The compound eye of insects is composed of hundreds of unit eyes called ommatidia. An ommatidium contains a cluster of photoreceptor cells surrounded by support cell, and pigment cells. The outer part of the ommatidium is overlayed with a transparent cornea. The photograph to the right shows a cluster of photoreceptor cells from a single ommatidium from Drosophila melanogaster (magnified 400X). It is about 85 μm in length and 5-10 μm in diameter. The nucleus and the rhabdomere from a photoreceptor cell are visible. Compound eye of a dragonfly Compound eye of Antarctic krill as imaged by an electron microscope A compound eye is a visual organ found in certain arthropods such as some insects and crustaceans. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Photoreceptor cells are contained in the retina and are responsible for transducing, or converting, light into signals that can be ultimately transmitted to the brain via the optic nerve. ... The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eyes optical power [1]. Together with the lens, the cornea refracts light and consequently helps the eye to focus. ... Binomial name Drosophila melanogaster Meigen, 1830 dorsal view Drosophila melanogaster Meigen , 1830 (Black-bellied Dew-lover) a dipteran (two-winged) insect, is the species of fruit fly that is commonly used in genetic experiments; it is among the most important model organisms. ... A micrometre (American spelling: micrometer), symbol µm, is an SI unit of length. ... In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells that contains most of the cells genetic material. ...

Ommatidia of Antarctic krill eye - click for higher resolutions

Superposition eye crossection - low light condition top with separating pigments contracted, so that the light reaches over many ommatida the nerve, bright condition below with pigments expanded