Accommodation microfluctuations vary with target vergence in myopes and emmetropes

Abstract

Abstract: : Purpose: Models of the accommodation system suggest that inaccurate responses to both near and distance targets play a role in the development of myopia. Accommodation microfluctuations provide a sensitive measure of the accuracy of static accommodation responses. Microfluctuations have been found to be greater in myopic subjects compared with emmetropes during sustained near viewing but it is uncertain whether these differences apply across the accommodation range. In this study we measure accommodation microfluctuations in myopic and emmetropic subjects over a range of accommodative stimulus levels. Methods: 20 (10 myopic and 10 emmetropic) healthy young adult volunteers with less than 0.50D of astigmatism participated with informed consent in the study. The subjects viewed a high contrast Maltese cross target through a +5D Badal lens in photopic conditions. Accommodation stimulus levels ranging from 0–4D in 1D steps were presented randomly. Accommodation was measured continuously over a period of two minutes using a Shin–Nippon SRW–5000 infrared autorefractor at a sampling rate of 52Hz. Myopic subjects were fully corrected using daily disposable soft contact lenses. Results: Significant (p<0.05) increases in the magnitude of accommodation microfluctuations were found with increasing target vergence in both the myopic and emmetropic groups. Power spectrum analysis revealed that these increases could be attributed to an increase on the power of the low frequency components (<=0.7Hz). The myopic group had significantly larger (p<0.05) microfluctuations than the emmetropic group at all accommodation stimulus levels and this difference became more pronounced as the stimulus level increased. Power spectrum analysis revealed that these differences could be attributed to low frequency components of the microfluctuations (<=0.7Hz). Conclusions:Accommodative microfluctuations were found to be larger in myopic subjects at all levels of stimulus. These differences result from increased low frequency drifts in the accommodation response of the myopic subjects. These results suggest a blur processing deficit in myopia which may be exacerbated at near viewing distances.

Keywords: ocular motor control • refractive error development • reading