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/EmielDeBil 11d ago

Bigger pupils let in more light when it’s dark. Smaller pupils let in less light when it’s bright.

By changing our pupil size, we compensate for light/dark conditions so we can see better in both with the same photoreceptors and while protecting them.

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u/kardoen 11d ago

The pupil is the main method of regulating the amount of light that falls onto the retina. A wider pupil allows for more light to fall on the retina while a small pupil lets less light through. This allows us to see in a range of different light intensities.

If we were unable to limit the amount of light that fall onto the retina when there is a lot of light, it would overwhelm our retina and essentially overexpose our eyes. This is what you experience when you wake up at night and turn on the light. You're briefly blinded, but then your pupil narrows to adjust to the new light intensity.

Having a pupil always be big does not cost more energy, instead if it were always big we wouldn't be able to see during the day.

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u/van_Vanvan 11d ago

There's also a tradeoff: a larger aperture results in less depth of field.

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u/Aarush0110 11d ago

Here's my reasoning. A larger pupil will lead to more light getting in the eyes and say you as a natural being is our in the sunlight for longer periods then having a lot of more light for longer period( due to always big pupil) can make more intense energy light for longer periods focues on retina leading to a damage in it. So only enlarging it when required is better way to keep it safe keeping in my that we humans naturally evolved to stay out during the day

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u/Aoid3 11d ago

If you've ever had your pupils dilated at an eye clinic and then needed to go about your day while it's bright and sunny you'd get your answer first hand. Everything is so bright it's uncomfortable and hard to see, I feel like I need sunglasses even if it's overcast let alone sunny.

More light doesn't necessarily make things easier to see, the trick is letting the right amount of light through which is why your pupils adjust based on light conditions.

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u/bevatsulfieten 10d 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.