What are refractive errors?
For our eyes to be able to see, light rays must be bent or “refracted” so they can focus on the retina, the nerve layer that lines the back of the eye. The cornea and the lens refract light rays. The retina receives the picture formed by these light rays and sends the image to the brain through the optic nerve. A refractive error means that the shape of your eye doesn’t refract the light properly, so that the image you see is blurred. While refractive errors are called eye disorders, they are not diseases. In a normal eye, the cornea and lens focus light rays precisely on the retina.
What are the different types of refractive errors?
MYOPIA (nearsightedness): A myopic eye is longer than normal or the cornea has too much focusing power, so that the light rays are focused in front of the retina. Close objects look clear but distant objects appear blurred. This condition affects over 25% of all people in the United States.
HYPEROPIA (farsightedness): The opposite of myopia. The eye is shorter than normal or the cornea lacks refractive power. Light rays are focused behind the retina and close objects are blurry.
ASTIGMATISM: This condition blurs and distorts both distance and near objects. A normal cornea is round and smooth (like a basketball). With astigmatism, your cornea is curved more in one direction than in the other (like an egg or football). You can 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. You can also have presbyopia in combination with myopia, hyperopia, or astigmatism. No exercise or medication can reverse presbyopia.
How are refractive errors corrected?
Eyeglasses: Glasses are an easy method to correct refractive errors. They can also help protect your eyes from harmful light rays, such as ultraviolet (UV) light rays. A special coating that screens out UV light is available when you order your glasses. Bifocals are glasses that are used to correct presbyopia. They have correction for reading on the bottom half of the lens and another for seeing distance on the top. Trifocals are lenses with three different lens corrections in one set of eyeglassses. If you don’t need correction for seeing distance, you can buy over-the-counter reading glasses to correct presbyopia.