Vision Beyond the Fovea: Evaluation and Stimuli Properties
Abstract: This research is about evaluating vision in the periphery. Peripheralvision is of fundamental importance in the performance of our everydayactivities. The aim of this thesis is to develop methods suitable for theevaluation of peripheral vision and to assess how different visual functionsvary across the visual field. The results have application both within thefield of visual rehabilitation of people with central visual field loss (CFL)and as well as in myopia research.All methods for assessing peripheral vision were implemented withadaptive psychophysical algorithms based on Bayesian statistics. A routinefor time-efficient evaluation of peripheral contrast sensitivity wasimplemented and verified for measurements out to 30° in the visual field.Peripheral vision was evaluated for different properties of the stimuli:sharpness, motion, orientation, and extent. Optical quality was controlledusing adaptive optics and/or corrective spectacles specially adapted for theperipheral viewing angle. We found that many peripheral visual functionsimproved with optical correction, especially in people with CFL. We alsofound improvements in peripheral contrast sensitivity for low spatialfrequencies when stimuli drifted at 5 to 10 Hz; this applies both for peoplewith normal vision and those with CFL. In the periphery, it is easier to seelines that are oriented parallel with respect to the visual field meridian. Wehave shown that this directional bias is present for both resolution anddetection tasks in the periphery, even when the asymmetric optical errorsare minimized. For accurate evaluation of peripheral vision, we thereforerecommend using gratings that are oriented oblique to the visual fieldmeridian. The directional bias may have implications in how peripheralimage quality affects myopia progression. Another proof that peripheralvision can influence central visual function is the fact that, when thestimulus extent was increased beyond the fovea, the blur in the stimulus wasless noticeable.
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