(Corrects to remove reference to Sanofi in second paragraph.)

March 25 (Reuters) - U.S. health regulators on Wednesday approved Regeneron Pharmaceuticals Inc's big-selling eye drug Eylea to treat diabetic retinopathy, the most common diabetic eye disease and a leading cause of blindness in adults.

The Food and Drug Administration decision marked the fourth approval for Eylea, an injectable medicine that had sales of $2.78 billion in 2014.

"Today's approval gives patients with diabetic retinopathy and diabetic macular edema another therapy to treat this vision-impairing complication," Edward Cox, director of the FDA's Office of Antimicrobial Products, said in a statement.

The agency had previously approved Roche's rival drug Lucentis for diabetic retinopathy, a condition in which blood vessels in the eye swell and leak fluid, or in which abnormal new blood vessels grow, hampering vision.

Regeneron shares were down 2.4 percent at $461.90 on the Nasdaq by 11:10 a.m. EDT (1510 GMT) on an off day for biotech stock indexes.

Eyelea was initially approved for wet age-related macular degeneration, the leading cause of blindness in the elderly. It is also approved for diabetic macular edema and macular edema following retinal vein occlusion, all eyesight robbing conditions.

(Reporting by Bill Berkrot; Editing by Alan Crosby)