Purchase this article with an account.
R. Suryakumar, E.L. Irving, W.R. Bobier; Dynamics of Accommodation Driven by Retinal Disparity . Invest. Ophthalmol. Vis. Sci. 2005;46(13):716.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: Previously, we studied the change in accommodation (CA) to assumed measures of ‘stimulus’ vergence. Peak velocity of CA and blur–driven accommodation (BA) were similar for any given amplitude. In this study, we have simultaneously assessed the response dynamics of two systems [disparity vergence (DV) and vergence–accommodation (VA)] and provide novel information about the dynamic differences in accommodation during a disparity ON/OFF paradigm. Methods: Four subjects (24.5±0.57 yrs) were selected. Crossed retinal disparities were created on a difference of Gaussian target which was presented as a disparity ON/OFF paradigm (step demands between 2 – 5 degrees) on a stereo monitor set at a distance of 1.4m. Subjects viewed the stereo monitor through a liquid crystal shutter goggle and video eye tracker assembly (Elmar 2020) which recorded eye position at 120 Hz. VA responses were measured using a custom designed digital photorefractor (sampling rate 60Hz). The eye tracker and photorefractor were synchronized using an input/output control board (NI6503, National Instruments Inc). The position traces of VA and DV were averaged over 6 trials and subsequently differentiated to obtain velocity. The main sequence of VA and DV were plotted and compared. In a separate session, BA responses to step changes in blur (0.5 – 2.5D) were measured on the same subjects through a Badal system. Results: VA increased following disparity ON and decreased to baseline during the disparity OFF paradigm. Peak velocities of DV and the associated VA changed linearly with amplitude. VA showed fluctuations in response after reaching steady state that were always linked to DV changes. Main sequence relationships of VA during disparity ON and OFF paradigms were 4.21x –0.71, R=0.9, p<0.001 and 2.98x +0.26, R = 0.8, p = 0.004 respectively. The confidence intervals (CI) of these VA slopes overlapped suggesting no statistically significant difference. The main sequence slope of DV during ON and OFF paradigms were 4.48x +3.63, R=0.7, p<0.05 and 3.22x + 0.67, R = 0.7, p <0.05 respectively. The mean values of sCA/C ratio, rCA/C ratio, and response duration of VA were 0.24±0.13 D/deg, 0.28±0.19 D/deg, 888.61±258.47 msecs respectively. BA slopes for accommodation and dis–accommodation were similar (3.391x –0.032, R = 0.7, p < 0.001; 2.647x +0.355, R=0.7, p<0.001) and CI’s overlapped with CA. Conclusions: Differences in the main sequence slope of DV between disparity ON/OFF does not appear to influence VA. When amplitudes are matched, BA and VA appear to be equally fast. The small differences found between stimulus and response CA/C ratios confirm the accurate dynamics of disparity vergence.
This PDF is available to Subscribers Only