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L.A. Ostrin, A. Glasser; Effects of Echothiophate, Pilocarpine and Atropine on Accommodative Amplitude and Dynamics in Rhesus Monkeys . Invest. Ophthalmol. Vis. Sci. 2005;46(13):714.
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Purpose: Accommodative amplitude decreases with age and presbyopia. Other characteristics of accommodation, such as dynamics, may also be altered with the age related decrease in accommodation. Accommodative amplitude can be pharmacologically manipulated using cholinergic drugs. This study is directed at characterizing how accommodative amplitude can be manipulated pharmacologically and how this may affect accommodative dynamics. Methods: The effect of topical instillation of 0.015% echothiophate on the time course, extent of pupil constriction and changes in resting refraction were measured in one eye each of five normal rhesus monkeys for 90 minutes. Pupil diameter was measured with infrared videography and resting refraction was measured with a Hartinger coincidence refractometer. Effects of 0.015% Echo, 6% pilocarpine and atropine iontophoresis on static and dynamic centrally stimulated accommodation were studied in two iridectomized monkeys (ages 5 & 6 years). Dynamic accommodative responses were measured with infrared photorefraction for increasing current amplitudes before and during the course of action of the drugs. Results: Echothiophate caused a significant decrease in pupil diameter of 3.09 ± 0.65 (mean ± SEM, p < 0.01), and a myopic shift in resting refraction of 1.30 ± 0.39 D (p < 0.05) 90 minutes after instillation. There was a slight increase in maximum accommodative amplitude of 0.83 D. While the main sequence relationship of accommodation was not significantly different after echothiophate (p = 0.66), the main sequence of disaccommodation was significantly decreased (p < 0.0001). Pilocarpine caused a 12.44 ± 2.27 D myopic shift in resting refraction after 90 minutes. Average accommodative amplitude before pilocarpine was 11.69 ± 0.02 D and after pilocarpine was 0.66 ± 0.65 D. Atropine caused a significant decrease in accommodative amplitude by 5 minutes. Average accommodative amplitude before atropine was 11.09 ± 0.17 D and after atropine was 0.55 ± 0.13 D. As pilocarpine was taking effect, for the same stimulus current, the accommodative response decreased along with a decrease in peak velocity in both monkeys. In one monkey, the peak velocity vs. amplitude relationship was increased (p < 0.05). Conclusions: Pilocarpine reduces accommodative amplitude by shifting the eye to a more myopic state, atropine reduces accommodation by cycloplegia and echothiophate does not appreciably alter accommodative amplitude. Although accommodative amplitude can be effectively reduced by pharmacological manipulations with pilocarpine and atropine, accommodative dynamics are not systematically altered.
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