Forty-five Years of Studying Intermittent Exotropia — What Have I Learned? The WSPOS Keynote Strabismus Lecture, October 3, 2020

ABSTRACT

There are three keys to understanding how the new way of classifying and treating intermittent exotropia (IXT) differs from Burian’s classic classification. First, the assumption that lateral rectus surgery selectively affects the distance deviation, recess/resect procedures affect the distance and near equally, and that medial rectus surgery selectively affects the near deviation, are false assumptions. Second, AC/A ratios in IXT can be calculated in all the usual manners, provided that any near measurement used in the calculation be made after prolonged monocular occlusion to eliminate the contaminating effect of the Scobee phenomenon. Third, the use of +3 diopter (D) lenses at near and prolonged monocular occlusion are not interchangeable and work on different mechanisms, the former on accommodative convergence and the latter on fusional convergence. All patients with IXT should have a measurement taken after prolonged monocular occlusion, as well as while fixating on a far distant outdoor target prior to surgery, which should target the largest angle measured.

KEYWORDS:

• Exotropia
• intermittent exotropia
• AC/A ratio
• convergence insufficiency
• Scobee Phenomenon
• tenacious proximal fusion
• lateral incomitance
• strabismus surgery
• patch test

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Acknowledgments

Presented at the 5th World Congress of the World Society of Paediatric Ophthalmology & Strabismus (WSPOS). The Journal is pleased to publish this as part of the series of Keynote strabismus lectures in conjunction with WSPOS.

Disclosure statement

The author is on the scientific advisory board of NovaSight.

Additional information

Funding

This work was supported by an unrestricted grant from Research to Prevent Blindness, Incorporated, New York, NY.