Investor interest in gene therapy has increased substantially over the past few years, and the next major catalyst for the field is likely to be Spark Therapeutics's phase III trial for the treatment of visual impairment caused by RPE65 gene mutations (often referred to as Leber congenital amaurosis type 2, or LCA2, but may include other retinal disorders). Analysis of the approach from the basic genetics, underlying visual mechanisms, clinical data, and commercialization considerations helps frame investor expectations and the potential implications for the broader field.