You might have noticed that some people seem to have red eyes when you examine a photograph taken at night with the camera's flash turned on. You might have as well looked for photo editing software or apps to adjust the photograph.
The appearance of red eyes in photographs is actually normal and occurs when light from the camera's flash reflects off the retinal blood vessels located towards the back of the eyes.
In dim light, the pupils dilate to accommodate more light into the eyes, helping you see better. So, when there is a sudden burst of light from a camera's flash in the dark, the light travels straight through the dilated pupil and strikes the blood-rich retina- the part of the eyes that converts light to electrical impulses. The camera then captures this, making a person appear to have red eyes in the photograph.
While red eyes in photographs is usually normal, white or yellow eye reflections in photos can sometimes signal eye diseases and conditions like cataracts, retinal detachment, infections or retinoblastoma. Abnormal eye reflections in photos have actually sometimes helped to identify eye disorders in people.
To decrease the appearance of red eyes in photos, you can make the environment brighter or use tools in your camera that eliminate the red eye appearance.