What is the structure of a compound eye of a cockroach and how does it work?

Compound eyes are organs of vision in arthropods (insects and crustaceans). A compound eye is characterized by a variable number (a few to thousands) of small eyes, ommatidia, which function as independent photoreception units with an optical system (cornea, lens and some accessory structures) and normally eight photoreceptor cells. The compound eyes do not form an image like the large lens eyes of vertebrates and octopi, but a "neural picture" is formed by the photoreceptors in ommatidia, which are oriented to receive light from different directions, defined by the optics of the ommatidia, the curvature of the eye and the spacing arrangement and density of the ommatidia.!