Pterygium, the dominant eye and the habit of closing one eye in sunlight.

Based on findings in 21 patients with pterygium and 22 normal controls a theory is proposed that pterygium develops initially in the dominant eye. In 13 patients with unilateral pterygium the disorder in 13 was located in the dominant eye. The visual response to intense sunlight of the 21 control subjects confirmed the clinical observation that the non-dominant eye is closed and the dominant eye held open in people facing the sun. These results might explain why pterygium usually occurs first in the dominant eye. A genetic pre-disposition for the disorder is likely.