SILVER SPRING, Md. (AP) — A potentially groundbreaking treatment for a rare form of blindness moved one step closer to U.S. approval Thursday, as federal health advisers endorsed the experimental gene therapy for patients with an inherited condition that gradually destroys eyesight.

The panel experts to the Food and Drug Administration voted unanimously in favor of Spark Therapeutics' injectable therapy, which aims to improve vision by replacing a defective gene needed to process light.

The vote amounts to a recommendation to approve the therapy. The FDA has until mid-January to make its decis...