Abstract
Abstract: :
Purpose: To evaluate the effect of age and accommodation on the location of the ciliary muscle. Methods: High–resolution magnetic resonance imaging provides unsurpassed soft tissue contrast and the ability to image the accommodative structures in the intact human eye in vivo1. Images were acquired from 25 subjects between the ages of 22 and 50 during accommodation and with accommodation at rest as previously described1. The position of the ciliary muscle apex with respect to the cornea was measured. Results: The ciliary muscle apex moves both inward and anteriorly with age. The cornea to ciliary muscle length / anterior segment length slope was –0.002 ± 0.0007 per year (P=0.005) with an intercept of 0.667 ± 0.023 (P<0.00001) for minimum accommodation and a slope of –0.002 ± 0.0007 per year (P=0.004) with an intercept of 0.662 ± 0.023 (P<0.00001) for maximum accommodation. No measurable change in ciliary muscle anterio–posterior position occurs with accommodation. A correlation between lens growth and ciliary muscle anterior position is also noted: anterior chamber depth is fixed at 84±1% of the distance between the cornea and the ciliary muscle plane. Conclusion: We see only inward ciliary muscle movement with in vivo physiological accommodation in the intact human eye; however, in vitro primate studies2 have indicated that with pharmacologically induced accommodation, the muscle also moves anteriorly. With age, we similarly find both inward and anterior ciliary muscle movement. These findings are consistent with the "geometric theory"3 of presbyopia and may also support the suggestion that the iris plays a more significant role in presbyopia4: age–related lens growth and consequent anterior and inward iris displacement may pull the muscle along. Pharmacological agents also act upon the iris, and may thus simulate the effect of aging on the ciliary muscle. Future work includes analyzing the effect of age and accommodation on iris geometry in our existing MRI database. 1) Strenk SA, Semmlow JL, Strenk LM, Munoz P, DeMarco JK. High resolution MRI of the accommodated lens and ciliary muscle: A preliminary cross sectional study. Invest Ophthalmol Vis Sci. 1999;40:1162–1169. 2) Lutjen–drecoll E, Tamm E, Kaufman PL. Age–Related Loss of Morphologic Responses to Pilocarpine in rhesus Monkey Cilary Muscle. Arch Ophthalmol. 1988;106:1591–1598. 3) Koretz JF, Handleman GH. How the Human Eye Focuses. Sci Am. 1988;259:92–99. 4) Pierscionek BK, Weale RA. Presbyopia – A Maverick of Human Aging. Arch Gerontology and Geriatrics. 1994;20:229–240.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • aging • ciliary muscle