Am Orthopt J  48: 77-84  (1998).

The Angle of Strabismus Varies Depending on the Fixation Target Used

Ashish M. Mehta, M.D.
Burton J. Kushner, M.D.
Gail V. Morton, C.O.

Objective. Traditionally, strabismus patients are measured while fixating on an accommodative target. Our objective was to compare strabismus measurements obtained on accommodative fixation targets to those obtained on other commonly used fixation targets and determine if this would alter the amount of surgery performed.

Design: A prospective comparative evaluation.

Participants: Forty-eight patients with partly accommodative esotropia and twenty-three patients with intermittent exotropia.

Intervention: All patients had their angle of strabismus measured while reading a 20/40 linear Snellen optotype, viewing a toy animal target, and watching a cartoon video at distance; and while reading the Jaeger 3 optotype, and viewing a picture of standard size at near.

Main Outcome Measure: Reproducibility of measurements.

Results: Twenty-four (50%) patients with partly accommodative esotropia and thirteen (56%) patients with intermittent exotropia had at least a three prism diopter or greater difference in the measured angle of strabismus while reading the distance Snellen Optotype as compared to viewing the cartoon video; twenty-three (48%) patients with partly accommodative esotropia and thirteen (56%) patients with intermittent exotropia had such a difference fixating the toy animal. At near, twenty (42%) patients with partly accommodative esotropia and ten (44%) patients with intermittent exotropia had at least a three prism diopter difference in their measured angle of strabismus while reading the Jaeger 3 optotype as compared to fixation on a picture of standard size.

Conclusions: The measured angle of strabismus can vary depending on the fixation target viewed. In patients in whom surgery is anticipated, the amount of surgery felt necessary might vary depending on the fixation target used. For patients who are sufficiently cooperative, the angle of strabismus should be measured with fixation on Snellen optotypes.

© 1998 The Board of Regents of the University of Wisconsin System