Researchers at the University of Florida have been experimenting with gene therapy to treat a common congenital blindness (Leber congenital amaurosis type 2) in children. Leber’s congenital amaurosis is a rare disorder caused by an autosomal recessive change, in which patients fail to express a protein responsible for development of photoreceptors. By delivering the missing RPE65 gene to a small section of the retina using a virus vector, the three patients in the study have seen marked improvement in their response to light. Moreover, it seems that the young adult brain, the vision areas of which were never used before, learns how to adapt to the new abilities of the eye.
“When one patient came back for her 12-month visit, she said she could read the digital clock in her parents’ car with her treated eye — something she was never able to do before,” said William W. Hauswirth, a professor in the ophthalmology department at the UF College of Medicine. “That prompted us to measure where her gaze was fixed while looking at a variety of dim targets. This showed that she now has two preferred centers of vision rather than one, depending on the brightness of the object.”
The new region is more sensitive to light, but it is not as precise as the fovea for making bright images sharp.
“Her brain tells her to use the best part of retina she can, depending on the situation, so she automatically shifts back and forth between the usual region and the region we supplied to her,” said Hauswirth, who is associated with the Powell Gene Therapy Center and the UF Genetics Institute.
In October 2008, researchers reported that the study volunteers — one woman and two men ranging from 21 to 24 years old — could see brighter areas and perhaps some images.
In the current New England Journal of Medicine report, scientists say vision in volunteers’ treated eyes remains slightly improved in dim lighting conditions. But the “excursions of fixation” from the usual focal point of the retina to the treated area nearby in one of the patients was a welcome surprise.