What are refractive errors?
In order for our eyes to be able to see, light rays must be bent, or refracted, by the cornea and the lens so they can focus on the retina, the layer of light-sensitive cells lining the back of the eye.

The retina receives the picture formed by these light rays and sends the image through the optic nerve to the brain.

A refractive error means that due to its shape or to changes in the function of the lens that occur with age, your eye doesn’t refract the light properly, so the image you see is blurred.

Common refractive errors are myopia (nearsightedness), hyperopia (farsightedness), astigmatism (distorted vision) and presbyopia (aging eyes).

What are the different types of refractive errors?

Myopia (nearsightedness)
A myopic eye is longer than normal or has a cornea that is too steep. As a result, light rays focus in front of the retina instead of on it. Close objects look clear but distant objects appear blurred.

Hyperopia (farsightedness)
A hyperopic eye is shorter than normal or has a cornea that is too flat. As a result, light rays focus beyond the retina instead of on it. Most children are farsighted, yet they do not experience blurry vision. With focusing (accommodation), children’s eyes are able to bend the light rays and place them directly on the retina. As long as the farsightedness is not too severe, hyperopic children will have clear vision for seeing objects at a distance and up close. As we get older we slowly lose our ability to focus, and adults with hyperopia may experience increased difficulties with reading or other tasks up close.

Astigmatism distorts or blurs vision for both near and far objects. It’s almost like looking into a fun-house mirror in which you appear too tall, too wide, or too thin. It is possible to have astigmatism in combination with myopia or hyperopia.

Presbyopia (aging eyes)
When you are young, the lens in your eye is soft and flexible. The lens of the eye changes its shape easily, allowing you to focus on objects both close and far away. After the age of 40, the lens becomes more rigid. Because the lens can’t change shape as easily as it once did, it is more difficult to read at close range. This normal condition is called presbyopia.

Since nearly everyone develops presbyopia, if a person also has myopia, hyperopia or astigmatism, the conditions will combine. People with myopia may have fewer problems with presbyopia.

How are refractive errors corrected?
Eyeglasses or contact lenses are the most common ways to correct refractive errors. They work by refocusing light rays on the retina, compensating for the shape of your eye. Refractive surgery is also an option to correct or improve your vision. These surgical procedures are used to adjust your eye’s focusing ability by reshaping the cornea, or front surface of your eye.

There is not adequate scientific evidence to suggest that eye exercises, vitamins or pills can prevent or cure refractive errors.

For more information, please visit
http://www.geteyesmart.org/eyesmart/diseases/refractive-errors.cfm