Assessment of amplitude and control of the distance deviation in intermittent exotropia

Purpose: A period of monocular occlusion (patch test) has been recommended to determine the magnitude of the distance exotropia to target with surgery. The hypothesis tested by this study was that patients with good control at distance are more likely to demonstrate tenacious distance fusion following occlusion than those with poor control. The results will assist in determining which patients require a preoperative patch test. Methods: This was a prospective study of 33 consecutive patients with exotropia scheduled for strabismus surgery. All had a complete sensorimotor examination in addition to measurement of convergence amplitudes and remeasurement of the strabismus following a 60-minute patch test. Results: The mean change in distance deviation following occlusion was 0.5 ± 0.6 prism diopters, and the median change was 0.0 prism diopters (P > .40). Eighteen percent had an increase in the distance exotropia of 5 prism diopters or more (tenacious distance fusion). Patients with poor control at distance by the cover-uncover test or convergence amplitude testing were unlikely to show tenacious distance fusion with the patch test (P < .001). Conclusion: The patch test may be avoided if control over the distance deviation is poor.