The effect of monocular and binocular viewing on the accommodation response to real targets in emmetropia and myopia.
OBJECTIVE
Decreased blur-sensitivity found in myopia has been linked with reduced accommodation responses and myopigenesis. Although the mechanism for myopia progression remains unclear, it is commonly known that myopic patients rarely report near visual symptoms and are generally very sensitive to small changes in their distance prescription. This experiment investigated the effect of monocular and binocular viewing on static and dynamic accommodation in emmetropes and myopes for real targets to monitor whether inaccuracies in the myopic accommodation response are maintained when a full set of visual cues, including size and disparity, is available.


METHODS
Monocular and binocular steady-state accommodation responses were measured with a Canon R1 autorefractor for target vergences ranging from 0-5 D in emmetropes (EMM), late-onset myopes (LOM), and early-onset myopes (EOM). Dynamic closed-loop accommodation responses for a stationary target at 0.25 m and step stimuli of two different magnitudes were recorded for both monocular and binocular viewing.


RESULTS
All refractive groups showed similar accommodation stimulus response curves consistent with previously published data. Viewing a stationary near target monocularly, LOMs demonstrated slightly larger accommodation microfluctuations compared with EMMs and EOMs; however, this difference was absent under binocular viewing conditions. Dynamic accommodation step responses revealed significantly (p < 0.05) longer response times for the myopic subject groups for a number of step stimuli. No significant difference in either reaction time or the number of correct responses for a given number of step-vergence changes was found between the myopic groups and EMMs.


CONCLUSIONS
When viewing real targets with size and disparity cues available, no significant differences in the accuracy of static and dynamic accommodation responses were found among EMM, EOM, and LOM. The results suggest that corrected myopes do not experience dioptric blur levels that are substantially different from emmetropes when they view free space targets.
Seidel
Dirk
D
Department of Vision Sciences, Glasgow Caledonian University, Glasgow, Scotland. D.Seidel@gcal.ac.uk
Gray
Lyle S
LS
Heron
Gordon
G
D000065:Accommodation, Ocular; D000328:Adult; D017668:Age of Onset; D016022:Case-Control Studies; D003290:Convergence, Ocular; D003463:Cues; D006801:Humans; D009216:Myopia / Q000453:epidemiology / Q000503:physiopathology*; D010775:Photic Stimulation / Q000379:methods; D015348:Vision, Binocular; D015349:Vision, Monocular