Nearsightedness

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What is nearsightedness?

Nearsightedness, also called myopia, is a condition in which your eyes can clearly see objects that are close but not objects that are far away. Usually, it can be completely corrected with glasses, contact lenses, or surgery.

How does it occur?

Nearsightedness occurs when the eye is too long for the focus point of the cornea (the clear outer layer on the front of the eye). Light rays that normally focus on the retina (light-sensitive tissue at the back of the eye) focus in front of it. This causes images to appear blurry.

The eyeball grows as the rest of the body grows. Sometimes the eyeball grows too long and becomes oval-shaped. This often becomes a problem between the ages of 8 and 12, but it can show up earlier or later.

Some experts think that nearsightedness is something you are born with. Some think it is caused by the stress of too much reading, close work, or computer use. It is likely that both factors play a role in this problem.

In older age, nearsightedness can be caused by cataracts. Cataracts can be removed and replaced with a clear plastic lens.

Nearsightedness may also be caused by a cornea that is too curved. This can be a problem you have had since birth or caused by diseases of the corneal thickness such as keratoconus and keratoglobus.

If you have extreme nearsightedness (called high myopia), you are at risk for more serious eye problems such as retinal detachment, degeneration of the retina, and bleeding under the macula. If you are extremely nearsighted, you should see an ophthalmologist regularly for a checkup.

What are the symptoms?

The major symptoms of nearsightedness are:

• blurred vision
• eye discomfort
• eyestrain

How is it diagnosed?

• Your eye care provider will ask you to read letters or numbers on a chart 20 feet away. This test measures your ability to see distant objects clearly.
• Usually, your provider will dilate your eyes by putting some eyedrops in them. Then he or she will look at your retinas through a lighted instrument called an ophthalmoscope.
• Your provider will have you look through various lenses like those in glasses to see which ones give you the best distance vision.

How is it treated?

Until recently, nearsightedness was almost always corrected with eyeglasses or contact lenses. However, now it can sometimes be corrected by surgery.

Corrective lenses:

Glasses or contact lenses can help the eyeball to focus light rays properly on the retina. Both have advantages and disadvantages. People choose contact lenses for comfort and personal appearance. Contacts also may allow better side vision, especially if you need lenses that give a lot of correction.

Surgery:

Two types of refractive surgery may be done to correct nearsightedness:

• PRK (laser photorefractive keratectomy): In this surgery a laser removes tissue from the surface of the cornea.
• LASIK: In this procedure a laser removes tissue from an inner layer of the cornea after the outer layer is cut and held aside. This is the more common procedure.

Both of these procedures flatten the cornea. If successful, they correct nearsightedness permanently. They have a high success rate when performed properly. However, they are expensive and are usually considered to be cosmetic, which means that an insurance plan may not cover the cost. These procedures are not recommended for every case of nearsightedness. Check with your provider to see if they might be right for you.

How can I take care of myself?

Prevent eyestrain by using bright light for reading or doing close work and by wearing your glasses as prescribed. Also, rest your eyes often if you read, do close work, or use a computer for long periods.

Have your eyes checked regularly to see if other problems develop or if you need a stronger prescription for your glasses or contacts.

How can nearsightedness be prevented?

Because the tendency to be nearsighted is inherited, there is nothing you can do to prevent it.

Reviewed for medical accuracy by faculty at the Wilmer Eye Institute at Johns Hopkins. Web site: http://www.hopkinsmedicine.org/wilmer/

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