Leber's congenital amaurosis, a common cause of blindness in infants and children,1 recently became the first human genetic retinal disease to show improved vision in response to treatment. Patients with mutations in the gene encoding retinal pigment epithelium–specific 65-kD protein (RPE65) had gains in vision within weeks after subretinal injection of a vector containing the gene in one eye.2-5 At 1-year follow-up after gene therapy, the three young adult patients in our trial4,5 remained without serious adverse events.
A noteworthy observation in one patient at 1 year after treatment prompted further studies. 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 numerals subtended a visual angle equivalent to a visual acuity of 20/200, which is not different from her formally measured visual acuities at baseline or at 1 year after treatment. The simplest explanation of this development would be increased visual sensitivity either at the fovea or in the treated region of the superotemporal retina. However, visual sensitivity (measured by means of microperimetry) was unchanged at this visit as compared with earlier post-treatment visits (Figure 1AFIGURE 1
Slow Emergence of a Pseudo-Fovea within the Treated Retinal Region and Perception of Previously Unseen Stimuli.
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