Abstract
Abstract: :
Purpose: Most studies on accommodative mechanism of myopia focus on the subjects with similar refractive errors in the two eyes. This study investigated differences in accommodative response between emmetropic and anisometropic eyes. Methods: Forty volunteers with ages from 18 ∼31 years were assigned into two groups: emmetropia group (20) and anisometropia group (20). The refractive error was fully corrected with contact lenses during the experiment. Accommodation was measured with an NW–500 auto–refractor when the subject was viewing a Maltese cross presented on a computer screen at 1, 2, 3, and 4 D distances. For each subject, the accommodative responses were obtained under six viewing and measuring conditions: when the subject was viewing the target monocularly, the measurements were taken from either the viewing eye or the occluded eye (4); when the subject was viewing the target binocularly, the measurements were taken from each eye (2). Results: The accommodative responses were plotted vs. accommodative stimulus for each viewing condition. A regression line was used to fit the data. Under the monocular viewing conditions, the accommodative response slopes measured from the viewing eyes and the occluded eyes for both emmetropes (i.e., the slopes were 0.79 and 0.83 when the right eye was viewing the target, and 0.74 and 0.73 when the left eye was viewing the target) and anisometropes (i.e., the slopes were 0.76 and 0.78 when the eye with lower refractive error was viewing the target, and 0.75 and 0.70 when the eye with higher refractive error was viewing the target) had no significant difference either between the two eyes or between the groups. Under binocular viewing condition, the mean slopes were 0.90 and 0.88 for emmetropes' right and left eye, respectively. For anisometropes, the means slopes were 0.80 in higher diopter eyes and 0.81 in lower diopter eyes. Again, there were no significant differences within and between groups. Conclusions: Our results showed that the difference in accommodative slope was not significant when one eye viewed the target and the responses were measured from the occluded eye or the viewing eye in both emmetropes and anisometropes. This result suggests that the equal innervation, which means that the two eyes accommodate equally, is held for these subjects. However, the anisometropes had slightly lower slopes than the emmetropes in 5 of the six conditions. The lower slope may be due to their refractive errors, which is similar to the case of myopes.