The red reflex is light which is reflected by the inside of the eye, which can sometimes be seen through the pupil. We normally don’t see this reflected light as it scatters in many directions but, when a beam of light goes into the eye and the light coming out of the eye are in line, the red reflex can be seen, especially in a dark room. Normally the reflected light is red because of the blood supply under the retina (the seeing layer of the eye). The most common time you see the red reflex is on flash photographs: the flash and the camera lens are so close together that the photo picks up the reflected light causing ‘red eye’ or ‘red pupil’.
Doctors, nurses, health visitors and optometrists can use the red reflex to check the health of the eye. All newborn babies have a ‘red reflex check’ twice within the first few weeks afterbirth. A health professional has a special torch (ophthalmoscope) which shines light into theeye and looks into the eye at the same time.
Anything in the eye blocking the light from travelling inside the eye or which causes the back of the eye to be more pale can cause an abnormal red reflex. Examples are a clouding of the lens of the eye (cataract), or a physical abnormality of the retina at the back of the eye. Very high glasses prescriptions can also make the red reflex look different.
Causes of abnormal red reflex on photos or when checked by a clinician
The most common reason for an abnormal red reflex on photos is that one or both eyes were not looking straight at the camera. The most common situation where healthcare professionals are not sure about the red reflex is in babies with dark brown eyes. In these babies, the back of the eyes is usually darker, so less light is reflected and the red reflex is not as bright.