Myopia (Short-sightedness)

Myopia tends to be a hereditary sight condition in which a person can make out nearby objects clearly whereas far away ones appear blurred to them. The habitual explanation for this is that their eye is longer than that of an average person or that the curvature in the cornea is too great. The rays of light therefore converge in front of the retina, creating blurred images.

In myopia, the rays of light converge in front of the retina and not over it

Hyperopia (Long-sightedness)

With this defect, the rays of light converge behind the retina, since the person's eyes are either shorter than average or their corneas, unlike those of a short-sighted person, are too flat. The result is that objects at close range appear blurred.

In hyperopia the rays of light converge behind the retina

Astigmatism

The cornea of a person with astigmatism has a greater curve at one axis than at the other.

One way to understand it is to say the cornea is shaped more like a rugby ball than a football.

Vision from whatever distance is blurred, distorting the image as do curved, convex and concave mirrors which create the illusion you are taller, broader or leaner than you are. Astigmatism can manifest itself of its own will or through short or long- sightedness.

In the case of astigmatism, inconsistencies in the curve of the cornea cause images to appear distorted