Editing Photoreceptor cell (section)

== Retinal mosaic ==
{{main|Retinal mosaic}}
[[File:ConeMosaics.jpg|thumb|250px|Illustration of the distribution of cone cells in the fovea of an individual with normal color vision (left), and a color blind (protanopic) retina. Note that the center of the fovea holds very few blue-sensitive cones.]]
[[File:Human photoreceptor distribution.svg|thumb|250px|Distribution of rods and cones along a line passing through the fovea and the blind spot of a human eye<ref>[https://foundationsofvision.stanford.edu/chapter-3-the-photoreceptor-mosaic Foundations of Vision], Brian A. Wandell</ref>]]

Most vertebrate photoreceptors are located in the retina. The distribution of rods and cones (and classes thereof) in the retina is called the '''retinal mosaic'''. Each human [[retina]] has approximately 6 million cones and 120 million rods.<ref name = Schacter137>{{cite book|last=Schacter|first=Daniel L.|title=Psychology Second Edition|year=2011|publisher=Worth Publishers|location=New York|isbn=978-1-4292-3719-2|pages=[https://archive.org/details/psychology0000scha/page/136 136–137]|url=https://archive.org/details/psychology0000scha/page/136}}</ref>  At the "center" of the retina (the point directly behind the lens) lies the [[Fovea centralis|fovea]] (or fovea centralis), which contains only cone cells; and is the region capable of producing the highest [[visual acuity]] or highest [[Optical resolution|resolution]].  Across the rest of the retina, rods and cones are intermingled.  No photoreceptors are found at the [[blind spot (vision)|blind spot]], the area where ganglion cell fibers are collected into the optic nerve and leave the eye.<ref name=Goldstein>{{cite book|last1= Goldstein|first1= E. Bruce| title= Sensation and Perception| publisher= Thomson and Wadswoth| edition = 7| year= 2007}}</ref> The distribution of cone classes (L, M, S) are also nonhomogenous, with no S-cones in the fovea, and the ratio of L-cones to M-cones differing between individuals.

The number and ratio of rods to cones varies among species, dependent on whether an animal is primarily [[Diurnal animal|diurnal]] or [[nocturnal]]. Certain owls, such as the nocturnal [[tawny owl]],<ref>{{cite web |url=http://www.owls.org/education/owl-information/eyes.html |title=Owl Eye Information |website=owls.org |publisher=World Owl Trust |access-date=1 May 2017 |archive-date=16 February 2018 |archive-url=https://web.archive.org/web/20180216215648/http://www.owls.org/education/owl-information/eyes.html |url-status=dead }}</ref> have a tremendous number of rods in their retinae. Other vertebrates will also have  a different number of cone classes, ranging from [[monochromat]]s to [[pentachromat]]s.