Comparison of ocular deviation between Chronos and real space using alternate prism cover test

Abstract

Purpose : Chronos (Topcon Corp.) is a binocular refraction system of the simultaneous looking-in type, and can be used to measure ocular deviation through an alternate prism cover test (APCT). This study aimed to evaluate wether there is a difference in ocular deviation between Chronos and real space using APCT.

Methods : Thirty-five healthy individuals (mean ± standard deviation was 20.9 ± 2.3 years old) participated in this study. APCT was performed to measure the ocular deviation at a distance of 5.0 m and near (33 cm) in Chronos and the real space. For the fixation target, a Landolt ring was used at a visual angle of 1.42 arcmin in both Chronos and the real space. The participants were asked to fixate on the gap of the Landolt ring during APCT. The ocular deviation was determined as one eye not moving after the removal of the occlusion for the esophoric participants, and prior to the reversal of eye movements after occlusion removal for the exophoric participants. The difference between Chronos and real space was evaluated using Bland–Altman analysis.

Results : For fixed errors, the distant exodeviation was significantly greater in Chronos [−4.1 ± 2.7 prism diopter (PD)] than in the real pace (−2.5 ± 2.6 PD) (P < 0.001). Similarly, near exodeviation was significantly greater in Chronos (−11.2 ± 4.8 PD) than in the real space (−6.3 ± 4.8 PD) (P < 0.001). In both exodeviations, there was no significant proportional errors between both conditions (R² < 0.001; distant, P = 0.99; near P = 0.97).

Conclusions : Chronos estimated the distant and near exodeviation more than conventional APCT in real space, and the amount of error depends on the testing distance, not on the subject, because there were no proportional errors. We consider this error due to the difference in condition between looking into Chronos and daily viewing.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.