(Adds details about Eylea, study findings, share price)
Oct 21 (Reuters) - Regeneron Pharmaceuticals Inc said its drug Eylea improved vision in a late-stage trial far better than standard laser treatment among patients with a common form of vision loss caused by blood clots in secondary veins of the retina.
Eylea has become a blockbuster product since winning U.S. approval in November 2011 to treat the "wet" form of age-related macular degeneration, a leading cause of blindness in which leaky blood vessels in the central part of the retina can endanger sight.
The injectable drug is also approved for macular edema - meaning fluid buildup under the central area of the retina - that occurs after central retinal vein occlusion, which is blockage of the retina's major vein. Both macular edema and retinal vein occlusion can cause vision loss.
Regeneron on Monday described results from a Phase III study called Vibrant, which tested 183 patients with macular edema following branch retinal vein occlusion, meaning blockages within branches of the central retinal vein. Such blockages can cause blood and fluid to back up and spill into the retina.
Some 53 percent of the patients who received Eylea injections every four weeks for 24 weeks gained at least 15 letters in vision, an eye chart test measuring sharpness of vision. That was deemed better by a highly statistical margin than the 27 percent of patients who achieved such vision gains with standard laser treatment.
Laser treatment cauterizes leaky blood vessels in the eye, to stop the leakage that leads to vision loss.
The company said 9.9 percent of patients in the Eylea group experienced serious adverse events, compared with 9.8 percent in the laser group.
There was one serious adverse event in a patient receiving Eylea, Regeneron said. The patient suffered from a traumatic cataract, a cataract which is related to eye injury.
Regeneron said common adverse events were bleeding from broken blood vessels in the eye and pain in the eye.
Based on results of the Vibrant study, Regeneron said it plans within several months to seek U.S. approval to market Eylea for treatment of macular edema following branch retinal vein occlusion.
Eylea in previous trials has also been shown to be significantly better than laser treatment at improving vision in diabetics who have macular edema.
Regeneron shares were down 1.4 percent at $299.30 on Monday morning on the Nasdaq, amid slight declines for the drug sector.
The company has U.S. rights to Eylea, and equally shares profit from the drug outside the United States with longtime partner Bayer AG.
U.S. sales of Eylea rose 70 percent in the second quarter to $330 million. Regeneron expects the drug to garner full-year sales of up to $1.35 billion. Eylea has been steadily grabbing market share from Roche Holding's similar drug, Lucentis.
(Reporting by Ransdell Pierson in New York; additional reporting by Vrinda Manocha in Bangalore; editing by Sriraj Kalluvila and Matthew Lewis)