What Is It?
Nearsightedness, also called myopia, is a condition in which a person has difficulty seeing objects in the distance, although vision of close objects is good.
In some cases, nearsightedness is an inherited condition caused by an abnormally long eye, as measured from front to back. Because there is an increased distance between the cornea (the clear “window” that covers the front of the eye) and the retina (the light-sensitive layer at the back of the eye), images tend to focus in front of the retina, rather than on the retina itself.
In other cases, nearsightedness is the result of a mismatch between the length of the eye and the ability of the eye’s lens to focus an image in the correct location. Again, this causes images to focus in front of the retina, resulting in nearsightedness.
Currently, nearsightedness is the most common form of vision problem in the United States, affecting an estimated 25 percent of all Americans. In many cases, genetic factors play a role in the condition, so that several generations of the same family suffer from the problem.
Symptoms of nearsightedness can include:
- Difficulty seeing distant objects, such as blurred vision when watching television or a movie or when trying to read a billboard, a traffic sign or a teacher’s notes on a chalkboard
- Headaches triggered by squinting
- Poor school performance — this is often the first clue in young children, who rarely complain about vision problems
After reviewing your symptoms, the doctor will perform a thorough eye examination, including tests of visual acuity (how well you can see).
To measure visual acuity, doctors use a ratio in which the top number represents the patient’s vision, and the bottom number represents the vision of someone who sees perfectly. For example, a person is said to have 20/20 vision if he or she can see at 20 feet what a person with perfect vision is expected to see at 20 feet. On the other hand, a mildly nearsighted person may see at 20 feet what a person with perfect vision can see at 30 feet. This is called 20/30 vision. A more severely nearsighted person might have a ratio of 20/40 or 20/100.
In older children and adults, visual acuity often is measured by having the person read letters from an eye chart (usually the Snellen eye chart) that is displayed at a precisely measured distance from where the person stands. A hand-held chart, called the Rosenbaum card, is also available. In young children and people who cannot read, the doctor can use alternative charts that display objects, animals or the capital “E” facing in different directions.
Nearsightedness is a long-term condition that usually stabilizes once a person reaches his or her 20s.
In most cases, nearsightedness is related to inherited factors that cannot be prevented.
If you are nearsighted, your doctor probably will prescribe eyeglasses or contact lenses to correct your problem. The lenses used in both of these treatments are thinner in the center and thicker around the edges, a configuration that brings the viewed image into proper focus on the retina.
Currently, many cases of nearsightedness also can be corrected with eye surgery. The goal of eye surgery is to improve the eye’s focus by flattening or reshaping the central portion of the cornea. Some of the procedures used, from most common to least common, are:
- LASIK (laser in situ keratomileusis) — The eye surgeon uses a tiny knife to slice into the cornea from the side. Next, a laser is used to remove a precise amount of corneal tissue from beneath the sliced area. The result is a flattening of the cornea that improves the nearsighted eye’s focus.
- Photorefractive keratotomy (PRK) — In this procedure, a laser beam is used to remove tissue from the outer surface of the cornea. This reshapes the cornea and improves the eye’s focus.
- Radial keratotomy (RK) — After the eye is anesthetized, tiny cuts are made in the periphery of the cornea. This causes the central portion of the cornea to flatten, improving the eye’s focus and resulting in better distance vision.
LASIK and PRK surgery have almost completely replaced radial keratotomy as the procedures of choice. People choose LASIK more than PRK because it offers excellent results, is a fast procedure, and recovery is painless.
Although the U.S. Food and Drug Administration (FDA) has approved several types of lasers for surgical treatment of nearsightedness, not every nearsighted person is a good candidate for this type of treatment. In general, laser procedures are not performed on people who are less than 18 to 21 years old, because the eye has not finished growing in these individuals.
For updates on the benefits and risks of laser eye surgery, and for a list of FDA-approved lasers, contact the FDA (see the “Additional Info” section for contact information).
When To Call A Professional
Make an appointment to see your primary care doctor or ophthalmologist (a doctor who specializes in eye problems) if your vision blurs when you try to see distant objects. In particular, call your doctor if blurry vision is interfering with your occupation, school work or ability to drive safely.
Call your pediatrician if your child complains about blurry vision, has difficulty seeing the chalkboard at school, squints while looking at distant objects or complains of frequent headaches.
Also, make sure that the doctor checks your child’s eyes as a part of every routine physical examination or well-baby visit. More formalized visual acuity testing should be done between ages 3 and 4, and then again at the start of school.
Eyeglasses and contact lenses can correct most cases of nearsightedness.
The long-term effects of laser eye surgery are still being evaluated. Many patients report that they are very satisfied with the results of laser eye surgery, and more than 100,000 laser eye procedures are performed successfully each year in the United States. However, as in other forms of surgery, the risks and benefits of laser eye surgery should be understood before the procedure is performed.
Diseases and Conditions Center