Questions we often get asked: Why do my eyes glow red in photos?

It is worth remembering that although the pupil looks like a black dot, is actually an opening or aperture. It doesn’t open into an empty space, but to the translucent jelly that fills the eye (vitreous humour). Pupils allow light to pass through this jelly and onto the back of the eye (retina). The retina is the light sensitive part of your eye (like a film inside a traditional camera) and it receives the light and converts it into nerve signals which it sends to your brain to interpret it. That is how you see. 

A camera works in a similar way. Instead of a pupil, it has a shutter that allows light to pass through the lens and onto a piece of film. The film records the image just like your retina does. 

Back to the eye: Normally, when you look at someone, some of the light passing through their eyes bounces around inside the eyes and reflects back to you. However, the amount of this light is so small that the pupils just look black. A camera flash, however, sends a tremendous amount of light into the eye in a very short time. If the camera lens is close enough, some of this light ricochets back off the retina and into the lens. And because the back of the retina is filled with blood vessels, the pupils look red. 

This problem has been perplexing photographers for over a century. One way to deal with it is to back off from the person you’re photographing: the farther away the camera lens, the smaller the amount of light that will reflect back into it.

Alternatively, some cameras also include a red-eye reducing dimmer flash. This is a small flash that goes off a few seconds before the main flash. The purpose of this flash is to cause the subject’s pupil to constrict (reduce in size – just as it does when you go out in the sun), which makes it harder for light to reflect back at the camera. 

However, this red reflex as it’s known has been very beneficial to eyecare practitioners. Back in the 19th century, the German physician Hermann von Helmholtz discovered that he could look inside the retina by holding a bright light near his own eye and shining it directly into a patient’s pupil. This allowed doctors of the time to see the inside of the eye non-invasively for the first time.

This technique was further refined and is known as direct ophthalmoscopy and is still used today. It is simple to use but gives a restricted view of the back of the eye and doesn’t offer the opportunity to record what is seen. However, modern advancements in technology now allow a much greater and more accurate view of the retina and it’s vital functions using optomap and OCT retinal scanners.
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