6.6 Intermittent Exotropia

Definition

  • Exophoria (XP) that breaks down to exotropia (XT) when it’s no longer controlled by convergence

History

  1. Onset < 5 years (usually ~ 2yrs)
  2. Parents notice eye is “turned out” under certain conditions (when the child is daydreaming, tired- end of the day, sick)
  3. Patient closes the affected eye in bright light
  • The natural history is debatable. The traditional teaching that intermittent XT progresses towards a constant XT has not been replicated in a retrospective review.[iii]

Romanchuk et. al. Natural History of surgically untreated intermittent exotropia. JAAPOS 2006; 10:225-31.

Classification

1. Divergence Excess (XT Distance (D) > Near (N) by >10-15Δ, High AC / A)

True

XT still D>N after 1-hour monocular patch or with +3D lens

Pseudo / Simulated

XT D=N after:
1 hour monocular patch (“fusional”)
+ 3D lens (“accommodative”)

Exo deviations for near are controlled by fusional convergence. This control can be abolished by dissociating the eyes with monocular occlusion or removing accommodative drive with a +3D lens. In pseudo-divergence excess, this causes the XT for near to increase to the same degree as that for distance (i.e. it breaks down to a basic XT). The significance of this is debated.

2. Basic (D=N)
3. Convergence Insufficiency (D<N, low AC / A)
  • Very rare in young children
  • Worse outcomes
Figure 6.6.1 Classification of Intermittent Exotropia

Figure 6.6.1
Classification of Intermittent Exotropia

Examination Structure

1. Visual Acuity (Best Corrected)

  • Amblyopia is uncommon

2. Spectacles

3. Inspection

  1. Abnormal head position?
  2. Hirschberg (pupil margin=30Δ, limbus=90Δ) - ± Exotropia (at time of examination)
  3. (Lids normal)
  4. (Pupils normal)
Figure 6.6.2 Intermittent Exotropia

Figure 6.6.2
Intermittent Exotropia

Left exotropia when looking in the far distance

4. Cover-Testing

± Comitant XT

  1. Without glasses: CTD, CTN
  2. ± With glasses: CTD, CTN
A. Assess Type

Divergence Excess

XT Distance (D) > Near (N)

Basic

D = N

Convergence Insufficiency

D < N

If divergence excess, test for divergence excess or pseudo-divergence excess by remeasuring after 1 hour of monocular occlusion. If divergence excess is confirmed, test with +3D lenses to differentiate between true and simulated divergence excess, see above)

B. Assess Control

Excellent

Only evident with cover test and controls rapidly

Good

Controls after blink

Fair

Controls after 5 - 10 seconds

Poor

Does not regain control / breaks spontaneously

C. Far Distance

The XT is often worst when asking the patient to look in the far distance (e.g. out a window). However, this may be difficult to examine in young children

5. Ocular Rotations

  • Full ductions

6. Stereopsis

  • Usually excellent because straight most of the time

7. Dilated Fundoscopy

  • Exclude sensory XT

8. Cycloplegic Refraction

Summary

  • Intermittent exotropia… divergence excess / basic / convergence insufficiency…
  • Excellent / good / fair / poor control

Management

Consider

1. Age
  • Risk of amblyopia with early surgery
2. Type / Size
  • Cosmesis
3. Control (Estimates Binocularity)
  • There are scoring systems for this (e.g. Newcastle, Mayo Clinic)
  • The size of the tropia does not predict control
  1. Percentage of day in XT, progressing?
  2. Vision (amblyopia rare): Binocular VA chart, Worth 4 dot, Synoptophore
  3. Speed of recovery of tropia (see above)
  4. Stereopsis for (distance) and near (eyes need to be straight for this)

A. Treat Amblyopia / Refractive error

B. Non-surgical

These methods are rarely definitive, but can be used to delay surgery until the child is older. There is little consensus between clinicians / orthoptists as to best practice

1. Spectacles to Correct Refractive Error
  • Myopia, astigmatism, high hypermetropia (consider if >+4D)

          

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