sim·ple eye • n. a small eye of an insect or other arthropod that has only one lens, typically present in one or more pairs. Also called ocellus. Contrasted with compound eye.

simple eye Eye consisting of a single ocellus. Such eyes are found in adult insects, and in the larvae of hemimetabolous insects. Usually there are three, arranged triangularly on the head. Simple eyes are not thought to be involved in the formation of images, but act only as monitors of the level of light intensity.