Abstract
Abstract: :
Purpose: A relationship between peak velocity and response duration as a function of amplitude of movement has been described and quantified for many eye movement systems including vergence and accommodation. However, there is a lack of this main sequence information for accommodation when it is induced through convergence–accommodation (CA). Methods: Disparity driven accommodation was measured in five subjects (26.2 ± 2.68 yrs). A computer monitor set at 1.7m projected a low pass filtered target that was viewed through liquid crystal shutters. Convergence–accommodation responses to vergence demands of 2 to 10 deg were captured by a photorefractor set at 1m. Blur driven accommodation (BA) to negative lenses (range= 1 – 3 D) was measured while subjects viewed a high contrast target set at 1.7m. The amplitude and duration of accommodation were determined from a polynomial curve fit which when differentiated provided peak velocity measures. These 3 values were averaged across subjects. Main sequences for peak velocity and response duration were calculated. The slope of the main sequence was compared between CA and BA. BA responses were truncated to match that of CA. Results: Amplitude–Peak Velocity: Mean slope (p<0.05) and R2 value for CA were 3.56±0.95 D/sec and 0.82 respectively. Mean BA slopes (p<0.05) were higher (7.10±2.64, R2=0.78) but the accommodative response showed significant inter–individual variation for a given amplitude compared to CA. Amplitude–Duration: Mean values of slope and R2 value for CA and BA were 436±202.6 msecs/D, 0.6 and 285.1±156.9 msecs/D, 0.62 respectively. The confidence intervals of the slope for BA and CA completely overlapped. Conclusions: Peak velocity and response duration of disparity driven CA change linearly with response amplitudes suggesting amplitude dependent response dynamics of CA. The response amplitude and peak velocity of BA showed greater inter–subject variation compared to CA
Keywords: vergence • ocular motor control