clipped from: singularityhub.com   

The emerging field of gene therapy took a huge leap forward in 2008 when vision was substantially restored to several blind patients. 

The patients in the study suffer from Leber’s congenital amaurosis (LCA), a rare inherited eye disease caused by a defective gene called RPE65. The condition appears at birth or in the first few months of life and causes progressive deterioration in vision.  Until now there have been no effective treatments available.

Normally, cells in the eye activate the RPE65 gene to produce an enzyme necessary for the function and health of a protective layer of cells underlying light- and color-detecting photoreceptor cells in the eye.  Patients with a defective RPE65 gene are unable to produce this enzyme, leading to photoreceptor cells that are otherwise healthy but unable to do their job.  Over many years the photoreceptor cells themselves steadily become damaged beyond repair.