of a prism as it passes through the prism and the image a person sees moves in the opposite direction from the base. To describe a prism in a prescription, the optometrist will list the amount prism diopters and then add the symbol “Δ” and one of these abbreviations:

BI (base-in) mean thickest part of the prism toward the nose

BO (base-out) mean thickest part of the prism toward the temples

BU (base-up)

BD (base-down)

When the patient is not looking directly through the optical center of a lens, an induced prismatic effect. The American National Standards Institute (ANSI) sets a standard for finished lens prism tolerances. They have determined how much induced prism will be allowed in a finished. The amount of induced horizontal prism can’t be greater than a total of +/-0.67 prism diopters for the two lenses combined. The total amount of induced vertical prism cannot be greater than +/-0.33 prism diopters for the two lenses combined, or the lenses will be out of tolerance. The amount of induced prism can be calculated with Prentice’s rule. Prentice’s Rule is a formula used to determine the amount of induced prism in a lens: Prism diopter (Δ) = Power of the lens (F) x the decentration distance in centimeters (dcm) between the optical center and the center of the pupil. (Prism = F x d). For example if we have prescription OS -1.50 sph Δ BO, to achieve a base-out prism, we are going to want to move lens toward client nose so client looking through the base-

out part of the lens. We can calculate: Prism = F x d. Divide both sides of our equation by 1.50. 0.5 ÷ 1.50 = d; 0.5 ÷ 1.50 = 0.33 cm = 3.3 mm. So, we’ll want to decenter client lens 3.3 mm inward from the optical center. Prism occurs whenever there is a difference in lens thickness between two points on the lens. Because lenses with power always have a variation in lens thickness, prescription eyeglass lenses produce prismatic effects away from the optical center of the lens. At any point away from the optical center of the lens, a minus lens, which is thicker at the edge and thinner at the center, produces a prismatic effect with the prism base pointed away from the optical center. Plus lens, which is thicker at the center and thinner at the edge, produces a prismatic effect with the prism base pointed toward the optical center (Figure 21).

Fig. 21. Prismatic effect of eyeglass lenses

7. Examination

7.1. Patient History

The patient history is the starting component of the examination and an important part of making an appropriate diagnosis. History and symptoms is elementary for the practitioner to acquire full details of the presenting symptoms suggestive of decompensation including onset, frequency, alleviating factors, associations in addition to ascertaining. Provider should ask if the client has any problem with general health (whether the patient has had any recent periods of illness or changes to medications) or any problem with visual requirements any increase in ocular activity with changes in occupation). Previous ocular history, any history of binocular vision anomalies including prismatic corrections or orthoptic exercises is very important too. A suggested history to investigate accommodative and vergence problems is shown in Table 4.

1 Do your eyes bother you? If yes, how often and under what circumstances?

2 How do your eyes bother you? Do you experience eyestrain, fatigue, headaches, sleepiness, etc., associated with near tasks?

3 Do you ever get headaches? If yes, explore further (e.g., frequency, location, type, and associated activities).

4 How long can you read comfortably? Have the patient specify an actual time.

5 When you read, does the print ever blur, double, or move around?

6 Do you experience car or motion sickness?

Table 4. Suggested questions for patient history

7.2. Direct observation

When patient come in the office we will see the position of the head and body, walk and eye movements. Watching the patient may be detected of strabismus. Direct observation can confirm nystagmus, abnormal position of the eyelids, ptosis, epicanthus or asymmetry.

Fig. 13. Child with nystagmus who adopts an abnormal head posture to improve vision by holding eyey in null position.

7.3. Measuring Pupillary Distance (PD)

For proper placement of the optical centers of the lenses, accurate PD measurements are necessary. Dispenser should be positioned at the same level directly in front of the patient whose PD is to be measured. The PD ruler should be positioned across the patient’s nose and the ruler positioned steadily in the dispenser’s fingers. The dispenser closes their right eye, viewing the patient’s eye with their left eye. While the patient is instructed to view the dispensers open eye, the dispenser lines up the zero mark on the PD ruler with the centre of the patient’s pupil or the temporal limbus of the right eye. After the zero mark is correctly lined up, the dispenser closes 33

their left eye and opens their right eye. The patient is now instructed to view the dispensers open eye. The PD is read as that mark falling in the center of the patients left pupil or nasal limbus of the left eye. An average PD for an adult range between 58 and 65.

Fig. 23. PD ruler

7.4. Symptoms of decompensation

The difficulty in making a diagnosis based on symptoms alone is that they can be non-specific ranging from general irritation to vertigo. The increasing stability of the binocular system prevents young adults from adapting to a decompensating heterophoria through suppression, making it increasingly likely that they present with different symptoms of: headaches (horizontal heterophoria is associated mostly with a bilateral frontal ache while hyperphoria results in occipital pain), asthenopia (eye ache, dull pain behind the eyes and/or general soreness), blurring of print and difficulty changing focus to distance following a period of near work ( the focusing capability of the eye is affected by the accommodative-vergence induced to control a heterophoria), intermittent diplopia usually following a period of intense work, intermittent ‘confusion’ or distorted vision (instability in binocular alignment results in the perception of letters or words moving, flickering or jumping so that words or lines of text are missed or patients may even report shapes or patterns on the page).

Less commonly patients describe difficulties in depth perception, particularly during sport. Adaptation to binocular discomfort by closing one eye to read, or adopting an abnormal head posture to prevent double vision by using the nose to block the image of one eye. Typically, these symptoms will be absent on waking, arising later in the day with increased visual activity. Patients may report that symptoms alleviate with breaks from work. Esophoria decompensated by uncorrected hyperopia and exophoria decompensated by uncorrected myopia. Reduces the acuity and dissociates the eyes, more pronounced where one eye is affected more than the other. Particularly with high refractive errors that can induce unwanted prismatic effects. Poor health, fatigue, worry and anxiety reduces fusional reserves, reduces amplitudes of accommodation and subsequent accommodative convergence. Head trauma can result in temporary or permanent reduction in fusion. Change in occupation, extended period of work at a particular distance. Reading at too close a distance for long periods, poor llumination or contrast of visual task. Certain antihypertensive and antidepressant agents can reduce accommodation. Alcohol has been found to reduce horizontal fusional reserves. Video games that involve rapid, repeated pursuit fixation movements. ‘Magic Eye’ 3D autostereograms that dissociate and disrupt accommodation and convergence. Difference in image size between the eyes makes fusion difficult. Night driving reduced visual information prevents binocular functioning between the eyes. Glaucoma reduces binocular matching between the eyes. [25]

8. The treatment of oculomotor anomalies

8.1. Correct the refractive error

Required to create two clear, same sized and shape images for binocular fusion. Even small corrections otherwise deemed clinically insignificant can improve control, or for example, uncorrected hypermetropia having a tendency to induce an esophoria.

8.2. Modification of refractive error

Modification of refractive error may ease oculomotor stress. For a patient with a poorly compensated esophoria at near or a convergence excess, an additional positive lens may be used to reduce accommodative demand and thus reduce accommodative convergence. Undercorrection as necessary for patient with hyperopic exophoria and myopic esophoria. For myopic exophoria overcorrection if enough accommodation by no more than -3.00 DS, gradually reducing this power over months allow fusional reserves to be exercised accordingly.

8.3. Orthoptic exercises

Orthoptoc exercise is eye exercises to treat ocular motor disorders such as vergence anomalies. Main goal is give comfortable binocular vision. The principle is to improve oculomotor control and re-establish accurate muscle coordination rather than to solely increase fusional reserves. The number of office visits required depends on the seriousness of the vision problem, diagnosis and the age of the patient. Vision therapy programs typically involve one to two in-office sessions throughout the week, for a

varying number of months depending on need. Vision therapy activities at the home are also prescribed weekly, to increase what is learned during the office therapy. Optometrist must be confident that the patient is in good health and that there is no underlying secondary cause of the problem, which requires medical or specialist management. The patient must be motivated and have the ability and cooperation to carry out the exercises, for them to be beneficial. Visual therapy is recommended in patients with convergence insufficiency, divergence excess, fusion vergence dysfunction, basic exophoria, accommodative excess or insufficiency, or motor dysfunction. The types of orthoptic exercises are very varied and wide. Visual therapy techniques can be dived in 6 groups: basic concept introduction, fusion vergence methods, voluntary convergence methods, anti-suppression methods, accommodative techniques and motor techniques. Basic concept introduction is instrumnet trainig with anaglyph and polarized filters, lenses, prism and mirrors, septum and apertures, paper, pencil and tasks, stereoscopes and afterimages, entoptic phenomenon and electrophysiological methods. Second type of vision therapy is fusion vergence methods like anaglypgs and polarizators, loose prism, aperture rule, free fusion pictures and stereoscope. Voluntary convergence methods are Brock string and Barrel card. Anti suppresion methods is: bar reader, TV trainer, red-green glasses with light, vertical dissociating prism and trainig of superposition with mirror. Accommodative techniques are anaglyph and polarized techniques (Red-red rock), prism and mirror (Lens sorting, Loose lens rock – mono and bino, binocular accommodative facility) and paper, pencil and tasks (Hart’s chart). Motor techniques is lenses, prism and mirrors (Loose prism jumps), paper, pencil and tasks (Hart chart, letter or symbol tracking, visual tracking, rotator, flashlight tag and afterimages. [24] Orthoptic (eye) exercises are not recommended for myopia, dyslexia, or other learning disorder, poor athletic performance, poor academic performance, juvenile delinquency, clumsiness, difficulty with eye tracking, excessive blinking or squinting, or visual perceptual problems.

Orthoptic exercises are not usually helpful in small misalignments which do not cause symptoms, large misalignments unless given prior to planned surgery, vertical ocular misalignments, paralysis of an eye muscle, paralyzed focusing mechanism, spasm of the focusing muscle, or any "nervous" conditions caused by psychological problems. [27]

Fig. 25. Brock String is for develop the kinesthetic awareness of converging and diverging, develop the ability to voluntarily converge and normalize the near point of convergence

8.4. Therapeutic prisms

Commonest therapeutic use of prism in orthoptocs exercises is for building up the fusional reserve of patients with convergence insufficiency. Therapeutic prisms are reserved for patients for whom surgery is not indicated. Reduce the angle of heterophoria remaining for the patient to control, with particular usefulness in vertical deviations. They also provide an option when exercises fail or are simply impractical given the patient’s age or poor health. and temporary relief for eg students with imminent exams. In strong ocular dominance with monocular slip, prism should be issued for this non- dominant eye. Larger prisms may be divided between the eyes but distributed unequally with the weaker power before the dominant eye. Before the final prescription is issued, confirm subjective appreciation of comfortable control using the near/ distance letter chart and repeat the Cover test with this prismatic correction to observe the rapid, smooth recovery to binocular. 38

8.5. Surgery

Surgery may be required for large angle deviations, as well as various incomitant anomalies that have not or are unlikely to respond to other treatment methods. Usually involves weakening one muscle and strengthening another to reduce the angle of heterophoria. It is often the only feasible option in cyclophoria, vertical phorias or unusually large horizontal phorias. Eye muscle surgery is generally recommended as the treatment for fourth nerve palsy in children and adults. For example, after surgery for fourth nerve palsy, abnormal head tilt usually disappears. Surgery is performed on one or both eyes depending on the extent of the eye misalignment, the change of the misalignment in different directions of gaze, the amount of head tilt, and the amount of torsion. Eye muscle surgery is generally not recommended until the amblyopia is maximally treated.

8.6. Botulinum Toxin A

Botulinum Toxin A, more commonly known as Botox, has been used to treat patients with strabismus since the 1970s, can be used in the management of large horizontal heterophoria by temporarily reducing the angle of deviation. It does however require repeated injections to maintain comfortable control. The reason why the effect of Botox wears off with time is because the muscle cells develop new receptors, so the signalling from the nerve to the muscle is restored.

Fig. 8. Botox treatment: Once the eye has been anesthetized the Botox can be injected directly into the eye muscle using a special needle connected to an electromyogram 39

9. Experimental section

The aim of this work is to analyze the presence and size heterophorias. Main focus on the presence of subjective complaints may be caused by the presence heterophoria. I suppose that most people diagnosed with heterophoria do not wear the resulting prismatic correction. For my research, I determined the following hypothetical questions that I will try to the practical part of this work to answer. Prismatic trial lenses in the following steps and number are used for my research: to 2.0 ∆ in steps of 0.25 ∆, to 5.0 ∆ in steps of 0.5 ∆ and to 10.0 ∆ in steps of 1.0 ∆.

Fig. 28. Prism bar set

Research on the practical part of this work was carried out from 2016 to 2017. In period from November to March at the Department of Optometry in the laboratory of the University of Applied Sciences Velika Gorica. Research are conducted in the afternoon under standard lighting conditions. In the area surrounding the test field perceived by the patient during refraction there must be no fusion stimuli in the form of objects or structures which might catch her or his eye. To keep the influence of accommodation to a minimum, the test distance was 6 metres. Research was done on Nidek sc-1600p polarised test chart.

9.1. Hypothesis

For my research assumed to a few questions to which I have during the research tried to answer.

9.1.1. Hypothesis 1

Measure of phoria will vary slightly on regardless of the method used of measure with von Graefe and Maddox test.

Von Graefe and Maddox test were performed on 93 clients at far and near distance. All of them had distance visual acuity of 1.00 or better for far, and near vision of N6. The absence of tropia was confirmed with Hirsberg and cover uncover test. Amblyopa, ocular pathology, history of surgery or distance visual acuity less then 1.0 were excluded from statistic.

Paired Samples Statistics

Std. Std. Error Mean N Deviation Mean Pair 1 VG far -0.2204 93 1.66846 0.17301 MAD far -0.0188 93 1.63863 0.16992 Pair 2 VG near -1.3602 93 2.31649 0.24021 MAD near -1.0726 93 2.15644 0.22361

Table 5. Mean values and standard deviation of horizontal heterophoria (PD) measured using Von Graefe and Maddox tests

The study population consisted of 93 subjects. Table 5 shows the mean and standard deviation for VG far (-0.2204±1.668) and MAD far (-0.0188±1.639) and VG near ( - 1.360±2.316) and MAD near (-1.0726±2.156). Positive numbers represent esophoria, negative numbers represent exophoria.

Paired Samples Correlations N Correlation Pair 1 VG far & MAD Far 93 0.923**

Pair 2 VG near & MAD near 93 0.949**

Table 6. Correlations between VG and Maddox test

** Correlation is significant at the 0.01 level

Correlation is significant at the 0.01 level between VG far and Maddox near

(0.923) and between VG near and Maddox near (0.949).

Paired Differences 95% Confidence Std. Interval of the Std. Error Difference Sig. (2- Mean Deviation Mean Lower Upper t df tailed) Pair 1 VG far – -0.2016 0.6493 0.0673 -0.3353 -0.0679 -2.9946 92 <0.01 MAD far Pair 2 VG near – MAD -0.2876 0.7288 .00756 -0.4377 -0.1375 -3.8059 92 <0.01 near

Table 7. Paired Differences VG far and Maddox far and VG near and Maddox near

Standard deviation for VG far i MAD far is -0.2016 ± 0.6493, and 95% confidence interval of the difference is -0.3353 to -0.0679. Standard deviation for VG near – MAD near is -0.2876 ± 0.7288 and 95% confidence interval of the difference is - 0.4377 to -0.1375. The difference between the examined variable (s) is statistically significant at 1% significance test (<0.01) and indicated significant differences between each of the mean findings obtained using the VG and MAD. In considering the mean values shown in Table 5, a significantly larger exo deviation was measured with the VG procedure when compared with the Maddox techniques. This hypothesis was not confirmed. 42

9.1.2. Hypothesis 2

More than 70% of the subjects will have heterophoria.

Subject between 19 -78 years participated in my research. Most of the subjects who participed in this research were heterophoria for far and near distance. Each patient performed the von Graefe test. The test were performed at 6 m and 40 cm throught the patient habitual correction. For this test, test object was a single letter one line below than the patient best visual acuity. The eyes were dissociated with 6 prism base down in front of right eye. A 12 prism base in measuring was placed in front of left eye. For the horizontal phoria measurement the patient was instructed to look at the bottom letter. Also controlling accommodation is important. Verify that the patient can see 2 targets (one up and one down). Client with exo or eso deviation will see the images in uncrossed and crossed diplopia. If the patient does not see two separate targets, we must try increase the amount of BI. Instruct patient to look at the upper target and it is very important keep it clear at all times. Patient must understand test and tell them “I am going to move the lower target and I want you to tell me when it’s directly below the upper target, like buttons on a shirt”. Once the direction of deviation has been determined, reduce BI prism (~2 Δ/sec) until the patient reports vertical alignment and record magnitude and direction of deviation. Normal expected value is ortho to 2 exo for distance and ortho to 6 exo for near. For presbiopy people expected ortho to 2 exo for distance and 11 exo to 5 exo for near. It is useful to take two reading, adjusting the prism power in opposite direction.

Chart.3. Representation ortophorie population

This hypothesis was confirmed. For 73 % of the subjects were diagnosed heterophorias. Ortophoria was only present in 27 % of the respondents.

9.1.3. Hypothesis 3

Corrected presbyops tend to be more exophoria for near vision than non presbyops.

In this cross sectional study, adults with mean age of years were included. All participants had best corrected visual acuity better than N6, more than 60 sec of arc stereopsis and had no heterotropia or other significant eye disorders. Study participants were divided into two age categories. The first category of 18-45 years and 34 participants in the category of 45 years and older. The first group of students and young productive. The second is the beginning of presbyopia and with greater foresight and pensioners. The values obtained heterophorias can compare between different age groups. The study was attended by 56 non presbyops and 37 corrected presbyops. The age range of presbyops clients were 45 years of age to 78 years. The average age of presbyops clients was 54,05 years, with a standard deviation of 11,63 years. The average of addition is +1,85 with SD ± 0,62.

Std. Std. Error Technique VG near N Mean Deviation Mean 0 56 -1.2054 2.22645 0.29752 1 37 -1.5945 2.45893 .040425

Table 9. Mean values, for horizontal heterophoria recorded using Von Graefe

For non presbyops client Mean values of horizontal heterophoria (PD) measured using the Von Graefe (VG) is – 1.2054 ± 2.226. For presbyop client Mean values of horizontal heterophoria (PD) measured using the Von Graefe (VG) is -1.5945 ± 2.4589 . Positive and negative values represent eso and exo deviations. From the results, ( Table 9) it is evident that corrected presbyops tend to be more exo deviations for near vision than non presbyops.

This hypothesis was confirmed. 45

9.2. Results

During the data collection are viewed 93 people. We can speak of a randomized study, because it was completely random customers optician optics. The study was attended by 54 women (%) and men 46 (%). The age range of clients were 18 years of age to 78 years. The average age of clients was 38,15 years, with a standard deviation of 15,80 years. There has monocular visual acuity with the best sphere correction ranging OR and OL of 1.0 to 1.6. Binocular visual acuity with best correction sphere is ranging from 1,0 to 1,6. Results were compared with several aspects. I focused on the presence heteoforie residents, heterophorias correlation by sex, age and refractive errors.

Chart 1. Structure of persons under investigation by gender

Chart 2. Distribution by age

Study participants were divided into four age categories.The first category of 18-29 years, and was attend 11 men and 20 women, second group is category of 30-45 years and was attend 18 men and 7 women, third group of 46-59 years was 12 men and 9 women and finaly last group of 60-78 years attend 2 man and 9 women.

Distribution heterophoria by gender 45 40 35 30 25 20 15 10 5 0 Female Male Chart 4. Distribution heterophoria by gender Orto Hetero The study was attended by 54 women (%) and men 46 (%). For 73 % of the subjects were diagnosed heterophorias. Ortoforie was only present in 27 % of the respondents. Ortophoria was present in 11 women (44 %) and 14 men (55 %). 47

Chart 5. Distribution of the size of the horizontal heterophory for far

We see the distribution of the size of the horizontal heterophory in the population. Horizontal heterophorias amount ≤ 1 PD are measured in the 35 participants. Heterophory ranging from 1.0 to 2 were measured in the participants 13. Amount between 2.0- 3.0 PD were measured in the 16 participants, amount between 3.0- 4.0 PD were measured in the 2 participants, and amount more that 4 PD were 2 participants. Ortophoria was present in 25 participants.

DISTRIBUTION OF PRESENCE OF THE BASIC TIPE OF PHORIA

Ortho Eso Egzo

Eso 34%

Ortho Egzo 27% 39%

Chart 6. Distribution of the presence of the basic tipe of phoria for far

We can see the percentage of the presence of the basic types heterophory in the population. Orthophoria are measured in the 25 participants, esophoria in the 31 participant and exophoria in the 36 participants.

Chart 7. Distribution of presence of the basic tipe of phoria 49

Ortophoria was present in 11 women (44%) and 14 men (56%). Esophoria was present in 21 women and 11 man and exsophoria was present in 18 women and 18 man.

Chart 8. Distribution of the size of the horizontal heterophoria for near

We see the distribution of the size of the horizontal heterophory in the population. Horizontal heterophorias amount ≤ 1 PD are measured in the 25 participants. Heterophory ranging from 1.0 to 2 were measured in the participants 9. Amount between 2.0- 3.0 PD were measured in the 7 participants, amount between 3.0- 4.0 PD were measured in the 10 participants, and amount more that 4 PD were 14 participants. Ortophoria was present in 28 participants.

Chart 9. Distribution of the presence of the basic tipe of phoria for near

We can see the percentage of the presence of the basic types heterophory in the population. Orthophoria are measured in the 29 participants, esophoria in the 13 participant and exophoria in the 51 participants.

Chart 10. Distribution of refractive error

For evaluation the refractive error of participants, I wondered spherical equivalent and each eye. For emetropic eye I consider spherical equivalent in the interval ≤ 0.25 and at the same time ≥ -0.25. Emetropic eye for a few consider prescribed conditions for emetropic eye to both eyes. If one eye has fulfilled the condition emmetropia and second instance falls for hyperopia, the eye pair is considered for hyperopic. According to the above described conditions, the sample 27 ( 29%) was emetrop, 44 (47%) myop and 22 hypermetrop (22%).

Chart 11. Heterophorias representation depending on the refractive error

For evaluation heterophorias depending on the refractive error, I wondered spherical equivalent and each eye. For emetropic eye I consider spherical equivalent in the interval ≤ 0.25 and at the same time ≥ -0.25. Heterophorias deviation is binocular and can not be related only to those refractive error eye. That's why I started this heterophorias depending on the refractive error eye in pair. Ocular pair calculates the average spherical equivalent. Emetropic eye for a few consider prescribed conditions for emetropic eye to both eyes. If one eye has fulfilled the condition emmetropia and second instance falls for hyperopia, the eye pair is considered for hyperopic.

According to the above described conditions, the sample 27 emetrop, 44 myop and 22 hypermetrop. Myopic participant with ortophoria was 12, with exophoria was 21 and with esophoria was 9. Emetropic participant with ortophoria was 9, with exophoria was 12 and with esophoria was 9. Hyperopic participant with ortophoria was 4, with exophoria was 9 and with esophoria was 9.

Ortophoria Exophoria Esophoria

Emetrop 36% 29% 35%

Myop 16% 50% 35%

Hypermetrop 48% 21% 31%

Table 2. Distribution refractive errors by heterophoria for far

Ortophoria Exophoria Esophoria

Emetrop 17% 43% 21%

Myop 59% 45% 14%

Hypermetrop 24% 12% 64%

Table 8. Distribution refractive errors by heterophoria for near

In the Table 8. we can se distribution refractive errors by heterophoria for near. The total number of participants with myopia was 41, with hyperopia was 22 and participants without refractive errors was 29. Myopic participants with ortophoria was 17, with exophoria was 22 and with esophoria was 2. Emetropic participants with ortophoria was 5, with exophoria was 21 and with esophoria was 32. Hyperopic participants with ortophoria was 7, with exophoria was 21 and with esophoria was 5.

10. Discussion

Most of the subjects who participed in this research were heterophoria for far and near distance. Similar research were noted in previous diploma thesis: Vyskyt heteroforie u ametropu v populace studentu, from Bc. Marketa Trnakova. She was found 77% heterophoria.

Fig. 16. Representation ortophorie population [22]

Similary research has been to University of Limpopo between 2000 and 2005. Number of client was of 475, 277 was males and 198 was females. To obtain heterophoria values was used the Von Graefe method. Data on heterophoria and related values such as age and gender were recorded. In 200 was found heterophoria for distance only one client was vertical heterophory. The distribution of horizontal heterophoria for distance vision is shown in Figure 27. For distance vision exophoria was more common, 61 % (N = 287), followed by orthophoria , 20% (N = 95) and esophoria 19.4 (N = 90). In my research distribution of horizontal exophoria for distance was 39%, ortophoria 27 % and esophoria was 34 %.

Fig. 24. Distribution of horizontal heterophoria for distance [14]

Another similar research was from Cvancigerova, Gabriela [7]. She was found 79 % heterophoria. Number of client was 200. Only 6.3% was ortophoria. The incidence of myopia is at exophoria in 40 % and incidence of esophoria is 17,5 %.

Third research is from Stašova Simona. She has diploma thesis: The incidence of orthophoria in the population of emethropes. During examination of binocular functions were these 164 people 23% ortoforie detected and thus 77% heterophoria. [18] Katerina Kopalova in his diploma thesis Use of prisms in optometric practice was found 80, 5 % heterophoria and 19,5 % ortophoria. The research involved 200 people, including 109 women and 91men. Persons were examined in terms of age range from 15 to 78 years. [12]

T test analysis indicated significant differences between each of the mean findings obtained using the Von Graefe technique when compared with the MAD. In considering the mean values shown in Table 5, a significantly larger exo deviation was measured with the VG procedure when compared with the Maddox techniques. The use of relatively small letters for the VG test should represent a good stimulus to 55

accommodation, and it seems unlikely that the accommodative response would be significantly reduced when compared with the light stimulus adopted in the MR technique. The differences between these procedures were present at both distance and near, and it would result from decreased proximal or tonic vergence. The patient is viewing a target through a 12 base-in prism under dissociated conditions, and this could be explanation for the greater exo deviation measured with the VG test. Even with nonfusible stimuli, subjects may still make a disparity divergence response in an attempt to reduce the horizontal separation between the diplopic images. The prism is present for several seconds, the initial fast disparity divergence may initiate a slow disparity divergence response, resulting in vergence adaptation. Evidence for disparity vergence even in the presence of nonfusible targets may be carried from studies of vergence adaptation in strabismic patients. If subjects do indeed exert a disparity divergence response in response to the base-in prism, this could lead to a sustained vergence response, which is still present during the remainder of the VG procedure. This would produce an exo compensation in the magnitude of deviation found with the VG test. Since neither the MR test start with a prism before the eye, this adaptive bias would not be present with these procedure. This proposal could be verified by beginning the VG procedure with a base-out measuring prism. If prism adaptation does produce a shift in the findings, then one would predict an eso compensation in the results under these circumstances when compared with the other two techniques. [5] Similar research was from Elizabeth Casillas Casillas and Mark Rosenfield, Comparasion of subjective heterophoria testing with a phoropter and trial frame. They were measured in 60 visually normal subjects between 20 and 34 years of age using Von Graefe, Maddox Rod and Modified Thorington tests. The mean values of horizontal heterophoria at viewing distance showed a greater exo deviation when compared with other tests. Mean value of VG far was -0,06 ± 0,09, for VG near was -3,85 ± 0,31,for MAD far was +0,73 ± 0,16 and MAD near was -2,48 ± 0,28. [5]

11. Summary

Optometrists measure heterophoria routinely in a clinical practice and this might help in the diagnosis of binocular conditions. The aim of this study was to provide a comprehensive overview of binocular vision, binocular vision disorders, test methods and possibilities of correction and information on the representation of any kind heterophoria and heterotropia population. The paper is divided into two main parts - theoretical and practical. In the theoretical part, I described binocular vision, its development and disorders that can be occur when the development of binocular vision is disturbed. The paper gives a detailed description heterophoria and heterotropia, provides an overview of the methods of testing with a focus on von Graefe test and Maddox test. Finally, the theoretical part outlines the possibility of correction of binocular vision. The part of the research I have conducted by screening heterophorias population with von Graefe, and Maddox test. The Cover test was used for screening tropias. All these tests are statisticaly analyzed, and described in thesis.

List of charts

Chart 1. Structure of persons under investigation by gender

Chart 2. Distribution by age

Chart 3. Representation ortophorie population

Chart 4. Distribution heterophoria by gender

Chart 5. Distribution of the size of the horizontal heterophora for far

Chart 6. Distribution of the presence of the basic tipe of phoria for far

Chart 7. Distribution of presence of the basic tipe of phoria

Chart 8. Distribution of the size of the horizontal heterophora for near

Chart 9. Distribution of the presence of the basic tipe of phoria for near

Chart 10. Distribution of refractive error

Chart 11. Heterophorias representation depending on the refractive error

List of abbreviations

AC/A Accommodative Convergence/Accommodation

ARC abnormal retinal corespodence

BI base in

BO base out

BU base up

BD base down

EOM extraocular muscles

Exo exsophoria

Eso esophoria

EF excentric fixation

MKH Mess- und Korrektionsmethodik nach H.-J. Haase

PRV positive relative vergence

NRV negativne relative vergence

PD pupillari distance

VG Von Graefe

MAD Maddox

ZCSBC zone of clear single binocular vision

List of tables

Table 1. Actions of the extraocular muscles

Table 2. Distribution refractive errors by heterophoria for far

Table 3. Amplitudes of fusional reserves at near and distance with prism orientations required for assessment

Table 4. Suggested Questions for Patient History, Optometric clinical practice guideline care of the patient with accommodative and vergence dysfunction, Jeffrey S. Cooper, M.S., O.D., Principal Author, 33

Table 5. Mean values and standard deviation of horizontal heterophoria (PD) measured using Von Graefe and Maddox tests

Table 6. Correlations between VG and Maddox test

Table 7. Paired Differences VG far and Maddox far and VG near and Maddox near

Table 8. Distribution refractive errors by heterophoria for near

Table 9. Mean values, for horizontal heterophoria recorded using Von Graefe

List of figures

Fig. 1. Extraocular muscles of the left eye, Noorden GK von: Atlas of Strabismus, ed

4. St Louis, Mosby–Year Book, 1983, p 33 Fig. 2. Sensory fusion, Robert B. Daroff, Joseph Jankovic, John C Mazziotta, Scott L Pomeroy, Bradley's Neurology in Clinical Practice,seventh edition, ISBN:978-0-323- 28783-8, p 531 Fig. 3. Madox rod test, Mukherjee P.K. Clinical Examination in Ophthalmology,

ISBN-13:978-81-312-0335-4, p 245 Fig. 4. Schematic diagram the kappa angle is related with the Journal of Vision. 2006;6(1):1. doi:10.1167/6.1.1 Fig. 5. The Hirchberg method Fig. 6. Modified Krimsky test. Traboulsi Elias I., Practical Management of Pediatric Ocular Disorders and Strabismus, ISBN 978-1-4939-2744-9 p.15 Fig. 7. Examples of the appearance of the Worth 4 Dot test, Carlson Nancy, Kurtz Daniel ,Clinical Procedures for Ocular Examination, Third Edition, ISBN: 978-0-07- 181151-4, p 49 Fig. 8 .Botox treatment, available from: https://www.aao.org/pediatric-center- detail/strabismus-botox-treatment

Fig. 9. Bagolini test, available from: http://clinicalgate.com/t-2/

Fig.10. Pseudostrabismus, Brad Bowling, Kanski's Clinical Ophthalmology: A Systematic Approach

Fig. 11. Classification of tropia/strabismus, von Noorden and Campos 2001

Fig. 12. Start point and the end point in Von graefe test, available from:ww.eyetec.net/images/stories/group6/VG2.gif

Fig.13. Child with nystagmus who adopts an abnormal head posture to improve vision by holding eyey in null position, Visual Handbook of Pediatrics and Child Health: The Core, Stephen Ludwig ISBN 978-0-7817-9505-0 61

Fig.14. Synoptophore, P. Vesely and S. Synek: Simple Binocular Vision Examination, Coll. Antropol. 37 (2013) Suppl. 1: 145–151 Fig. 15. Schober test Fig. 16. Trnakova Marketa, Diploma thesis,The incidence of heterophoria in a population of ametropic students, Brno 2015.[25] Fig. 17. Cover and Cover-Uncover Tests for Detection of Tropias and Phorias, available from: http://www.fprmed.com/documents/books/TORNO09/ 2009/textbook/textBook_354_22_1.htm Fig. 18. Cover test Fig. 19. MKH test chart, available from: http://journals.plos.org/plosone/article/ figure/image?size=medium&id= info:doi/10.1371/journal.pone.0138871.g003

Fig. 20. Percival's and Sheard's zones of comfort, available from: http://jov.arvojournals.org/article.aspx?articleid=2121032

Fig. 21. Prismatic Effect of Eyeglass Lenses

Fig. 22. Prisms displace the real image

Fig. 23.PD ruler, available from: https://www.clearlycontacts.ca/imageresources/EG- PP-PopUps/whatisPD-CA_pop.html

Fig. 24. Distribution of horizontal heterophoria for distance [21]

Fig. 25. Brock String

Fig. 26. Prism

Fig.27. Madox lens

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