In the near future, ophthalmologists may have two new, powerful tools to treat diseases of the retina that can cause blindness, such as age-related macular degeneration (AMD) and others. The retina converts images into nerve signals that are then transmitted through the optic nerve to the brain. A healthy retina is essential for good vision.
In early 2012, researchers reported positive results from the first test of embryonic stem cells to treat vision problems in human patients. Both patients had been legally blind — one due to AMD and the other to Stargardt disease — and both regained some vision.
Any type of cell can be derived from embryonic stem cells, and in this case they were used to develop retinal pigment epithelium (RPE) cells. These cells were injected into the space behind the eye's retina to replace RPE cells that have died.
Another stem cell approach, just approved in February 2012 for human trials, instead uses stem cells taken from the retinal epithelium itself. This type of cell works by protecting the light-sensitive (photoreceptor) cells in the retina, rather than by replacing damaged RPE cells. This could be especially useful for treating "dry" AMD, which damages photoreceptor cells.
In a separate test using gene therapy, researchers restored vision in both of the eyes of three patients with Leber congenital amaurosis (or LCA), an inherited disorder.
One type of LCA is caused by a defect in the gene RPE65 that blocks the production of an enzyme that the retina needs to function. Without the enzyme, toxins build up in retinal cells, eventually causing them to die. Gene therapy for LCA involves injecting a normal version of RPE65 into the retinal cells.
Gene therapy researchers are particularly encouraged that a 47 year old woman was one of the patients to regain vision in both eyes. In the same trial, based at Children's Hospital Philadelphia, 11 other patients received RPE65 gene therapy in one eye, and 2 children in this group have been treated in both eyes.
Overall, children in the trial showed more improvement than adults, probably because their retinal cells were not yet as damaged by LCA. All of the children in the trial can now read books, ride bikes, and enjoy doing many things that had once been impossible for them. Eventually it might be possible to treat children with LCA very early in their lives, before any damage to vision occurs.
Though physicians say much work remains before stem cells or gene therapy can be considered fully safe and effective and receive FDA approval as treatments for AMD, LCA, Stargardt, and other diseases that damage the retina, these early results are highly encouraging.