Presbyopia, accommodation, and the mature catenary.

OBJECTIVE To demonstrate a plausible explanation of aging changes and to reduce the controversy relative to accommodation by using a mechanical model of the catenary theory of lens change. MECHANICAL MODELING: A mechanical model was used to simulate a human lens in both the accommodated and unaccommodated state to demonstrate changes in the mechanism of accommodation with age. METHODS Fluid-filled latex balloons were supported by a plastic wrap hammock to form a catenary that models the human lens. Increasing volumes were used to simulate that of the aging lens, and variations in curvature were measured. MAIN OUTCOME MEASURES The degree of curvature of a simulated anterior lens surface was measured and compared with mathematical modeling of its optical surface based on the catenary hydraulic suspension theory. RESULTS The measurements showed that accommodative loss and other features such as mass displacement, reproducible lens surfaces, and zonule support are consistent with the catenary theory of accommodation and an increasing lens volume with age. CONCLUSIONS The catenary theory of accommodation provides a basis for evaluating age changes of the human lens. Variable results with surgical procedures for presbyopia are also predictable with the model. These results can be used to provide a basis for intraocular lens design.

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