Why Do My Eyes Glow Red in Photos?

Y’know that thing where your eyes glow bright
red in photos? It’s called the red-eye effect. But it doesn’t mean you can secretly fire
laser beams from your eyes or anything. Instead, you can blame the bright flash of
a camera, and how your eye adapts to changes in light. Your eyes are basically fluid-filled orbs
that can detect light and send messages to your brain, so you can see images. Light passes through a thin membrane called
the cornea, then a hole called the pupil, and then a lens – so it can be focused,
and absorbed by photoreceptor cells in the back of your eye. Your pupil is surrounded by this muscle-filled
structure called the iris, which is the colored part of your eye. You don’t consciously move these muscles,
but they control how big your pupil is, and how much light you let in. When it’s dark, your iris makes the pupil
wider to let more light into your eye. But when there’s bright light, your iris
makes the pupil smaller. So, the red-eye effect usually happens in
a dark environment, when your pupils are really wide. Normally, all the light that enters your eye
is absorbed by photoreceptors, or by a pigment called melanin in a tissue layer in the back
of your eye – the same pigment that influences the color of your iris, hair, and skin. And since all the light’s absorbed, your
pupils look black. But if there’s suddenly a bright camera
flash, all that light floods into your eyes before your iris muscles have time to contract. Some of it might reflect off the blood vessels
in the back of your eye, and shows up as a glowing red light to ruin that group photo
you were trying to take. To fix this, some cameras make a couple quick
flashes of light before the actual flash when the photo’s taken, so that your iris muscles
start contracting, and let in less light. You could also try brightening the room, so
your pupils aren’t as wide in the first place, or avoid looking directly at the camera
lens. The red-eye effect is pesky, but it isn’t
always bad. It can actually be a handy tool for diagnosing
eye problems. If someone was looking directly at the camera
lens in dim lighting, and they have a glowing white or yellowish eye, there might be an
infection, some cancerous cells, or those blood vessels might be twisted or leaking. Sometimes photos will only have one glowing
red eye, which might mean someone’s eyes aren’t looking in the exact same direction. Or, it could mean there’s different amounts
of melanin in the back of each eye, so they’re different colors. So mostly the red-eye effect is just annoying,
but you might want to keep an eye on it. Thanks for asking, and thanks especially to
all of our patrons on Patreon who keep these answers coming. If you’d like to submit questions to be
answered, or get some videos a few days early, go to patreon.com/scishow. And don’t forget to go to youtube.com/scishow
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