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Physical Model of Intraocular Scattering using a Spatial Light Modulator


Purpose: Intraocular scattering affects the retinal image and quality of vision. It is produced by the interaction of light with local variations of the refractive index and its angular distribution depends on the spatial characteristics of the scatterers. A better understanding of the physical basis of scattering in the eye would help with possible compensation methods. In this context, we developed a realistic physical model to reproduce the light scattering occurring in the eye.

Methods: Theoretical analysis identified the spatial characteristics of the required phase to reproduce intraocular scattering, represented by the wide-angle point-spread function (PSF). Sampling of the phase at the pupil plane should be comparable to the size of the features that scatter light within the eye. The experimental setup used a liquid crystal on silicon spatial light modulator (SLM) (PLUTO, Holoeye, Germany) to generate the phase patterns. The SLM plane was conjugated with magnification of about 0.17 with the eye’s pupil. The induced scattering was evaluated in single pass by using the optical integration method (Ginis et al., J Vis, 2012) and compared with typical scatter occurring in normal eyes as given by the CIE wide-angle PSFs. The physical characteristics of the SLM (8 μm pixel size), in combination with the particular magnification and diffraction effects limit the angular range for the generation of the PSF up to 4 degrees.

Results: The experimentally induced straylight for different phase map was in good agreement with the theoretical predictions. Contrast reduction in extended images associated to light scattering was documented for demonstration purposes. The straylight parameter (S) of the experimentally induced scatter was associated to the RMS amplitude (h) of the phase map by the following formula: log(S) = 0.9748*log(h) + 1.826. This permits to reproduce intraocular scatter conditions ranging from normal clear eyes to early cataract.

Conclusions: An accurate physical model of scatter was developed using a spatial light modulator and appropriate phase distributions. The instrument is suitable for the generation of light scattering similar to that found in human eyes. This is not only is a useful tool for psychophysical experiments but also documents the physical requirements for possible compensation of light scattering in the eye.

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