The human eye gives the sharpest vision when it is perfectly spherical, or round like a basketball. This is called Emmetropia. Distortion occurs when the eyeball is too short from front to back (Hyperopia), too long (Myopia), or the curvature of the cornea is egg shaped rather than a perfect sphere (Astigmatism).

How the eye works

Light from object (A) is focused by the cornea and crystalline lens to form an upside-down image on the light-sensitive cells of the retina. Information is transmitted as impulses from these cells to the brain via the optic nerve. The iris regulates the quantity of light entering the eye. The pupil is the variable-sized black circular opening in the center of the iris.

This is an animated example of normal spherical vision. And in case you’re wondering, the brain re-interprets the image, making it appear right-side up.

How the eye ages

Just like any other part of your body, your eyes will age as you get older. You may notice that you need more light to see. That’s because your eyes have a reduced sensitivity to light as they age. You may also notice that colors appear dim or that glare forms when light shines directly at you. The lens also becomes less elastic and is not able to focus as well as it once could. This is the reason that most people will develop presbyopia at some point after age 40.