Objective measurement of straylight in the human eye with a Shack–Hartmann (SH) wavefront aberrometer is limited in imaging angle. We propose a measurement principle and a point spread function (PSF) reconstruction algorithm to overcome this limitation. In our optical setup, a variable stop replaces the stop conventionally used to suppress reflections and scatter in SH aberrometers. We record images with 21 diameters of the stop. From each SH image, the average intensity of the pupil is computed and normalized. The intensities represent integral values of the PSF. We reconstruct the PSF, which is the derivative of the intensities with respect to the visual angle. A modified Stiles Holladay approximation is fitted to the reconstructed PSF, resulting in a straylight parameter. A proof-of-principle study was carried out on eight healthy young volunteers. Scatter filters were positioned in front of the volunteers’ eyes to simulate straylight. The straylight parameter was compared to the C-Quant measurements and the filter values. The PSF parameter shows strong correlation with the density of the filters and a linear relation to the C-Quant straylight parameter. Our measurement and reconstruction techniques allow for objective straylight analysis of visual angles up to 4 deg.
The Vision Assistant is designed as an intelligent tool to assist people with different disabilities. The goal of this project is to replace the mouse and keyboard by an adaptive eye-tracker system (so called mouseless cursor) which Using a camera, it works with a pattern recognition algorithm based on a Hough-transform core to process the streaming image sequences. This technique is known for its performance in locating given shapes. In particular, it is used to extract the shapes that relate to the human eye and analyze them in real-time with the purpose of getting the position of an eye in an incoming image and interpreting it as the reference position of a mouse cursor on the user's monitor. The possibility of the Hough transform parallelization and its execution on the Hubel-Wiesel Neural Network for ultra fast eye-tracking is also discussed in this paper. The results of several experiments in this paper proved that the system performs quite well with different colours of the subjects' eyes as well as under different lighting conditions. In the conclusion we paid attention to the problems of further improvement of the functional and algorithmic parts of the Vision Assistant.
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