Rays of light pass through the cornea, pupil and lens of the eye to get a clear vision for a normal eye
This is the most common type of refractive error. In the near sighted person the cornea is too steep or the eye is too long and the focal point is in front of the retina resulting in blurred distance vision.
For the far sighted person the focus of the eye is behind the retina. People who are farsighted can have trouble seeing at near.
In this type of refractive error, shape of the cornea is not completely round but more like an egg. Light entering the eye focuses on more than one spot on the retina resulting in blurring of vision. Astigmatism can occur with near sightedness, or far sightedness.