Joe Fitzsimmons, age 10, of Casper, Wyo., for his question:

WHAT CAUSES NEARSIGHTEDNESS?

Nearsightedness is a defect of sight in which distant objects that should be clearly seen are blurred. Doctors call this condition myopia. The cause of nearsightedness is that the affected person's eyeballs are too long. Heredity is the most important cause of the defect.

When a person's eyeballs are too long, his eyes bring distant objects into focus improperly. The image fails too far in front of the retina to produce a sharp picture.

To correct nearsightedness, people often wear contact lenses or eyeglasses with lenses that are thin in the middle and thick at the edges.

Very few babies are born nearsighted. The defect usually develops in childhood and adolescence and sometimes progresses rapidly until about the age of 21.

Nearsightedness cannot be cured. Vision should he kept as near to normal as possible by using properly fitted glasses.