Assessment of Amplitude and Control of the Distance Deviation in Intermittent Exotropia

Educational Objectives 1. To compare convergence amplitude testing with the cover–uncover test as two methods for assessment of control over an intermittent exodeviation. 2. To determine whether level of control over an intermittent exodeviation can predict the presence of tenacious distance fusion as revealed by a 60-minute period of monocular occlusion. 3. To identify those patients with intermittent exotropia who may require a preoperative patch test to reveal the full distance deviation. 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. [J Pediatr Ophthalmol Strabismus 2008;45:150–153.]