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M. Baumeister, M. Wendt, C. Shooner, A. Glasser; Edinger-Westphal Stimulated Accommodation in Rhesus Monkeys Using a Pulse-Step Stimulation Model. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4561.
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In recently developed models of human accommodation it has been suggested that amplitude and dynamics of human accommodation are controlled by pulse-step signals, modification of which could allow for neural compensation of age-related changes to the accommodative plant. The aim of this study was to examine the effect of a pulse-step stimulation paradigm on Edinger-Westphal stimulated, open-loop accommodation in anesthetized rhesus monkeys.
One eye each of three rhesus monkeys (age 10 to 12 years) was studied. Accommodation was elicited by stimulation of the Edinger-Westphal nucleus. Stimulus amplitudes were chosen to produce accommodative response amplitudes of 1 D, 3 D and 7 D. Four different stimulus shapes were used: either i) a single 4-second step, or 4-second steps preceded by a pulse with an amplitude in µA of 150% of the step amplitude and a duration of ii) 50 ms, iii) 100 ms and iv) 200 ms, respectively. The amplitude of each stimulus pulse in µA was 150% of the amplitude of the following step. Changes in lens thickness were recorded by dynamic ultrasound biometry at 100 Hz. Dynamic A-scan lens thickness measurements were converted into accommodation and the velocity and acceleration of the responses were determined using a two-point difference algorithm.
For each of the four stimulus shapes, there was a linear relationship of peak velocity and peak acceleration of the accommodative response to the accommodative amplitude. The slopes of the peak velocity versus amplitude regression lines increased linearly with the duration of the pulse (y=0.0115x+1.8922, r²=0.99, p=0.005). The slopes of the peak acceleration versus amplitude regressions were not influenced by the pulse duration.
The results suggest that the relationship between peak velocity and amplitude of Edinger-Westphal -stimulated accommodation in anesthetized rhesus monkeys can be influenced in a systematic way using combined pulse-step stimuli.
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