Why do dog’s or cat’s eyes flash blue when a photo is taken?
In: Biology
There is a reflective layer behind the retina that reflects back light, it gives the light a second chance of getting absorbed by the photoreceptors. This results in better night vision with the drawback of a slight bluring of the vision, the light will not get reflected straight back from where it came.
It might seem like a huge disadvantage because it make them easier to spot. What you then forget is you need a light source that emits light that gets reflected back, It needs to be close to the observer because the light is mostly reflected from where it came. Only humans has light sources like that and we have got effective light sources quite recently. So reflecting light has not been an evolutionary disadvantage.
Cats and dogs and other members of Order Carnivora have an extra reflective layer behind the retina called the tapetum lucidum which allows them to see better in low light levels. All it really does is reflect light that wasn’t absorbed by the rods and cones back into them so that they capture more of it. That blue flash is the reflection of your camera’s flash on the tapetum lucidum being sent back in your direction.
That reflective layer is also why cats’ and dogs’ eyes sometimes look like they’re glowing in the dark, as some light source in their field of view gets shone back your way.
They have a reflective layer on their retinas, it helps with low-light vision.
The light from the flash is being reflected back at the camera.
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