(C) Myopia (also called nearsightedness) is the most common cause of impaired vision in people under age 40 — and in recent years, its prevalence is growing at an alarming rate. This causes distant objects to be blurry while close objects appear normal. Other symptoms may include headaches and eyestrain. Severe nearsightedness increases the risk of retinal detachment, cataracts, and glaucoma. The underlying cause is believed to be a combination of genetic and environmental factors.