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Squint Flashcards

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1
Q

What is Binocular Single Vision (BSV)?

A

The ability to fuse images from both eyes simultaneously and perceive binocular depth

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2
Q

What are the requirements for normal binocular vision development?

A
  1. Proper eye alignment (no strabismus)
    1. Equal image clarity
    2. Presence of sensory and motor fusion
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3
Q

What is Retinomotor value?

A

The functional value assigned to each retinal element
which is proportional to its distance from the fovea
Guides the amplitude of saccadic movement to look at it.

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4
Q

What is Common Relative Subjective Visual Direction?

A

The shared visual direction for object points that stimulate both foveae simultaneously, belonging equally to the right and left fovea

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5
Q

What are Corresponding Retinal Points?

A

Retinal elements of both eyes that have a common visual direction

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6
Q

What is Normal Retinal Correspondence (NRC)?

A

A state where:
• Fovea corresponds with fovea
• Nasal elements of one eye correspond with temporal elements of the other, and vice versa.

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7
Q

What are the requirements for normal binocular vision development?

A
  1. Proper eye alignment (no strabismus)
    1. Equal image clarity
    2. Presence of sensory and motor fusion
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8
Q

What is Abnormal Retinal Correspondence (ARC)?

A

A condition where the fovea of one eye corresponds with an extrafoveal retinal area in the other eye, allowing single binocular vision despite a manifest squint.

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9
Q

Can the cover test reveal ARC?

A

Yes — under monocular conditions, central fixation is retained by the fovea, which is the basis of the cover test.

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10
Q

What is Sensory Fusion?

A

The brain’s central process of unifying corresponding retinal images into a single visual percept.

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11
Q

Requirements for Sensory Fusion?

A

Images on corresponding retinal areas
Same size
Same brightness
Same sharpness

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12
Q

What is the hallmark of Retinal Correspondence And Retinal Disparity?

A

Single vision.

Double vision (diplopia).

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13
Q

What is Motor Fusion?

A

The ability to align the eyes to maintain sensory fusion
primarily controlled by extrafoveal retinal periphery.

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14
Q

Does motor fusion operate when the images of a fixated visual object fall on the fovea of each eye?

A

No — there is no stimulus for motor fusion in that case.

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15
Q

Amblyopia definition

A

.U/L or rarely B/L decrease in BCVA
.Due to Vision Deprivation &or Abnormal blBinocular Interaction
.No identifiable pathology of eye or visual pathway

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16
Q

Types of Amblyopia

A

Strabismic
Anisometropic
Stimulus deprivation
Bilateral Ametropic
Meridional

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17
Q

Diagnosis of amblyopia is made when____

A

In the absence of organic lesion
Difference in BCVA
-2 Snellens lines or more

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18
Q

Crowding phenomenon

A

VA better reading a single letter than letters in a row

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19
Q

Treatment of Amblyopia

A

Occlusion
Penalization

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20
Q

What is Brown Syndrome?

A

A mechanical restriction, typically of the superior oblique tendon at the trochlea, causing limitation of elevation in adduction.

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21
Q

Is Brown Syndrome usually congenital or acquired?

A

It is usually congenital but can be acquired (trauma, inflammation, surgery).

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22
Q

Key movement limitation in Brown Syndrome?

A

Deficient elevation in adduction.

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23
Q

How is elevation deficiency different in adduction vs. abduction in Brown Syndrome?

A

Marked in adduction, minimal or absent in abduction.

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24
Q

Forced duction test in Brown Syndrome?

A

Positive (restricted).

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25
What strabismus pattern is associated with Brown Syndrome?
V-pattern with divergence in upgaze.
26
Wilson’s diagnostic features of Brown Syndrome (must have 6)?
1. Deficient elevation in adduction 2. Less elevation deficiency in midline 3. Minimal or no elevation deficiency in abduction 4. Minimal or no SO overaction 5. V-pattern divergence in upgaze 6. Restricted forced ductions “EEEOVF”
27
Clinical features of mild Brown Syndrome?
**Limitation of elevation in ADDUCTION** No hypotropia in primary position no down-shoot in adduction.
28
Clinical features of moderate Brown Syndrome?
No hypotropia in primary position but **down-shoot** in adduction.
29
Clinical features of severe Brown Syndrome?
Hypotropia in primary position, down-shoot in adduction, chin-up posture, face turn away from affected eye.
30
Head posture in Brown Syndrome?
Chin elevation and face turn away from affected eye.
31
Differential diagnosis of Brown Syndrome?
Inferior oblique palsy double elevator palsy congenital fibrosis syndrome blow-out fracture of the orbital floor.
32
How to differentiate Brown Syndrome from IO palsy?
Brown: Mechanical restriction, positive forced duction. IO palsy: Neurogenic, negative forced duction.
33
Treatment of congenital Brown Syndrome?
Usually none if binocular function and acceptable head posture are maintained; may improve spontaneously.
34
Treatment of acquired Brown Syndrome?
Depends on cause: steroids (inflammatory), surgery (SO tendon lengthening) if symptomatic.
35
What is considered normal ocular alignment up to 4 months of age?
Infrequent episodes of convergence are normal up to 4 months; after that, any ocular misalignment is abnormal.
36
What is early-onset (essential infantile) esotropia?
An idiopathic esotropia developing within the first 6 months of life in an otherwise normal infant, with no significant refractive error or limitation of ocular movements.
37
What is the usual angle of deviation in early-onset esotropia?
Fairly large (>30Δ) and stable.
38
How does fixation typically present in early-onset esotropia?
Alternating fixation in the primary position. Cross fixation
39
What is cross-fixation in early-onset esotropia?
Child uses the left eye in right gaze and the right eye in left gaze, giving a false impression of bilateral abduction deficits.
40
How can true abduction be demonstrated?
By doll’s head manoeuvre, rotating the child, or by uniocular patching to unmask abduction.
41
What type of nystagmus is common in early-onset esotropia?
Usually horizontal latent or manifest latent nystagmus.
42
What is latent nystagmus (LN)?
Nystagmus that appears when one eye is covered; fast phase beats towards the fixing eye.
43
What is manifest latent nystagmus (MLN)?
Nystagmus present with both eyes open, but amplitude increases when one eye is covered.
44
What is the typical refractive error in early-onset esotropia?
+1 to +2 D, normal for age.
45
What is asymmetry of OKN (optokinetic nystagmus) in early-onset esotropia?
Nystagmus response is reduced in one direction.
46
What secondary features may develop in early-onset esotropia?
Inferior oblique overaction and Dissociated Vertical Deviation (DVD).
47
What percentage of children with early-onset esotropia develop DVD by age 3?
About 80%.
48
What are key differential diagnoses for early-onset esotropia?
Bilateral congenital sixth nerve palsy, sensory esotropia due to organic disease, nystagmus blockage syndrome, Duane and Möbius syndromes, strabismus fixus.
49
When should surgical alignment be performed?
Within 4 months of the onset of constant esotropia after correcting amblyopia and refractive error.
50
What is the initial surgical procedure for angles >30Δ but <50Δ?
Bilateral medial rectus recession or unilateral medial rectus recession with lateral rectus resection.
51
What is the surgical option for angles >50Δ?
Bilateral medial rectus recessions plus one lateral rectus resection.
52
What is the surgical option for angles >65Δ?
Bilateral medial rectus recessions plus bilateral lateral rectus resections.
53
Why are medial rectus recessions of more than 6.5 mm avoided?
They lead to late overcorrections.
54
What is the goal of surgery for early-onset esotropia?
Alignment within 8Δ, allowing peripheral fusion with central suppression.
55
What complication may appear at ~2 years of age?
Inferior oblique overaction, often becoming bilateral within 6 months.
56
What procedures are used for inferior oblique overaction?
Disinsertion, recession, or myectomy.
57
What is Dissociated Vertical Deviation (DVD)?
Up-drift with extorsion of one eye when under cover or inattention, reversing when uncovered, usually bilateral.
58
When is surgery indicated for DVD?
For psychosocial reasons or large deviations.
59
What surgical options exist for DVD?
Superior rectus recession with/without posterior fixation sutures, inferior rectus resection or tuck, inferior oblique anterior transposition.
60
What percentage develops amblyopia after surgery?
About 50% due to unilateral fixation preference.
61
When should accommodative esotropia be suspected postoperatively?
If eyes are initially straight after surgery but later become convergent again.
62
How should accommodative element be monitored?
By regular refraction and optical correction if required.
63
What condition must inferior oblique overaction be distinguished from?
Dissociated Vertical Deviation (DVD).
64
What is the goal of surgery for early-onset esotropia?
Alignment within 8Δ, allowing peripheral fusion with central suppression.
65
What is the horopter?
Locus of points in space stimulating corresponding retinal points
66
What is Panum’s fusional area?
Region around horopter where images fall on non-corresponding but near-corresponding points, still seen single
67
Horopter: nature
Geometric / theoretical
68
Panum’s fusional area: nature
Physiological / functional
69
Horopter: shape
Line/curve (theoretical = Vieth–Müller circle)
70
Panum’s fusional area: shape
Zone/area around horopter
71
Horopter: location
Passes through fixation point and nodal points
72
Panum’s fusional area: location
Extends slightly in front of and behind horopter
73
Horopter: perceptual outcome
Images seen single without need for fusion
74
Panum’s fusional area: perceptual outcome
Images seen single due to cortical fusion
75
Horopter: tolerance
No disparity (exact correspondence only)
76
Panum’s fusional area: tolerance
Allows small horizontal > vertical disparity
77
Horopter: function
Provides reference for binocular single vision
78
Panum’s fusional area: function
Explains fusion of small disparities and diplopia with large disparities
79
Mnemonic for Horopter
CRPF In shape of Line or Curve Passing at Fixed Nodal pts Seen singly in a plane With no disparity Providing reference for BSF Explaining CRP
80
Mnemonic for BSV question
BRAG that V R CommON RSVP Correspondence
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