AMBLYOPIA AND ITS MANAGEMENT

AMBLYOPIA

SIVA TEJA CHALLA

AMBLYOPIA• DEFINITION• EPIDEMIOLOGY• PATHOPHYSIOLOGY• CLASSIFICATION AND TYPES• CLINICAL FEATURES AND DIAGNOSIS• TREATMENT MODALITIES.

DEFINITION• U/L or less commonly B/L reduction in

BCVA that cannot be attributed directly to the affect of any structural abnormality of the eye or the posterior visual pathways

• M.C.C of dec vision in childhood• For practical purposes defined as atleast 2

snellen line difference b/w two eyes

EPIDEMIOLOGY

• In developed countries 1-5% of the population

• In india affects 1-4% of children• Goel et al. found the incidence to be 0.7% in

rural schools than in urban schools 0.5%• Onset is birth to 7 yrs of age• SE Factors does not significantly influence

the age of presentation of amblyopia• Earlier the onset greater the defecit

• Four times more frequent in premature children

• Six times more frequent in children with delayed mile stones

• Smoking and use of dugs and alcohol during pregnancy have been asso with risk of amblyopia

PATHOPHYSIOLOGY

Amblyogenic factors

Role of retina

Active cortical inhibition

Amblyogenic factorsVISUAL

DEPRIVATION

monocularSeen in strabismic ,

anisometropic, stimulus deprivation

amblyopiaBinocular

Seen in bilateral cataract, ametropia and bilateral high refractive errors

LIGHT DEPRIVATION.Usually seen in children with

unilateral or bilateral complete cataracts.

ABNORMAL BINOCULAR

INTERACTION-produces profound amblyopia due to

competition amblyopia.

-seen in strabismic, anisometropic and unilateral stimulus

deprivation amblyopia.

RETINA IN THE DEVELOPMENT OF AMBLYOPIA

• Decreased sensitivity of foveal cones in amblyopia

• The reduced input from rods and cones in the affected eye causes certain neurophysiologic changes, transmitted to the CNS which triggers amblyopia.

ACTIVE CORTICAL INHIBITION1)      A developmental defect of spatial visual processing occurring in the visual pathway.

2)      Poor transmission from the fovea, optic nerve to the Striate Cortex of the affected eye.

3)      LGB & Striate cortex develop abnormally.

4)      Ganglion cells in foveal area are affected; Shrinkage of LGB Nucleus & Striate cortical fibres in the amblyopic eye.

5)      Loss of binocularly driven cells in LGB & Striate Cortex

CLASSIFICATION & TYPES• Strabismic amblyopia.• Stimulus deprivation or amblyopia of disuse.• Anisometropic amblyopia.• Meridional amblyopia.• Isoametropic amblyopia .• Amblyopia secondary to nystagmus.• Idiopathic amblyopia.• organic amblyopia.

Amblyopia

‘Organic Amblyopia’

Irreversible

Structural abnormal Mac scar, Optic

atrophy

‘Functional Amblyopia’

Reversible(when t/t early)

•Strabismic•Anisometric•Visual Deprivation

STRABISMIC AMBLYOPIA• M/C form of amblyopia• A.K.A amblyopia of arrest• Seen in unilateral constant squint who

strongly favour one eye for fixation.• cortical suppression from deviating eye

thought to be due to inhibitory interactions from neurons carrying non fusable images which cause visual confusion

• Esotropia more likely to develop amblyopia as compared to exotropia

• Does not develop in alternating or intermittent strabismus as there are periods of normal binocular interaction that preserve the integrity of visual system

• Severity of amblyopia does not correlate with angle of strabismus

STIMULUS DEPRIVATION AMBLYOPIA

• Amblyopia ex anopsia disuse amblyopia.• Least common but most damaging.• Cause when the visual axis is obstructed.• Monocular congenital or traumatic

cataract, complete ptosis, corneal opacity & prolonged patching of the normal eye for treatment of amblyopia.

• Less than 6 yrs – severe amblyopia.• After 6 yrs – less harmful .

• Visual loss resulting from unilateral deprivation is worse than that produced by bilateral deprivation of similar degree

ANISOMETROPIC AMBLYOPIA

• 2nd m.c.c of amblyopia• develops when unequal refractive errors in

the 2 eyes causes the image on 1 retina to be chronically defocused.

• Most patients with anisometropic amblyopia have straight eyes and appear “normal,” so the only way to identify these patients is through vision screening.

• Hypermetopic anisometropia is more amblyogenic than myopic anisometropia

• The amount of anisometropia that can induce amblyopia varies according to the type of refractive error

• Amount of anisometropia Hypermetropia > 2D

Myopia > 4D

Astigmatism > 1.25D

However unilateral high hyperopia or myopia (>6D) causes severe amblyopia

MERIDIONAL AMBLYOPIA• Resolution of eye is reduced in selective

meridians as a result of un corrected astigmatism

• Cylinder >1.5D is comsidered amblyogenic• Doesn’t develop until first year of age

ISOMETROPIC AMBLYOPIA• Bilateral amblyopia occurring in children

with bilateral uncorrected high refractive error.

Hyperopia > +5 D.

Myopia > -10 D.

astigmatism > 2D

Mechanism – effect of blurred retinal images alone

AMBLYOPIA SECONDARY TO NYSTAGMUS

• Difficult to establish ascertain whether nystagmus is the cause or effect of amblyopia

• Bilateral

IDIOPATHIC AMBLYOPIA

• Occurring in apparently normal patients with a negative history of strabismus & in the absence of other amblyogenic factors.

• Mech- foveal suppression of amblyogenic eye d/t transient amblyogenic factor during infancy

CLINICAL CHARACTERISTICS• Decreased visual acuity• Decreased stereoacity• Fixation reflex• Crowding phenomenon• Effect of neutral density filter• Contrast sensitivity • Fixation pattern

VISUAL ACUITY• Two line difference between amblyopic and normal

eye• For B/L amblyopia the VA should be less than

20/40 in each eye• But in children there will be difficulty in assesing

VA

Infants-fixation preference

preverbal children-preferential looking test,OKN test,VEP

2-3 yrs- E charts,pictoral charts

>3 yrs-snellens charts,HOTV charts

PREFERENTIAL LOOKING TEST

STEREOACUITY• Presence of amblyopia can be detected by

defective performance on various stereograms

• Two pencil test is a clinically useful test and can be applied even when VA recording is unreliable or not possible

• Can also be easured by titmus fly test,random dot stereogram

FIXATION REFLEX• useful tool to assess VA in children <5yrs of age• Central steady and maintained (CSM) fixation

implies good VA

Affixation <3/60

unsteady fixation 3/60 to 6/60

Central but not maintained 6/60 to 6/18

Central but strong preference for other eye 6/18 to 6/9

Alternate fixation 6/6

CROWDING PHENOMENON• Amblyopia pts exhibit better VA for single

optotypes than for letters placed in a row• Although not specific for amblyopia,it may be

pronounced in amblyopic eye compared to better eye

• Single line acuity improves more than line acuity during treatment

• So it is important to record both single letter and line visual acuity every time as it is prognostic indicator

• Vision testing with single optotypes is likely to over estimate VA in pts with amblyopia

• More accurate assesment of mono ocular VA is obtained with the presentation of line of optotypes or single optotype with crowding bars that surround the optotype being identified

NEUTRAL DENSITY FILTER• A neutral density filter reduces overall luminance

without inducing a color change.• Decreased luminance of the visual target results in

diminished central acuity in normal eyes.• Decreased illumination of visual targets has less of

an effect on amblyopic eyes because they are not using central acuity

• It was found that neutral filters profoundly reduce vision in eyes with organic amblyopia whereas vision of eyes with functional amblyopia was not reduced and occasionally even slightly improved.

• Hence it can be used to differentiate the two.

CONTRAST SENSITIVITY• Reduction in contrast

sensitivity more for higher frequencies

• Improves during amblyopia therapy and useful to monitor the progress

• Contrast threshold becomes normal in strabismic amblyopia when luminance levels were reduced, while the deficit persists in anisometropic amblyopia

pelli robson contrast sensitivity chart

FIXATION PATTERN• Bangerter’s classification of fixation patterns in

amblyopia

I. Central fixation

II. Eccentric fixation (nonfoveolar)- common type

III. No fixation• Patients with eccentric fixation appear to be

looking to the side,not directly at the fixation target. They have poor smooth pursuits,so they do not accurately follow a moving target.

• Can be tested in old coperative children by visuoscope

OTHER FEATURES• VEP Reduction in amplitude and slightly

prolonged latency• Afferent pupillary defect may be seen• Normalisation of VA in dim light

occasionally• Occasionally latent nystagmus

CLINICAL EVALUATION & DIAGNOSIS

• Thorough clinical history• Binocular red reflex test• Binocularity/stereo acuity testig• Evaluation of visual acuity and fixation pattern• Binocular alingnment and ocular motility• External examination• Pupillary examinaion• Thorough ocular examination including fundus examination.• Cycloplegic retinoscopy/Refraction• Neutral density filter and testing for crowding phenomenon.

TREATMENT MODALITIESTreatment of amblyopia involves following steps:-

1) eliminate any obstacles to vision , such as cataract.

2) correct any significant error.

3) force use of the poorer eye by limiting use of the better eye.

• Refractive correction• Occlusion therapy• Penalisation• Drug therapy• Pleoptics • Cam stimulator• Surgery to treat the cause of amblyopia

CATARACT REMOVAL

• Removal of congenital lens opacity- first 4 -6 week of life.

• If symmetrical b/l cases- interval b/w 1st & 2nd eye should not be not more than 1-2 weeks.

• Developing severe traumatic cataract in children less than 6 yrs removed within few weeks of injury.

REFRACTIVE ERROR CORRECTION• Improves VA in 25-33% of patients with anisometropic

amblyopia and also in strabismic amblyopia• Cycloplegic refraction followed by adequate optical

correction• ATS 5 concluded that amblyopia improved with

optical correction in 77% and resolved in 27%• Chen et al (AJO 2007) concluded that penalisation

and occlusion is required only if the child doesn’t improve with glasses for four months

• In general eye glasses are well tolerated by children especially when there is improvement in visual function

OCCLUSION THERAPY• Occlusion of the sound eye is the most effective

treatment for amblyopia treatment• When fixation is central, simple & effective.• When fixation is eccentric, <7yrs central fixation

will be recovered.• Older the child harder to regain central fixation.• Success rate 30-92%• MOAprevent fixating eye taking part in act of

vision and removes inhibitory stimulus that arises from stimulation from fixating eye

Types of occlusion• Total or partial• Conventional or inverse• Full time or part time

• Patching is most commonly prescribed,however contravercy exists concerning how much treatment is necessary

• Most data on response according to daily dosage of patching are retrospective and uncontrolled

TOTAL VS PARTIAL OCCLUSION

total

partial

•All light is prevented from entering eye.•Employed in amblyopic eyes with acuity less than 6/24•Occlusion using elastoplast, gauze pad, tape, doynes rubber occluder.

•Does not cut off the total light entering eye•Degrades the vision of normal eye such that amblyopic eye gets better vision and preference•Occlusion using cellophane, transparent nail polish, or a higher plus lens.

CONVENTIONAL VS INVERSE OCCLUSION Conventional Inverse

•Occlusion of sound eye

•Occlusion of amblyopic eye so that eccentric fixation becomes less fixed

FULL TIME VS PART TIME Full time Part time

Removed only while going to bed at night

Short time each day during close work or watching television.

Choice of initial Rx In relapses after Rx and also for maintanence

Types of occluders• Adhesive skin patches made of micropore• Commercially available opticlude• Spectacle occluder• Contact lens occluder

OPAQUE CONTACT LENS

• Patches • Micropore tape with soft tissue paper

• Spectacle patch / frost glass • Doyne’s occluder

Paediatric eye disease investigator group(PEDIG) has conducted several amblyopia treatment trials (amblyopia treatment study or ATS) over the past several years. Results have shown that• Spectacles alone are powerful treatment for

amblyopia; patching is superior to spectacles• Initiating fewer hours of prescribed patching

seems to be as effective as traditional treatment• Patching is effective in older children particularly

if they have not been treated earlier• Atropine is as effective as patching• Weekend atropine is as effective as daily atropine

How much patching??The amblyopia treatment study have helped to define the role of full time patching vs part time patching• In patients aged 3-7 years with severe

amblyopia (VA B/W 6/30 to 6/120) full time patching produced similar effect to that of six hours patching per day

• In patients aged 3-7 years with moderate amblyopia (VA better than 6/30) 2 hours patching produced similar effect to that of six hours patching per day

Treatment of amblyopia in 7-17 yrs• For 7-13 yrs age group 2-6 hours of

patching can improve VA only if previously treated

• For 13-17 yrs age group 2-6 hous of patching improved VA even if not treated previously

• Long term results from these studies are still pending

HOW TO GO ABOUT OCCLUSION

• Motivation of child and parents.• Active vision exercises by amblyopic eye like dotting

O’s and encircling E’s in a newspaper, joining dots,reading comics and story books.

• In case of vision improvement, occlusion is continued till amblyopic eye has not only developed equal vision but also equal preference of fixation.

• May take 3-6 months.• If there is no improvement. Then treatment is stopped.

Also other causes to be ruled out.• Maintainence treatment is continued atleast upto 9 yrs

of age with part time occlusion and exercises

Rx schedule for initial occlusionAge in yrs Period of

occlusion(days)Direct : inverse

Follow up after every

Upto 2 2 :1 15 days

3 3 : 1 15 days

4 4 : 1 1 month

5 5 : 1 1 month

6 & older 6 : 1 1 month

• Follow up-depending on age,severiy of amblyopia and compliance

• To look for-VA, fixation pattern and occlusion amblyopia

• When to stop occlusion

VA equals in both eyes

alternation of fixation• When VA is stable patching may be

decreased slowly• Because amblyopia recurres in large no. of

patients maintanence therapy or tapering of therapy should be strongly considered.

Disadvantages of occlusion• Occlusion amblyopia• Non compliance• Psychological distress• Appearance of constant deviation• Allergic skin rash• Diplopia• Cosmetically inacceptable

Prognostic considerations• Younger the age better the prognosis

• Type of amblyopia myopic anisometropia> hyperopic anisometropia> strabismic amblyopia> stimulus deprivation

• Pretreatment VA

• Type of occlusion

• Type of fixation

• Near exercises

• Patient compliance and parent education• Presence of astigmatism• Method of treatment termination• Previous treatment• Refractive correction

TREATMENT OF ANISOMETROPIC AMBLYOPIA

TREATMENT OF STRABISMIC AMBLYOPIA

PENALISATION• Therapeutic technique performed by

optically defocussing the eye with better vision by using cycloplegia or altering the eye glass lens

INDICATIONS No compliance for occlusion.Mild degrees of amblyopia.Maintainence after occlusion.Anisometropic amblyopia

• Advantages cheap,better compliance• DisadvantagesS/E of drugs

risk of occlusion amblyopia

systemic absorption• Unless penalisation decreases the VA of

dominant eye below the amblyopic eye this form of treatment is not adviced

Methods of penalisationa. Near penalization: fixing eye is

atropinized & fully corrected for distance, amblyopic eye is overcorrected with +2 to +3D .

b. Distance penalization : fixing eye is atropinized & overcorrected, amblyopic eye is fully corrected.

c. Total : fixing eye is atropinized & undercorrected by 4 to 5 D, amblyopic eye is fully corrected.

PLEOPTICS• Involves active stimulation of fovea to

overcome eccentric fixation & improves Va.

• The peripheral retina including the eccentrically fixing area around the fovea is dazzled.

• After lights are turned off, fovea functions better because the surrounding retinal area is in a state of hypofunction

• ONLY INDICATION IS coperative and intelligent child older than 6yrs having eccentric fixation

ORE PLEOTOPHORE

CAM STIMULATOR• Slowly rotating high contrast square wave

grating of different spatial frequencies• Principle – rotating gratings provide

specific stimulation for cortical neurons• the visual improvement was found to be

better in emmetropes and hypermetropes than those in strabismus amblyopia

• Not used these days

PHARMACOLOGICAL THERAPY• LEVADOPA is the only most extensively

studied drug in western and Indian population• Precursor of dopamine known to influence

visual system at retina and cortical level• Advantages

Augments conventional occlusion

Speeds up recovery of visual functions

Improves compliance

Reduces cost and duration of treatment

• Catecholamine based medical treatment citicholine has been demonstrated to improve VA in amblyopic eyes

SURGERYBy reducing anisometropia refractive surgeries has reported to• Improve spectacle tolerance• facilitate amblyopia thearpy• Enhance binocular vision

Also used for children who has finished amblyopia therapy and cannot comply with spectacles or contact lens

Surgical therapy for strabismus generally should occur after amblyopia is reversed. • Disadvantages to surgical therapy prior to

correction of amblyopia include difficulty in telling if amblyopia is present

because there is no longer a strabismus to assess fixation preference and higher potential to being lost to follow-up, as the child cosmetically looks better.

The improved cosmesis gives the parents a false sense of security about the vision improving

RECURRENCE• Chances are high until child is visually

mature.• Careful monitoring every month upto 1

year, every 2 months upto 2 years and 4- 6 months upto visual maturity is required.

• Maintainence occlusion to be given

SCREENING• AAO recommends screening by the age of 3 yrs

and thereafter every 2yrs• Includes visual acuity, corneal reflex test,

refraction, fixation preference and stereo acuity• AAP suggests that vision screening should

begin at birth and continue as a part of child regular medical check up

• All new born infants should be screened in nursery with the use of red reflex

• Infants at risk should undergo detailed evaluation

Severe amblyopia can be eliminated as a public health problem• The goal can be achieved by improvements in public awareness better screening protocols at the level of

primary health care provider full access to medical care for at risk

patients

THANK YOU