Accommodative responses under various viewing conditions in surgical patients with intermittent exotropia: an institutional, retrospective study

Abstract

Purpose To investigate the difference of spherical equivalent (SE) and pupil diameter in adult patients with intermittent exotropia (IXT) under various viewing conditions before and after surgery. Methods We retrospectively analyzed the medical records of 23 adult patients who underwent a surgery for IXT. The angle of deviation was measured by the prism and alternative cover test. Refractive error and pupil diameter were measured using the Grand Seiko WAM-5500 open-field autorefractor under binocular and monocular viewing conditions when patients stared at distance (6 m) and near (33 cm). Regression analyses were performed between accommodative load and the angle of deviation. Results Twenty-three patients (10 males, 13 females) with a mean age of 31.17±8.95 years, of whom 13 (56.5%) had the right eye as the dominant eye. The mean angle of deviation at near and at distance was 69.57±26.37 and 65.43±28.92 prism diopters respectively. There were no significant differences in accommodative response and pupil diameter between the dominant and non-dominant eyes. SE decreased when patients changed from monocular to binocular viewing, and from distant to near viewing (all P< 0.05), so as the pupil diameter (all P< 0.001). During binocular, not monocular viewing, SE was significantly greater after operation than it was before operation (P< 0.001). Accommodative load and pupillary constriction narrowed (p< 0.001) after the operation. Linear regression analysis showed a correlation between the angle of deviation at distance and accommodative load at distance (r2=0.278, p=0.010) and at near (r2=0.332, p=0.005). Conclusion In order to maintain ocular alignment, patients with IXT suffer a large accommodative load, which is related to the angle of deviation. Surgery helps eliminating extra accommodation.

Comparing myopic error in patients with basic and convergence insufficiency intermittent exotropia in China

“…As shown in Table 3 , our results demonstrated that SE of the dominant eye was significantly less myopic than that of the non-dominant eye in the CI group(P = 0.002), but not in the basic group(P = 0.08), indicating that CI IXT patients have a greater difference in SE of the two eyes. Yang and Hwang [ 24 ] found that IXT patients displayed a greater lag of accommodation in the non-dominant eye compared to the dominant eye during binocular fixation, which provides a potential mechanism for why the nondominant eye becoming more myopic [ 25 ]. Patients with IXT suffer a large accommodative load, which has been proven to be related to the degree of exodeviation [ 25 ].…”

“…Yang and Hwang [ 24 ] found that IXT patients displayed a greater lag of accommodation in the non-dominant eye compared to the dominant eye during binocular fixation, which provides a potential mechanism for why the nondominant eye becoming more myopic [ 25 ]. Patients with IXT suffer a large accommodative load, which has been proven to be related to the degree of exodeviation [ 25 ]. CI IXT patients exhibit a larger near-distance deviation difference than basic IXT, which might require greater accommodation at near viewing, leading to greater interocular asymmetry.…”