Iris pigmentation and visual-geometric illusions.
Blur or degrading of the retinal image has been shown to be a factor in the formation of visual-geometric illusions where intersecting line elements are present. Light irises allow more scattered light within the eye, which results in more image degradation than found in dark-eyed subjects. Measurements on 755 observers show that illusion magnitude varies as a function of iris pigmentation for a configuration with intersecting line elements (Müller-Lyer illusion), but not for a configuration devoid of such features (Ebbinghaus illusion).
D005127:Eye Color; D005556:Form Perception; D006801:Humans; D007088:Illusions; D009903:Optical Illusions; D012858:Size Perception; D014785:Vision, Ocular