Recently doctors began gene-therapy trials to treat Leber’s congenital amaurosis, a common cause of blindness in babies and children. Now, a group of doctors reports that they’ve found an unexpected benefit of the gene therapy. After treatment, vision may continue to improve with time — because the brain can re-wire itself to better accommodate the new site of perception.
In a trial reported last year, three young adults got the gene therapy: an injection to the eye of an important gene variant that they’re missing. Vision improved somewhat. Later, at their one-year follow-up meeting, none of the patients had serious complaints. But one patient in particular piqued the researchers’ interest. “For the first time in her life, the patient reported that she could read the illuminated numerical clock display on the dashboard of the family vehicle while she was sitting in the front seat,” the researchers write this week in a Correspondence article in the New England Journal of Medicine. They continue:
The simplest explanation of this development would be increased visual sensitivity either at the fovea [the part of the eye that’s responsible for sharp vision] or in the treated region […]. However, visual sensitivity (measured by means of microperimetry) was unchanged at this visit as compared with earlier post-treatment visits.
In other words, the eye was the same as it had been straight after treatment. What worked differently was the brain — by making more effective use of the signal it now receives from the treated part of the eye. It was as if the patient had developed a second fovia — “a pseudo-fovia,” as the researchers write — or a new site for central vision. It’s just one more sign of the brain’s remarkable plasticity. Well into adulthood, the brain can still adapt to its environment.