Eyes with mirror optics

Most eyes have optical systems that are based on refraction by a lens or a cornea. However, there are two eye types that form images using mirrors. These are concave mirror eyes, similar in principle to a Newtonian telescope, and reflecting superposition compound eyes, where the mirrors are arranged radially in a square array. The concave mirrors are found in scallops (Pecten), where they allow the eye to see moving objects, and in a modified form in a few deep-sea crustaceans. The reflecting superposition eyes are confined to the long-bodied decapod crustaceans-the shrimps, prawns, crayfish and lobsters. Recently this second mechanism has found a number of uses in x-ray optics.