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M. Wendt, A. Glasser; Topical Pilocarpine Stimulated Accommodation in Anesthetized Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3787.
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Many studies have used topically administered pilocarpine to stimulate accommodation in both humans and monkeys. However, the concentrations of pilocarpine used and the methods of administration have varied. In this study, different concentrations of pilocarpine eye drops were tested for their effectiveness in stimulating accommodation in rhesus monkeys.
Iridectomized eyes were studied in 14 anesthetized rhesus monkeys aged 5 to 16 years. Maximum accommodation was stimulated in all these monkeys with a 2% pilocarpine solution maintained on the cornea for at least 30 minutes in a specially designed perfusion lens. In subsequent topical pilocarpine experiments, baseline refraction was measured with a Hartinger coincidence refractometer. While upright and facing forward, commercially available pilocarpine (2, 4, or 6 %) was applied to the surface of the cornea using a pipetter in volumes of either 25 µl (1 drop) or 50 µl (2 drops). Monkeys received 2 or 4 drops in two applications or 6 drops in three applications over a five minute period with the eyelids closed between applications. Alternatively, while supine, 10-12 drops of pilocarpine were maintained on the cornea in a scleral cup for five minutes. After pilocarpine administration, the eyelids remained closed except for brief periods when they were opened for refraction measurements. Refraction measurements were begun five minutes after the second application of pilocarpine. Measurements continued for at least 30 minutes after initial administration until no further change in refraction occurred.
Constant 2% pilocarpine solution on the eye in the perfusion lens produced 10.88 ± 2.73 (mean ± SD). The results of topically applied pilocarpine were 3.81 D ± 2.41, 5.49 D ± 4.08, and 5.55 D ± 3.27 using 2%, 4%, and 6% solutions respectively. When expressed as a percentage of the accommodative response amplitude obtained in the same monkey with constant 2% pilocarpine solution on the eye, the responses were 34.7% for 2% pilocarpine, 48.4% for 4% pilocarpine, and 44.6% for 6% pilocarpine. Topical 4% and 6% pilocarpine achieved similar accommodative responses, but neither achieved maximum accommodation.
Considerable variability in response amplitude occurred and maximum accommodative amplitude was rarely achieved with topical application of a variety of concentrations of commercially available pilocarpine. Although widely used as a simple procedure for stimulating accommodation, topical application of commercial pilocarpine solutions appears to be a remarkably unreliable method for stimulating accommodation in rhesus monkeys.
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