Why Do An­i­mal Eyes Glow On Pic­tures Taken In The Dark?

If you take a photo of your cat in dark­ness or point a strong torch into the jun­gle, the re­sult is scary. What is it that makes an­i­mal eyes re­flect?

Science Illustrated - - ASK US -

The eyes of cats and other an­i­mals glow in the dark be­cause of a spe­cial layer in the an­i­mal eyes called tape­tum lu­cidum. The layer is lo­cated at the back of the light-sen­si­tive retina and re­flects the light that passes through the retina. This way, the light-sen­si­tive cells in the eye can use the light once more. The re­flec­tion in­creases the light sen­si­tiv­ity of the eyes by up to 50%.

Fe­lines have the re­flect­ing layer in their eyes, but it is found in a num­ber of dif­fer­ent species – but not in hu­mans and other pri­mates. "Red eye" in a photo, is due to re­flec­tions from the retina it­self. Here, the red colour is due to the many blood ves­sels that sup­ply the eyes with oxy­gen and nu­tri­ents.

Yet, some an­i­mals have a red tape­tum lu­cidum, and red eyes are wide­spread among noc­tur­nal birds. In some species, the eyes even shine with dif­fer­ent colours. In fish, the re­flec­tion can be so strong the an­i­mals use it as a lamp to find their prey or lure it closer.

Only ver­te­brates have tape­tum lu­cidum, but sim­i­lar kinds of light­en­hanc­ing struc­tures are found in the eyes of moths. Here, how­ever, a nanofilm cov­ers the eyes to make sure that the light is not re­flected and re­veals the in­sect to preda­tors.

A beam of light or cam­era flash pointed into the dark­enss of the sa­van­nah will show whether a pack of li­ons is nearby.

A re­flect­ing layer called tape­tum lu­cidum behind the retina makes the an­i­mals's eyes glow.

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