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Eagles have much more perfect vision than humans, which is explained by the fact that their retina is much more densely dotted with so-called cones - special light-sensitive cells. It is like a camera sensor with a higher pixel density that increases the resolution of the cameras.

Secondly, their central fossa (Latin fovea centralis) - a small depression located in the center of the macula lutea (Latin macula lutea) of the retina - is much deeper than in humans. This light-receptor-rich structure in the back of the eyes of both humans and eagles enhances our central field of vision. Researchers believe that the deep fovea allows eagle eyes to act as a telephoto lens.

This is where the essence of my question begins: how tightly can the cones be punctured and the central pit made deep before it begins to interfere with seeing?

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  • $\begingroup$ Related: youtube.com/watch?v=Rk2izv-c_ts $\endgroup$ Commented Oct 30, 2020 at 15:12
  • $\begingroup$ Eagles are already over the point where it would interfere with seeing. They have great pinpoint forward vision. But distorted and incomplete panoramic vision. No eagle will ever read, even if it knew how. the eye is too inconsistent outside of its prey-focus spot. $\endgroup$
    – user79911
    Commented Oct 30, 2020 at 15:32
  • $\begingroup$ The eyes of birds are not exactly like those of mammals. For starters, they have very much fewer blood vessels blocking the light in front of the retina; this is compensated by the presence of the pectens (or pectines if you prefer Latin plurals), which are specialized structures tought to serve the purpose of nourishing the retinas via diffusion through the vitreous humor. (That's like the difference between an old-school front-illuminated and a modern back-illuminated sensor.) Then consider that eagles with myopia won't live to reproduce... $\endgroup$
    – AlexP
    Commented Oct 30, 2020 at 15:40
  • $\begingroup$ How, then, is it necessary to improve (change) the human eye in order to enable it to clearly see objects in the distance, perhaps even better than the same eagle does? So ideal vision is usually denoted by 1 (100%), but how, in this case, to make 1000-5000%? $\endgroup$ Commented Oct 30, 2020 at 16:12

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It is not just about resolution. ThisIsAQuestion commented with a link to a video explaining that for human sized eyes, you lose a lot of detail over distance regardless. There is more to Eagle eyes than just a higher cone count and a deeper fossa.

This is a cross section of a human eye:

Cross section of a human eye

This is a cross section of an eagle eye:

Cross section of an eagle eye

This is the source for both images above.

That huge lens helps correct distortions caused by light going over long distances within an atmosphere.

Two more things about birds with awesome vision:

Pecten

From the name you'd think this is a sexual organ, but it's actually an organ that diminishes the area of blood vessels over the retina. With their great eyesight resolution, they would see their own blood vessels if they were laid out the same way as in mammalian eyes.

Secondary fovea

We mammals only see sharply in the one fovea we have. Outside that we don't get much detail. But over half of bird species have a secondary fovea around the primary one, which is better usage of space that would otherwise have few cones. Their "peripheric vision" is limited to a very thin circle which surrounds the primary fovea.

To have the same eyesight as eagles, we would need those changes on our eyes. The result is that our eyes would not look human - they would look like the eyes of a bird. And our heads would need more space to accommodate for that.


But that is not what you asked about. So back to your question, the only limit for the amount of cones is how many you can fit over an area. Eagles and buzzards seem to have this maxed out, at a concentration of cones per area that is five times greater than that of humans. Their count is at about a million cones per square millimeter.

Also notice, from the wiki on bird eyes:

The photoreceptors are not all individually connected to the optic nerve, and the ratio of nerve ganglia to receptors is important in determining resolution. This is very high for birds; the white wagtail has 100,000 ganglion cells to 120,000 photoreceptors.

If you just had a lot of cones but the same amount of ganglion cells, your vision would still have the same resolution. Ganglions take space, and they are pretty much packed in a human eye. We'd have to change our anatomy of the optic nerve to accommodate (hence my previous comment on head space). But if you are already changing the anatomy of the head, then the limit is up to you.

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  • $\begingroup$ How, then, is it necessary to improve (change) the human eye in order to enable it to clearly see objects in the distance, perhaps even better than the same eagle does? So ideal vision is usually denoted by 1 (100%), but how, in this case, to make 1000-5000%? $\endgroup$ Commented Oct 30, 2020 at 16:02
  • $\begingroup$ @FrenchThompson3 that should be another question. $\endgroup$ Commented Oct 30, 2020 at 16:31
  • $\begingroup$ worldbuilding.stackexchange.com/questions/189288/… $\endgroup$ Commented Oct 31, 2020 at 11:33

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