2. Cause of Exotropia
• In most cases cause is unknown
• Theories
– Excess divergence
– Deficient convergence
– Anatomic factors
• Familial tendency present
• Refractive errors
– Average for age unless sensory due to marked anisometropia
4. Classification According to AC/A
Deviation AC/A Example
Convergence
Insufficiency
Low X= 0, X’= 12, or
X(T)= 20, XT’=40
Basic Normal XT= XT’= 20
Divergence
Excess
High XT= 35, XT’=10
6. Secondary Exotropia
• Confusing term but still used at times
• May mean occurs following surgery for ET, or
• May mean sensory exotropia due to an
underlying condition, e.g., anisometropic
amblyopia, retinoblastoma, cataract
• Better to use either consecutive or sensory
rather than secondary to describe exotropia
11. Congenital Exotropia
• Rare
• Constant Exotropia
• Large angle
• Often associated with other neurologic defects
• Only treatment is surgical
12. Sensory Exotropia
• Poor vision in one eye leads to exotropia
• Sensory esotropia or exotropia may occur
• Causes
– Marked anisometropia
• E.g., unilateral high myopia
• Retinoblastoma (22% present with strabismus)
• Unilateral cataract
13. Sensory Exotropia: Treatment
1. Treat underlying cause if possible
• E.g. remove cataract, treat amblyopia
1. Surgery for exotropia
• Fusional outlook variable
• Small XT often best left alone
14. Convergence Insufficiency: Two
Subtypes
1. Ex= 0, Exophoria or Exotropia at near
• Low AC/A ratio
• Remote NPC
• Poor fusional convergence amplitudes
• Usually responds to convergence exercises
• Website: “ Computer Orthoptics (HTS)” exercises online
or in office vision therapy combined with home therapy
• May treat with base in prism
• Usually do poorly with surgery
15. Convergence Insufficiency: Second
Subtype
• XT at distance, larger XT at near
– Deficient accommodative convergence
– Very low AC/A ratio
– Poor response to convergence exercises
– Often undercorrected with recess LR OU
– Treatment: unilateral recess/resect or recess/tuck
16. Typical Childhood Exotropia
or Intermittent Exotropia
• Onset 6 months to 6 years of age
• Average refractive errors
• Deviation usually noted first with distance vision
• Often normal sensory pattern when eyes aligned
• Many progress through different phases
• Some remain stable and do not progress
17. Progression of Exotropia
• Phoria→ Tropia
• Distance deviation> Near deviation
• Progression more rapid under age 6, but
progression in adulthood common also(may
present with diplopia)
19. Typical Childhood Exotropia
Phase 1
• X (T) present, Ex’ = 0
• Mostly controlled
• Symptoms often present
– Diplopia: may close one eye
– Noted by peers
25. Typical Childhood Exotropia
Phase 2
• XT constant at distance, X’ or X(T)’
• Deviation noticeable
• Fewer symptoms: suppression usually present
• Divergence excess pattern ( or pseudo-
divergence excess) common
26. Typical Childhood Exotropia
Phase 3
• XT constant at distance and near
• Noticeable
• Usually no diplopia present
• Amblyopia may be present
27. Clinical Course of Typical Childhood
Exotropia
Phase Deviation
at
distance
Deviation
at near
Diplopia Suppression
0 X X’ _ _
1 X(T) X’ + _
2 XT X(T)’ or X’ _ +
3 XT XT’ _ +
28. Kushner’s Classification of
Exotropia
Type Description Percent
Basic XT=XT’ 37
Tenacious Proximal fusion XT>XT’, but after 60
minutes occlusion,
XT=XT’
40
High AC/A Ratio XT>XT’ and hi AC/A with
minus lenses
5
True Divergence Excess XT>XT’ even after 60
minutes occlusion, but
AC/A normal
4
Convergence Insufficiency Ex= 0, X’or XT< XT’ 4
Pseudo convergence
insufficiency
XT<XT’, but after 1 hour
occlusion, XT=XT’
<1
29. Non Surgical Treatment of Exotropia
1. Maximize vision
– Glasses especially for myopia
– Treat amblyopia
1. Minus lenses
2. Base in prism with or without minus lenses
3. Orthoptics
• Mainly useful for convergence insufficiency with
Ex=0, X’ or X(T)’
5. Part time patching: may improve control
30. Prisms for Exotropia
• Base In Prisms useful in
– Small angle exotropia
– For reading with convergence insufficiency
• Base out Prisms:
– Temporary treatment of esotropia after exotropia
surgery
31. Non Surgical Treatment of XT
• 7 y/o: VA OD 20/80, OS 20/80
• X (T) = 30
• Refraction: OD –1.50 20/20
• OS –1.50 20/20
• Rx: glasses
• Six weeks later Ex=0 with glasses
32. Surgical Treatment of Exotropia
• Rarely if ever improves (4% in one study)
• Natural course
– Neonatal exotropia often improves spontaneously
– Some infantile exotropia remains intermittent
– Other cases become constant exotropia
– Most progress to some degree
33. Surgical Treatment of Exotropia
• Maximize vision first
• Phase 0: X, no XT
– No treatment needed
35. Surgical Treatment of Exotropia
• Phase 2: XT at distance, X’ or X(T)’ near
– Surgery recommended without delay
– Patient in danger of losing binocular vision
• Phase 3: XT far, XT’ near
– Surgery for social reasons if desired
– Small chance of improving binocularity
36. Surgery for Exotropia
• Children under age 5
– 18 diopters or less: can recess one lateral rectus
– Over 20 diopters: recess LR OU but use 2/3 amount
of adult “numbers”
– High chance of overcorrection with recession LR OU
if use regular adult numbers for surgery in young
children
37. Surgery for Exotropia
• Usually recess LR OU as initial operation
• Convergence insufficiency with XT distance less
than XT at near:
– Recess one LR, Resect one MR
• Poor vision in one eye
– Recess LR, Resect/Tuck MR of eye with reduced
vision
38. Surgery for Exotropia
• Beware of surgery for high AC/A ratio
– Surgery for distance deviation likely to cause esotropia and
diplopia at near
• If prolonged cover testing reveals no deviation at near:
patch one eye 60 minutes
– If XT or X appears at near less than XT at distance: recess
LR OU
– If no deviation at near after patching: measure AC/A ratio at
distance with minus lenses
• If high AC/A ratio: prescribe minus lenses
• Can do recession LR OU with posterior fixation MR OU
39. Exotropia: Clinical Examples
1. 2 y/o X(T) = 30, X’=18
2. 6 month old XT=XT’=55
3. 6 y/o VA OD 20/20, OS 20/200
• CR: OD + 0.25, OS –6.00
• LXT = 25
40. Exotropia: Clinical Examples
4. 12 y/o XT= 30. Surgery for ET age 3
5. 23 y/o medical student
– Eyes tired with reading
– Ex=0, X(T)= 15
41. Surgical Treatment of Exotropia
• Basic Exotropia XT=XT’
– May be treated with Recess LR OU or
recess one LR, resect/tuck one MR
– Various studies show different results, some
advocate one operation over the other
– Most surgeons currently use recess LR OU
42. Surgical Treatment of Exotropia
• Desired position of eyes one week post op is:
– LR recession OU over age 5: ET 4-10 diopters
– Eyes become more exo in the weeks following
surgery
– High recurrence rate if XT undercorrected at age one
week
– With Recession one LR, desire smaller E after
surgery (2-6 diopters)
