To determine the frequency of amblyopia and anisometropia in intermittent exotropia and to evaluate the relationship between anisometropia and amblyopia.

The medical records of 471 intermittent extotropia patients, who were followed up over a period of 6 months and ranged from 3 to 15 years of age had been retrospectively reviewed. Anisometropia patients, who had either spherical or cylindrical anisometropia of more than 1.00D, were divided into 4 groups: spherical hyperopic anisometropia (SHA), spherical myopic anisometropia (SMA), cylindrical hyperopic anisometropia (CHA), and cylindrical myopic aniometropia (CMA).

The frequency of amblyopia in the intermittent exotropia group was 41/471 (8.7%). Amblyopia results in a significant increase in the incidence of anisometropia and a decrease in binocular function when compared with non-amblyopic patients. In the amblyopia group, 14 patients had anisometropia (34.1%) consisting of 2 patients with spherical myopic anisometropia (SMA), 2 patients with spherical hyperopic anisometropia (SHA), 2 patients with cylindrical myopic anisometropia (CMA) and 8 patients with cylindrical hyperopic anisometropia (CHA). In the anisometropia group (n=56) 14 patients (25.0%) had amblyopia and in the non-anisometropia group (n=415) 27 patients (6.5%) had amblyopia.

Intermittent exotropia is susceptible to amblyopia, especially when combined with anisometropia. Among the 4 types of anisometropia, cylindrical hyperopic anisometropia has a higher risk for developing amblyopia.