See­ing in the dark

Whether you’re a car­ni­vore skulk­ing through the un­der­growth in the dead of night or a prey an­i­mal try­ing to sur­vive un­til sun­rise, in the un­for­giv­ing wild, night vi­sion is a mat­ter of life or death

World of Animals - - What’s Inside... - Words Amy Gris­dale

Dis­cover the species with noc­tur­nal pow­ers


Cats can see with one-sixth of the light hu­mans need There are two types of light-sen­si­tive cells in the eyes. Cones are re­spon­si­ble for colour vi­sion and re­quire a lot of il­lu­mi­na­tion to work, while rods can’t pick out colour but func­tion in ex­tremely dim con­di­tions. Hu­man eyes con­tain around 120 mil­lion rods, but cats have up to eight times as many. This cre­ates su­per-charged night vi­sion abil­i­ties that al­low cats to sense their sur­round­ings with a frac­tion of the light re­quired by the hu­man eye.

Rods are also re­spon­si­ble for pe­riph­eral vi­sion due to their po­si­tion­ing around the outer edge of the retina. Ad­di­tion­ally, low-light rod cells are the eye’s most sen­si­tive mo­tion sen­sors and no­tice minis­cule move­ments in the dark. Cats use their ex­panded field of vi­sion and finely tuned mo­tion de­tec­tion to snare prey that a hu­man wouldn’t even no­tice.

Iris Pupil Cornea Lens Retina Tape­tum lu­cidum

The crys­tals are rec­tan­gu­lar in shape and are ar­ranged neatly like bricks in a wall. When light hits these minia­ture mir­rors it bounces around and has an­other chance to be ab­sorbed by the eye. The tape­tum lu­cidum is 35 lay­ers deep in the very cen­tre of the eye for max­i­mum re­flec­tion. Minis­cule sliv­ers of light are am­pli­fied in order to cre­ate a pic­ture of the en­vi­ron­ment. Shiny crys­talline cells coat the rear of a cat’s eye. This is the tape­tum lu­cidum, re­sem­bling an iri­des­cent pearl. Fewer crys­tals are em­bed­ded around the edge of the retina than the mid­dle as less light is likely to hit the pe­riph­ery.

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