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S. Schramm, B.-U. Seifert, D. Link; Influence of the Shell Structure of the Human Lens on Accommodation Using Ray Tracing. Invest. Ophthalmol. Vis. Sci. 2010;51(13):790.
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© ARVO (1962-2015); The Authors (2016-present)
For stray light analysis in the human eye a variety of schematic eyes with different degrees of complexity exist. In this work a new eye model with a shell-based lens and the ability of accommodation is introduced. To validate the influence on the accommodation power due to the inner shell structure of the lens ray tracing is used.
The new eye model was developed according to Gulstrand in FRED 8.50.0. The contour of the lens was designed based on hyperbolic cosine and hyperbolic tangent functions from the literature including the deformation during accommodation from 0 dpt to 10 dpt. For basic investigations a constant refractive index was assumed. The contours of the inner shells were derived from the outline of the lens. Thus, the radii and thicknesses decrease towards the inner structures. The variations of the radii and thicknesses as well as the refractive index gradient on the optical axis were calculated by parameterized exponential functions. Discrete refractive indices were assigned to each shell. A collimated light source was added to compute the best RMS focus and hence the focus shift, which is used to find a minimum number of shells. Considering the accommodative power, the shell-based eye model (SBEM) was compared to the constant refractive index model.
With a constant refractive index of 1.42 the simulation showed an accommodative power of 10 dpt. A minimum number of 400 shells could be found. In the SBEM the accommodation power is reduced. For example compared to the expected value of 2 dpt a value of 1.7 dpt was simulated.
The new model enables the describtion of the contours of the inner shell structure of the human lens during accommodation. The minimum number of shells (400) is in good accordance with the literature and cell size. The accommodation power depends on geometry of the inner shell structure and its deformation. To achieve the expected accommodative power, a combination of radius and thickness, and refractive index gradient distribution has to be found. The new model can be used for stray light analysis during accommodation by assigning different scatter parameters to individual shells. Furthermore it is also possible to simulate the accommodation process in the presence of presbyopia. Upcoming investigations will address optical properties of the cornea, andspherical and chromatic aberrations.
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