Abstract:
PURPOSE The aim of this study was to describe the amplitude and time-course of choroidal thickness changes induced by imposed hyperopic and myopic retinal defocus and to compare the responses in emmetropic and myopic subjects. METHODS Twelve Asian subjects (6 emmetropes and 6 myopes) aged between 18 and 34 years had OCT images of the choroid taken in both eyes at 5 min intervals while exposed to monocular defocus (random right or left eye) for 60 min; the fellow eye was kept optimally corrected (no defocus). Two different monocular defocus conditions (2 D hyperopic or 2 D myopic defocus) were tested on separate occasions. Thickness changes were measured as absolute changes in microns. RESULTS Prior to applying defocus, mean choroidal thickness in myopic eyes (mean ± SD, 256.30µm ± 41.24µm) was significantly less than in emmetropic eyes (mean ± SD, 423.09µm ± 60.69µm) (p<0.01). Repeated Measure ANOVA (GLM) analysis revealed that short-term monocular defocus caused small but significant changes in choroidal thickness (P<0.05). In both myopes and emmetropes, 2D of myopic defocus caused an increase in choroidal thickness (P<0.05) whereas 2D of hyperopic defocus caused a decrease in choroidal thickness (P<0.05) in 60 minutes. No significant difference was found between emmetropes and myopes in changes of choroidal thickness with the two types of defocus. CONCLUSIONS Small but significant choroidal thickness changes occurred when human eyes were exposed to both myopic and hyperopic monocular defocus. In each case these changes acted to move the retina towards the altered image plane, so as to reduce the degree of defocus. In this small sample we could detect no difference in responses of myopic eyes compared to emmetropic eyes.
