The human eye is a truly fascinating structure.
For one, it’s the only place in the human body where you can see bare blood vessels without cutting into tissue.
Secondly, it’s remarkably similar to a camera. Those exposed vessels are actually coursing through something called the retina. The retina is equivalent to the film of the eye; it develops the light that enters through the pupil and gets focused by the cornea and lens. One of the nine layers of the retina is the photoreceptor layer, filled with substances called rods and cones, which processes that light and relays it to your brain in the form of electrical impulses. The density of those photoreceptors correlates with the sharpness of our vision.
The limit of human vision is about 20/10, while some think it’s about 20/8. Meanwhile, hawks, owls, and other birds of prey have much more densely packed rods and cones so their central visual acuity is believed to be closer to 20/2! So you may ask yourself why refractive surgery can improve your best corrected vision if doesn’t do anything to the density of rods and cones. Well, custom refractive surgery reduces or eliminates the intrinsic flaws in your optical system called aberrations that glasses or contacts can’t even correct.