Some of shape-related conditions cause significant glare as the light entering the eye scatters and causes discomfort or reduced vision. More commonly conditions that result in a dilated pupil let too much light into one eye, which is uncomfortable and can reduce vision. In cases of Aniridia, when people are born without one or both irises they have very large pupils. We use contact lenses that give an artificially smaller pupil to limit the light entering the eye, reducing the glare, resulting in normal vision.
Other patients with certain conditions such as albinism or cone dystrophy are naturally sensitive to light even with normally sized pupils. For these conditions we use contact lenses, often ones tinted like sunglasses, to limit the light entering the eye, thus effectively reducing glare.