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S. Kasthurirangan, A. Glasser; Dynamics of Accommodation and Disaccommodation from Various Starting Points . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3894.
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Amplitude and starting point of accommodation (far–to–near) and disaccommodation (near–to–far) influence their dynamics (Kasthurirangan & Glasser, 2005). When separated out by starting point, peak velocity of disaccommodation is independent of response amplitude and dependent on starting point with larger peak velocities at more proximal starting points (Bharadwaj & Schor, 2005). Our prior results show that peak velocity is dependent on starting point for accommodation and disaccommodation. We analyzed our accommodation and disaccommodation data as a function of response starting point to describe the relative influences of starting point and response amplitude on dynamics.
Accommodative and disaccommodative responses were recorded at 25 Hz in 9 subjects between 22 and 30 years of age with a PowerRefractor. The relationship between response amplitude and starting point was manipulated in three conditions; Fixed Far, Fixed Near and Fixed Amplitude. 10 – 15 dynamic accommodative and disaccommodative responses ranging from 1 to 6D from starting points from 1 to 6D were recorded. Responses were fit with an exponential function to calculate amplitude, starting point, time constant and peak velocity. Responses from all three conditions were pooled and divided into 1D response starting point bins. For each bin, peak velocities and time constants were compared with accommodative and disaccommodative response amplitudes.
Time constants increased linearly with response amplitude within each starting point bin (accommodation: p < 0.05 for 5 of 7 starting point bins; disaccommodation: p < 0.05 for 6 of 7 starting point bins). Smaller time constants occurred with more proximal starting points. The peak velocity vs response amplitude relationships were described with analytical models derived using the linear relationship between time constant and response amplitude (Kasthurirangan & Glasser, 2003). The modeled responses showed saturation of peak velocity at larger amplitudes (>2D) of accommodation and disaccommodation with higher peak velocities at more proximal starting points.
Peak velocity is largely influenced by the starting point and less by response amplitude. Time constants are influenced by both response amplitude and starting point. Dynamic trends of accommodation and disaccommodation depend on the metric, i.e., time constant or peak velocity used to describe the dynamics. The dynamic trends as a function of response amplitude are similar for various starting points.
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