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S. Norrby; Eye Model as Function of Age and Accommodation With Aspherical Surfaces and a Gradient Index Description of the Lens . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1187.
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© ARVO (1962-2015); The Authors (2016-present)
To develop an eye model that is in accordance with measured ocular dimensions and optical performance.
The author previously published the Dubbelman eye model as function of age and accommodation based on published data on ocular dimensions obtained from corrected Scheimpflug images. This model assumed a homogeneous refractive index for the lens. For a more realistic description of the lens, published measurements of protein density across human lenses were used to calculate the corresponding refractive index profile. There is an increase in index from the surface towards the centre in the cortex, while the nucleus has constant index. The closed curve contour description of the lens published by Kasprzak was used to model the lens as a shell structure with this index profile and with the central 3mm fitted by least squares to agree with the Dubbelman model. For accommodated shapes a constraint of constant lens volume was applied.
At ages 20, 35, 50 and 70 years the longitudinal spherical aberration (LSA) over a 4mm pupil was found to be 0.15, 0.22, 0.40 and 1.09mm, respectively, for an object at infinity. For the 35 year eye LSA was found to be 0.22, –0.12, –0.44 and –1.03mm for, respectively, object distances infinity, 1000, 500 and 250mm. The lens diameter decreases by 0.22mm over this range of accommodation.
An increase of LSA with age is in agreement with published data. A trend towards more negative LSA with increasing level of accommodation is also in agreement with published data. The decrease in lens diameter is plausible for a 4D accommodative effort.
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