Incomitance and Eye Dominance in Intermittent Exotropia

Area of Science:

• Ophthalmology
• Strabismology
• Binocular Vision

Background:

• Comitance, the constancy of deviation angle, is a key feature differentiating strabismus types.
• Intermittent exotropia is a common form of strabismus characterized by outward turning of the eye that is controlled intermittently.

Purpose of the Study:

• To investigate whether the deviation angle in intermittent exotropia varies when patients alternate fixation between their right and left eyes in primary gaze.

Main Methods:

• A prospective observational cohort study involving 37 subjects with intermittent exotropia.
• Video tracking of eye position during monocular fixation on a central target.
• Cover-uncover test with continuous binocular eye tracking to measure deviation angles.

Main Results:

• The mean exotropia was 18.2° ± 8.1°.
• A difference in deviation angle (incomitance) between right and left eye fixation was detected in 16 out of 37 subjects (approximately 43%).
• The mean amplitude of incomitance was 1.7°, averaging about 10% of the exotropia, and was not linked to fixation stability or eye preference.

Conclusions:

• Incomitance is unexpectedly present in a significant proportion of individuals with intermittent exotropia.
• The measured incomitance, though generally small, can be substantial in some cases and warrants consideration in surgical planning for strabismus correction.