Dissertation on
“A CLINICAL STUDY OF PARTIAL OCCLUSION THERAPY IN MANAGEMENT OF AMBLYOPIA IN
CHILDREN AGED 5YEARS TO 15 YEARS”
Submitted in partial fulfillment of requirements of MASTER OF SURGERY DEGREE
(Ophthalmology) BRANCH – III
GOVERNMENT RAJAJI HOSPITAL MADURAI MEDICAL COLLEGE
MADURAI- 20
THE TAMILNADU
Dr. M G R MEDICAL UNIVERSITY CHENNAI
2015
Madurai 20. 24.09.2014
CERTIFICATE
This is to certify that this dissertation entitled“A CLINICAL STUDY OF PARTIAL OCCLUSION THERAPY IN MANAGEMENT OF AMBLYOPIA IN CHILDREN AGED 5 YEARS TO 15 YEARS” is a bonafide record of the research work done by Dr. AYESHA TASNEEM MOHAMED ALI, Post Graduate in Department of Ophthalmology, Madurai Medical College, Madurai in partial fulfillment of the regulations laid down by The Tamil Nadu Dr. M.G.R. Medical University for the award of M.S. Ophthalmology Branch III, under my guidance and supervision during the academic years 2012-2015.
Dr. P. THIYAGARAJAN M.S, D.O., HOD and Professor of Ophthalmology, GRH and Madurai Medical College, Madurai.
Capt. Dr. B. SANTHA KUMAR MD (F.M), PGDMLE, DNB (F.M)
The Dean, Govt. Rajaji Hospital & Madurai Medical College
CERTIFICATE FROM GUIDE
This is to certify that this dissertation entitled “A CLINICAL STUDY OF PARTIAL OCCLUSION THERAPY IN MANAGEMENT OF AMBLYOPIA IN CHILDREN AGED 5YEARS TO 15 YEARS” is a bonafide record of research work done by Dr. AYESHA TASNEEM MOHAMED ALI, Post Graduate Resident in Department of Ophthalmology, Madurai Medical College, Madurai.
Dr. P. SARAVANA SANKARM.S., D.O., Assistant Professor of Ophthalmology,
GRH, Madurai Medical College, Madurai.
Dr. S.V. CHANDRAKUMAR M. S., D.O., Associate Professor of Ophthalmology, GRH, Madurai Medical College, Madurai.
DECLARATION
I, Dr. AYESHA TASNEEM MOHAMED ALI, solemnly declare that this dissertation titled “A CLINICAL STUDY OF PARTIAL OCCLUSION THERAPY IN MANAGEMENT OF AMBLYOPIA IN CHILDREN AGED 5YEARS TO 15 YEARS” was done by me.
I also declare that this bonafide work / a part of this work were not submitted by me / anyone else, for any award, for Degree / Diploma to any other University / Board either in India / abroad. This is submitted to The Tamilnadu Dr. M. G. R. Medical University, Chennai in partial fulfilment of the rules and regulation for the award of Master of Surgery Degree Branch -
III (Ophthalmology) to be held in April 2015.
Dr. AYESHA TASNEEM MOHAMED ALI
PLACE : Madurai
DATE :
ACKNOWLEDGEMENT
I express my sincere thanks and gratitude to Prof. Dr SANTHA KUMAR, M.Sc(Forensic science).,MD(FM),PGDMLE.,DNB(FM), the Dean, Government Rajaji Hospital and Madurai medical college for permitting me to conduct this study.
I am extremely grateful to Dr P THIYAGARAJAN M.S D.O, HOD and Professor of Ophthalmology, GRH and Madurai Medical College, for his valuable advice in preparing this dissertation. I take this opportunity to express my deep sense of gratitude to Dr S V CHANDRAKUMAR M.S D.O, Associate Professor of Ophthalmology, GRH and Madurai Medical College, for being constant source of support and encouragement for completing this thesis.
I have great pleasure in thanking my beloved guide Dr P.
SARAVANA SANKAR M.S, Assistant Professor of ophthalmology and to all my Assistant Professors and staff of ophthalmology department for their constant source of encouragement throughout the study. I express my deep sense of gratitude to the Department of Radiology and Department of Neurology GRH Madurai for their support during this study.
TABLE OF CONTENTS
PART – 1
S.NO TITLE PAGE NO.
1. INTRODUCTION
2. REVIEW OF LITERATURE
3. ANATOMY OF VISUAL PATHWAY
4 PHYSIOLOGY OF BINOCULAR VISION
5. PATHOGENESIS AND PATHOPHYSIOLOGY OF AMBLYOPIA
6. CLASSIFICATION OF AMBLYOPIA 7. CLINICAL FEATURES OF AMBLYOPIA
8. MANAGEMENT OF AMBLYOPIA
9. OCCLUSION THERAPY
10 COMPLIANCE
11 PROGNOSIS
PART 2
S.NO. TITLE PAGE NO.
1. AIM AND OBJECTIVES OF THE STUDY
2. MATERIALS AND METHODS
3. OBSERVATION AND ANALYSIS
4. SUMMARY
5. DISCUSSION
6. CONCLUSION
LIMITATIONS
FUTURE SCOPE OF THE STUDY
PART 3
S.NO. TITLE PAGE NO.
1. BIBLIOGRAPHY
2. PROFORMA
3. MASTER CHART
4. KEY TO MASTER CHART
PART ONE
INTRODUCTION
Emmetropia and orthophoria of both eyes is mandatory for the foundation of binocular single vision. Binocular single vision encompasses a point to point normal correspondence of the two retinae with fovea‟s being the principle corresponding points. In spite of normal anatomical development of both eyes, interruption of physiological development in visual acuity of one eye can lead to ambylopia.
The word Amblyopia is taken from the Greek work Amblyos = dull vision and Ops = vision as described by Hippocrates
Clinically amblyopia has been defined as unilateral or bilateral reduction in the best-corrected visual acuity caused by form vision deprivation and or abnormal binocular interaction, without a visible organic cause commensurate with this visual loss.
A best corrected central visual acuity less than 6/12 is labelled as bilateral amblyopia and a difference of two or more lines between normal and amblyopic eye is required toclassify it as unilateral amblyopia. This visual loss is correctable if appropriate measures are applied at the appropriate time." This definition is based solely on visual acuity; however,
this definition does not take into account thequalitative differences in vision that amblyopes often experience resulting in poorer vision than that measured by Snellen‟s chart. Amblyopia till date remains a diagnosis of exclusion.
Amblyopia is the most common cause of preventable monocular blindness in children which often leads to sensory,motor and spatial perpetual deprivation of experience that reflects on an individual‟s performance in academics, sports and also his/her self-esteem. Amblyopia is significant in that it is a potentially reversible condition.
Why should we screen children for amblyopia?
Amblyopia is one of the common causes of childhood visual impairment. Others being Nutritional blindness, Trachoma, Congenital cataract, Genetic and metabolic disorders of the eye, Corneal opacity, Retinopathy of prematurity and Trauma.
Children constitute 35-40% of the general population. Surprisingly 30% of Indian blind lose their sight before the age of 20 years, which makes early detection and treatment of visual impairment in children mandatory.
School going children therefore, form an important large target group and school vision screening plays an important part in early detection of amblyopia and institution of appropriate therapy, which is of immense value towards preventing the development of lifelong visual morbidity.
Hence my work is purely dedicated towards screening the children, the future of the nation in whom early identification of visual disability and proper management can drastically improve their scholastic performance, since binocular single vision is the basic requirement for good performance in both academics and sports.
Simple and cost effective treatment when instituted along with proper motivation from the parents and children can go a long way in the management of amblyopia.
The concept of „critical period‟ which explains the reversibility of amblyopia at younger age groups when the brain and visual system are immature and connections between neurons are still being formed and stabilized ,stresses the importance of introducing the treatment at an early age thereby enhancing the visual outcome.
Hence this concept explains the fact that the success rates following the treatment often decline as the age increases. So ambylopia treated at a younger age group is fully correctable.
ANATOMY OF VISUAL PATHWAY
Definition
Visual pathway is a pathway wherein a visual sensation is transmitted from the retina to the brain.It is broadly divided into afferent and efferent visual pathways based on the anatomical and physiological knowledge of the ocular motor system.
The afferent visual system:
Retina:
The focused electromagnetic image is transduced photochemically into a series of impulses which take place in the outer segments of rods and cones. The physiological scotoma (blind spot) over the optic disc is due to the absence of retinal receptors. The retinal pigment epithelium is in direct contact with the retinal photoceptors providing both metabolic support and regeneration of chromophore 11 Trans retinal to the cis form for restoration
of receptor sensitivity. Processing of retinal signal occurs through the bipolar cells which connect the photoceptors to the ganglion cells.
Ganglion cells are subdivided into:
Larger M cells for luminance contrast and motion
Smaller P cells for colour perception
Optic nerve
It is the backward continuation of axons from the ganglion cell layer of retina through the optic nerve head and extends upto the optic chiasma.Each optic nerve is about 47-50mm in length and can be divided into four parts.
Intraocular (1mm)
About 1mm long, traverses the sclera through the lamina cribrosa and appears in the eye as optic disc.It is arbitrarily divided into 4 portions from anterior to posterior
Surface nerve fibre layer.
Prelaminar region.
Lamina cribrosa.
Retrolaminar region.
Intraorbital (30mm)
Extends from back of eyeball to optic foramina. This part is slightly sinuous to give play for the eye movements. Here optic nerve is surrounded by all the three layers of meninges & subarachnoid space. The central retinal artery along with enters the subarachnoid space to enter the nerve midway on its inferomedial aspect.
Near optic foramina, optic nerve is closely surrounded by Annulus of Zinn and the origin of four recti muscles. Some fibres of superior & medial rectus are adherent to its sheath which accounts for painful ocular movements in retrobulbar neuritis.
Intra canalicular (6-9mm)
This part is closely related to ophthalmic artery. It crosses the nerve from medial to lateral side in the dural sheath. Sphenoidal sinus and posterior ethmoidal sinuses lie medial to it and it is separated by thin bony lamina, this relation accounts for retrobulbar neuritis following infection of sinuses.
Intracranial (10mm)
This measures about 10mm and lies above cavernous sinus, converges with its fellow to form chiasma. It is ensheathed in pia mater. Internal carotid artery runs below and then lateral to it. It also contains the afferent fibres of light reflex
Optic Chiasm
It is a flattened structure, which measures 12 mm horizontally and 8mm antero-posteriorly which is ensheathed by pia mater with the cerebrospinal fluid. It lies over diaphragma sellae
Posteriorly, the chiasm is continuous with the optic tracts forming the anterior wall of 3rd ventricle.Nerve fibres arising from nasal half of two retina decussate at the chiasm.
Optic Tract
These are cylindrical bundles of nerve fibres that run outwards and backwards from posterolateral aspect of optic chiasm, between anterior perforated substance andtuber cinereum to unite with the cerebral peduncles.
Each tract consists of fibres from temporal half of retina of same eye
& nasal half of opposite eye. Posteriorly they end in Lateral Geniculate Body.
Lateral Geniculate Body
These are oval structures situated at termination of the optic tracts that consist of 6 layers of neurons (grey matter) alternating with white matter (optic fibres )Fibres of 2nd order neuron coming via optic tract relay here.
Visual Cortex
A synapse in the LGN is followed by the axons travelling posteriorly as optic radiations to terminate in the primary visual cortex in the occipital lobe. Inferior fibres travel anteriorly, then laterally and posteriorly to loop around temporal horn of lateral ventricles (Meyer‟s loop). Superior fibres travel posteriorly through deep white matter of the parietal lobe. Central macular fibres course laterally and peripheral fibres are seen more at superior and inferior aspects of radiation. Primary visual cortex (Striate cortex/Broadmann‟s area 17) is seen along the horizontal calcarine fissure dividing the medial surface of occipital lobe.
The efferent visual system (Ocular motor pathways)
They help in establishing clear and stable binocular vision. Functionally they are divided into:
1. Visual fixation 2. Optokinetic system 3. Saccades
4. Smooth pursuits
5. Nystagmus quick phases 6. Vestibular system
7. Vergence
A knowledge of the efferent visual system is important in diagnosis of amblyopia sinceDecreased saccadic impulses and impaired pursuit movements are characteristically seen in amblyopia
Saccades
These are sudden, conjugate jerky eye movements which occur when the gaze shifts from one object to another, hence bringing the image of an object on the fovea.
Smooth pursuit eye movements
These are the tracking movements of the eye as they follow the moving objects.
Vergence movements
These are slow disconjugate movements which focus an object that moves away from or towards the observer i.e., when visual fixation shifts from one object to another object at a variable difference.
Vestibular eye movement system
They effectively compensate for the effects of head movements in disturbing visual fixation.
Optokinetic system
On sustained head rotation the images of the seen world are kept steady on the retinae due to this system.
Position maintenance system
This system helps in the maintenance of specific gaze positions by slow micromovements called “drifts” and fast micromovements called
“shifts”.
Ocular motor cranial nerves
Extra ocular movements are innervated by cranial nerves three,four and six which control the ocular movements. Any palsy associated with the extrao ocular muscles may lead to restriction of movement causing diplopia
which if goes untreated may lead to deprivation of vision followed by amblyopia.
They are : Oculomotor Nerve
Nucleus : Situated at the mid brain at the level of superior colliculus ventral to the aqueduct of sylvius.
Course : The rootlets leave the midbrain on the medial aspect of the cerebral peduncle, pass forward between the posterior cerebral and superior cerebellar arteries and laterally parallel to the posterior communicating artery. On the lateral side of posterior clinoid process, pierce dura and enter the lateral wall of cavernous sinus above the sixth cranial nerve. They further divide into superior and inferior divisions which enter the orbit through the superior orbital fissure within the annulus of zinn.
Supply : Superior rectus, inferior rectus, medial rectus, inferior oblique and levator palpebrae superioris.
Trochlear Nerve
Longest and slender intracranial nerve. Dorsal emergence from the tectum.
Nucleus : Situated in the midbrain at the level of inferior colliculus.
Ventral to the sylvian aqueduct.
Course : Emerges on posterior surface of brain stem, decussates and passed forward around cerebral penduncle between posterior cerebral and superior cerebellar artery. Enters lateral wall of cavernous sinus and lies below III Cranial Nerve and above first division of Fifth Cranial nerve.
Passes through the upper part of superior orbital fissures outside the tendinous ring.
Supply : Superior oblique muscle.
Trigeminal Nerve :
Nucleus : Extends from Pons, throughout medulla oblongata up to second cervical segment in spinal cord
Supply : Ophthalmic division is entirely sensory and innervates the ocular structures through three branches – Lacrimal, Frontal and Nasociliary nerve
Abducens Nerve :
Nucleus : Lies in Mid level of Pons ventral to the floor of fourth Ventricle.
Course : Emerges between Pons and Medulla oblongata, runs upward, forward and laterally, makes an acute ben across sharp border of petrous par of temporal bone and runs within carvernous sinus infero lateral to Internal carotid artery. Enters orbit through superior orbital fissure between the two divisions of III cranial nerves
Supply : Lateral rectus muscle.
Facial Nerve :
Nucleus : Lies within Pons
Course : Emerges on anterior surface of brain stem at the lower border of Pons and passed laterally in the posterior cranial fossa. Travels through the internal acoustic meatus along with eight cranial nerve, descends through posterior wall of the middle ear and emerges from skull via stylomastoid foramen.
Supply : Motor supply to muscles of facial expression and orbicularis oculi, sensory innervation to the anterior 2/3rds of tongue i.e. taste.
PHYSIOLOGY OF BINOCULAR VISION
Definition
It is defined as the state of simultaneous vision with two seeing eyes (neither of which need necessarily be normal) that occurs, when an individual fixes his visual attention on an object of regard.
Grades of binocular vision
Binocular vision consists of the following
Simultaneous perception (First grade of binocular vision)
Simultaneous perception exists when signals transmitted from the two eyes to the visual cortex are perceived at the same time.
Fusion (Second Grade of binocular vision)
It constitutes second grade of binocular vision. It implies the ability of the two eyes to produce a composite picture from two similar pictures, each of which is incomplete in one small detail.
Steropsis (Third Grade of Binocular Single Vision)
It implies the 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.
Development of binocular vision
Pre-requisites for development of binocular vision
Normal optical media.
Binocular similar images.
Normal visual pathway.
Neural pathways from retinal receptors to visual centres.
The extra ocular muscle function.
Retinal correspondence
Binocular coordination of eye movement.
1. Fixation: There must be proper fixation with each eye. The muscles controlling the movements of each eye must function normally and turn both eyes in such a manner that the object of regard is fixated by corresponding retinal points, i.e. the two foveas.
2. Visual fields of the two eyes must overlap to a large extent
Image formed on each retina must be approximately similar, i.e.
should be of the same size, shape, colour and intensity. This necessitates approximate equality in the optical apparatus of each eye.
3. Common visual direction must be there for two eyes, i.e. the retinae must possess physiologically corresponding points., the retinal areas from each eye that are physiologically linked to the same cortical binocular cells are called corresponding retinal points. In other words, the most important prerequisite to single binocular vision is appropriate eye alignment, so that similar images from each eye fall on retinal points that project to the same cortical binocular cells
4. Reflex activities which produce fusional movements are very important. The eyes must be coordinated by this complex mechanism at all times so the retinal receptors which have a common visual direction will receive the same image at all the time.
Disturbances in the development of binocular vision Diplopia and Confusion
Diplopia usually results from an acquired misalignment of the visual axes that causes an image to fall on the fovea of one eye and simultaneously on a non-foveal focal point other eye ie. two non corresponding points.
Suppression
Suppression is defined as temporary active cortical inhibition of the image of an object formed on the retina of the squinting eye. It is a protective phenomenon against diplopia.
Types of suppression:
It is broadly classified into
Physiological suppression
Pathological suppression, is further classified into
Facultative suppression
Obligatory suppression
Obligatory suppression often leads to amblyopia because it refers to a constant suppression of the image from one eye which occurs even when the fixating or dominating eye is covered.
Abnormal Retinal Correspondence
Abnormal retinal correspondence (ARC) is an active cortical adjustment in the directional values of the two eyes which occur in a child with early onset of squint (especially esotropia, occurring before 2 years of age.
In short, it is the binocular sensory defence mechanism against peripheral diplopia and confusion.
Angle of anomaly is defined as the difference between the subjective and objective angle of deviation.
In normal retinal correspondence, the angle of anomaly is zero since the objective and subjective angles of deviation are equal.
In abnormal retinal correspondence, the subjective angle is always lesser than the objective angle thus making the angle of anomaly more than zero.
Types of ARC
Harmonious ARC is present, when the angle of anomaly (difference between the objective and subjective angles of the squint) equals the objective angle of squint
Unharmonious ARC is present, when the angle of anomaly is less than the angle of deviation
Amblyopia: Clinically amblyopia has been defined as unilateral or bilateral reduction in the best-corrected visual acuity caused by form vision deprivation and or abnormal binocular interaction, without a visible organic cause commensurate with this visual loss.
PATHOGENESIS AND PATHOPHYSIOLOGY OF AMBLYOPIA
Around the age of two to four weeks, a period of dramatic developmental plasticity is found to occur during which the developing functional and anatomic organization of the visual system is influenced markedly by visual experiences, which are both uniocular and binocular.
Visually significant conditions like monocular or binocular visual deprivation,, anisometropia,strabismus or abnormal visual environment
during this period results in significant electrophysiological and anatomic abnormalities in striate cortex and the lateral geniculate nucleus(LGN).
There occurs losses in the number of cells responsive to the deprived eye, a loss of binocularly responsive cells, shrinkage of cells in the Lateral Geniculate Nucleus laminae serving the deprived eye and significant abnormalities in the response qualities of the cells that remain throughout life. Primate models of amblyopes have repeatedly shown the primary visual cortex(area VI) to be dysfunctional. Functional imaging confirms the presence of processing abnormalities in the area VI of the human cortex and also hints at deficits within the higher cortical areas.
CLASSIFICATION OF AMBLYOPIA
Strabismic
Anisometropic
Deprivation
Meridional
Organic
Toxic amblyopia, nutritional amblyopia and amblyopia in various neuropathies do not fit into the definition of amblyopia and are not described here.
Strabismic amblyopia
It is commonly associated with a constant unilateral strabismus. In strabismic amblyopia, the loss of visual acuity is usually moderate to severe.
The monocular fixation pattern most frequently found in the strabismic eye with amblyopia is eccentric fixation
The mechanism of amblyopia is due to the active inhibition of visual input that originates in the fovea of the deviating eye within the retinocortical pathway. Strabismic amblyopia is based on the principle of suppression. The image thatis received by the fovea of the deviating eye is different and out of focus from that of the fixating, sound eyedue to the inhibitory interaction between the neurons carrying non-fusible inputs from the two eyes.
Amblyopia does not develop when the fixation alternates as itprovides each eye with a similar access to higher visual centers and does not develop if strabismus is intermittent since there are periods of normal binocular interaction which preserve the integrity of the visual system. Constant non-
alternating eso-deviations are the most likely causative factors in amblyopia.. There is no correlation between the depth of amblyopia and the angle of deviation.
Strabismic amblyopia is characterized by better grating and pattern acuity when compared to Snellen‟s acuity. The neutral density filter effect and eccentric fixation are commonly observed in strabismic amblyopia than in other types of amblyopia.
Anisometropic amblyopia
It is the second most common form of amblyopia. It is due to thechronically blurred image seen in one or both eyes which prevents the development of normal visual acuity in anisometropic amblyopia. There develops an active inhibition of the fovea in anisometropic amblyopia to eliminate sensory interference caused by superimposition of a focused and a defocused image originating from a fixation point(abnormal binocular interaction).Hence, visual acuity of the anisometropic eye is usually lower under binocular conditions than when tested monocularly.
If the anisometropia is optically corrected, the retinal images of different sizes may present as an obstacle to fusion, which further give rise to anisokenia as another amblyopiogenic factor in anisometropic amblyopia.
As the amount of anisometropia increases, the severity and prevalence of amblyopia also increases..The retina of the more ametropic eye of a pair of hypermetropic eyes never receives a clearly defined image, since with details clearly focused on the fovea of the better eye, no stimulus is further provided for the further accommodative effort required producing a clear image in the fovea of the more hypermetropic eye. When the more ametropic eye is mildly myopic with the far point approximating normal near viewing distance, amblyopia does not develop.
When myopia is unequal, the more myopic eye can be used for near work and the less myopic eye for distance. Therefore, unless the myopia is of a higher degree, both retinas receive adequate stimulation and amblyopia does not develop.Thus, hypermetropic patients with anisometropia of one dioptre difference may have amblyopia, while myopic anisometropes usually do not have amblyopia until anisometropia is large. But, unilateral high hyperopia or myopia (greater than 6 Ds) can cause severe amblyopia.
The delay in diagnosis and treatment of anisometropicamblyopia is because the eyes of a child with anisometropic amblyopia appear normal in the absence of strabismus.
Visual deprivation amblyopia
It occurs when the retinal image quality is degraded severely by an obstruction of the visual axis, as in cases of congenital or traumatic cataract, congenital ptosis, corneal opacity, or it can be produced iatrogenically in the formerly fixating eye of an amblyopic patient after prolonged and indiscriminate patching (occlusion amblyopia), form deprivation or visual deprivation amblyopia results.
The most common cause of this type of amblyopia is congenital cataract which is also the most damaging and difficult to treat. Unilateral form deprivation results in severe degree of amblyopia than in cases of symmetrical bilateral lesions, suggesting that abnormal binocular interaction is an important factor in its pathogenesis.Stimulus deprivation if present during the first 3 months of life, can lead to a profound and permanent reduction in visual acuityas well as nystagmus.Hence, it is mandatory to remove significant unilateral cataract before the age of three months and the child should be optically rehabilitated.
Meridional amblyopia
A special form of optical defocus amblyopia called meridional amblyopia occurs when the resolution of the eye is decreased in selected
meridians as a result of uncorrected astigmatism, which can be either unilateral or bilateral. Though the degree of cylindrical ametropia necessary to produce meridional amblyopia is not known, there is consensus that a cylinder of greater than +1.5 D is definitely amblyiopiogenic.
Organic amblyopia
Organic amblyopia is defined as reduced visual acuity in an eye in the absence of gross, readily detectable anomalies; even though the possibility of subtle, sub-ophthalmic morphologic changes cannot be excluded.
Association with retinal hemorrhages, cone deficiency syndrome and nystagmus has been described, along with hysterical and idiopathic amblyopias.
CLINICAL FEATURES OF AMBLYOPIA
Diminution of vision
The hallmark of amblyopia is decreased foveal acuity .The amblyopia treatment study (ATS) defined amblyopia as a visual acuity of 6/12 or worse with at least a 3 log MAR line difference between the eyes
Various methods of visual acuity testing in children
In the amblyopia treatment study {ATS}, the HOTV optotypes were used frequently for measuring visual acuity, whereas in infants, fixation preference is a useful tool for the estimation of visual acuity.
Visual acuity in infants by fixation preference
No fixation <3/60
Unsteady fixation 3/60-6/60
Central fixation but will not hold fixation 6/60-6/18 Central fixation strongly prefers other eye 6/18-6/9
Alternate fixation 6/6
In nystagmus, visual acuity testing requires blurring of the other eye with a high plus lens (+6 diopter lens). Visual acuity should be measured separately in each eye.Binocular vision and near vision testing is mandatoryin patients with nystagmus. Visual acuity should be tested using the same parameters at each visit.
Birth to age 2 Years
Simple Observation Occlusion Test, Pupillary Light Response,
Fixation and following of target, Optokinetic Nystagmus,
Catford Drum test ,
Preferential looking charts,
Hundreds and thousands sweet test, STYCAR Graded Ball Test,
Boeck Candy Test, Rotation Test, Ophthalmosopic
Examination, Electrophysiological Tests
Age 3 to 6 Years
Illiterate 'E' or Tumbling Test, Landolt C Test,
Sheridan letter Test, HOTV Test of Lippeman, Snellen's Chart Test
Older than 6 Years
Snellen's Chart Test
Stereoacuity
The Titmus fly test of random dot stereogram measures stereoacuity, thus providing sufficient clues to visual acuity and binocularity. The presence of amblyopia is detected by defective performance on various stereogram tests, which necessitates further investigations for amblyopia and strabismus.
When visual acuity recording is unreliable or not possible, two-pencil test can be applied. Binocular vision assessment in the clinic in a cooperative child may also indicate the presence of amblyopia in the absence of binocularity and/or a constant deviation.
Anisometropic and strabismic amblyopes behave differently. Snellen letter or recognition acuity is affected more in strabismic or mixed (strabismic + anisometropic) amblyopes compared to anisometropic amblyopes. Both Snellen‟s acuity and grating acuity are affected equally in anisometropic amblyopes, whereas in strabismic amblyopes the grating acuity is affected to half the extent of Snellen‟s acuity.Thus, strabismic amblyopia is underestimated on grating tests.
Fixation reflex
One of the most commonly used clinical methods for diagnosing amblyopia in preverbal children is subjective assessment of fixation behavior as described by Zipt.Presence of alternate fixation rules out amblyopia. However, preference of fixation for one eye suggests poor vision in the other eye in the presence of strabismus.
Behavioral response to unilateral occlusion is also another commonly employed method for amblyopia assessment. The child resists occlusion of the sound eye, but will not object if the amblyopic eye is covered. A central, steady and maintained fixation in each eye implies good visual acuity in each eye.
However, the fixation preference technique as described by Zipt is not useful in patients with microtropia or orthophoria. Wright et al. have described the 10 D vertical prism test in such circumstances.
The normal response to a 10 D vertical prism test is that the patient always prefers to fixate with the eye without a prism in front of it; if the patient fixates through the prism,it suggests that the other uncovered eye is amblyopic.
Crowding phenomenon
Amblyopic patients exhibit a better visual acuity for single optotypes (e.g. Sheridan Gardiner chart) thanfor letters placed in a row (e.g. Snellen's chart). It is important to compare the vision obtained with visual acuity symbols presented in a row to that obtained withisolated symbols on a uniform background.
The crowding phenomenon represents an abnormality of contour interaction between the point of fixation and adjacent objects. Abnormal contour interaction is seen in the form of degradation of visual acuity for objects placed in a row or line (linear acuity), compared to the acuity of the same object viewed separately.
Crowding phenomenon becomes more pronounced during the course of treatment wherein single letter acuity improves more than line acuity.
Therefore, crowding phenomenon is a prognostic indicator. Depth of amblyopia and response to treatment is quantified by the difference between linear and isolated acuities. Near visual acuity is a more reliable indicator during amblyopia therapy as near acuity often improves faster than distant visual acuity.
CROWDING PHENOMENON IN AMBLYOPIA
Amblyopic patients exhibit a better visual acuity for single optotypes (e.g. Sheridan Gardiner chart) than for letters placed in a row (e.g. Snellen's chart).
Effect of neutral density filter
If we apply a neutral density filter in front of the normal eye, there is a decrease in visual acuity; however, if we apply a neutral density filter in front of the amblyopic eye, the vision does not decrease but might, in fact, improve during amblyopia therapy. This means that amblyopic eyes can act under mesopic conditions.
Color vision
Colour vision is often normal in amblyopic eyes. Defects are seen only in dense amblyopia and are secondary to impaired form vision, reduced visual acuity or eccentric fixation.
Contrast sensitivity
Strabismic or anisometropic amblyopia shows contrast sensitivity loss affecting either all spatial frequencies or limited to high spatial frequencies.
There is a loss of high frequencies in stimulus deprivation amblyopia.
Contrast sensitivity improves during amblyopia therapy and can be used to monitor the progress
Accommodation
Accommodation has been found to be normal or reduced in some amblyopic eyes. However, visual acuity at near fixation has been found to be better than at distance.
Fixation pattern
Eccentric fixation is characteristic of amblyopic eyes and is usually seen in 23-89% of patients.
Visually evoked potential
In amblyopic eyes, there is a reduction in amplitude and a normal or slightly prolonged latency and summation results are similar for unilateral and bilateral testing indicating that there is suppression of the eye.
Amblyopiogenic factors
A search for amblyopiogenic factors isa useful strategy for early detection of amblyopia, even when vision recording and detailed examination is not possible.
Unilateral congenital cataract, ptosis or other media opacities have a high amblyopiogenic tendency but bilateral cataract and opacities should not be ignored either.
Presence of a high refractive error especially hypermetropic of more than 3.5 D and astigmatism of more than 1.5 D should be considered suspicious of amblyopia. Presence ofmicrotropia and small angle esodeviations are also associated with amblyopia in a significant number of cases.
Ruling out alternate causes of visual loss
Complete ocular examination including a proper history and examination is mandatory to rule out any organic lesion like macular pathology, optic nerve or retinal diseases before making a diagnosis of amblyopia. However, the two conditions may coexist. Fundus examination is a must.
Should amblyopia be treated?
There has been a debate, in public health circles at least, about whether amblyopia should be treated at all
In the context of amblyopia, it has often been stated that treatment is ineffective after the age of 8 years. While this may be true for some types of amblyopia, for example, complete unilateral congenital cataract, where treatment must be commenced within a few weeks of birth to be effective,
for other causes of amblyopia there is increasing evidence that treatment may be effective beyond this age.
Evidence for effectiveness of Amblyopia therapy
Visual acuity improved following amblyopia treatment was demonstrated in a number of case series, such as that of Lithander.
The evidence base for amblyopia treatment was questioned in a government sponsored United Kingdom report in 1997. The report pointed out that there had been no randomized controlled trials of treatment and that views of treatment efficacy based on clinical experience and teaching might be biased. Series of papers produced, in part, as a response to this report demonstrated that amblyopia treatment does work, for most patients.
Clarke et al showed that, in a population of children who had failed pre-school screening, at a mean age of 4 years, on account of poor vision in one eye, treatment resulted in a significant improvement in visual acuity. Other studies, particularly those by the US Pediatric Eye Disease Investigator Group (PEDIG) and the Monitored Occlusion Treatment for Amblyopia Study (MOTAS) have advanced our knowledge of how much treatment is required for amblyopia.
Amblyopia can be treated effectively in the first decade of life, greater success being achieved when therapeutic measures are instituted at the earliest as the success rates of amblyopia treatment may decline with increasing age. However, all children should be considered for treatment of amblyopia regardless of age.
MANAGEMENT OF AMBLYOPIA
Primary goal is to maximise and potentially normalise the visual acuity.
Strategies used are:
Provision of a clear retinal image in the amblyopic eye by eliminating the cause of visual deprivation.
Correction of ocular dominance.
Perceptual training.
Removal of amblyopiogenic factor:
Early recognition and treatment of amblyopiogenic risk factors in period of plasticity may increase the chance of development of binocular vision. The therapy needs to be individualized according to the age, baseline vision and cause of amblyopia for a particular child. The basic strategy is to allow the formation of sharp and clear images by removing amblyogenic factor and then to increase the visual stimulation of the worse eye.
This can act as prevention for the development for amblyopia if done early.
Media clearance is usually the first step in management of amblyopia.
a) Childhood cataract: It should be operated as early as possible with institution of appropriate aphakic correction. The following guidelines are to be followed for the same
Significant congenital cataract should be removed during the first 2-3 months of life.
Bilateral symmetrical cataract should be removed at an interval of 1 to 2 weeks.
Acutely developing traumatic cataract in children under 8- 10years of age should be removed within few weeks of injury.
b) Severe congenital ptosis-It should be corrected by ptosis surgeries as early as possible to prevent stimulus deprivation amblyopia.
c) Corneal opacity should treated by penetrating keratoplasty.
Appropriate refractive correction
Refractive correction alone improves visual acuity in at least 25- 33%
of patients with anisometropic amblyopia. It is mandatory to carry out a cycloplegic refraction and prescribe adequate optical correction in every case of amblyopia. The ATS 5 (eye glass phase) concluded that amblyopia improved with optical correction by more than 2 lines in 77% patients and amblyopia resolved with optical correction in 27% patients .Atropine penalization or occlusion therapy is required only if the child does not improve by use of optical correction for four months.
The refractive correction for children should be done by following a set of rules .:
Guidelines for prescribing spectacles for young children
1. Refractive error without strabismus should be corrected when
Myopia is greater than 3D
Hyperopia is greater than 5D
Anisometropia greater than 2 D if not oblique, and greater than 1D if oblique.
2. Refractive error with strabismus: treat
Hyperopia or hyperopic astigmatism greater than astigmatism greater than 1.25D (ESOTROPIA)
Myopia greater than 1 D.(EXOTROPIA).
Correction of ocular dominance:
It is done by stimulating the amblyopic eye by using the following modalities:
Occlusion therapy.
Penalization.
Active stimulation.
Pleoptics.
Pharmacological stimulation.
OCCLUSION THERAPY
Since 1722, occlusion of the sound eye has been the most effective therapy in the treatment of amblyopia. Occlusion of the sound eye with an adhesive skin patch is perhaps the most effective means of therapy. The success rate of occlusion therapy varies from 30% - 92% in various studies reported in literature.
The variation in success rate is due to various factors like patient selection, treatment durations, age, definition of amblyopia used in the study and type of amblyopia. The occlusion therapy for amblyopia improves vision as well as strabismus in some patients.
Mechanism of action
Occlusion therapy prevents the fixating eye from taking part in the act of vision so that the patient is forced to use the amblyopic eye and it removes the inhibitory stimuli to the amblyopic eye that arise from stimulation of the fixating eye.
When to start occlusion?
Occlusion of the sound eye may be instituted at any age; the final level of central visual acuity attainable is not clearly dependent on the age at which treatment is begun.
Types of occlusion
Total or partial
Conventional or inverse
Full time or part time
Continual Inverse occlusion
It was described initially for amblyopes with steady eccentric fixation, part time for intermittent strabismic or non-strabismic amblyopes and full time for constant strabismic amblyopes to familiarize the patient with occlusion in cases of eccentric fixation in the initial stages.
The continual wear is rarely used and refers to day and night patching with no period of non-occlusion.
At the onset of treatment, the family must be taught how to recognize which eye is fixating and explained the significance of alternating fixation.
Instructions should be given to discontinue or alternate occlusion on successive days if a constant preference for the amblyopic eye is noted, prior to placing the patch in the morning.
The benefits of occlusion are indisputable, although there is controversy on the amount of patching required for success.The Paediatric Eye Disease Investigator Group (PEDIG) is a collaborative network, which was formed in 1997 to facilitate research in strabismus and amblyopia. The multicentre randomized controlled studies to answer several questions on amblyopia are collectively and popularly known as the ATS (Amblyopia Treatment Studies.)
Amblyopia treatment study 2 was initiated to address the following questions
a) Is minimal intensity patching (two hours/day) as effective as moderate intensity patching (six hours/day) in the treatment of moderate amblyopia (6/12 to 6/24)?
b) Is full time patching (all waking hours) more effective than part time patching (6 hours/day) in treating severe amblyopia (6/36 to 6/120)?
c) What is the recurrence rate and what are the factors influencing recurrence after cessation of therapy in successfully treated amblyopia?
Intermediate reports concluded that minimal patching (2 hours/day) is as effective as moderate patching (6 hours/day) in the treatment of moderate amblyopia and prescribing greater numberof hours of patching does not seem to have significant beneficial effect during the first four monthsof treatment.Further , the study concluded that for severe amblyopia, part time patching (six hours) and full time patching are equally effective in patients ranging from 3 to7 years of age.
Types of Occluders
The eye can be occluded in various ways. The patient may be prescribed occluders that can be attachedto spectacles. Various types of commercially available occluders are also available in the market, but essentially, any occluder can be used.
a) Adhesive skin patch (self-made with micro-pore) b) Commercially available Opticlude
c) Doyen's occluder d) Contact lens occluder Occlusion schedule
Once occlusion therapy has been initiated, the child must be re- examined at frequent intervals as described below for several reasons.
Frequency of follow up visits
Younger the patient, greater is the risk ofocclusion amblyopia; hence, intervals between office evaluations should be in relation to the patient age.
A simple rule of the thumb is to examine the patient “one week for every year of age”. If at the time of re-examination, fixation has not improved, the period of occlusion should be doubled prior to next scheduled examination;
if there is still no improvement occlusion should be stopped after three months.
What to look for during follow up?
a) The visual acuity of both eyes on the same chart after giving 5-10 minutes for acclimatization
b) Fixation pattern
c) Presence of occlusion amblyopia
First, determine whether such treatment has brought about any change of fixation. Children upto 5 years ofage may develop occlusion amblyopia.
The development of occlusion amblyopia indicatesthat the patient has potential for equal vision in both eyes and is not a totally unfavourable development. Reversing the occlusion and examining the patient at frequent intervals can almost always treat the condition. Empirical occlusion schedules have been developed to avoid occlusion amblyopia.
When should occlusion be stopped?
Occlusion can be stopped when the visualacuity becomes equal in both eyes.
a) When there is true alternation of fixation.
b) There is no visual improvement after 3 - 6 months of occlusion despite good compliance (depending on the age of patient).
Follow up after completion of treatment a) Follow up till 12 years of age
b) Infants should be followed up every 6 weeks
c) Children between 3 - 6 years shouldbe followed up every 3 months d) Children above 6 years of age should be followed up every 6
months
Maintenance of improved vision
a) Part time occlusion of the normal eye (4-6 hours/day) b) Partial occlusion
c) Penalisation
Disadvantages of occlusion
a) Direct occlusion is not without disadvantages. It can lead to occlusion amblyopia as described above.
b) Another problem with full time occlusion, particularly in severe amblyopia is the functional debilitation that itcauses, especially early in treatment. Poor vision during occlusion of the sound eye presents a significant deterrent to good compliance. The child may require additional supervision to avoid accidental injury.
c) Non-compliance is probably the greatest cause of failure. This is often a confounding factor in assessing the success of patching; the compliance rate in various studies varies from 49-87%.
d) The appearance of a constant manifest deviation after occlusion in a child who does not have strabismus or only intermittent deviation is distressing.
e) Occlusion may be cosmetically unacceptable.
f) Psychological problems.
g) Allergic skin rash while using adhesive skin patch-
The problem of allergic skin reactions can be stopped by taking the following measures:
Tincture benzoin application over the skin before applying the patch. The protective layer that is formed over the skin increases the adhesiveness of the patch preventing the child from removing it frequently.
Newer patches called opticlude patches replace the older ones and are known for causing very less allergic reactions.
Occluding soft contact lens are recommended when the other two methods have failed.
h) Diplopia.
Prevention of recurrence of amblyopia
There is a 50% risk that amblyopia will recur following successful primary treatment. Alternating fixation usually helps to maintain good vision but when preference for one eye persists, amblyopia can recur in the non- preferred eye within one to three months. To regain the higher visual acuity, the original treatment regimen should be restarted and followed by maintenance therapy of part-time occlusion varying from of one hour patching to a maximal period.
Compliance
A very important issue to be addressed in the management of amblyopia is the issue of compliance.
DEFINITION:
Compliance is referred to as the degree of correspondence between the recommendations from the health care provider and the patients‟ actual dosage.
The first devices that measured compliance electronically were developed to monitor the administration of pilocarpine eye drops in the treatment of glaucoma. Poor compliance decreases the effectiveness of treatment and increases costs to the health care system.
Since the development of the Occlusion Dose Monitor (ODM) by Fielder and Moseley (Fielder, et al. 1994) compliance with occlusion therapy for amblyopia can be measured electronically and therefore objectively. They developed an ODM that measured skin conductance at the border of the patch.
The modified version of ODM measures 24x12x3.6 mm and weighs 1.8 g. It is taped to the outside of a standard eye patch and measures the
temperature difference between the front and the back of the ODM every 2 minutes, instead of skin conductance.
List of actions undertaken to deal with noncompliance with occlusion therapy
1. Explain amblyopia and occlusion therapy to the parent once more 2. Identify the reason(s) for noncompliance and find solutions for these 3. For example, determine how occlusion therapy best fits into their
daily lives
4. Make the next appointment sooner, or make more frequent appointments
5. Explain the consequences of not patching Give the parents informational material about amblyopia and occlusion therapy
6. Confront, alarm or frighten the parent when no patching has taken place
7. Allow the child to choose the colour of the eye patches
8. Distribute a commercial poster on patching designed by a firm that produce eye patches
9. Reward the child with small toys when it has patched well 10. Involve the child‟s school
11. Emphasize the parents‟ responsibilities
12. Threaten to stop treatment if the child had not worn the patch 13. Increase the prescribed occlusion hours
14. Pay more attention to the parent 15. Explain the benefits of patching
16. Invent a reward system for the parent to use at home Decrease the prescribed occlusion hours
Penalization
The principle applied here is penalization of the sound eye for distance and near with the help of cycloplegic refraction and glasses and therefore forcing the amblyopic eye to increase its potentiality for both distance and near. The main prerequisite for penalization is orthophoria of both eyes.
It is mainly used in patients with
anisometropic amblyopia,
Patients who have poor compliance with occlusion therapy and
maintenance of vision that is obtained through previous occlusion therapy.
Occlusion nystagmus.
There are two types of penalization:
Atropine penalization – It is done for both near and distance.
Near penalization –
The fixing eye is atropinized and fully corrected for near vision wheras the amblyopic eye is overcorrected with +2.00 to +3.00 D.
This forces the amblyopic eye to be used in near vision and stimulates alternate of two eyes for near and distance.
Distance penalization –
The fixing eye is atropinized and overcorrected by +3.00D lens while the amblyopic eye is fully corrected. Hence the sound eye is penalized for distance and used for near only whereas the amblyopic eye is used for distance.
Total penalization-
The fixing eye is atropinized and undercorrected by 4.0 or 5.0D , while the amblyopic eye is fully corrected.this prevents the fixing eye being used for both near and distance.
Optical penalization –
It includes over plussing the sound eye to force fixation to the amblyopic eye for for distance targets. Hence the patient uses the sound eye for near targets.
Disadvantages of penalization therapy are:
Active inhibition is not eliminated
Cost of drugs
Injury with drug vial
Allergic reaction to drugs
Potential side effects due to systemic absorption of drugs
Active Stimulation Therapy
It is done with the help of a vision stimulator device called CAM vision stimulator. Here the amblyopic eye is stimulated for seven minutes by rotating the high contrast square wave grating which has different spatial frequencies and all this is done after occluding the sound eye. It is based on the principle that rotating grating provides specific stimulation for cortical neurons.
Pleoptics
This technique is used for the active stimulation of fovea so that the visual acuity improves by overcoming the eccenttic fixation. Here, the peripheral retina including the eccentrically fixing area is dazzled with intense light, while protecting the fovea. It is done directly by using a pleoptophore or indirectly by producing after images.
Pharmacological Manipulation
It has been established through studies that the plasticity of the visual system during the sensitive period is related to the input generated from the non-adrenergic neurons and hence can be subjected to pharmacological manipulation.
The main drug that is used as a pharmacological manipulator is levodopa.
Mechanism of action:
It primarily acts at the retina or cortex through a neurotransmitter thus increasing the dopamine concentration which is clinically manifested as an increase in visual acuity, improvement in contrast sensitivity and a reduction in binocular suppression.
Side effects
Nausea, vomiting, diarrhoea, heart burn, mood alterations, tiredness, hallucination are some of the adverse effects seen with pharmacological therapy.
Perceptual Learning
It involves the practice of a visual discrimination task like positional acuity, stereoacuity and contrast sensitivity repeatedly for a period of nine months.
Its role in management of amblyopia is still controversial.
Amblyopia is a major public health problem and amblyopia management requires a multi-disciplinary approach with involvement of not only ophthalmologists, but also, paediatricians, general practioners, school teachers and parents.
Hence its mandatory that all the physicians along with the school teachers and parents motivate the child and reward him for his compliance so that proper treatment is followed resulting in better outcome.
OUTCOME
Outcome of amblyopia therapy depends on the following factors:
The patient‟s age
Type of amblyopia and
Treatment modality instituted.
a) Younger the child better the prognosis
b) Amblyopia due to deprivation (e.g. – due to congenital cataract) carries the poorest prognosis
c) Strabismic amblyopia has the best prognosis
d) Anisometropic amblyopia has a prognosis intermediate between strabismic amblyopia and deprivation amblyopia
e) Presence of eccentric fixation worsens the prognosis
f) Amblyopia with unilateral high hypermetropia has a poor prognosis than the amblyopia with unilateral high myopia
g) Prognosis is better when treated with total and full time occlusion than when treated with penalization or other methods
PART TWO
AIMS AND OBJECTIVES OF THE STUDY
To determine the prevalence of amblyopia in school going children in the age group of 5 -15 years in and around Madurai
To study the types of amblyopia occurring during school years.
MATERIALS AND METHODS
Study Design
This is cross sectional and time bound study. This study is to be conducted among 50 children attending the OP in Govt. Rajaji hospital as well as the screening school health programs
Subjects shall be evaluated for entry into the study if they are 5-15 years of age .Subjects believed to fulfill all eligibility criteria, and none of the exclusion criteria, will be invited to participate in the study.
Duration of the Study:
April 2014 to September 2014
Selection of Study Subjects:
A total of 50 patients attending the O.P units of the department of Ophthalmology, Government Rajaji Hospital Madurai and children attending the screening school health programs, who satisfy the inclusion criteria
Ethical committee clearance was obtained for the study . Financial support-nil.
Inclusion Criteria Patients aged 5-15 years.
Exclusion Criteria
Patients with known cause of reduced visual acuity
Patients with myopia greater than spherical equivalent of -6.00D
History of previous amblyopia treatment within one year of involvement.
Prior intraocular surgery.
Known skin reaction to patch or bandage adhesive
Dropouts and non-compliant patients were excluded from final analysis
Hypothesis Being Tested
Partial occlusion therapy in treatment of amblyopia is associated with better scholastic performance in children
Methodology
A detailed analysis of the children (aged 5 -15 years) who attended our OPD, Government Rajaji hospital, Madurai Medical College was done and fifty patients with decreased visual acuity and complaints of asthenopia and deviation of eye were thoroughly examined and their refractive status, anterior segment evaluation and posterior segment examination was done.
A diagnosis of Amblyopia was made and they were further grouped into moderate and severe Amblyopia according to their degree of visual loss.
A few number of the patients who presented with temporal pallor on dilated fundus examination were further subjected to CT scan to rule out a possibility of organic lesion.
A thorough refractive correction was done and patients with hight myopia and hypermetropia were excluded from the study.
These patients were explained the importance of treatment of amblyopia wher stress was given on EARLY INTERVENTION, Self- motivation and dedicated follow up.
Compliance to treatment for more effective results was stressed to both the patient and his / her parents.
Treatment options like refractive error correction and occlusion were discussed with the patients.
The duration for occlusion therapy was three hours where the patients was emphasised to do near activity tasks.
They were asked to come for follow up after three months of occlusion.
Significant improvement in visual acuity was seen in younger patients with good compliance which was tested with Snellen‟s Visual acuity chart that showed an improvement in visual acuity by one or two lines.
Patients whose visual acuity failed to improve after three months of occlusion therapy were counselled for better compliance and motivation was given to increase the duration of occlusion to six hours a day.
However, a very limited number of patients who failed to improve even after six months of age were referred for alternate method of treatment and explained about use of low visual aids etc.
Patients with significant amount of ptosis or congenital cataract were explained about the possibility of stimulus deprivation amblyopia and were referred for surgical correction. In each case after analysis of the type of amblyopia proper counselling was given and the prognosis for each case was discussed with both the parents of the patient and the teachers also.
OBSERVATION AND ANALYSIS
Statistical Method
The information collected regarding all the selected cases were recorded in a Master Chart. Data analysis was done with the help of computer using Epidemiological Information Package (EPI 2010) developed by Centre for Disease Control, Atlanta.
Using this software range, frequencies, percentages, means, standard deviations, chi square,„t‟ value and „p‟ values were calculated. Student‟s
„t‟ test was used to test the significance of difference between quantitative variables and Yate‟s and Fisher‟s chi square tests for qualitative variables. A 'p' value less than 0.05 is taken to denote significant relationship.
ANALYSIS - RESULTS AND INTERPRETATION:
Table 1: Age Distribution:
Age distribution of cases varied from 5-15 years.
The number of patients in the age group of (5-10) years of age was 32, and those in the age group of (11-15) years were 18.
AGE Frequency Percent
5 – 10 years 32 64.00%
11 – 15 years 18 36.00%
Total 50 100.00%
CHART NO.1
A Higher incidence of amblyopia was detected among the younger age group (5-10 years) of age i.e. (64.00%) as compared to the older age group (11-15 years) which is (36.00%) in our study.
