Editing Retina (section)

==== In birds ====
The bird retina is devoid of blood vessels, perhaps to give unobscured passage of light for forming images, thus giving better resolution. It is, therefore, a considered view that the bird retina depends for nutrition and oxygen supply on a specialized organ, called the "pecten" or [[pecten oculi]], located on the blind spot or optic disk. This organ is extremely rich in blood vessels and is thought to supply nutrition and oxygen to the bird retina by diffusion through the vitreous body. The pecten is highly rich in alkaline phosphatase activity and polarized cells in its bridge portion – both befitting its secretory role.<ref>{{cite journal |author1 = Bawa S.R. |author2 = YashRoy R.C. |year = 1972 |title = Effect of dark and light adaptation on the retina and pecten of chicken |url = https://www.researchgate.net/publication/18108932 |journal = Experimental Eye Research |volume = 13 |issue = 1 |pages = 92–97 |doi = 10.1016/0014-4835(72)90129-7 |pmid = 5060117 |url-status = live |archive-url = https://web.archive.org/web/20141009111444/http://www.researchgate.net/publication/18108932_Effect_of_dark_and_light_adaptation_on_the_retina_and_pecten_of_chicken?ev=prf_pub |archive-date = 9 October 2014 }}</ref> Pecten cells are packed with dark melanin granules, which have been theorized to keep this organ warm with the absorption of stray light falling on the pecten. This is considered to enhance metabolic rate of the pecten, thereby exporting more nutritive molecules to meet the stringent energy requirements of the retina during long periods of exposure to light.<ref>{{cite journal |last1 = Bawa |first1 = S.R. |last2 = YashRoy |first2 = R.C. |year = 1974 |title = Structure and function of vulture pecten |url = https://www.researchgate.net/publication/231569868 |journal = Cells Tissues Organs |volume = 89 |issue = 3 |pages = 473–480 |doi = 10.1159/000144308 |pmid = 4428954 |url-status = live |archive-url = https://web.archive.org/web/20150714070339/http://www.researchgate.net/publication/231569868_Structure_and_function_of_vulture_pecten?ev=prf_pub |archive-date = 14 July 2015 }}</ref>