MRI Study of the Aging Uveal Tract: The Modified Geometric Theory of Presbyopia and Its Implications for Posterior Chamber Phakic IOLs

Abstract

Abstract: : Purpose: To evaluate the effect of age on the uveal tract. Methods: High–resolution magnetic resonance imaging provides unsurpassed soft tissue contrast and the ability to image the accommodative structures simultaneously, in the intact human eye in vivo, thus the geometric relationship between the various accommodative structures can be obtained¹. Images were acquired from 30 subjects between the ages of 22 and 91 during accommodation and with accommodation at rest as previously described¹. The location of the ciliary sulcus was obtained as a function of age and accommodation and compared with the previously reported location of the ciliary muscle² and the previously reported age–related change in lens thickness¹. Results: The ciliary sulcus and the ciliary muscle both move anteriorly with age, when normalized to the anterior segment length (ASL), at statistically the same rate (–0.002 ± 0.0003)ASL mm/year (P=0.0005) for both minimum and maximum accommodation. A correlation between lens growth and ciliary muscle and sulcus anterior displacement is also noted: the rate of lens growth is (0.002 ± 0.0005)ASL mm/year (P=0.0003). Conclusions: The Geometric Theory³ attributes presbyopia development to lens growth. Our data suggests that the uveal tract plays a significant role in presbyopia⁴: age–related lens growth and consequent anterior and inward iris displacement⁴ may pull the ciliary muscle and ciliary sulcus along, ultimately rendering ciliary muscle contraction ineffective. Since posterior chamber phakic IOLs rest in the ciliary sulcus and vault over the crystalline lens, these findings also have implications for their sizing, placement and long–term stability. 1) Strenk, S.A., et al., Age–related changes in human ciliary muscle and lens: a magnetic resonance imaging study. Invest Ophthalmol Vis Sci, 1999. 40(6): p. 1162–9. 2) Strenk, S.A., L.M. Strenk, and J.L. Semmlow. MRI study of the effect of age and accommodation on ciliary muscle location. in IOVS;45:ARVO E–Abstract 2395. 2004. 3) Koretz, J.F. and G.H. Handelman, How the human eye focuses. Sci Am, 1988. 259(1): p. 92–9. 4) Strenk, Strenk, and Koretz, The Mechanism of Presbyopia, Progress in Retinal and Eye Research, in press.

Keywords: refractive surgery: phakic IOL • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • uvea