1
Q
What is a comitant deviation?
A
A deviation where the angle remains the same in all gaze directions
This indicates that the deviation does not change with different positions of gaze.
2
Q
How are comitant deviations classified?
A
Based on distance (D) vs near (N) deviation
This classification helps in understanding the nature of the deviation.
3
Q
How are exodeviations classified by D vs N?
A
- D > N → Divergence Excess (DE)
- D = N → Basic Exophoria
- D < N → Convergence Insufficiency (CI)
These classifications indicate the relationship between distance and near deviations.
4
Q
What is convergence insufficiency (CI)?
A
Exo greater at near
Associated with low AC/A ratio leading to poor convergence response.
5
Q
Why does CI occur?
A
Accommodation does not generate enough convergence → exo at near
This results in the eyes drifting outward when focusing on near objects.
6
Q
What is divergence excess (DE)?
A
Exo greater at distance
Often associated with high AC/A ratio.
7
Q
What is basic exo deviation?
A
Exo equal at distance and near
No strong AC/A association.
8
Q
How is basic exo typically managed?
A
Primarily vision therapy, not surgery or lenses
Vision therapy focuses on improving convergence abilities.
9
Q
How are esodeviations classified by D vs N?
A
- D > N → Divergence Insufficiency (DI)
- D = N → Basic Esophoria
- D < N → Convergence Excess (CE)
This classification helps in diagnosing the type of esodeviation.
10
Q
What exotropias are NOT related to AC/A ratio?
A
- Infantile exotropia
- Secondary exotropia (due to vision loss)
- Microexotropia
These conditions have different underlying mechanisms.
11
Q
What history suggests incomitancy or pathology?
A
- Recent onset
- Diplopia
- Trauma
- Surgery
- Neurological or thyroid disease
These factors may indicate a more serious underlying condition.
12
Q
What investigations are used if incomitancy is suspected?
A
- Hess screen
- Suppression testing
- Full ocular health exam
These tests help assess the nature of the deviation.
13
Q
What is convergence insufficiency (CI)?
A
An exo deviation that is greater at near than distance (N > D) due to a low AC/A ratio
This means accommodation produces insufficient convergence.
14
Q
What is the key mechanism in CI?
A
Accommodation does not drive enough convergence → eyes drift outward at near
This leads to symptoms associated with CI.
15
Q
What are the main symptoms of CI?
A
- Headaches and eyestrain (asthenopia)
- Blur or diplopia at near
- Difficulty concentrating/reading
- Words moving on page
These symptoms can significantly affect daily activities.
16
Q
What are the key clinical signs of CI?
A
- Exo greater at near than distance
- Receded NPC (>10 cm)
- Low PFV (positive fusional vergence)
- Reduced binocular accommodation
- Often no specific refractive error pattern
These signs help in diagnosing CI.
17
Q
Why is NPC receded in CI?
A
Because the patient cannot sustain convergence at near
This indicates a deficit in convergence ability.
18
Q
Why is PFV reduced in CI?
A
PFV represents convergence ability, which is the primary deficit in CI
This reduction leads to the symptoms experienced by patients.
19
Q
What is the prevalence of CI?
A
~3% of the population (varies with criteria)
This indicates how common CI is among the general population.
20
Q
What is an important differential diagnosis for CI?
A
Convergence paralysis
This condition can present similarly but has different underlying causes.
21
Q
How do you differentiate CI from convergence paralysis?
A
- CI → gradual, chronic onset
- Convergence paralysis → sudden onset, may indicate neurological pathology
Understanding the onset helps in diagnosis.
22
Q
What do you assess during cover testing in CI?
A
- Phoria vs tropia
- Recovery speed
- Presence of vertical deviation
- Difference between distance and near
These assessments provide insight into the nature of the deviation.
23
Q
What is Sheard’s Criterion?
A
Fusional reserve should be ≥ 2× the phoria to maintain comfortable vision
This criterion helps in evaluating the adequacy of fusional reserves.
24
Q
Why is Sheard’s Criterion important in CI?
A
CI patients often fail it due to insufficient PFV, explaining symptoms
This highlights the need for effective treatment.
25
What are the **treatment options for CI**?
* Correct refractive error
* Vision therapy (most effective)
* Base-in prism (temporary relief)
* Minus lenses (stimulate accommodation in young patients)
* Patching (if suppression present)
* Surgery (rare)
## Footnote
These options vary in effectiveness and application.
26
What is the most effective **treatment for CI**?
Office-based vision therapy with home reinforcement
## Footnote
This approach has shown significant improvement in symptoms.
27
Why is **vision therapy effective** in CI?
It improves:
* PFV (convergence ability)
* NPC
* Symptoms
## Footnote
This multifaceted approach addresses the core issues of CI.
28
Why are **prism glasses** not very effective in CI?
They do not improve underlying convergence ability → only temporary relief
## Footnote
This makes them less effective for long-term management.
29
Why can **minus lenses** help in CI?
They stimulate accommodation, which increases AC-driven convergence
## Footnote
This can provide some relief for patients.
30
Why must **prism use** be monitored?
Risk of prism adaptation, reducing effectiveness over time
## Footnote
This necessitates careful management of treatment.
31
What is the link between **CI and concussion**?
CI is common post-concussion (~50%)
Associated with longer recovery time
## Footnote
This highlights the importance of assessing CI in concussion patients.
32
What is **divergence excess (DE)**?
An intermittent exotropia where the deviation is greater at distance than near (D > N), often associated with a high AC/A ratio.
## Footnote
DE is characterized by a greater outward drift of the eyes at distance.
33
What is the key mechanism in **DE**?
High AC/A → relatively less convergence demand at distance, so the eyes drift outward more.
## Footnote
This mechanism explains why DE is more pronounced at distance.
34
What are the main **clinical signs** of DE?
* Exotropia greater at distance (~20–30Δ)
* Reduced or absent distance stereopsis
* Often suppression instead of diplopia
* Eye closure in bright light
* No consistent refractive error pattern
## Footnote
These signs help in diagnosing DE.
35
Why do patients with **DE** often not report **diplopia**?
Because they develop suppression, especially at distance.
## Footnote
Suppression is a common adaptive response to avoid double vision.
36
Why might patients close one eye in **bright light**?
To reduce diplopia/confusion when fusion breaks down in high visual demand conditions.
## Footnote
This behavior is a compensatory mechanism.
37
How can **DE** present across distances?
* Large XT at distance
* Smaller XT or phoria at near
* May even become eso at very near (due to high AC/A)
## Footnote
This variability is important for diagnosis and treatment planning.
38
What is the difference between **true DE** and **simulated DE**?
* True DE → near deviation remains smaller
* Simulated DE → near deviation increases after fusion is broken
## Footnote
Understanding this difference is crucial for appropriate management.
39
How do you differentiate **true vs simulated DE**?
Using a prolonged cover test:
* Near deviation increases → simulated DE
* No change → true DE
## Footnote
This test helps clarify the nature of the deviation.
40
Why is this differentiation **important**?
Because treatment approach differs, especially regarding surgery and management planning.
## Footnote
Accurate diagnosis influences the choice of intervention.
41
What additional tests can help assess **DE**?
* Minus lens test (improves control)
* Distance >10 m testing
* Crossover point
* ARC testing
## Footnote
These tests provide further insights into the patient's condition.
42
What are the main **treatment options** for DE?
* Correct refractive error
* Vision therapy (anti-suppression, fixation, vergence training)
* Prism (if needed)
* Minus lenses (short-term)
* Patching
* Surgery (if severe)
## Footnote
Treatment options vary based on severity and patient needs.
43
Why are **minus lenses** used in DE?
They stimulate accommodation → increase convergence, helping control exo deviation.
## Footnote
This approach leverages the relationship between accommodation and convergence.
44
Why must **minus lenses** be used cautiously?
They can affect refractive development, especially in children.
## Footnote
Careful monitoring is essential to avoid negative impacts.
45
What is the role of **patching** in DE?
Reduces suppression
Helps preserve stereopsis
Can delay or avoid surgery
## Footnote
Patching is a non-invasive method to improve visual function.
46
When is **surgery** indicated in DE?
* Large deviation (>30Δ)
* Poor control or cosmesis
* Persistent binocular dysfunction
## Footnote
Surgical intervention is considered when conservative measures fail.
47
What is the role of **vision therapy** in DE?
Improve control
Reduce suppression
Train vergence with large jumps
## Footnote
Vision therapy aims to enhance visual coordination and reduce symptoms.
48
What is **convergence excess (CE)**?
An eso deviation where near > distance (N > D) due to a high AC/A ratio, meaning accommodation causes excessive convergence.
## Footnote
CE is characterized by an inward drift of the eyes at near.
49
What is the key mechanism in **CE**?
Accommodation → too much convergence → eso at near.
## Footnote
This mechanism explains the nature of the deviation.
50
What is the management approach for **CE**?
* Correct ametropia
* Prescribe near add (bifocals/PALs) → reduce accommodative demand
* Vision therapy → improve negative fusional vergence (NFV)
## Footnote
These strategies aim to alleviate symptoms and improve visual function.
51
Why are **near adds** used in CE?
They reduce accommodation → reduce AC-driven convergence → decrease near eso.
## Footnote
This approach helps manage excessive convergence.
52
Why is **NFV training** important in CE?
Patients need better divergence ability to counteract excessive convergence.
## Footnote
Training helps improve visual stability.
53
What is a key clinical sign used when prescribing **near adds**?
Normalising MEM lag and improving fusional balance.
## Footnote
These indicators guide the effectiveness of the prescription.
54
What defines **divergence excess (DE)**?
Exo deviation greater at distance than near (D > N), typically by ≥10Δ, often with high AC/A.
## Footnote
This definition is crucial for understanding the condition.
55
What are typical **findings** in DE?
* Distance exotropia (intermittent)
* Suppression at distance
* Normal fusion at near (latent NRC)
* Good near stereopsis
* Normal NPC
* Normal PFV
* High AC/A ratio
## Footnote
These findings assist in diagnosing DE.
56
Why is **stereopsis normal at near** in DE?
Because alignment is better at near → fusion maintained.
## Footnote
This phenomenon is important for understanding visual function.
57
Why is **suppression common at distance** in DE?
To avoid diplopia when exotropia becomes manifest.
## Footnote
Suppression is a protective mechanism against double vision.
58
What is the significance of **vertical deviation** in DE?
~45–55% show vertical deviation when exotropia manifests.
## Footnote
This statistic highlights the complexity of DE.
59
What does a **high AC/A ratio** indicate in DE?
Accommodation strongly influences convergence → can be used therapeutically.
## Footnote
This relationship is key in managing DE.
60
What is the standard **management approach** for DE?
* Correct ametropia
* Vision therapy (VT):
* Monocular skills → anti-suppression → accommodation → vergence
* Home training (HTS)
## Footnote
A comprehensive approach is necessary for effective management.
61
Why does **vision therapy** help even though it is done at near?
Improves overall vergence control, which transfers to distance stability.
## Footnote
This transfer effect is beneficial for long-term outcomes.
62
What is the role of **overminus lenses** in DE?
Stimulate accommodation → increase convergence → reduce exo deviation.
## Footnote
This method leverages the relationship between accommodation and convergence.
63
Why are **overminus lenses** effective in DE?
Because of high AC/A ratio, so accommodation strongly drives convergence.
## Footnote
This effectiveness is crucial for managing DE.
64
What are the **risks** of overminus lenses?
May affect refractive development, especially in children.
## Footnote
Monitoring is essential to avoid adverse effects.
65
When is **surgery** considered in DE?
* Large deviation
* Poor control
* Failure of conservative treatment
## Footnote
Surgical options are explored when other treatments are insufficient.
66
What is **overminus therapy** and why is it effective in DE?
Using extra minus lenses to stimulate accommodation → increases AC-driven convergence → reduces exotropia
## Footnote
Overminus therapy is particularly effective in DE due to its mechanism of enhancing convergence through accommodation.
67
Why is **overminus therapy** particularly effective in DE?
Because DE has a high AC/A ratio, so even small increases in accommodation produce large increases in convergence
## Footnote
This relationship between accommodation and convergence is crucial for managing exotropia.
68
What is a key limitation of **overminus therapy**?
May affect refractive development (myopia progression) → use cautiously, especially in children
## Footnote
Monitoring is essential to prevent potential adverse effects on vision development.
69
What is the **Intermittent Exotropia (IXT) Control Scale**?
A grading system to assess control of exotropia
## Footnote
This scale helps clinicians evaluate the severity and control of the condition.
70
How is the **IXT Control Scale** graded?
* 5 → constant XT
* 4 → XT >50% of time
* 3 → XT <50% of time
* 2 → recovery >5 sec
* 1 → recovery 1–5 sec
* 0 → recovery <1 sec
## Footnote
Each grade indicates the frequency and recovery time from exotropia.
71
What does the **IXT scale** measure clinically?
How well the patient can regain fusion after deviation
## Footnote
This measurement is critical for assessing treatment effectiveness.
72
What defines **divergence insufficiency (DI)**?
* Eso deviation greater at distance than near (D > N)
* Low AC/A ratio
* Reduced NFV at distance
## Footnote
These characteristics help in diagnosing DI.
73
What are key **symptoms** in DI?
* Intermittent horizontal diplopia at distance
* Often worse when tired
## Footnote
Symptoms can vary based on fatigue and distance.
74
What are key **clinical signs** in DI?
* Distance esotropia > near
* Reduced distance NFV
* Normal NPC
* Normal near findings
## Footnote
These signs are essential for differentiating DI from other conditions.
75
Why is **NPC normal** in DI?
Because convergence at near is not impaired → issue is divergence at distance
## Footnote
Understanding this helps clarify the nature of the problem.
76
What is the most important **differential diagnosis** for DI?
CN VI (abducens) palsy
## Footnote
Distinguishing DI from nerve palsy is crucial for appropriate management.
77
How do you rule out **CN VI palsy** in DI?
* No abduction deficit
* Comitant deviation (same in all gazes)
* Normal motility
## Footnote
These criteria help confirm the diagnosis of DI.
78
Why is **comitancy** important in this case?
It suggests a binocular vergence problem, not a nerve palsy
## Footnote
This distinction is vital for treatment planning.
79
What is first-line **management** for DI?
Prism correction (most effective)
## Footnote
Prism therapy is often the initial approach to manage symptoms.
80
How should **prism** be prescribed?
Base-out prism
Often split between both eyes
## Footnote
Proper prism prescription is key to effective treatment.
81
What is the role of **Fresnel prism**?
Temporary, adjustable prism used to trial and assess response
## Footnote
This allows for flexible management of symptoms.
82
What is the role of **vision therapy** in DI?
Limited effectiveness → may attempt to improve NFV, but often insufficient alone
## Footnote
Vision therapy may be considered but is not the primary treatment.
83
Why did VT have **limited effect** in this case?
Because DI is primarily a divergence weakness at distance, which is harder to train compared to convergence
## Footnote
This highlights the challenges in treating DI.
84
When is **surgery** considered in DI?
Persistent diplopia
Poor response to prism
## Footnote
Surgical intervention may be necessary when conservative measures fail.
510 BV
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