Purchase this article with an account.
L.M. Strenk, S.A. Strenk, J.F. Koretz; MRI Study of the Relationship Between Ciliary Muscle and Lens Position in the Development of Presbyopia . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4223.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Purpose: To define the geometric relationship between the ciliary muscle and lens in the aging eye. Methods: High–resolution MRI 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 28 subjects between the ages of 22 and 62 during resting accommodation as previously described1. MRI has demonstrated that the ciliary muscle moves anteriorly with age2. Here we determine the intersection of the ciliary muscle plane with the lens. Results: The intersection between the ciliary muscle apex plane and the lens occurs anterior to the lens equator and forms a circle that is of constant radius with age and has a mean value of 3.80 ± 0.09 mm. Conclusions: Analyzing in–vitro data on zonular location3, and without considering the ciliary muscle, Weale4 independently determined that the zonular insertion on the anterior lens surface forms a circle of radius 3.80 mm that is constant with age. Taken together with our findings, this suggests that the anterior zonules run horizontally to the ciliary muscle apex, which is well anterior to the lens equator, and that this relationship remains unchanged with age. Consequently care must be taken when interpreting data from in–vitro lens stretching experiments, which assume the muscle is at the lens equator and thus apply a non–physiological downward force to the lens. The Geometric Theory5 attributes presbyopia to lens growth and a changing angle of zonular insertion. Our current findings suggest an alternate avenue (the Modified Geometric Theory6) by which lens growth may lead to presbyopia: lens growth causes an anterior displacement of the uveal tract which ultimately renders ciliary muscle contraction ineffective. 1) Strenk, S.A., et al., Age–related changes in human ciliary muscle and lens: a magnetic resonance imaging study. IOVS,1999. 40(6): p. 1162–9. 2) Strenk, S.A., L.M. Strenk, and J.L. Semmlow. IOVS;45:ARVO E–Abstract 2395. 2004 3) Farnsworth, P.N., S.E. Shyne, Anterior zonular shifts with age. Exp Eye Res, 1979. 28(3): p. 291–7. 4) Weale, R.A., Why we need reading–glasses before a zimmer–frame. Vision Res, 2000. 40(17): p. 2233–40. 5) Koretz, J.F, G.H. Handelman, How the human eye focuses. Sci Am, 1988. 259(1): p. 92–9. 6) Strenk,S.A., Strenk,L.M. and Koretz,J.F. The Mechanism of Presbyopia, Progress in Retinal and Eye Research, in press.
This PDF is available to Subscribers Only