Invertebrate Photoreceptor

Invertebrate Photoreceptor

A simple eye (sometimes called a pigment pit) refers to a type of eye design or optical arrangement that contains a single lens which detects light. A "simple eye" is so-called in distinction from a multi-lensed "compound eye", and is not necessarily at all simple in the usual sense of the word. The eyes of humans and large animals, and camera lenses are classed as "simple" because in both cases a single lens collects and focuses light onto the retina or film. Many insects have compound eyes consisting of multiple lenses (up to tens of thousands), each focusing light onto a small number of retinula cells.

The structure of an animal's eye is determined by the environment in which it lives, and the behavioural tasks it must fulfill to survive. Arthropods differ widely in the habitats in which they live, as well as their visual requirements for finding food or conspecifics, and avoiding predators. Consequently, an enormous variety of eye designs is found in arthropods: nature has repeatedly developed novel solutions to overcome visual problems or limitations (for a review of arthropod visual systems see Warrant, 2006).