Finite-Difference Time-Domain Simulations of Light Scattering from Retinal Photoreceptors
Abdallah, Samer S.
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Recently, a novel optical imaging technique was successfully used in measuring the functional response of living retinal tissues. The technique, functional ultra high resolution optical coherence tomography, measures localized differential changes in the retina reflectivity over time resulting from external white light stimulation. This result can be used to develop a non-invasive diagnostic method for the early detection of retinal diseases. However, the physiological causes of the experimentally observed optical signals, most of which originate from the photoreceptors layer, are still not well understood. Due to the complexity of the photoreceptors, using purely experimental methods to isolate the changes in light reflectivity corresponding to individual physiological processes is not feasible. Therefore, we have employed the finite-difference time-domain method to model the changes in light scattering patterns of the photoreceptor cells caused by light-induced physiological processes. Processes such as cell swelling, cell elongation and hyperpolarization of doublelipid membrane structures were simulated by changing the size parameters and optical properties of the cells components. Simulation results show that the hyperpolarization of double-lipid membranous structures and cell swelling are the most likely causes for the experimentally observed changes in optical reflectivity. A number of experiments were suggested to verify the conclusions drawn from this numerical work. This numerical work includes an analysis of various errors in FDTD computational models.