The France-based biotech Gensight Biologics is developing gene therapy treatments for rare, mitochondrial, and neurodegenerative diseases of the eye. Its lead therapeutic candidate is in late-stage trials for Leber’s Hereditary optic neurophathy, a sudden condition that afflicts young adults and leaves almost all of them blind. We spoke to Gensight’s CEO Bernard Gilly about the company, the challenges and promises of gene therapy, and why eye disease is a particularly attractive target for this emerging area of treatment.