Editing Red-eye effect (section)

== Causes ==
The red-eye effect occurs in the eyes of humans when a photography [[Flash (photography)|flash]] is used in low light or at night.{{Sfn|Webster's Dictionary|2025}}{{Sfn|Rodrigues|2019}} The flash travels through the eyes and rebounds at the rear of the eye, turning the eyes red ([[red reflex]]) in a photograph.{{Sfn|Johnson|2009}}{{Sfn|Bailey|2020}}{{Sfn|Yang|2011}}{{Sfn|Mukamal|2024}} The main cause of the red color is the ample amount of blood in the [[choroid]], which supports the back of the eye and lies behind the [[retina]].{{Sfn|Yang|2011}}{{Sfn|Evans|2025}}{{Sfn|Yoo|Park|2009|p=1006}} [[Melanin]] also plays a role in the effect, as individuals with less melanin, such as [[albinos]], reflect more light.{{Sfn|Yang|2011}} The close distance of the flash to the [[camera lens]] can also have an impact, especially on cameras with built-in flash.{{Sfn|Evans|2025}}

The effect could also infrequently occur in only one eye of persons with [[cataract]]s or tumors, or it may be exacerbated by photographing subjects that are drunk.{{Sfn|Rodrigues|2019}}{{Sfn|Bailey|2020}} In children, if the red reflex is white, it may indicate [[retinoblastoma]] malignancy,{{Sfn|Mukamal|2024}}{{Sfn|NHS|2014}} whereas yellow color may indicate [[Coats' disease]]. If the effect is asymmetrical, it may indicate [[strabismus]].{{Sfn|Mukamal|2024}} A similar reaction to the red-eye occurs in animals, turning their eyes different colors.{{Sfn|Bailey|2020}}