Why are pupils black?

The "hole pupil" is black because when the fundus reflex is not visible, the interior of the pupil is equivalent to a darkroom, so it is black (except cataract, of course).

But not all races are black. Pupils of different races have different colors, some are brown, some are blue, and some are even green, but such people are only a few.

If the pupil is large and has light, if the fundus is highly reflective, the pupil will show the color of the fundus (generally orange-red). In the case of mydriasis, normal eyes can see the red reflection of fundus from the pupil (fundus examination).

Extended data:

Pupil position

The anterior part of the ocular vascular membrane, that is, the center of sclera and the round hole. Smooth muscle arranged in a ring along the pupil is called pupillary sphincter. Sphincters constrict pupils. Smooth muscle radially arranged along the pupil is called mydriatic muscle. When muscles contract, they dilate the pupils.

Because the pupil can be enlarged or contracted, the amount of light entering the eyeball can be adjusted. Normal people's pupils can adjust their size reflexively. When the light is enhanced, the pupil shrinks; When the light weakens, the pupil will enlarge.

If the pupillary reflex is abnormal or disappears, it indicates that the adjustment function of the nervous system is impaired. Therefore, the pupil's reflection of light is often used to check the functional state of the nervous system in clinic.

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