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Causes
By Mayo Clinic staff
Your eye has two parts that focus images:
- The cornea, the clear front surface of your eye
- The lens, a clear structure inside your eye that changes shape to help focus objects
In a perfectly shaped eye, each of these focusing elements has a perfectly smooth curvature like the surface of a rubber ball. A cornea and lens with such curvature bend (refract) all incoming light in such a way as to make a sharply focused image directly on the retina, at the back of your eye.
A refractive error
However, if your cornea or lens isn't evenly and smoothly curved, light rays aren't refracted properly, and you have a refractive error. Farsightedness is one type of refractive error. It occurs when your cornea is curved too little or your eye is shorter than normal. Instead of being focused precisely on your retina, light is focused behind your retina, resulting in a blurry appearance for close-up objects. However, if you haven't reached the age when the eye becomes presbyopic (gradually loses the ability to focus actively on nearby objects) — usually around middle age — you may be able to exert enough focus so that nearby objects are seen clearly.
Other refractive errors
In addition to farsightedness, other refractive errors include:
- Nearsightedness (myopia). This occurs when your cornea is curved too much or your eye is longer than normal. The effect is the opposite of farsightedness. Light is focused in front of your retina, making faraway objects blurry. You're able to see nearby objects clearly.
- Astigmatism. This occurs when your cornea or lens is curved more steeply in one direction than in another. Uncorrected astigmatism blurs your vision. Typically, the blurred vision occurs more in one direction than in another — horizontally, vertically or diagonally.
