Diagnosis and treatment of exotropia with a high accommodation convergence-accommodation ratio.
BACKGROUND
Patients with exotropia often have a slow-to-dissipate fusional mechanism at near, which masks the true near deviation. Consequently, determination of the accommodation convergence-accommodation (AC/A) ratio in patients with exotropia must be based on near measurements obtained after prolonged monocular occlusion (typically 1 hour). When determined in that manner, the presence of a high AC/A ratio before surgery in an exotropic patient 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 studied. In addition to the usual measurements, measurements were obtained at near after 1 hour of monocular occlusion, with and without additional +3.00-diopter 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 thought 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 had sensitivity, specificity, and positive and negative predictive values of 100% for predicting a postoperative esotropia at near associated with a high 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 have been followed up to at least 18 years of age, by which time 9 have shown normalization of the AC/A ratio.


CONCLUSIONS
Near measurements used to calculate the AC/A ratio in exotropic patients must be made after prolonged monocular occlusion. Otherwise, many patients with a pseudo-high AC/A ratio will be thought to have a true high 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.
Kushner
B J
BJ
Department of Ophthalmology and Visual Sciences, University of Wisconsin, Madison, USA. bkushner@facstaff.wisc.edu
D000065:Accommodation, Ocular; D002648:Child; D002675:Child, Preschool; D003290:Convergence, Ocular; D005099:Exotropia / Q000175:diagnosis* / Q000628:therapy*; D005139:Eyeglasses; D005500:Follow-Up Studies; D006801:Humans; D009801:Oculomotor Muscles / Q000601:surgery; D012683:Sensory Deprivation; D014787:Vision Tests