The impact of higher-order aberrations on orientation selectivity

• Main Author: Tahir, Humza
• Published: University of Manchester 2008
• Subjects: 612.84
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493940

This thesis describes a set of experiments investigating the impact of the higher-order aberrations of the eye on contrast sensitivity. The principal aim is to investigate if asymmetric blur induced by the aberrations of the eye can produce orientation selective effects. Orientation in contrast sensitivity testing has been largely ignored as it has been thought that the oblique effect, the preference for vertical and horizontal stimuli over obliques, was entirely neural in origin. Studies measuring the oblique effect were conducted using diffraction-limited pupils yet in larger pupils the higher order aberrations have an increasing impact on visual performance. These aberrations can be circularly asymmetric and so this raises the possibility that they may influence orientation selectivity when the pupil is large. The second aim of the study is to investigate orientation selective contrast sensitivity in refractive surgery patients.