In the Western world hereditary retinal diseases are the most common cause of blindness in people under 70 years of age, affecting about 1.5 million individuals. Various attempts have been tried but none of the enumerated treatments had any scientifically confirmed beneficial effect.1 Gene therapy holds the promise of revolutionising the treatment of genetic diseases and might be an “ideal” approach to treat many forms of hereditary retinal diseases. Indeed, hereditary retinal diseases meet all of the major requirements for gene therapy.2 Firstly, their genetic basis is well characterised and the biochemical defects are known in several diseases (for example, Refsum disease, gyrate atrophy, Kearns-Sayre syndrome). Secondly, efficient gene delivery techniques that can be relatively well controlled are available and allow even local ocular application. Lastly, reliable animal models of hereditary retinal diseases are available that permit preclinical testing.

However, fundamental challenges in gene therapy are still present and it appears that clinical trials in non-life threatening disorders such as retinal dystrophies are far …