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RR Peddada, RM Davis, VA Pakalnis; Age-Related Macular Degeneration is Associated With Enhanced Stress in Bruch's Membrane Secondary to Hyperopia, Hypertension, and Tobacco Smoking: A Hypothesis . Invest. Ophthalmol. Vis. Sci. 2002;43(13):694.
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Purpose:To propose a mechanism for the development of age-related macular degeneration (ARMD) in terms of mechanical failure of Bruch's membrane. Methods:We developed a theoretical/computer model for the human eye and calculated mechanical stress within the Bruch's membrane. For this purpose we applied a modified Lame's analysis to an elastic spheroidal composite shell. Results: Our calculations show that the stress at any fenestration in Bruch's membrane increases with large radius of curvature at the posterior pole, low choriocapillaris pressure, and high intraocular pressure. (See Figure.) We note from literature that these parameters are associated with conditions that are shown to be risk factors for ARMD, namely, hyperopia (associated with increased posterior pole radius of curvature), hypertension and tobacco smoking (associated with increased choroidal arteriolar resistance, i.e., with decreased choriocapillaris pressure). Our analysis also demonstrates that the effect of each of the three parameters on the mechanical stress may be offset by the remaining two parameters. So, for example, a high intraocular pressure need not necessarily produce large stress if the choriocapillaris pressure is not too low or if the radius of curvature of the posterior pole is not too high. Finally, our mechanical analysis shows that large number of cycles (over a period of a few decades) of increasing and decreasing mechanical stress may lead to fragmentation of the Bruch's membrane whereas a moderate level of constant or transiently elevated load may not. This is similar to breaking of a steel paper clip with repeated bending and straightening when the same clip cannot be broken by a continuous pulling. Conclusion:Therefore, we arrive at the hypothesis that factors that increase mechanical stress in Bruch's membrane including elevated intraocular pressure may be associated with age-related macular degeneration. Experiments and clinical studies are necessary to confirm or refute this hypothesis. View OriginalDownload SlideView OriginalDownload Slide
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