Question

What is a fovea in a primate eye and why is it better at acuity than the other parts of the retina.

Answer 1

The fovea centralis is a specialization of the primate retina to support high-acuity vision. It contains the highest density of red and green cone photoreceptors in the retina.
On the fovea of the retina because here, in the central area, are the greatest concentration of cone cells needed to see color but also to focus clearly. The light shines through the lens and the focal point of that light, in persons with normal vision, is on the fovea. These cells connect with neurons that go through the optic nerve to visual cortex of the brain, and if the images are not focused clearly on the fovea, the brain will interpret them as unclear.
Persons with normal vision, or 20-20 vision, have lenses in their eyes which focus light directly on the fovea. Persons who are far-sighted have longer, thinner lenses which puts the focal point behind the fovea, so they cannot see well in close vision, such as reading.
Persons who are near-sighted have shorter, thicker lenses and so the light is focused in front of the fovea rather than on it.
Eventually, most of us will need reading glasses and perhaps permanent correction because with age, our lenses lose their flexibility and can no longer focus images on the fovea, especially in close vision, but some of us also will need glasses for medium vision as well, especially if we were far-sighted when we were young and our lenses were longer and narrower than usual to begin with.