What does it mean when scientists say “an eagle can see a rabbit in a field from a mile away”. Is their vision automatically more zoomed in? Do they have better than 20/20 vision? Is their vision just clearer?
In: Biology
People can have better than 20/20 vision, this is just a metric that has been deemed to be good vision, it is not the maximum a person can see and it’s not even an indication of perfect vision. They don’t go any further because generally there just isn’t a need for it.
It just means you can see clearly from 20 feet away.
There are also a number of other areas of our vision that make up ‘perfect vision’ and these are not even considered in a 20/20 test.
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20/20 vision doesn’t mean “perect vision” it means that someone sees at 20 feet what an average person sees at 20 feet. Eagles have better vision than that but by the title you seem to think that its odd that an eagle has better than perfect vision.
edit: Thanks for the gold fellow redditor!
Not zoomed in, just extremely sharp. Their eyes are also capable of sending more information to the brain per unit time.
An eagle’s field of view is actually *less* “zoomed in” than ours. Eagles can see 340 degrees around them while humans can only see about 180 (sometimes a tad bit more). But just the sheer amount of photo receptive cells in an eagles eye and their ability to process more visual input is what makes their sight so much better at a distance than ours.
Their vision is sharper. If you have good vision, you can probably easily spot a small crumb on a table several feet away, while to an old person, that image is more blurred and the crumb is simply not visible. Your vision is not “zoomed in” to see the crumb, it’s just sharper. Comparing the vision of a typical person to that of an older person, is similar to comparing an eagle’s vision to that of a typical person.
Bonus fact: 20/20 is not perfect vision, it’s typical human vision. It’s possible to have better than 20/20, e.g. 20/10 vision, which means you can see at 20 feet what a typical person can only see at 10 feet. Or if your vision was worse than average, say 20/40, you need to be 20 feet away to see something that a typical person can see from 40 feet away.
Eagles’ retinas have cone-rich structures found towards the back of the eye. This causes them to have outstanding vision of 20/5, which gives them the ability to spot small prey 100’s of ft above the ground (and allows them to identify shapes separately from a distance with less blur).
They also have the ability to see colors more vividly than humans can, including different shades of particular colors. They have a supreme ultraviolet light range as well, allowing them to see traces of the bodies that their prey make from far away in addition to urine.
Due to the position of their eyes they have a 340 degree field of vision which makes their peripherals pretty good.
Last, their cornea has the ability to change shape to better focus on near and far objects.
So all in all, their eyes have significantly different structures to them that allow them to have crazy good sight.
Eagle’s eyes are very good as compared to humans. The reasons very simply are to do with the number of sensory cells in the back of their eye which acts as a film on which the image is read from. Imagine a screen of a old computer vs newer ones. And that being the image formed in your eye. The old ones were good for the time and were what we had and accepted as being satisfactory. But the new ones are what eagle has and we can’t imagine what it’s like because we haven’t seen that. To add a bit more technically, eagles don’t have good 3d vision because their eyes are on opposite sides of the head. They do have good long range vision because of the high definition of the image.
Actually, eagles can see rabbits *two* miles away.
Their eyes are about the same size as human eyes, so relative to their size much bigger than ours, but they have better focusing (no near- or farsightedness, constant focusign during movement) and, most importantly, they have about 5x more cells in their retina. You can think of eagles having higher resolution – where you as a human see just HD, they see more than 4K.
https://en.wikipedia.org/wiki/Eagle_eye
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