The clear front window of the eye, the cornea, works like the lens of a camera focusing light rays onto the retina. The retina, in turn, acts like film for the "camera". The cornea may not sharply focus light onto the retina in the following conditions:

Myopia or nearsightedness occurs when light rays focus in front of the retina. Distance vision is blurred.

Hyperopia or farsightedness occurs when light rays focus behind the retina. Near vision, and often times, distance vision is blurred.

Astigmatism is a condition where the cornea is not round but shaped more like a football. This causes two focal points of light resulting in blurred or ghost images.

Presbyopia occurs when the lens in your eye is no longer able to focus images of objects close to you. This condition starts at the age of 40 to 45 and requires the patient to use reading glasses regardless of the clarity of their distance vision. In other words, patients over 40 who have had refractive surgery to clear their distance vision will probably still need reading glasses. Exceptions to this are people who are willing to make one eye slightly nearsighted and allow the other eye to function for distance vision, a condition called monovision. Since the nearsighted eye is designed for near vision, it will be blurred for distance vision.

Cataracts occur when the internal focusing lens of the eye becomes cloudy and is generally the result of the natural process of having birthdays.

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