A myopic, or nearsighted person has difficulty seeing distant objects clearly, such as road signs, blackboards in a classroom, or scoreboards at a sporting event. Myopia varies in its severity. Extremely nearsighted people may only have clear vision up to a few inches from their eyes; mildly nearsighted people may not even be aware of the disorder.
Myopia develops during childhood. The child's eyeball grows too long, which interferes with the light-focusing mechanism. Rays of light from distant objects focus in front of the retina rather than on the retina, resulting in blurry vision. This can also occur if the cornea is curved too acutely.
Incidence and Prevalence of Myopia
Myopia is fairly common worldwide. Approximately 25 percent of the U.S. population is myopic to some degree, and the condition affects men and women equally. There is greater prevalence of this disorder among children from higher socioeconomic groups, although the reasons for this remain unclear.
Incidence is much higher in certain Asian countries. Taiwan experiences the world's highest rate. In some nations, such as Singapore, the incidence has rapidly increased over the past decade. In 1990, one in five grade school students there was diagnosed with myopia, and by 2000 that number had risen to one in three.
Risk Factors for Myopia
While the exact cause of myopia remains unknown, it is believed that an interaction of heredity and environment may play a role. It tends to run in families. When both parents are nearsighted, their children have a greater than average chance of developing myopia. Environmental factors such as reading in dim light or doing excessive amounts of close work may contribute to myopia.
Signs and Symptoms of Myopia
Symptoms of myopia usually are first noticed in childhood. Myopic children may hold their books very close to their face or be unable to read the blackboard at school. They may squint and complain of headaches and eyestrain. These signs often alert a teacher or parent that the child is having vision problems and that an eye exam is needed.
A diagnosis of myopia can be made only after a basic eye examination performed by an ophthalmologist or an optometrist. The initial diagnosis of myopia is usually made by having the patient read letters from an eye chart. Other tests are performed to determine the degree of myopia.
Treatment for Myopia
Treatment for nearsightedness is most commonly prescription eyeglasses or contact lenses. Wearing the glasses or contact lenses allows the patient to experience normal or at least dramatically improved, vision.
Myopia often worsens progressively during adolescence, and the eyeglass or contact lens prescription may need to be adjusted periodically. However, myopia tends to stabilize once the patient is in their twenties.
A number of surgical procedures are used to correct refractive errors, including radial keratotomy, photorefractive keratotomy, clear lens replacement therapy, and LASIK.
These procedures reshape the central area of the cornea. In many cases, correction makes eyeglasses unnecessary. Not every patient is a good candidate for surgical correction. Surgery is not recommended for people under the age of 18 because their eyes are still growing.
There is no way to prevent myopia. Avoiding eyestrain, reading and studying in a well-lit room, and taking breaks from working in front of a computer screen or doing close work may help. Eye health can be supported by the following:
- Eating a healthy diet that is rich in vitamins A and C
- Protecting the eyes from excessive amounts of ultraviolet light by wearing sunglasses when outside
- Drinking adequate fluids to prevent eye dryness
- Protecting the eyes when working with hazardous or caustic substances
- Having regular eye exams, especially if at high risk for eye disease (e.g., people with diabetes)