Why are human eyes so bad with sunlight that we need sunglasses to operate normally? Bright sunlight doesn’t seem like a new phenomenon for humans to deal with.

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Why are human eyes so bad with sunlight that we need sunglasses to operate normally? Bright sunlight doesn’t seem like a new phenomenon for humans to deal with.

In: Biology

As long as you dont stare directly into the sun, our eyes seem to work pretty well in sunlight.

Your eyes adapt to the light around you. 10,000 years ago people spent most of their day walking in the sun, so their eyes had plenty of time to adapt.
Now we spend lots of time indoors where it’s darker. Your eyes need time to adapt again to the outdoors, and given that we go inside and outside quite frequently, sunglasses make it much easier.

The photoreceptors in your retinas are nerves, but they work a little differently. Unlike muscle nerves, which send an impulse that produces a contraction, they’re “always on.” Their level of activity is inversely related to how much light is available. Your pupils assist in this by dilating or contracting to allow more or fewer photons to enter. That’s why going from a dark area to an area that’s very bright can lead to “light blindness” or after-images. Those nerves have been overloaded, and need time to adjust. It’s also why you have a hard time seeing on very bright days; your pupil can only constrict so much, so your photoreceptors are more taxed.