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Eyes

Types of eyes

Nature has produced ten different eye layouts indeed every way of capturing an image has evolved at least once in nature, with the exception of zoom and Fresnel lenses. Eye types can be categorized into "simple eyes", with one concave chamber, and "compound eyes", which comprise a number of individual lenses laid out on a convex surface. Note that "simple" does not imply a reduced level of complexity or acuity. Indeed, any eye type can be adapted for almost any behaviour or environment. The only limitations specific to eye types are that of resolution the physics of compound eyes prevents them from achieving a resolution better than 1°. Also, superposition eyes can achieve greater sensitivity than apposition eyes, so are better suited to dark-dwelling creatures. Eyes also fall into two groups on the basis of their photoreceptor's cellular construction, with the photoreceptor cells either being cilliated or rhabdomic. These two groups are not monophyletic; the cnidaira also possess cilliated cells, and some annelids possess both.

Simple eyes

Pit eyes
Pit eyes, also known as stemma, are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eyespot, to allow the organism to deduce the angle of incoming light...More

Pinhole eye
The pinhole eye is an "advanced" form of pit eye incorporating several improvements, most notably a small aperture and deep pit. It is only found in the nautiloids....More