Nearsightedness (myopia)
If your eye is no longer than usual or the cornea and lens have too much focusing power, light rays focus in front of the retina instead of on it. This refractive error is called myopia, or nearsightedness, and means you have a hard time seeing objects at a distance. The image is focused in front of the retina, causing distant objects to appear blurry.

Farsightedness (hyperopia)
If your eye is shorter than usual, or the cornea and lens lack the necessary focusing power, light rays focus beyond the retina. This refractive error is called hyperopia, or farsightedness, ad means you can't see close objects clearly. A young person may be mildly farsighted but unaware of it because the lens is flexible and compensates for the error by bringing the light rays forward and onto the retina.

Astigmatism
Astigmatism occurs when the curve of the cornea is uneven - steeper in one direction than in the other - like the back of a spoon. This uneven curve causes light rays to focus on many points on the retina, distorting both near and far vision.

Refractive Eye Surgery / AAO
Appropriate Management of the Refractive Surgery Patient / AAO