Spatial amplitude modulation for vision improvement in cataractous eyes.

Abstract

Purpose : To use spatial amplitude modulation method for vision improvement by deblurring the retina images in cataractous eyes.

Methods : The image formation on retina is the result of light propagation and focusing through crystalline lens, therefore the interaction of light with the opacities (cataractous lens) results in scattering and forming blur retinal images. We used spatial amplitude modulation method of masking the pupil plane, in such a way that light can only pass through the remained transparent parts of lens. The method depends on the imaging of pupil plane of cataract eye to estimate the spatial location of opacities to make an opacity map. This is used to design a complementary mask, which can be conjugated at the pupil plane by a spatial light modulator. The proposed method has been verified via simulation, where cataractous lens with opacities has been generated. The point spread function (PSF) was calculated by taking the FFT of the cataractous lens. Retinal image was calculated by convolving the PSF with ground truth image (I_g). The phase map of cataractous lens was used to generate a complementary binary mask to mask the pupil plane and retinal image was again generated by convolution of PSF of masked pupil with I_g. The quality of the retinal images was quantified by structural similarity (SSIM) index without and after applying the method.

Results : Cataractous lenses were simulated as phase elements with circular function acting as pupil with diameter 2.7 mm. Three levels of straylight described by Log₁₀(s) = 1.75, 2 and 2.37 (at an angle of 6 degrees), corresponded to nuclear cataracts of rank 3 or higher in the Lens Opacity Classification System III (LOCS III) has been simulated. Images of sine-wave grating of 6, 12 and 20 CPD, were used as ground truth images. Measured SSIM has shown improvement for higher CPD for all grading’s of cataract. For 20 CPD, the SSIM for Log₁₀(s) = 1.75 has been improved from 0.33 to 0.38, for Log₁₀(s) = 2, from 0.1 to 0.22 and for Log₁₀(s) = 2.37, from 0.008 to 0.11.

Conclusions : Spatial amplitude modulation has been evaluated by numerical simulations of retinal images, corresponding to different grades of cataracts and by SSIM which has shown significant improvements after applying the method.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.