Is Myopia Hereditary?

Q:  I am 20 years old and just got my first eyeglass prescription. From what I read, nearsightedness is a hereditary condition, but neither of my parents had eyeglasses.

Did I do this to myself because of all my work on the computer?

A:  Don't fret; you're in good company: about 30% of Americans are nearsighted.

Nearsightedness (myopia) and farsightedness (hyperopia) are the most common "refractive errors." Refractive errors usually occur in otherwise healthy eyes, and are caused mostly by an imperfectly shaped eyeball, cornea, or lens.

Myopia is caused by the eyeball being too long. People with myopia see near objects clearly, while distant ones are blurred. Myopia occurs in different degrees from minimal to extreme. The more myopic you are the blurrier your vision is at a distance and objects will have to be closer to you so you can see them clearly.

What you read is true: myopia is generally hereditary. Inherited cases usually are first noticed during the adolescent years, and often require thicker lenses to correct the vision. However, some specialists are now describing a different origin for nearsightedness: "school myopia."

School myopia develops because of increased use of near vision (such as reading or looking a computer screen), especially if done during the early teen years to the mid-20s. As an illustration of this principle, more than 60% of medical students are nearsighted.

School myopia probably occurs only in those with a genetic predisposition.

According to the National Eye Institute (NEI), 60% of Americans have refractive errors that need correcting for sharper vision. Glasses, contact lenses, and various eye surgeries and procedures are aimed at reducing refractive errors by focusing light rays properly on the retina.

The NEI estimates that more than 150 million Americans spend over $15 billion each year on corrective eyewear to compensate for refractive errors.

At the same time, it may be useful to follow the "rule of 20s": every 20 minutes, spend at least 20 seconds looking at a faraway object at least 20 feet away. You could also spend that 20 seconds simply with your eyes closed. Set your computer alarm to remind you.

Julie L. Mitchell, MD, MS, is an Assistant Professor of Medicine at the Medical College of Wisconsin. She practices at the Froedtert & The Medical College of Wisconsin General Internal Medicine Clinic - East. Her column appears in the Milwaukee Journal-Sentinel.