Washington ? The first drug shown to significantly improve the vision of patients threatened by a major cause of blindness in the elderly won federal approval Friday.

The drug, called Lucentis, treats the wet form of age-related macular degeneration, a disorder where blood vessels behind the retina leak blood and fluid, worsening vision and often causing blindness. An estimated 90 percent of the 1.4 million Americans who have lost their eyesight due to the disorder have the wet form.

Lucentis, made by Genentech, Inc., a South San Francisco, Calif., biotechnology company, inhibits the growth of blood vessels when injected into the eye. Other Food and Drug Administration-approved treatments can arrest progression of the disease, which can lead to blindness in just weeks or months, but none has been shown to significantly reverse deteriorating vision.