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R. Navarro, F. Palos, L. M. González; An Adaptive Model of the Gradient Index of the Aging Crystalline Lens and Their Changes With Accommodation. Invest. Ophthalmol. Vis. Sci. 2007;48(13):5627.
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© ARVO (1962-2015); The Authors (2016-present)
To develop an adaptive model of the refractive index distribution (GRIN) of the crystalline lens. The model must be able to adjust individual GRIN distributions (customization), as well as the changes of the lens shape and internal structure with age and accommodation.
We carried out the following steps: (1) Mathematical formulation, which consisted of a generalization of previously proposed GRIN models, assuming concentric iso-indical surfaces. (2) Validation of the model and its customization capability by fitting recently published in vitro data, of lenses of different ages. (3) A global fit to the complete set of lenses to obtain the average changes of the parameters of the GRIN lens model with age. (4) Recent in vivo data of the changes of the shape of the aging lens with accommodation, were used to build an aging and accommodating lens model, assuming that the structural parameters obtained in vitro are valid for the living lens. (5) The optical performance of the resulting model was examined, including the crucial role of the conic constants. (6) Optimization of the optical performance of the model by adjusting the changes of the anterior and posterior conic constants with age.
The resulting aging GRIN model is extremely compact, as it considers only 3 structural parameters, from them, the central and edge refractive indexes do not change with age. Thus, the model has only one structural age-dependent parameter. As the refractive index distribution adapts to the changes of shape with accommodation and aging, it is surprisingly simple, despite the generality of its formulation. A novel effect has been found, associated to the adaptive GRIN model: A strong coupling between the adaptive GRIN distribution and the conic constants, which has an important impact on the optical performance, even on paraxial refractive power.
The proposed adaptive model has shown to fit individual data, as well as the changes with age and accommodation with a high accuracy. The changes of the optical performance of the resulting lens model with age and accommodation are fully compatible with those observed experimentally.
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