This document summarizes adaptations in the visual system that can occur in response to abnormal binocular vision due to strabismus. It describes sensory adaptations that depend on factors such as the age when abnormal vision began and its severity. In a mature visual system, diplopia and confusion may occur, while an immature system can develop suppression, amblyopia, monofixation syndrome, or abnormal retinal correspondence. The document outlines tests to diagnose these conditions and explains adaptations like suppression, fusion, and diplopia that the visual system employs to eliminate double vision. It provides examples of sensory tests and their results in different binocular alignment conditions.

1. Adaptive Mechanism
Of Squint
Presenter- Dr. Om Patel
Moderator – Dr Alka

2. Sensory Adaptations
• Visual neurodevelopment changes in response to
abnormal stimulation from blurred retinal image
• Depends on:-
1. When abnormal visual stimulation occurred
2. Severity of abnormal stimulation
3. Type of binocular disruption

3. • Based on onset of sensory insult, adaptations are
divided into
1. Visually mature
2. Visually immature

4. Mature Visual System
• Occurs after development of bifoveal fusion
• Usually after 7-8 years of age
• Includes diplopia and confusion

5. Confusion and Diplopia
• Diplopia : occurs due to formation of an image on a
dissimilar point on two retinae
• Confusion : occurs due to formation of image of
two different objects on the corresponding points of
two retinae

7. Diplopia
• Usually seen in acquired strabismus over 7-8 years of
age
• In younger children, transient i.e. for 2-4 weeks
• Patient will fixate on an object with one fovea and
see diplopic image from perifoveal retina of the
deviated eye, with fovea of deviated eye suppressed

8. • Esotropia causes uncrossed diplopia
• Exotropia causes crossed diplopia
• Aniseikonia > 10% causes diplopia

9. Uncrossed diplopia Crossed diplopia

10. Immature Visual System
• Occur when binocularity disrupted before 6 years
of age
• Results in
1. Cortical suppression
2. Amblyopia
3. Monofixation syndrome
4. Anomalous Retinal Correspondence(ARC)

11. Suppression
• Defined as temporary active cortical inhibition of
image formed on retina of the deviated eye
• Occurs during binocular vision
• Disappears when deviating eye fixates

12. Types of suppression
• Depending on etiopathogenesis
1. Physiological
2. Pathological
a) Facultative
b) Obligatory
• Depending upon retinal area where image suppressed
1. Foveal
2. Macular
3. Peripheral

13. • Depending upon constancy
1. Intermittent
2. Constant
• Depending upon eye involved
1. Monocular
2. Alternating

14. Tests
1. Worth 4 dot test
2. 4D base out prism test
3. Red glass test
4. Bagolini striated lens test
5. Vectographic test
6. Synoptophore test

15. Monofixation Syndrome
• Small angle strabismus (<10 PD) or mild to moderate U/L
retinal image blur in young children and infants causes
suppression of central visual field of deviated eye
• Small suppression scotomas cause peripheral fusion
• Suppression localized to central 4-5 degrees
• Size of suppression scotoma directly proportional to amount
of image blur and size of strabismus

16. • >10PD strabismus or severe U/L image blur will disrupt
even peripheral fusion
• These patients will lack binocular fusion and will not have
monofixation syndrome
• Central suppression scotoma between 2-5 degrees

17. • Seen in patients with anisometropic amblyopia,
U/L partial cataract, small angle strabismus
• Sensory tests to diagnose are :-
1. Bagolini striated lens test
2. Worth 4 dot test for near normal but for distance
nondominant eye suppressed

18. Monofixation
syndrome

19. Monofixation with microtropia and
visual perception with Bagolini lenses

20. Abnormal Retinal Correspondence
• Normal retinal correspondence(NRC) is binocular
relationship in which true anatomic fovea of each eye are
functionally linked together in occipital cortex
• ARC is when fovea of normal eye and extrafoveal point on
retina of squinting eye acquire common representation
• ARC is adaptation to moderate angle infantile strabismus
usually between 15-30 PD

21. • Factors affecting development of ARC:-
1. Age of onset of squint- <6 years
2. Patient profile- where single binocular vision
previously existed
3. Type of squint- more common in esotropes, less
common in vertical deviations, in uniocular squint
than alternating

22. • Binocular sensory adaptation used to eliminate diplopia by
accepting eccentric image location in deviated eye
• Allows brain to accept parafoveal images from deviated eye
and superimposes with image from fixing eye
• New functional fovea called pseudofovea(PF)

23. • If strabismus of ARC patient corrected, image displaced
from PF onto retina which is cortically noncorresponding,
even if image falls on fovea, leading to diplopia called
paradoxical diplopia
• If after neutralization of squint patient has diplopia, it means
he has ARC
• paradoxical diplopia stays only for few weeks after surgery

24. • If a strabismic patient perceives a complete cross (normal
response) with bagolini lenses, they have ARC
• ARC provides crude binocular vision
• Do not have stereoacuity
• Can occur with intermittent squint
• A/w good vision or mild amblyopia
• Amount of pseudofoveal offset called angle of anomaly

25. Subjective angle (SA)- amount in degrees examiner
must move amblyoscope to allow patient to see 2
pictures superimposed, measured under binocular
viewing
Objective angle (OA)- measured by alternating target
presentaion till there is no refixation, measured
during monocular viewing

26. • When angle of anomaly = angle of squint(objective
angle), it is harmonious ARC
• When angle of squint does not match location of
pseudofovea, it is unharmonious ARC

27. ARC with right
esotropia

28. ARC as tested with Bagolini lenses

29. Large regional suppression
• Large angle strabismus or severe U/L image blur
patients develop large suppression scotoma
• These patients will have no binocularity, peripheral
fusion or ARC
• Can be intermittent

30. Worth 4 dot in
patient of
large
suppression
scotoma

31. Horror Fusionis
• Normal sensory and motor fusion once established, usually
permanent
• Binocular fusion can be lost if there is severe, sustained
abnormal visual stimulation
• If this occurs late in visual development or adulthood, patient
is too old to suppress
• Inability to fuse or suppress causes diplopia called horror
fusionis
• Can occur with anti-suppression therapy

32. Sensory Tests
• Diplopia tests
 Most dissociating
1. Maddox rod
2. Dark red filter
3. Worth 4 dot with room lights out
 Least dissociating
1. Bagolini striated lenses

33. • Maddox rod test
• Identifies horizontal, vertical and torsional deviations
• Most dissociating as image projected to each eye are totally
different
• Orthophoria and harmonious ARC- streak of light passes
through penlight
• Can be performed only if there is no suppression

34. Maddox rod test

35. Red Filter Test
• Place red glass over one eye and fixate on a single light
source
• Patients with orthotropia and NRC will see one
pinkish red light
• Esotropia with NRC causes uncrossed diplopia and
EXT causes crossed diplopia, neutralization of
deviation causes disappearance of diplopia

36. • Patient with ARC will also see one light even in presence of
squint, neutralization of deviation causes diplopia
• Patient with suppression will see only one light, white or red
• Patient with alternate fixation will see alternately red and white
light
• Test can be made more dissociating by using denser red color or
turning down the lights

37. Red Filter Test In NRC and ARC

38. Red filter test in patient with RE suppression

39. Worth 4 dot test
• Worth 4 dots separated by 6°at near(at 1/3m) and by
1.25° for distance( at 6m)
• In dark, white light is the only binocular fusion target
• In brighter illumination patient can see room
environment with strong fusion clues, hence testing
in dark more dissociating

40. • Normal response- is seeing 4 lights, 2 red and 2 green or 1 red,
2 green and 1 light flickering between red and green
• Acquired squint and diplopia- will see 5 lights, 3 green and 2
red
• Cortical suppression- will see 3 green or 2 red
• Large scotoma- suppress both distance and near worth 4 dot
test
• Monofixation syndrome- fuse near but suppress distance
worth 4 dot test

42. Bagolini Lenses
• Clear lenses with a linear scratch through center of
the lens providing a streak of light on retina
• Placed obliquely at 45° and 135°
• Provide free binocular view without dissociation

43. Orthotropia and NRC, harmonious ARC – will see a
cross
Large regional suppression – will see only 1 line
Monofixation syndrome- will see a cross with central
gap
NRC, ET and diplopia- will see a “V”
NRC, XT and diplopia- will see a “A”

44. Bagolini Lens Test

45. Haploscopic Tests
• In diplopia tests, there is 1 stationary fixation target
viewed by both eyes while in haploscopic tests, 2
fixation targets which can be moved separately are
used

46. • Mirrors placed in front of each eye angled so that RE sees
right temporal side and LE sees left temporal side
• Transparent picture slides placed in front of each eye
• Can measure fusional vergence amplitude, angle of deviation,
area of suppression, retinal correspondence and torsion
Amblyoscope

47. • Subjective angle (SA)-
• Amount in degrees examiner must move
amblyoscope to allow patient to see 2 pictures
superimposed, measured under binocular viewing
• Objective angle (OA)-
• Measured by alternating target presentaion till there
is no refixation, measured during monocular viewing

48. • Strabismus with NRC and diplopia- SA=OA
• NRC and large regional suppression- no SA
• Monofixation syndrome- SA measured by stimulating
peripheral retina
• Harmonious ARC- significant OA but SA zero, ∴ OA = angle
of anomaly
• Unharmonious ARC- pseudofovea does not compensate for
objective deviation

53. • Each fovea individually marked during monocular viewing with
linear stroke light that bleaches retina, causes linear afterimage
shadow for 10sec
• Center of light masked to spare fovea ∴ line has break in middle
• NRC with any type of tropia- see a cross
• ARC- each fovea has monocular afterimage but binocularly
afterimage perceived as coming from peripheral visual field
Afterimage Test

54. Steps Of After Image Test

55. Perception of
after image test

56. Other tests for suppression and
fusion
• Vectographic test
• 2 superimposed polarized slides of letters projected
onto an aluminized screen
• Patient reads while wearing polarized glasses
• Some letters seen only with RE and some with LE,
∴ in suppression, letters projected to suppressed eye
not seen

57. Vectographic Test

58. Four PD Base Out Test
• Normally 4 PD base out test induces fusional
convergence
• 2 movements seen normally
• 1st- version movement of BE in direction of apex
of prism
• 2nd- fusional vergence of eye without prism
towards the nose

59. • Motor fusion and large regional suppression- no
movement when prism over nondominant eye,
version in direction of apex when prism over fixing
eye
• Monofixation- no movement when prism over
nondominant eye, version and fusional convergence
in some when prism over fixing eye

60. 4D prism base out test in RE esotropia

61. Treatment Of Suppression
• Proper refractive correction
• Occlusion therapy
• Alignment of visual axes
• Antisuppression exercises

62. • Thank You