Two reports published online this week by the New England Journal of Medicine have described the use of gene therapy to correct the causes of one form of congenital blindness. Although the gains in both cases were modest, media reports have greeted them with jubilation and the suggestion that the results can be extrapolated to a wide range of eye conditions.

This reaction has prompted one researcher who recognises the value of the new work to regret that, once again, enthusiasm for gene therapy may be running dangerously ahead of its actual achievements.

Infants born with Leber’s congenital amaurosis have profound visual impairment throughout childhood and become …