2. Theories – Historical
Theories
– Innervational imbalance between convergence and
divergence (Duane)
• Divergence: active or passive
– Active- Divergence burst cells
» Mesencephlic reticular formation (near
oculomotor nucleus) in monkeys
– Passive
» Relaxation of accommodation
» Absence of simultaneous contraction of LR
– Anatomic (Bielschowsky)
– Abnormal position of rest
3. • Theory of Defective fusion (Worth)
• Hemiretinal suppression (Knapp and Jampolsky).
• Uncorrected refractive errors (Donders)
4. Exotropia
Exodeviation less common than esodeviation
in West
F > M
Exodeviation found areas with more sunlight
Frequently seen in neonatal period – resolves
Redevelops before 2nd year of life (35-40%)
Often positive family history
Common with facial asymmetry and
neurological defects
5. Classic presentation
• Begins as exophoria – shortly after birth
– Binocular fixation and NRC
– Progresses to intermitent exotropia X(T)
• Adults have diplopia
• Children develop hemiretinal suppression
• Periods of phoria and tropia
• Frequent pseudo-oblique dysfunction
– Associated with tight laterals
– Called “leash phenomenon”
6. Natural History
• Progression occurs in 35% - 75% of pts.
• Improvement occurs in 16% - 65%
• Factors:
– Age
• Decreasing tonic convergence
– Suppression sets in
• “The key to unlocking fusion”
– Worsening seen at distance first
– Decreased accommodation
– Orbital divergence from maturation of facial
features
8. Intermittent Exotropia
• Onset
– Infancy to 5 years
– May progress
• Noticed by the parents when the child is tired or ill or
during daydreaming
• very little visual symptoms
• Transient diplopia or asthenopia especially after
prolonged reading.
• Diplophotophobia, or closure of one eye in bright
light is
a very common symptom
9. Phase - Deviation -Sensory
I Exophoria at distance,
orthophoria at near Asymptomatic
II Intermittent exotropia
for distance, Symptomatic for
orthophoria/ exophoria at near distance
III Exotropia for distance,
exophoria or BV for near,
intermittent exotropia at near. suppression scotoma
for distance
IV Exotropia at distance as
well as near Lack of binocularity.
10. classification
Burian has classified IDS into 4 types based on
measurements of the distance and near
deviation.
1. Basic type: distance deviation and near
deviation are within 10 PD of each other.
2. Divergence excess type: distance
measurement 10 PD or greater than the near
deviation.
11. 3. Convergence insufficiency type: near
deviation 10 PD greater than the distance.
4. Simulated or pseudo divergence excess
type:
near deviation is less than the distance
deviation but it increases to within10 PD of
distance deviation after 30 – 60 minutes of
monocular occlusion
12. Kushner has further modified this
classification by taking into account AC/A
ratio.
He introduced two new groups
1)Pseudo divergence with tenacious
proximal fusion (near deviation increase
after 60 minutes of monocular occlusion)
2)Divergence with High AC/A ratio.
13. Basic Type XT
• Burian and Kushner
– Distance = Near
– Normal AC/A
14. Convergence Insufficiency
• Burian
– Near 10 PD more than
at Distance
• Kushner
– Low AC/A
– Fusional convergence
insufficiency
– Pseudo-convergence
insufficiency
• Patching increases
distance deviation to
match near
15. Divergence Excess
• Burian
– Distance 15 PD more
than at Near
• Kushner
– True Divergence
Excess
– Simulated
– Tenacious proximal
fusion
16. Examination
• Comprehensive ophthalmologic
examination
• Check fusion and stereopsis before
occluding eyes for visual acuity examination
– So ARC and suppression do not set in
• Check stereo acuity for distance and for
near
• Versions
• Cover test
17. Examination
• Important to obtain cycloplegic retinoscopy
• “Pseudoamblyopia”
– Exodeviation often manifests with fixation
preference
– Misinterpreted as evidence of amblyopia
– Excellent fusion and stereopsis when eyes are
aligned
– Patching may worsen situation and induce
iatrogenic loss of fusion and stereopsis
18. Measurement of the deviation
1. Prolonged alternate cover test:
To maximally suspend the tonic fusional
convergence during the ACT the occluder
must be placed in front of either eye for a
sufficient duration and alternated .
2. Patch Test: Mono ocular occlusion for 30
– 60 minutes
It differentiates true and pseudo divergence
excess
19. 3. High AC/A ratio (Lens gradient test / +3.0
D test): This test helps in diagnosing the
patients with divergence excess due to a
high AC/A ratio. In such cases the near
deviation increases by 20 PD or more on
addition of a +3.0 D lens.
4. Far distance measurement: Apart from
the near and distance (20 feet)
measurement, the deviation must also be
measured for far distance (100 – 200 feet).
20. XT response patterns with tests
• Occlusion
– Distance deviation increases
– If Near = Distance with occlusion
• Simulated divergence excess
– Near<distance
• +3.00 lens
– Near= Distance
» High AC/A
– Near< Distance
» True divergence excess
21. Fusional Control
The level of fusional control is an
baseline evaluation and
indicator of progression.
1.Home control: percentage of waking
hours when the squint is noticed by the
parents .
Deviation manifesting more than 50% of
waking hours indicates poor control.
.
22. 2. Clinical control: fusional control can be
assessed using cover test
a. Good control: The patient resumes fusion
rapidly without blinking or re-fixation.
b. Fair control: Patient blinks or re-fixates to
control the deviation.
c. Poor control: Patient breaks
spontaneously without any disruption
23. 3. Stereo-acuity: (mainly for distance)
Indicator of both control of the deviation and
deterioration of fusion.
The distance stereoacuity can be assessed
using
Random dot E test or
Mentor B- Vat tests.
24. The unique features of IDS that make its
management controversial are
1. Variable angle of deviation
2. Unpredictable course of progression (i.e.
deterioration of control)
3. Good binocularity (for near till late)
4. Rarity of amblyopia or ARC (abnormal
retinal correspondence)
25. • Treatment
1) Non-Surgical
2) Surgical
Goal of Non-surgical treatment is
-To improve the neuro-physiological
vergence control mechanism to
• decrease the frequency of the manifest
phases
• prevent the progression from latent to
constant squint.
26. Ideal candidates for conservative therapy
1. Young patients (4-5 years old)
2. Phase I or II.
3. Fair or better control of deviation.
4. Angle of deviation d”20 – 25 PD.
These patients must be monitored closely
for any signs of progression.
27. Treatment-Non surgical
• Correction of refraction
– Over-minus
• To produce High AC/A
• XT usually recurs
– Hyperopia
• Mild to moderate – no treatment
• High – treatment (partial to full plus)
• Prisms
– Not generally used, base in prisms
– Decreases convergence amplitude
• Occasionally slow weaning from prism
– may improve convergence amplitude
28. Treatment
• Patching
– Preoperatively
• May reduce frequency and magnitude of deviation
– XT becomes X(T)
– X(T) becomes X
– Unknown mechanism
• Speculation
– Reduces depth of suppression
– XT typically recurs when patching stopped
29. Treatment
• Orthoptics
– Antisuppression treatment.
• Controversial
– Diplopia awareness
• May lead to intractable diplopia
• “Orthoptic cripples”
– Fusional amplitudes
• Pencil pushups
• Convergence amplitudes
• Observation
– Frequency
30. Signs of Progression
1. Gradual loss of fusional control
evidenced by the increasing frequency of
the manifest phase of squint
2. Development of Secondary convergence
insufficiency
3. Increase in size of the deviation
4. Development of suppression as indicated
by absence of diplopia during manifest
phase
5. Decrease of Stereoacuity
31. Surgical Treatment
• The primary aim for any squint surgery is
the
Restoration of appropriate binocular function
Improve cosmesis.
32. INDICATIONS
• Large angle deviations (> 20 PD)
• Documented worsening of the deviation
(Signs of progression)
• Deviation present for more than 50% of
waking hours.
• Failure of conservative therapy.
33. The Newcastle Control Score (NCS)
It differentiates and quantifies the various
levels of severity in IXT
NCS total-Home+Clinic near+Clinic distance
3 groups
1. Well controlled (NCS 2): high probability
of stable course or spontaneous recovery.
Candidates for vision therapy
34. 2. Poorly controlled (NCS 7 or more):
Definite surgical intervention needed, as
spontaneous recovery is unlikely.
3. Moderate control (NCS 3- 6) show better
results with surgical management as
compared to conservative approach.
35. NEW CASTLE SCORE Component
• Home control
0. Squint eye do sure never noticed
1. Squint eye do sure seen occasionally
(<50% of time child observed) for distance
2. Squint eye do sure seen frequently
(>50% of time child observed) for distance
3. Squint eye do sure seen for distance
& near fixation
• Clinic control near
0.Manified only after cover test and resumes
fusion without need for blink or refixation
1. Blink or refixate to control after CT
2. Manified spontaneously or with any form of
fusion disruption without recovery
36. Timing of surgery
Early surgery may offer to
- prevent the development of sensory changes
- risk of consecutive esotropia leading subsequently to
monofixation.
Delayed surgery
-advantage of accurate diagnosis and
- quantification of the amount of deviation and
- to avoid consecutive esotropia.
For small angle deviations (< 20 PD) and
for young children (< 4 years)
Defer the surgery and
Use vision therapy with a close watch for signs of progression.
37. SURGERY OF CHOICE
• Pure divergence excess type- bilateral
lateral rectus recession
• Simulated divergence excess type and
basic types - unilateral recess- resect
procedure.
38. Goal of surgery
Visually immature infant: avoid consecutive esotropias
(can have the consequences of amblyopia and loss of
binocularity)
Older children, who develop intermittent exotropia after
age 10 years, aim for orthotropia on the first
postoperative day.
Adults with longstanding IXT will tolerate under
correction, but will have symptomatic diplopia when
overcorrected.
39. Surgical Success
Anatomical Cure: Alignment within 8 – 10
PD of orthotropia.
Functional Cure: Near Stereopsis between
40 – 60 sec of Arc
40. UNDERCORRECTION
Patients with
• large angle deviations
• high myopic refractive error
• Undiagnosed oblique muscle overaction
• small vertical deviations
41. OVER CORRECTION
• Small over correction of up to 10 – 15 PD in a
visually mature patient is acceptable
• A high AC/A ratio and
• Undiagnosed lateral incomitance are the risk
factors for larger angle esodeviation.
• A 6 – 8 week trial of conservative measures
like part time occlusion, bifocals (high AC/A ratio) or
neutralizing prisms may be tried before resorting to
surgery.
42. • Overcorrection
– ET > 6months
– Significant risk of amblyopia
– Risk for monofixation syndrome
– Treatment:
• Maximum plus in Rx
• Prisms for deviation
–Fresnel prism early ,then built in
–Fusion restoration
–Wean slowly of prism
• Reoperation(BMR)
43. Convergence Insufficiency
• XT greater at near
• Asthenopia with near work
• Decreased convergence amplitudes
• Uncommon < 10 years of age
• Females > males
• Treat with pencil push ups
• May need surgery
– BMR recess
44. Conclusion
• Duration of constant strabismus is the
controlling factor
– Aligned within 12 months of the onset of strabismus
• Do well
– Those whose strabismus persisted beyond 12
months
• Do very poorly
• Better the sensory outcome the greater
likelihood of long-term stability of the alignment
