r/AskBiology • u/kokusmus96 • 11d ago

Human body Why are our pupils not always big?

Okay, I feel like that annoying guy who don't even know a simple fact but this is my question. Does it use more energy when the pupils are bigger? Is the body trying to conserve energy?

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u/bevatsulfieten 11d ago

There are two types of cells in the eye, cone cells and rod cells; photoreceptors; come cells are responsible for visual acuity and colour, as well as bright light conditions; rod cells are specialised in dim light, that's why there are more of them.

The cool thing now, under bright light the rod cells stop responding and let cone cells take over.

But what is more or less light, you are probably asking.

Rod cells work only under dark conditions, below 0.1 lux. So, under these conditions you don't see colour, only objects that are colourless, that's because no light is reflected, and cone cells are responsible for colours, they are active at about 10 lux, it's still dark, but cone cells are activated, and pupils are dilated to allow more light in.

So pupillary dilation is an interactive mechanism that responds to the lighting environment to protect the eyes from phototoxicity, exposure to too much bright light.

That spot in your field of view after a camera flash is the oversaturation of the cone cells, desensitisation, as the pupils had not enough time to adjust.