This is the first of a small series regarding stem cells and their potential benefits to retinal diseases; principally macular degeneration and retinitis pigmentosa.
As diabetic retinopathy is primarily a disease of blood vessels, i.e.poor blood flow, loss of blood flow, leaking vessels, etc., macular degeneration is actually a disease of one of the layers of the retina. Specifically, the layer affected is called the Retinal Pigment Epithelium (RPE). It is a layer of cells that have numerous functions and responsibilities, one of which is keeping the photoreceptor healthy and happy. Remember photoreceptors are also known as rods and cones.
The retina is a laminated tissue. It lines the inside of the eye in the same way that wallpaper lines the inside of a room. Just underneath the retina is a layer of cells, the Retinal Pigment Epithelium (RPE). The RPE layer is uniformly found underneath the entire retina, even the macula. For us to “see,” the retina must be attached and all the layers of the retina be healthy. This is not so in macular degeneration. While the retina is attached, the RPE layer becomes sick and dysfunctional; it degenerates. It is the RPE layer that is diseased in macular degeneration.
In areas of the macula where the RPE has become dysfunctional, the vision is impaired. Symptoms include blurry vision and distortion. The actual cause of the degeneration of the RPE is not known; it may be due to poor blood supply from a vascular layer deep to the RPE (the choriocapillaris, aka choroid), it may be purely bad genetic programming or it may be due to environmental factors (e.g. sun, smoking, etc.).
How to Replace Damaged Cells? Retinal Pigment Epithelium cells do not reproduce or regenerate. Once the RPE is damaged, the eye can not make more. The focus of research has been, how to replace damaged RPE cells?
Several approaches to replace Retinal Epithelium Cells are under experimentation. Attempts at direct transplantation have had some success. Stem cell transplantation, in theory, seems very promising.
Randall V. Wong, M.D.
Ophthalmologist, Retina Specialist