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A. Glasser, L.A. Ostrin; Comparisons Between Edinger–Westphal (EW) and Pharmacologically Stimulated Accommodation in Rhesus Monkeys . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2188.
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Purpose: Accommodation occurs due to contraction of the ciliary muscle, resulting in increased lens surface curvatures and thickness. Accommodation is often stimulated pharmacologically. A previous study in humans suggests that pharmacological stimulation produces non–physiologic accommodative lens movements. In this study pharmacologically and centrally stimulated refractive and biometric changes were compared following maximal and supramaximal accommodative stimulation in rhesus monkeys. Methods: Accommodation experiments were performed on one eye each of 4 rhesus monkeys (ages 4, 5, 5 and 11 yrs) with permanent indwelling electrodes in the EW nucleus. Dynamic EW stimulated accommodative refractive changes were measured with infrared photorefraction and dynamic lens biometric changes were measured with high resolution continuous A–scan ultrasound for increasing stimulus current amplitudes, including supramaximal amplitudes. Accommodation was then stimulated with 40% carbachol iontophoresis and biometry was measured for 30 minutes. Results: During centrally stimulated accommodation, lens biometric changes occur linearly with accommodation, with an anterior movement of the anterior lens surface of 0.04±0.001 mm/D and a posterior movement of the posterior lens surface of 0.02±0.003 mm/D. Supramaximal stimulus currents tended to cause a further increase in peak velocities of both accommodation and lens thickening over that achieved for max stimulus currents, but without further increase in amplitudes. Carbachol stimulation results in normal accommodative lens changes during the first 5–7 minutes with a posterior movement of the posterior lens surface of 0.19±0.062 mm, but with a subsequent anterior movement of the posterior lens surface of 0.23±0.068 mm that is not observed with centrally stimulated accommodation. Pharmacologically induced change in lens thickness was 0.11±0.04 mm greater than with central stimulation (p<0.05). Conclusions: Supramaximal current amplitudes result in a normal centrally stimulated accommodative response, but with faster dynamics than max stimulation. Supramaximal pharmacological stimulation initially produces a normal accommodative response, but ultimately results in a forward movement of the lens that is not observed with central stimulation.
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