Editing Eye (section)

====Pit eyes====
Pit eyes, also known as [[Simple eyes in invertebrates#Stemmata|stemmata]], are eye-spots which may be set into a pit to reduce the angles of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. Found in about 85% of phyla, these basic forms were probably the precursors to more advanced types of "simple eyes". They are small, comprising up to about 100 cells covering about 100&nbsp;μm. The directionality can be improved by reducing the size of the aperture, by incorporating a reflective layer behind the receptor cells, or by filling the pit with a refractile material.<ref name=Land1992/>

[[Crotalinae|Pit vipers]] have developed pits that function as eyes by sensing thermal infra-red radiation, in addition to their optical wavelength eyes like those of other vertebrates (see [[infrared sensing in snakes]]). However, pit organs are fitted with receptors rather different from photoreceptors, namely a specific [[transient receptor potential channel]] (TRP channels) called [[TRPV1]]. The main difference is that photoreceptors are [[G protein-coupled receptor|G-protein coupled receptors]] but TRP are [[ion channel]]s.