Nearsightedness (distant objects appear blurry) typically begins between the ages of eight and fifteen but can start earlier. Farsightedness is actually normal in young children and not a problem as long as it is mild. If a child is too farsighted, vision is blurry or the eyes cross when looking closely at things. This is usually apparent around the age of two or three. Almost everyone has some amount of astigmatism (oval instead of round cornea). Glasses are required only if the astigmatism is strong.
Unlike adults, children who need glasses may develop a second problem, called amblyopia or lazy eye. Amblyopia means even with the right prescription, one eye (or sometimes both eyes) does not see normally. Amblyopia is more likely to occur if the prescription needed to correct one eye is stronger than the other. Wearing glasses can prevent amblyopia from developing in the more out-of-focus eye.
Children (and adults) who do not see well with one eye because of amblyopia, or because of any other medical problem that cannot be corrected, should wear safety glasses to protect the normal eye.