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M. Wendt, L. Ostrin, A. Glasser; Accommodative Changes in Lens Diameter and Refraction in Rhesus Monkeys . Invest. Ophthalmol. Vis. Sci. 2005;46(13):720.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: During accommodation, the eye adjusts to change focus from far to near. The change in focus is associated with changes in lens shape resulting in increased thickness and curvature and decreased diameter. In this study, we determine the dynamic relationship between refraction and lens diameter during accommodation. Methods:Five experiments were performed on two rhesus monkeys (Macaca mulatta), aged 5 & 6 years with one experiment repeated on one eye. The monkeys had previously undergone complete bilateral iridectomies and surgical implantation of a stimulating electrode in the Edinger–Westphal (EW) nucleus of the brain. Experiments were performed on anesthetized monkeys held prone with their head upright and facing forward. A Hartinger coincidence refractometer was used to measure a static EW stimulated stimulus response function. Refraction and lens diameter were measured sequentially at 30 Hz for the same EW stimulus current amplitudes. Refraction was measured using an infrared photorefractor and lens diameter was measured by image analysis of slit–lamp gonioscopic videography of the iridectomized eyes. Results:Refraction and lens diameter were plotted as a function of time relative to the initiation of stimulation. These results were then compared against each other and the slopes calculated using linear regressions. During accommodation, lens diameter decreased with refraction from a mean resting diameter of 8.55 mm ± 0.33 to a mean accommodated diameter of 7.94 mm ± 0.30 (SD). A mean maximum decrease in lens diameter of 0.611 mm ± 0.053 (SD) was found for 10.20 D ± 1.54 (SD) of accommodation. The mean slope was 0.0614 mm/D ± 0.0118 (SD). During disaccommodation, lens diameter increased with refraction. The average slope for disaccommodation was 0.0602 mm/D ± 0.0110 (SD). Experiments repeated on the same eye resulted in mean accommodative amplitudes of 9.7 D and 12.9 D, mean changes in diameter of 0.679 mm and 0.649 mm and mean slopes of 0.0666 and 0.0476 mm/D respectively. Conclusions:Although some inter–individual and inter–subject variability exists, lens diameter consistently decreased by roughly 0.6 mm for 10D of accommodation. These results are in accordance with the Helmholtz accommodative mechanism.
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