For the one in 50,000 people born with the genetic disorder choroideremia, there's no treatment that can slow the progressive vision loss. Scientists from the University of Oxford have been developing a gene therapy treatment to reverse the effects of the disease, and, though the initial results seemed promising, they had not been sure the treatment would work in the long term.

According to a study published today in the New England Journal of Medicine, the treatment has worked well in patients over the course of four years, buoying hopes that treatment for the condition (and for other genetic degenerative eye conditions like retinitis pigmentosa or macular degeneration) may become available to other patients soon.

Many gene therapy treatments have been focused on conditions that affect the eyes. These diseases are often caused by just one or two genes, the eyes are easy to access to administer the treatment, and results are often easy to detect by comparing a patient's treated and untreated eyes.