Laser Vision Correction is a term that includes several different techniques to treat "refractive errors" like nearsightedness, farsightedness, astigmatism, and presbyopia. These refractive errors are the reasons that people wear glasses and contact lenses. Laser vision correcting procedures attempt to improve your ability to see without corrective lenses.
 
NORMAL VISION
The eye sees normally when light rays focus on the "picture screen" or retina, located at the back of the eye. Clear sight is possible when the lignt rays pass through the cornea, pupil, and lens focusing exactly on the retina. 

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NEARSIGHTEDNESS OR MYOPIA
If the eye is too long, or the "clear window" called the cornea is too curved, the eye is nearsighted or myopic. Light will focus in front of the retina causing blurred distance vision. 

 

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FARSIGHTEDNESS OR HYPEROPIA
If the eye is too short, or the cornea is too flat, light focuses to a point behind the retina at the back of the eye, causing blurred close, and sometimes blurred distance vision as well.  

 

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ASTIGMATISM
The eye is astigmatic when the cornea is shaped like the back surface of a teaspoon instead of like the back of a soup spoon. This causes light to focus at more than one point, resulting in distorted vision. Astigmatism commonly occurs along with nearsightedness or farsightedness