Diagnosis and treatment of exotropia with a high accommodation convergenceaccommodation ratio

Background: Patients with exotropia often have a slow-to-dissipate fusional mechanism at near, which masks the true near deviation. Consequently, dete rmination of the accommodation convergence-accommodation (AC/A) ratio in pa tients with exotropia must be based on near measurements obtained after pro longed monocular occlusion (typically I hour). When determined in that mann er, the presence of a high AC/A ratio before surgery in an exotropic patien t has been reported to be predictive of an esotropia at near after surgery. Objective: To investigate the diagnosis and management of exotropia with a high AC/A ratio. Methods: Three hundred four consecutive patients with exotropia were studie d. In addition to the usual measurements, measurements were obtained at nea r after 1 hour of monocular occlusion, with and without additional +3.00-di opter lenses. Also, a gradient AC/A ratio was obtained by using additional minus lenses at distance fixation. Results: One hundred fifty-four (50.7%) of 304 patients would have been tho ught to have a high AC/A ratio if that diagnosis was based on measurements obtained before prolonged monocular occlusion.-In fact, only 22 patients (7 .2%) actually had a high AC/A ratio; 132 patients (43.4%) had a pseudo-high AC/A ratio. Six of 22 patients with a high AC/A ratio underwent surgery to correct the exotropia. The presence of a high AC/A ratio before surgery ha d sensitivity, specificity, and positive and negative predictive values of 100% for predicting a postoperative esotropia at near associated with a hig h AC/A ratio. The remaining 16 patients with high AC/A ratios were treated with overcorrecting minus lens therapy (including a bifocal). Ten of them h ave been followed up to at least 18 years of age, by which time 9 have show n normalization of the AC/A ratio. Conclusions: Near measurements used to calculate the AC/A ratio in exotropi c patients must be made after prolonged monocular occlusion. Otherwise, man y patients with a pseudo-high AC/A ratio will be thought to have a true hig h AC/A ratio. The presence of a high AC/A ratio is infrequent: in patients with esotropia, but it is highly predictive of a postoperative esotropia at near fixation.