This document defines and classifies different types of amblyopia, including strabismic amblyopia, stimulus deprivation amblyopia, anisometropic amblyopia, meridional amblyopia, and bilateral ametropic amblyopia. It discusses the pathogenesis and pathophysiology of amblyopia, noting that visual deprivation during early development can cause changes in visual system neurons. The evaluation, diagnosis, and management of amblyopia are also outlined, including prevention through early vision screening, treatment by eliminating causes of visual deprivation and correcting refractive errors, and occlusion therapy to correct ocular dominance.

1. AMBLYOPIA

2. DEFINITION
• Amblyopia is the unilateral, or rarely bilateral,
decrease in best-corrected visual acuity
• caused by form vision deprivation and/or
abnormal binocular interaction, for which there
is
• no identifiable pathology of the eye or visual
pathway.

3. CLASSIFICATION
1. Strabismic amblyopia
2. Stimulus deprivation
3. Anisometropic amblyopia
4. Bilateral ametropic amblyopia
5. Meridional amblyopia

4. Strabismic amblyopia
• Amblyopia seen in those patients with unilateral
constant squint who strongly favour one eye for
fixation.
• Typical Features :
 Grating acuity is better than snellen’s acuity
 Always unilateral
 More often in esotropes than exotropes
 Very rare in hypertropia (anomalous head posture)
 Do not occur in alternate strabismus.

5. Stimulus deprivation
Amblyopia of Disuse
Amblyopia ex anopsia
Amblyopia resulting from those conditions wherein
one eye is totally excluded from seeing early in life.
Monocular congenital or traumatic cataract, complete
ptosis, corneal opacity, prolonged patching of the
normal eye for the treatment of amblyopia etc.

6. • Features :
 Most damaging and difficult to treat
 Amblyopic visual loss resulting from U/L
deprivation is worser than that produced by B/L
deprivation of similar degree.
This is because, in U/L deprivation, interocular
effects add to image degradation.

7. Anisometropic amblyopia
• Amblyopia caused by a difference in refractive error
between the eyes and may result from a difference
of as little as 1.0 D sphere
• More common in anisosohypermetropia than in
those with anisomyopia.
• Strabismus is frequently associated with
anisometropia and hence both strabismic
amblyopia and anisometropic amblyopia can
coexist.

8. Meridional amblyopia
• In patients with uncorrected astigmatic refractive
error due to selective visual deprivation at certain
special orientaion.
• Even small amount of U/L astigmatism may cause
amblyopia

9. Bilateral ametropic amblyopia
• Amblyopia results high symmetrical refractive
errors, usually hypermetropia (+5.0D).
• Myopia in excess of -10.0 D also can induce B/L
amblyopia
• Astigmatism > 2.5 D

10. PATHOGENESIS & PATHOPHYSIOLOGY
 Still not elucidated fully
 Amblyogenic Factors
 Role of retina
 Active cortical inhibition

11. Amblyogenic Factors
• Form vision deprivation – all forms
• Light deprivation – strabismic
• Abnormal binocular interaction - all monoocular
forms

12. Neurophysiologic Studies
- Hubel and Wiesel
Deprivation Studies
By suturing the eyelids of experimental
animals
• Observations :
In the LGB, cells in those layers receiving input
from deprived eye showed a profound shrinkage.
Cells of primary visual cortex either lost their
ability to respond to stimultion or showed
significant functional deficiency.

13. • Conclusions :
 Visual deprivation produces amblyopia by
changes in the visual system neurons.
 Deprivation during the early part of the critical
period of development is more deleterious
 Amblyopia produced by binocular deprivation
was less severe than that produced by uniocular
deprivation.

14. Role of Retina
• There is some evidence that the retina itself is
abnormal in amblyopia.
• Decreased sensitivity of foveal cones in amblyopia
• Quicker dark adaptation
• However V.A is reduced disproportionately to
reduction in cone function.
• ERG - Normal

15. Active Cortical Inhibition
• Physiologic Evidence – Perhaps the normal eye may be
responsible for an active cortical inhibition in
unilateral amblyopia
• Pharmacologic Evidence - Perhaps in amblyopia active
cortical inhibition might be mediated by inhibitory
neurotansmitter GABA.

16. Clinical Charecterisics
1. Visual Acuity – Difference in 2 lines on V.A
chart should be there to diagonse amblyopia
 Recognition Acuity – (Snellen) is more affected than
resolution acuity ( Teller’s or VER)and detection
acuity ( Catford Drum test)
Grating Acuity is less affected in strabismic
amblyopia

17. Effec of neutral density filter – when placed infront
of affected eye V.A improves by one or two lines.
 Crowding Phenomenon - (Separation difficulty)
Refers to the inability of an amblyopic eye to
distinguish letters crowded together. Therefore V.A
is better when tested with optotype charts.

18. 2. Fixation Pattern -
 Central fixation – foveolar fixation
 Eccentric viewing – Extrafoveal point because of
central suppression scotoma.
Fovea still not lost its principal
visual direction.
Patient look past the object they
have been asked to fix.
 Eccentric fixation – Fovea lost its principal visual
direction

19. • If an image is pojected onto the fovea patient
report that the object is seen in some other
direction than straight ahead.

20. • The Heimann-Bielschowsky phenomenon –
Unusual ocular motility pattern which may
develop years following uniocular visual loss.
Strictly monocular coarse, pendular vertical
oscillations occurring only in the amblyopic eye.
• Paradoxical eccentric Fixation –
Ordinarily, there develop nasal eccentricity in
esotropia and temporal eccentricity in exotropia.
Reverse is called paradoxical fixation.
- surgical overcorrection of deviation
- spontaneous reversal of deviation

21. • Absolute central scotoma
• Localisation of object of regard - normal
in patients with amblyopia & eccentric fixation but
abnormal in eccentric viewing.
• Colour Vision - Impaired only if V.A is below
6/36. Related to eccentric fixation.
• Light Perception & Form vision -
Dissociated.
• Pupillary light reflexes – generally normal.
RAPD may occur in deep amblyopia.

22. • Light and Dark Adaptations - Usually
normal. Difference in the region of Kohlrausch’s
bend (bend in the adaptation curve) has been
found.
• Critical Flicker Frequency - Central CFF
tends to approach that of periphery or of rod
mechanism. Also, CFF is faster in eccentric fixation.
• ERG & EOG - ERG is normal but EOG shows
unsteadiness of fixation.

23. EVALUATION AND DIAGNOSIS
• Evaluation of V.A & Refraction
• Neutral density filter test
• Test for crowding phenomenon
• A/S and fundus examination
• Evaluation of fixation
• Other sensory anomalies

24. Binocular Fixation Pattern (BFP)
Grade 0 Spontaneous alternation
Grade 1 Simply fixates with one eye but can use the other eye too
Grade 2 Moderate fixation preference
Grade 3 Holds fixation for 1-2 seconds but switches before blink.
(Strong fixation preference)
Grade 4 Uses only one eye for fixation

25. Prism Induced Tropia Test
• 25-D Base in Prism Test : It induces large esotropia
creating diplopia. So normaly infant will not
attempt to see through he prism but if it shows
prefernce still, indicates amblyopia in the uncovered
eye.
• Vertical Prism Test : 10 – 15 D vertical prism is used
to induce diplopia
• CSM method of Rating : C – Central, S- Steady, M –
Maintained (orthotropic)

26. Evaluation of Central Vs Eccentic
Fixation
1. Angle kappa method –
• Hand light method – Occlude the non fixing eye,
ask the patient to fix at light held directly below
patient’s eye. Same repeated on the other eye.
Corneal reflex is noted. Angle is positive, if reflex
is displaced nasally and negative,if displaced
temporally.
In eccentric fixation, significant difference in
location of corneal reflex will be noted.

27. • Arc Perimeter Method – Patient is asked to fixate at
the central mark on the perimeter. A very fine light
is moved along the arc until the light refel is
centered on the cornea. Location of light on the
perimeter arc tells the angle kappa in degrees.
• Major amblyoscope Method - Using special slides
with synoptophore
2. Visuscope Method - In patients above 4-5 years
3. Haidinger’s brushes Method - Patient is made to
percieve the entopic pattern of Haidinger brushes
and asked to touch is center.

28. 4. Maxwell’s spot Method – Round dark purplish spot
of about 3 arc degrees in d.m. It is percieved
entopically when the eyes are exposed to
homogenous blue or purple field. In eccentric
fixation Maxwells spot is displaced to the side of
fixation target.

29. Management of Amblyopia
 Prevention and Early Detection
 Treatment of Amblyopia

30. Prevention
• Best Way – Vision Screening programmes right
from birth : I-ARM
Steps Neonates
(Birth- 2m)
Babies
(3m – 2 years)
Children
(>3 years)
Inspection Symmetry of
face & eyes
Face or head tilt Face turn or
head tilt
Acuity Poor fixation,
pupillary
response
Good fixation
and smooth
pursuit
Allen card, E-
game
Red Reflex Red reflex test Bruchner red
reflex
Bruchner red
reflex
Motility Gross alignment Light reflex and
bruchner
Any
misalignment is

31. TREATMENT
 Elimination of cause of Visual depriation – eg
congenital cataract, congenital ptosis,corneal
opacity
 Correction of refractive error and spectacle
adaptation should be fully tried before starting
occlusion therapy.
 Correction of ocular dominance : Occlusion
therapy, penalization, active stimulation,pleoptics,
pharmacological manipulation.

32. Occlusion therapy
• Methods – Patch on skin, gauze pad and tape, use
of Doyne’s rubber occluder, opaque contact lens
etc.
• Timing- Amblyopia Treatment Studies (ATS)
In children (3-7y) with severe amblyopia full time
patching produced a similar effect to that of
patching for 6 hours a day
In children (3-7y) with moderate amblyopia 2 hours
of daily patching produced same improvement as to
that of 6 hours.

33.  In children (7-13y) prescribing 2-6 hours of
patching can improve visual acuity even if
amblyopiahas been previously treated
In patients (13-18y) precribing 2-6 hours of patching
might improve visual acuity, but not if amblopia Rx
has already been tried previously.
Active vision exercises by amblyopic eye during
occlusion; simple tasks such as joining dots to make
drawing, tracing, threading beads, watching t,v,
reading comics, may enhance visual improvement.

34. • In patients with visual improvement assessed at
monthly follow up visits, occlusion should be
continued till equal vision and equal fixation
preference is achieved
• Younger the patient, better is the visual
improvement.
• In patients with no improvement on 3 monthly
follow up, futher occlusion is unlikely to be
fruitful
• Management Occlusion Treatment – Once the
vision has ben equalised occclusion therapy for
2-3 hours has to be continued till atleast 9yrs.

35. Penalisation
• To force the amblyopic eye to greater use by
penalizing the sound eye with the help of glasses nd
a cycloplegic drug.
• Prerequisite – Eyes should be straight
• Indications - As good as patching in moderate
amblopia
• Methods – 1) Atropine penalization
2) Optical Penalization

36. 1) Atropine penalization
 Near Penalization – Normal eye is atropined and
fully corrected for distance vision, while amblyopic
eye is overcorrected with +2 or +3 D.
 Distance Penalization – Normal eye is atropinized
and overcorrected by 4 – 5 D, while amblyopic eye
is fully corrected.
 Total penalization – Normal eye is atropinized and
undercorrectedby 4-5D, while amblyopic eye is
fully correcteed.

37. 2) Optical Penalization – Prescribing more pluses to
sound eye to force amblyopic eye to fix for
distance targets.

38. Active Stimulation Therapy
• Using CAM vision stimulator has been used in the
past.
• Method – After occluding the sound eye, amblyopic
eye is stimulated for 7 min by slowly rotating high
contrast square wave raing of different spatial
frequencies. Done once in a week.

39. Pleoptics
• Only of historical interest
• In this peripheral retina including eccentrically fixing
area around the fovea is dazzled with an intense
light while protecting the foveal area.
• This is followed by direct stimulation of fovea by
pleoptophore or after image(Cupper’s method).

40. Pharmacological Manipulation
• Levodopa, a precursor for catecholamine dopamine
has been studied as an adjunct ti patchinf, but
remains controversial.

41. Role of perceptual learning
• It employs practicing a visual discrimination task eg;
Positional acuity, Contrast acuity, Stereo acuity etc.
• Recommended period for perceptual learning is
2hrs/day, 5 days/ week, for a period of 9 months.
• Still controversial

42. Prognosis of Amblyopia Treatment
• Younger the child better the prognosis
• Deprivation amblyopia carries the poorest
prognosis
• Strabismic amblyopia has best prgnosis
• Presence of eccenric fixation worsens the prognosis
• U/L hypermetropes ahs poorer prognosis than
myopes
• Occlusion therapy is better than other methods.