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L. He, M. Wendt, A. Glasser; Influence of Pharmacologically and Edinger-Westphal Stimulated Accommodation on Anterior Chamber Pressure in Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2010;51(13):798.
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Uncertainty exists on the relationship between accommodation and intraocular pressure (IOP). Accommodation can be stimulated in anesthetized monkeys in a variety of ways, including EW stimulation and using pharmacological stimulation. The aim of this study was to evaluate the effect of stimulated accommodation on transient IOP changes in anesthetized rhesus monkeys.
Experiments were performed on the iridectomized eyes of 4 adolescent rhesus monkeys. The monkeys were anesthetized, with their heads held upright and facing forward in a head holder. Accommodative responses were stimulated by EW stimulation or by intravenous bolus administrations of pilocarpine 0.25-2 mg/kg over 30 seconds and measured with continuous 100 Hz ultrasound biometry or 60 Hz infrared photorefraction. The ocular perfusion system was developed using preliminary testing on pig eyes and was applied to the monkey eyes using sterile procedure. A 27-gauge needle was inserted into the anterior chamber of monkey eyes to record IOP. The needle was connected to a pressure transducer and a saline reservoir. IOP changes were analyzed as a function of accommodative response. IOP was also manipulated by raising or lowering the saline reservoir to observe the effect on refraction.
Accommodation ranged from 4.53 to 12.08 D. Maximal change in lens thickness was about 900 µm. Transient changes in IOP associated with accommodation were observed in 3 of 4 monkeys. EW stimulation caused maximal IOP increase of about 10 mmHg. One of the pilocarpine stimulated monkeys showed a decrease in IOP from 0.26 to 0.43 mmHg, independent of the bolus doses. 3 mmHg increase in IOP caused a hyperopic shift (0.29-0.87 D) and was dependent on baseline pressure (r2 = 0.996, p = 0.002). Another monkey had an IOP increase of 0.58±0.12 mmHg with the same bolus dose.
Pharmacologically or EW stimulated accommodation does not always result in reliable and consistent changes in anterior chamber pressure. Since accommodation induced intraocular pressure changes are not consistently similar between monkeys, this indicates that the changes in intraocular pressure can not be fundamental to the accommodative mechanism.
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