(a) Gene therapy One of our overriding targets is to understand how to prevent the loss of retinal vision. Gene therapy, which has a great deal of promise in preventing vision loss, is in its infancy. Gene therapy techniques must be tailored for the specific disease in question. Recessive diseases are generally the most straightforward to treat with gene therapy. In recessive diseases, neither chromosome has a correct gene copy and the gene product is usually missing. Adding the normal gene will correct the disease. In dominant diseases, a patient will have a normal functioning gene and a gene with a disease-causing mutation. The mutant gene produces a dysfunctional protein that damages the cell. Ribozyme gene therapy is used to disrupt the mutant gene's ability to produce the harmful protein. With the disease gene inactivated, the healthy gene can usually supply the cell with the needed normal protein.
(b) Retinal Stem Cell Research Our second target is restoring lost vision using stem cells. Individuals with macular degeneration and retinitis pigmentosa lose their vision because of the death of retinal photoreceptor cells. In many tissues, old cells are continuously being replaced with new cells. This process of cell renewal does not take place in the retina. When a photoreceptor cell is lost from the human retina, it cannot be replaced. When photoreceptors in the retina are lost in individuals with photoreceptor disease, the energy of light coming into the eye cannot be converted into an electrical signal and the special sensory function we know as vision is no longer possible. The ability to restore macular vision through transplantation of photoreceptor stem cells would be an outstanding contribution to ophthalmology.