Bilateral Occlusion Reduces the Ocular Deviation in Intermittent Exotropia

Area of Science:

• Ophthalmology
• Neuroscience
• Vision Science

Background:

• Intermittent exotropia is the most common form of strabismus.
• It is hypothesized that intermittent exotropia manifests when fusion drive is overcome by divergent muscle tone.

Purpose of the Study:

• To test the principle that intermittent exotropia is influenced by muscle tone by examining eye alignment without vision.
• To compare ocular deviation in intermittent exotropia patients under monocular versus binocular occlusion.

Main Methods:

• A prospective study enrolled 18 patients with intermittent exotropia.
• Eye positions were recorded using video eye trackers.
• Ocular deviation was measured during monocular and binocular occlusion.

Main Results:

• A majority of patients (11/18) showed a smaller deviation with binocular occlusion.
• Mean exotropia decreased from 13.5° (monocular) to 6.0° (binocular), a 56% reduction (P < 0.001).
• This reduction persisted during bilateral occlusion but reversed upon restoring vision.

Conclusions:

• Bilateral occlusion reveals a distinct fixation-free alignment state, typically less exotropic than during binocular viewing.
• The study demonstrates that visual feedback actively mediates the deviation angle in intermittent exotropia.
• The fixating eye alone can provide the necessary visual feedback.