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A Gwon, E WoldeMussie, A Lang; The Effect of Cholinergic Agents on Accommodation: A New Approach to Accommodation and Presbyopia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3254.
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Purpose: Most current theories of accommodation assume that the condition of physiological rest of accommodation is when the emmetropic eye focuses on a distant target demanding good resolution. The current hypothesis places the natural resting eye in a "tonic accommodative" state that is capable of both further active positive accommodation as well as active negative accommodation. We hypothesize that presbyopia may be characterized as a continual recession of the resting state of the eye, parallel to the continuous growth of the lens and/or a disparity between the advanced growth of the lens and the neutral position of the zonule/ciliary muscle apparatus. If so, application of muscarinic agonists should affect tonic contraction of the ciliary muscles without affecting normal positive and negative accommodation. Methods: Pilocarpine 0.3% (a dose not known to affect accommodation) was instilled into both eyes of a myopic presbyope, and one eye of a hyperopic presbyope. Refraction at distance and near was performed with a Hartinger Refractometer by an independent observer at baseline, 30-50 minutes, and 60-90 minutes post-treatment. The mean of three measurements was taken at each time point. Results: No notable change in pupil size was observed. For the myopic presbyope: at baseline, the mean refraction at distance was -1.25 D for the right eye (OD) and -1.53 D for the left eye (OS). This changed to -1.06 (OD) and -1.42 (OS) at 30 minutes, and -1.05 (OD) and -1.25 (OS) at 60 minutes post Pilocarpine administration. Refraction at near underwent a similar change. Baseline at near was -2.0 (OD) and -1.47 (OS). Refraction at 30 minutes was -1.8 (OD) and -1.53 (OS), and -1.5 (OD) and -0.95 (OS) at 60 minutes. Change after Pilocarpine was in the opposite direction for the hyperopic eye. Refraction at distance was +0.78 (OD) at baseline, +1.15 (OD) at 50 minutes, and +0.42 (OD) at 90 minutes. Refraction at near was +0.7 (OD) at baseline, +0.17 (OD) at 50 minutes and +0.38 (OD) at 90 minutes. Conclusion: At both distance and near, the change in refraction was similar in degree and direction, suggesting a change in the neutral accommodative state (tonic accommodation) of the eye.
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