Editing Photoreceptor cell (section)

== Ganglion cell photoreceptors ==
{{main|Intrinsically photosensitive retinal ganglion cell}}
[[Intrinsically photosensitive retinal ganglion cells]] (ipRGCs) are a subset (≈1–3%) of [[retinal ganglion cell]]s, unlike other retinal ganglion cells, are intrinsically [[photosensitive]] due to the presence of [[melanopsin]], a light-sensitive protein. Therefore they constitute a third class of photoreceptors, in addition to [[rod cells|rod]] and [[cone cells]].<ref name=":1">{{cite journal | vauthors = Do MT, Yau KW | title = Intrinsically photosensitive retinal ganglion cells | journal = Physiological Reviews | volume = 90 | issue = 4 | pages = 1547–81 | date = October 2010 | pmid = 20959623 | pmc = 4374737 | doi = 10.1152/physrev.00013.2010 }}</ref>

In [[human]]s the ipRGCs contribute to non-image-forming functions like circadian rhythms, behavior and [[pupillary light reflex]].<ref name="Zaidi et al 2007">{{cite journal |vauthors=Zaidi FH, etal |title=Short-wavelength light sensitivity of circadian, pupillary, and visual awareness in humans lacking an outer retina.|journal=Current Biology|volume=17|issue=24|pages=2122–8|year=2007|pmid=18082405|pmc=2151130|doi=10.1016/j.cub.2007.11.034|bibcode=2007CBio...17.2122Z }}</ref> Peak [[spectral sensitivity]] of the receptor is between 460 and 482&nbsp;nm.<ref name="Zaidi et al 2007" /> However, they may also contribute to a rudimentary visual pathway enabling [[conscious]] sight and brightness detection.<ref name="Zaidi et al 2007" /> Classic photoreceptors (rods and cones) also feed into the novel visual system, which may contribute to color constancy. ipRGCs could be instrumental in understanding many diseases including major causes of blindness worldwide like glaucoma, a disease that affects ganglion cells, and the study of the receptor offered potential as a new avenue to explore in trying to find treatments for blindness.

ipRGCs were only definitively detected ipRGCs in humans during landmark experiments in 2007 on rodless, coneless humans.<ref name=ns1>Coghlan A. [https://www.newscientist.com/article/mg19626354.100-blind-people-see-sunrise-and-sunset.html Blind people 'see' sunrise and sunset]. New Scientist, 26 December 2007, issue 2635.</ref><ref name=mnt>Medical News Today. [http://www.medicalnewstoday.com/articles/91836.php Normal Responses To Non-visual Effects Of Light Retained By Blind Humans Lacking Rods And Cones] {{Webarchive|url=https://web.archive.org/web/20090206030830/http://www.medicalnewstoday.com/articles/91836.php |date=2009-02-06 }}. 14 December 2007.</ref> As had been found in other mammals, the identity of the non-rod non-cone photoreceptor in humans was found to be a ganglion cell in the inner retina. The researchers had tracked down patients with rare diseases wiping out classic rod and cone photoreceptor function but preserving ganglion cell function.<ref name=ns1/><ref name=mnt/> Despite having no rods or cones the patients continued to exhibit circadian photoentrainment, circadian behavioural patterns, melanopsin suppression, and pupil reactions, with peak spectral sensitivities to environmental and experimental light matching that for the melanopsin photopigment. Their brains could also associate vision with light of this frequency.