Notes:

To illustrate what the retinal image would be like with super-normal optics, imagine yourself viewing the Statue of Liberty at a distance of 3 kilometers from a boat in the New York Harbor. Under optimal viewing conditions and 20/15 vision (i.e. a normal 3 mm pupil), your retinal image of the statue would look like the picture at the left on this slide. However, if the eye's optics were perfect and we could use a fully dilated pupil, the retinal image would be like the picture in the middle. Notice the dramatic increase in contrast and sharpness of the borders and fine spatial details. But does this mean your visual acuity will be correspondinly better than 20/15? Unfortunately, to quote Porgy from "Porgy & Bess", it ain't necessarily so.

The reason visual acuity will probably not improve dramatically is that the retina itself imposes limitations on our spatial resolution which come into play only when the eye's optical limitations are overcome. These retinal limitations are caused by the finite size of the cone photoreceptors of the retina.

Cones are the light-sensitive cells of the retina and their job is to transduce the retinal image into a neural image for transmission to the brain. However, because individual cones have a finite size, the array of cones samples the retinal image discretely as shown schematically at the right. Consequently, if two points in the retinal image are so close together that they fall on the same cone, then the cone cannot tell them apart. Thus the size of the cones places a neural limitation on our visual resolution that cannot be overcome by perfecting the eye's optics.