What having red eye in photos really means - and why it could be GOOD for your health

It has long been known that the way your eyes look in a photograph can tell you a lot about your health.

This is because the light from the flash reflects reflects off the color of the retina in the back of the eye, which converts images to electric signals that are sent to the brain.

Doctors have warned that if one or both pupils are bright white, it could mean that there is too little blood in the retina. And this problem can signal a range of conditions - from common cataracts to life-threatening eye cancer.

But now, experts have flagged that a selfie taken with flash doesn't only show up problems — it can also signal perfectly healthy eyes. 

The above graphic shows different eye colors in photos with their meaning. On the top right, the eye shown could indicate a rare childhood cancer - retinoblastoma - and on the bottom left, the white eye pictured could be a sign of a disease where blood vessels leak in the eye

Doctors at the American Academy of Ophthalmology recently raised concerns that too few people are benefitting from this handy healthy check — due to the advent of image editing features on smartphone cameras that scrub out imperfections.

The experts said a flash reflection that illuminate the eyes in a bright red color is a useful indicator that the retina is 'blood-rich' — a 'good sign' that 'both eyes are unobstructed and healthy'. 

'A red reflex happens when the flash of a camera lights up the blood-rich retina,' the doctors said. 

Cancer spotted on the baby monitor 

While Benny's mom was monitoring him in his crib one night, she noticed one of her son's eyes looked completely black and the other looked like a shining light on the screen. 

'If the eyes are looking directly at the camera lens and the color of the relfex in both eyes is red, that's usually a good sign that the retinas of both eyes are unobstructed and healthy.'

Crucially, the flash reflection can show signs of unhealthy eyes too.  

For instance, cases where one eye is less red than the other — medically termed asymmetrical red reflex —  could be a warning sign of strabismus, a disorder where both eyes do not line up in the same direction.

This happens because of problems with the muscles that control eyeball movement, affecting about four percent ofAmerican adults.

Other warning signs include vision problems, walking into objects and eyes that don't move together.

Doctors say it is best to detect the condition early, when it is easiest to treat.

Treatments include wearing eye glasses or having surgery to strengthen one of the eye muscles. 

In cases where one or both eyes are white, the opthamologists said this may be a sign of a rare type of cancer called  retinoblastoma, or eye cancer.

The coloring is caused by the light reflecting off white-colored cancer cells at the back of the eye.

Retinoblastoma is a rare childhood cancer that happens when cells start to divide uncontrollably in the retina, suffered by about 300 children every year. Other warning signs include poor vision and pain in the eye.

Doctors said a white eye could also be an indication of the retina becoming detached, or an infection.

When the retina becomes displaced, it reflects light differently, while the structure of the cells can be altered if it is infected.

About one in eight children suffer an eye infection every year, doctors say.

In some cases, eyes may also appear yellow in photos, doctors said.

This could be a warning sign for Coats' Disease - when blood vessels inside the eye become twisted and leaky.

Scientists suggest the disease may be caused by genetic mutations that lead to a build-up of cholesterol deposits in the eye — which reflect yellow against the flash of a camera.

There are roughly 100 cases per year, which are usually in boys, and the condition can be treated using surgery or cryotherapy, where blasts of cold air are used to remove abnormal tissue.