This document discusses amblyopia, including its classification, etiology, and diagnosis. It defines amblyopia as a decrease in visual acuity caused by pattern vision deprivation or abnormal binocular interaction that cannot be corrected by optical or surgical means. Amblyopia can be functional, resulting from stimulus deprivation, strabismus, refractive errors, or anisometropia, or organic, caused by retinal diseases, nutritional deficiencies, or toxins. The document covers various types of amblyopia in detail and discusses methods for detecting, investigating, and determining the prognosis of amblyopia.

1. AMBLYOPIA:
cLAssIfIcAtIOn, etIOLOgY And
dIAgnOsIs
BY:RAJU KAItI
OPtOMetRIst

2. AMBLYOPIA
• Defn
– “A unilateral or bilateral decrease of visual acuity
caused by pattern vision deprivation or abnormal
binocular interaction for which no obvious causes
can be detected by physical examination of the
eye and cannot be corrected by optical or surgical
means but in appropriate cases is reversible by
therapeutic measures.’

3. • Researches have pointed to the fact that
amblyopia was not simply a reduction in the
visual acuity in an eye, but a complex visual
processing disorder that involved the decrement
virtually in all areas of visual functions including-
– Accommodative accuracy and facility
– Fixation stability
– Pursuit and saccadic accuracy
– Localization in space
– Contrast sensitivity

4. • Amblyopia originated from Greek word:
Amblyos - dullness / blunt
Ops – vision
• Condition in which the observer sees nothing &
patient very little
• Significance difference in acuity between eyes may
be sign of amblyopia
• Mainly result due to visual stimulus deprivation /
suppression usually associated with strabismus or
anisometropia

5. • conflicting inputs from the two eyes to the visual
cortex that result in active suppression and
development of amblyopia in non dominant eye
• usually unilateral
• Bilateral amblyopia can occur when high
hypermetropic (+4D) or myopic (-8 D) or astigmatic
refractive error not corrected during visual
immaturity
• Defective VA even after correction
• may be due to organic causes

6. AMBLYOPIA
• Prevalence
– Variable
– 2.0 -2.5 % of general population
– Preschool/school age children : 4-5.3%

7. sensItIve PeRIOd
 Developmental time frame early in life during which
there is robust plasticity within the visual system,
particularly the visual cortex.
– Retinocortical connection not firmly established
– Period – sensitive /critical / susceptible period
– Strabismic amblyopia – 7 years
– Sensitive period for recovery - ? 8 years
• Critical period - 2 months of age

8. RIsK fActORs
• 4 times more prevalent in
– LBW & Premature baby
• 6 times more in
– delayed milestones & CNS disorders
• parent with amblyopia
• Maternal smoking

9. • Criteria for Excellent VA
-early retinal stimulation of each eye
-proper ocular alignment
-binocularity
- stereopsis

10. • Any blurred retinal image
• Difference in VA b/w two eyes
• Leads to abnormal fixation
• Inhibition of visual cortex
Amblyopia

11. 11

12. 12

13. cLAssIfIcAtIOn
• Can be divided in to two groups;
• Functional amblyopia
Stimulus deprivation
Strabismic
Refractive
Anisometropic
Psychogenic
• Organic amblyopia
Due to retinal diseases
Nutritional
Toxic
Idiopathic

14. stIMULAtIOn dePRIvAtIOn AMBLYOPIA
• primary cause is due to disuse/under
stimulation of the retina
– i.e. opacities or occlusion
• cong cataract, Ptosis, corneal opacities, surgical lid
closure ,Vitreous haemorrhage, may be due to
occlusion amblyopia
• unilateral or bilateral
– unilateral more severe and often associated with
secondary ET or XT & anisometropia
• eccentric fixation may develop.

15. 15

16. • Pattern deprivation amblyopia
- dense congenital cataract
-corneal opacity (Peters' anomaly )
-corneal opacity ( Trauma, Infections, HSV)
- large uncorrected refractive errors
-Nystagmus - poor visual outcome

17. stIMULUs dePRIvAtIOn AMBLYOPIA
Aphakia
Congenital cataract
Corneal scar Congenital ptosis

18. • WHICH IS MORE LIKELY TO PRODUCE
AMBLYOPIA-UNILATERAL OR BILATERAL
PTOSIOS.WHY??????
Unilateral ocular abnormalities are much more likely to
lead amblyopia than binocular ones. If one eye has a
competitive advantage over the other, its afferent
connections become stronger and more numerous
while those of other eye atrophied and retract.

19. StrabiSmic amblyopia
• occurs as a result of neural changes in the deviated eye
• pt having one eye for fixation in unilateral rather than
alternating fixation more likely to develop Strabismic
amblyopia
• often seen in ET than XT
– the fovea of the deviated eye has to compete with a strong
temporal hemi field of the fellow eye
• always unilateral & caused by active inhibition
• aetiology similar to that of suppression.
– thus called suppression amblyopia.

20. • turning and consequent disuse of one eye will
arrest the development of VA –amb. of arrest.
– if amblyopia of arrest is allowed to persist suppression
amblyopia develops – amblyopia of extinction.
• constant untreated acquired ET under 3 years will
dev strabismus amb in100% of cases
• doesn’t occur in X(T)

21. aniSometropic amblyopia
o abnormal binocular interaction caused by unequal fovea
images in the two eyes causes dev of the Anisometropic
amb.
o always unilateral.
o active inhibition of the fovea as the Strabismic amb.
o 30% of the cases are associated with strabismus.
o with reduction in central VA , overall reduction of the
contrast sensitivity

22. 22

23. • it occurs when dioptric power differs over
+1D in hyperopes , more than –3D in myopes
&more than 1.5 D in astigmatism.
• when corrected optically resulting
aneisokonia may be amblypiogenic factor
since retinal images of dif sizes present an
obstacle fusion
• more common in anisohyperopia than
anisomyopia

24. refractive amblyopia
• caused by uncorrected ref error where there is blur image
at all distance
• may be unilateral or bilateral
• if unilateral then Anisometropic amblyopia
• meridional amb. occurs in principal meridian of high
uncorrected astigmatism.

25. refractive : iSoametropic
• Hyperopia : > + 5.00 Ds
• Myopia : > -8.00 Ds
• Astigmatism : > +/- 2.50 Ds
• Cause
– Equal pattern deprivation
• Other term
– Meridional amblyopia
• Selective visual deprivation for visual stimuli of a certain spatial
orientation

26. pSychogenic amblyopia
• also called hysterical amblyopia.
• occurs as a visual conversion reaction.

27. organic amblyopia
 Irreversible type which results from some pathological or
anatomical abnormalities of the retina
Retinal eye diseases
eg.-neonatal macular hemorrhage receptor
dystrophy pathogenic lesion
affecting the fovea & surrounding retinal area such as
toxoplasmosis chorioretinitis ,a
retinoblastoma, traumatic retinal lesion
May be associated with abnormality of visual
pathway

28. • Nutritional amblyopia
-Occurs from nutrition deficiencies
• Toxic amblyopia -
visual loss due to damage to the optic nerve fibrosis due
to effect of exogenous or endogenous poisons
• -Its types are as follows:
– tobacco amblyopia
– ethyl alcohol amblyopia
– methyl alcohol amblyopia
– quinine amblyopia
– ethambutol amblyopia

29. Tobacco amblyopia
Typically occurs in men in pipe smokers, heavy
drinkers ,diet deficiencies in protein & vit.B complex
deficiencies
Pathogenesis:
Toxic agent – cyanide found in tobacco
Excessive tobacco smoking - Excessive
cyanide in blood – degeneration of ganglion cells
particularly in macular lesion –
degeneration of papillomacular bundle in the
nerve - toxic amblyopia

30. • Characterized by gradually progressive impairment in the
central vision
• Patient complains of fogginess & difficulty in doing near
works
• V.F.-B/L centrocaecal scotoma with diffuse margins,
defects more for red than white
• Fundus: normal/slight temporal pallor
• ethyl alcohol amblyopia
Usually in association with tobacco amblyopia
May occur in
nonsmoker but heavy drinkers suffering from chronic
gastritis
• Clinical picture same as tobacco amblyopia

31. MEthyl alcohol amblyopia
It is typically acute usually resulting in optic atrophy &
permanent blindness
Etiology :
usually occurs due to intake of wood alcohol or
methylated spirit in cheap adulterated /fortified
beverages
- sometimes may be due to inhalation of fumes in
industries

32. • Pathogenesis; Metabolized very slowly thus stays in body
for longer period of time – oxidized in to formic acid &
formaldehyde in the tissues -toxic agents cause edema
followed by degeneration of the ganglion cells of the retina
resulting in complete blindness due to optic atrophy
• Clinical features:
• Symptoms:
• In acute poisoning - headache , vomiting ,nausea ,dizziness,
abdominal pain
• Presence of characteristic odor
• Patient usually brought with complete blindness noticed
after 2-3 days

33. • Fundus: mild disc edema , markly narrowed blood
vessels
FINALLY: B/L primary optic atrophy

34. • Quinine amblyopia
o May occur even with small doses of the drugs in susceptible
individuals.
• Near total blindness ,deafness & tinnitus
• Pupil –fixed & dilated
• Fundus - retinal edema , marked pallor of the disc , extreme
attenuation of retinal vessels
• V.F.-markly contracted

35. • Ethambutol amblyopia
• Caused due to anti -tubercular drugs
• Used in doses of 15mg/kg per day
• usually occurs in patient who have associated
alcoholism & diabetes
• Fundus: sign of papillitis

36. • Idiopathic amblyopia
• -unknown etiology
• -may be cortical or sub cortical

37. • Is color vision affected in amblyopia??
– Generally not affected
– Mild abnormalities reported in severe amblyopia,
particularly those with loss of foveal fixation
• Does amblyopia cause a relative afferent
pupillary defect??
– Generally not affected
– Pathologic changes located in posterior visual
pathway, not in retina or optic nerve

38. ??? Necessity for testiNg
AmblyopiA
• Differential Diagnosis and prognosis .
• Differentiating the functional from the organic
amblyopia.
• The decision , type and extent of the amblyopia
therapy depends on the test results.
• Guides the therapy.

39. DetectioN & iNvestigAtioN
• Full routine examination
• History and symptoms
• age of onset
• onset of strabismus
• previous treatment; with glasses ,occlusion
• V.A measurement
first amblyopic eye then non-amblyopic eye
-line acuity
-Single letter acuity

40. • Line acuity
Called morphoscopic acuity
Ask the patient to read until the real limit of
acuity is reached
Where there is eccentric fixation , small
foveal scotoma may result in patient missing
out letters
• Single letter acuity
called angular acuity
E cube , S.G charts- measure minimum
recognizable acuity in children
Usually higher V.A with angular acuity than
morphoscopic acuity called crowding
phenomenon due to contour interaction

41. spAtiAl iNterActioN (crowDiNg
pheNomeNoN)
• Persons with amblyopia have increased difficulty identifying
test letters when they are presented in a linear or two-dimensional
array rather than as isolated characters. -
"separation difficulty/ crowding phenomenon"
– when figures near the limit of resolution are surrounded
by other closely spaced forms
• A similar effect can be produce by placing interactive bars
around a single letter

43. • In the normal fovea, contour interaction
– when forms are separated by a distance of 1 to 3
minutes of arc (0.4 to 0.6 times the overall size of
6 meter Snellen letter)
– In the normal periphery its extent is much greater.
• In the amblyopic fovea,
– contour interaction typically extends over an
increased distance, to a degree that is roughly
proportional to the reduction in acuity.

44. • Crowding phenomenon more enhanced in Strabismic
amblyopia
• Contrast sensitivity
Strabismic & Anisometropic amblyopia -Have
poorer C.S than normal eye
• Electrodiognostic tests
Helps in detecting the presence of organic
amblyopia in which there is no response to
treatment

45. • Pinhole
Helps to confirms the presence of amblyopia if
VA is not improved with its use
• Bruckner test
• Fixation pattern & amblyopia in strabismus
• Presence of free alteration indicates equal V.A
• No alternate fixation ,likely to suppress so develops
amblyopia
• Eccentric fixation may be present

46. ecceNtric fixAtioN
• Unfavorable prognostic factor for therapy.
• Objectively determined by Visuoscopy
• Subjectively determined when the patient fixating
the centre of the rotating field that creates the
Haidingers brush effect , and the brush is seen
eccentric to the central fixation spot rather than
superimposed on it.

47. • Eccentric fixation tests
• Visuoscope / fixation graticule present in
ophthalmoscope
• Area used for fixation is noted
Parafoveal fixation- 1-3 degrees
paramacular fixation- 3-5 degrees peripheral
fixation- more than 5 degrees

48. • Neutral density filter
• difference between organic & strabismus amblyopia
• In strabismus amblyopia, there is eccentric fixation
amblyopic eye is not affected by the filter as the
slightly peripheral retina adapts better since
it contains rod & cones
• In organic amblyopia –usually central fixation, likely
to be reduction of several lines

49. • After image transfer method
• asked to indicate the position of the after Image
in relation to the fixation point in eccentric
fixation ,image will appear slightly to the side of
the fixation pattern

50. telescope test
• Chart is viewed with amblyopic eye with
2.5xtelescope.
• If organic amblyopia acuity increase by a factor
of 2.5
• (20100 improve to 2040)
• If further improvement in visual acuity it is
functional amblyopia.
• (20100 to 2025)

51. coNtrAst seNsitivity fuNctioN
• Useful in predicating the degree and the rate of
improvement before amblyopia therapy.
• Mild , middle spatial frequency (6to 12
cyclesdegree) support a better prognosis for
recovery.

52. Visually EVokEd PotEntial
tEsting
• Stimulus subtense is increased in size(lower spatial
frequency)until a minute of arc size is found where the
monocular wave form looks similar with regard to
latency and amplitude.
• The higher the spatial frequency at which this occurs ,
the better the prognosis for improvement.
• Below 14 minutes of arc the prognosis is excellent
below 55 minutes it is poor.

53. • Entopic phenomenon
Haidingers brushes and Maxwell's spot
• These phenomenon are centered on the fovea,
eccentrically fixing patient will not see them at
the point of fixation
-will be slightly to the side of fixation
Some cannot see at all

54. • Perimetry method
• Amsler charts
Used to show early signs of organic amb where
there is typically a small dense central scotoma
• Past pointing test
• Gives an indication if the localization of objects in
space has been disturbed with an amblyopic eye

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56. Functional amblyopia Organic amblyopia
Normal decrease in VA with
neutral density filter
Marked decrease in VA
Disproportionate increase in
VA with 2.5x telescope
Expected improvement in VA
Normal color vision Abnormal color vision
Interigity of Haidingers brush Diminution of Haidingers
brush
Normal electroretinogram Abnormal electroretinogram
Normal VEP Attenuated VEP

57. Prognostic Factors in amblyoPia
Positive factor Negative factor
functional organic
Central fixation Eccentric fixation
Random dot stereopsis No random dot stereopsis
Short duration Long duration
Young patient ,motivated Older patient, un -motivated

58. diagnosis
• Amblyopia – Diagnosis of exclusion
U/L amblyopia
- fixation behavior differs in two eyes
-difference –not eliminated by corrective
lenses
• Not attributable to a structural abnormalities

59. diagnosis
B/L amblyopia
- diagnosed when sig. Refractive errors present
- fixation behaviors falls below the N range
- acuity is not normalized by corrective lenses
- reduced VA is not attributable to the ocular
findings

60. PrEVEntion & Early dEtEction
• Paramount important
• Infants & children- susceptible to permanent central
loss
• Screening program
- Red reflex test ( media opacity )
-Penlight corneal reflex (Hirschberg test)
-Cover test
-Binocular red reflex test (Buckner test)

61. • Others :
• Photographic Screening
• Auto refractive devices
• Refractive errors & Amblyopia – can be
detected by VA screening of normal children >
3 years

62. • Unfortunately cases – missed
• Children with risk factors for Amblyopia
• Referral system:
• -Premature baby
-Low birth weight 6 mo
- Prenatal complications
-CNS & delayed milestones 18 mo
-Genetic syndromes with others

63. diagnosing thE risk oF amblyoPia
MEAC approach

64. •Monitor qualitative fixation:
– VA evaluation-measure gross fixation abilities
• Evaluate red reflex:
– Bruckner test-whiter/brighter reflex represents a
Strabismic eye
• Alignment evaluation:
– Hirschberg with infant or CT for toddler
• Compare refractive error:
– Cycloplegic refraction

65. thumb occludEr (Fixation
PrEFErEncE)

67. Glasses wear Patching good eye