Abstract
Purpose:
Defocus blur affects refractive error development. Various human studies report decreased ability to accurately accommodate in myopic adults and children compared to emmetropes, however other studies have found no differences. We hypothesize that myopes have a decreased ability to accurately accommodate, but only when certain 3D cues to accommodation are not available to them.
Methods:
Binocular accommodative responses were measured using a PowerRefractor while subjects wore shutter glasses and viewed naturalistic images on a 3D display. Stimuli were “dead leaves” images that capture the spatial characteristics of real world images.<br /> <br /> Subjects viewed five types of images, each randomly presented five times at 40cm for 5 sec, with various cues to accommodation: (1) flat [2D], (2) blur gradient, (3) disparity gradient, (4) size gradient, (5) all cues. Subjects were instructed to fixate on a central green dot at all times.<br /> <br /> Thirty-eight young (22 to 31 years) healthy adults participated; reliable data was obtained for 21 (n=10 myopes). Refractive error was determined by binocular subjective refraction that followed a vision screening and objective refraction.
Results:
Myopes show less stable accommodation responses than emmetropes, which are significantly more variable when viewing 2D flat images (Wilcoxon, p=0.01), but become as stable as emmetropes’ responses when 3D and blur cues are available.<br /> <br /> Accommodation response latencies appear larger in myopes for all conditions, particularly for the “size” and “disparity” conditions. A positive correlation was found between amount of myopia and accommodation response latency when size and/or disparity cues were available (R2>0.4).<br /> <br /> The amplitude of accommodation was not significantly different between the refractive groups for any condition, although myopes appear to accommodate more (smaller lags) for all conditions.
Conclusions:
Our results indicate larger variability in accommodation responses in myopes when viewing flat images. Only when additional cues are added (disparity, blur, size), do myopes’ accommodation responses stabilize. In addition, the time lag to achieve adequate accommodation is larger for myopes. Inaccuracies of accommodation when viewing 2D images (typical of indoor activities) may cause long-term blur on the retina, which may impede precise emmetropization.