On some occasions, when we take a picture it happens that someone gets a reddish color in the eye region. But why this happen?
In fact, the human eye works like a darkroom. Although the pupil is black on the outside, the area at the back of the eye, called the retina, is provided with several blood vessels, giving it a reddish color.
What happens in photos is that the light from the flash falls on the pupil and reaches the retina. Upon reaching this part of the eye, light strikes the blood vessels and the red color is preferentially reflected. Another question: why doesn't this always happen?
The occurrence or not of reddish eyes in the photos will depend on the brightness of the environment. When the room is brightly lit, the pupils naturally contract, making it difficult for flash light to enter.
Current cameras have features that reduce the effect of "red eyes", firing lights before the flash in order to retract the subject's pupils. Another solution is to look at a luminous object a few moments before taking the picture, causing the pupil to contract.
Curiosities - Brazil School
Source: Brazil School - https://brasilescola.uol.com.br/curiosidades/olhos-vermelhos-nas-fotos.htm
