This past November, Acuity Pharmaceuticals in Philadelphia began testing an RNAi-based therapy in 12 patients suffering from age-related macular degeneration, the leading cause of blindness in people over 55. The treatment, which involves an injection of engineered RNA strands into the patient's eyes, is a simple, if not painless, process [see illustration]. The strands are designed to intercept faulty instructions sent by sick genes inside eye cells, thereby halting the deterioration of the macula. Although
scientists are still unsure about potential side effects, given the alternative of almost certain blindness, patients feel that it's worth the risk.