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HA Weeber; Influence of the Stress-free Shape of the Lens on Accommodation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):410.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: During disaccommodation, the crystalline lens is stretched by the zonular system. When the zonular system is relaxed, the total of capsule and lens is relaxed. Nevertheless, while in mutual equilibrium, both capsule and lens may be under stress. This is indicated by observations in the literature, saying that the lens changes shape, when the capsule is removed: therefore, the stress-free shape of the capsule is not equal to the stress-free shape of the lens. The present study was undertaken in order to show the influence of the stress-free shape of the lens on the accommodative ability. Methods: A model of accommodation and disaccommodation was made using the finite elements method (FEM). The model is based on literature data of the geometry and material properties of lens, capsule and zonule. Using this method, the amount of accommodation and disaccommodation can be calculated under different conditions. For the purpose of this study, the amount of accommodation and disaccommodation was calculated for two models. In model one, the stress-free shape of the lens was identical to the accommodated state of the lens-plus-capsule. In model two, the stress-free shape of the lens was identical to the disaccommodated state of the lens-plus-capsule. The capsular bag is the same shape in both models. Results: The two models show an almost identical accommodation behavior. For both models, the accommodative amplitude is approximately 3 diopters. Also, the zonular force needed to stretch the lens equator a certain distance is identical. The change in center thickness of the lens during accommodation is less for the model with the disaccommodated stress-free shape. Conclusion: Although the real stress-free shape of the lens has never been precisely measured, these model calculations show that the stress-free shape does not influence accommodative ability.
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