Effects of brief periods of clear vision on the defocus-mediated changes in axial length and choroidal thickness of human eyes.

Abstract

To investigate the influence of brief, repeated periods of clear vision on the changes in axial length and choroidal thickness in response to short-term imposed defocus. The right eye of 16 young adults was exposed to 60min episodes of continuous and interrupted defocus conditions (+3DS and -3DS) over five separate sessions, with the left eye optimally corrected for distance. For interrupted defocus, 2min episodes of clear vision were imposed before each 15min episode of myopic or hyperopic defocus (2/15min). For hyperopic defocus, the effect of frequency of clear vision exposure was also assessed by imposing 1min of clear vision before each 7.5min of defocus (1/7.5min). The right eye axial length and choroidal thickness were measured before, during and after each defocus condition. After 60min of continuous hyperopic defocus the eye elongated significantly by +9±9μm (p=0.02). When exposed to interrupted (2/15min) hyperopic defocus, axial elongation was significantly reduced by 77% compared to continuous hyperopic defocus (p=0.03), with a final change of only +2±10μm relative to baseline. During interrupted (1/7.5min) hyperopic defocus, axial elongation reduced slightly compared to continuous hyperopic defocus (+6±8μm relative to baseline, p=0.12). For continuous myopic defocus, a reduction in axial length occurred but was not statistically significant (p>0.05). A similar pattern of response was observed for choroidal thickness changes with continuous and interrupted (1/7.5min) hyperopic defocus conditions. Brief periods of clear vision can diminish axial elongation and choroidal thinning induced by hyperopic defocus exposure in human eyes. If hyperopic defocus contributes to myopia progression in humans, then interruption with brief periods of clear vision could reduce its myopiagenic effects.