The clinical course of intermittent exotropia.

PURPOSE: To report the clinical course for patients with intermittent exotropia.
METHODS: The clinical records of patients diagnosed with intermittent exotropia from 1983 to 1991 who had at least 4 years of follow-up were reviewed. All patients with neurological or medical abnormalities, developmental delays, ocular disease, or having strabismus surgery during the follow-up period were excluded.
RESULTS: Of the 468 records reviewed, 73 met the inclusion criteria. Forty-four patients were female, and 29 were male. Fifty-two patients had basic intermittent exotropia, 11 patients had divergence excess intermittent exotropia, and 10 patients had convergence insufficiency intermittent exotropia. The mean age at initial visit was 20 years (range, 1 to 63 years). The mean follow-up was 10 years (range, 4 to 23 years). Four patients had amblyopia of 20/30 or worse, nine patients had a vertical deviation in the primary position, and 10 patients had undergone extraocular muscle surgery before coming to our clinic. Sixty patients received some form of treatment during follow-up. The mean stereoacuity at the initial and final visits were 59 and 70 s arc, respectively. The initial mean spherical equivalent refraction was -0.48 D and increased to -1.15 D at the end of the study. The mean exodeviation changed from 17.2 Delta at distance and 17.6 Delta at near at the initial visit to 13.7 Delta at distance and 13.5 Delta at near at the final visit. At the initial visit, 63 patients were exotropic and 10 patients were either heterophoric or orthophoric at distance, whereas, 60 patients were exotropic and 13 patients were either heterophoric or orthophoric at near. At the final visit, 37 patients were exotropic and 36 patients were either heterophoric or orthophoric at distance whereas 33 patients were exotropic and 39 were either heterophoric or orthophoric at near. One patient was esotropic at near at the last visit. Changes in the size and quality of the exodeviation, although statistically significant (p < 0.001), were not associated with any specific treatment regimen or with longer periods of follow-up. Measurements exhibited a regression toward the mean.
CONCLUSIONS: Intermittent exotropia improved for many patients quantitatively and qualitatively over time. That the improvement was unrelated to any treatment and length of follow-up suggests that the changes at least quantitatively are not associated with any physiologic process and may be due, in part, to regression toward the mean.