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M. Wendt, M. A. Croft, J. McDonald, P. L. Kaufman, A. Glasser; Lens Diameter Changes With Age and Pharmacologically Stimulated Accommodation in Rhesus Monkeys. Invest. Ophthalmol. Vis. Sci. 2007;48(13):984.
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In the unaccommodated human eye, lens diameter is independent of age while lens thickness increases with age. In monkeys, lens thickness has also been shown to increase with age. However, the relationships between lens diameter, age and changes in lens diameter with accommodation have not been established in rhesus monkeys. This study was undertaken to measure rhesus monkey lens diameter and thickness before and during pharmacologically stimulated accommodation as a function of age.
Iridectomized eyes were studied in 33 rhesus monkeys aged 4 to 23 years, 21 at the University of Houston and 12 at the University of Wisconsin. A plano perfusion lens filled with saline was placed on the eye to effectively neutralize the corneal power. Images were captured via a slit lamp which was adjusted to illuminate the perimeter of the monkey lens. Lens diameter was measured using Optimas image analysis software. Refraction was measured with a Hartinger coincidence refractometer. Ocular biometry was measured using A-scan ultrasound. Accommodation was stimulated pharmacologically in the 21 Houston monkeys by replacing the saline in the perfusion lens with 2% pilocarpine in 0.1% citrate-borate solution, pH 7.4. Accommodative progression was monitored by measuring lens diameter once every 10 seconds until no further decrease was recorded. Refraction and biometry were measured again after the eye was fully accommodated.
Unaccommodated lens thickness increased linearly with age by 0.028 mm/year (p = 0.003). Unaccommodated lens diameter appeared to increase from age 4 to 12 with no further increase thereafter. During accommodation, lens thickness increased by 0.405 to 1.107 mm and lens diameter decreased by 0.3787 to 0.9664 mm. Pharmacologically stimulated accommodation declined linearly with age by 0.478 D/year (p < 0.0001). Accommodative increase in lens thickness declined linearly with age by 0.022 mm/year (p = 0.009). Accommodative decrease in lens diameter declined linearly with age by 0.023 mm/year (p = 0.001).
Lens diameter decreases systematically with pharmacologically stimulated accommodation in accordance with the Helmholtz accommodative mechanism. Unaccommodated lens diameter does not increase after 12 years, although accommodative amplitude decreases linearly beyond this age. The age related decrease in accommodative amplitude in rhesus monkeys cannot be attributed to an age related increase in lens diameter.
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