Medical Hypothesis, Discovery Innovation Ophthalmology Journal | Harvey Siy Uy, MD, Pik Sha Chan, MD, and Franz Marie Cruz, MD | 2013 Summer | 2(2) | 52–55.
Unfortunately, at present, degenerative retinal diseases such as retinitis pigmentosa remains untreatable. Patients with these conditions suffer progressive visual decline resulting from continuing loss of photoreceptor cells and outer nuclear layers. However, stem cell therapy is a promising approach to restore visual function in eyes with degenerative retinal diseases such as retinitis pigmentosa. Animal studies have established that pluripotent stem cells when placed in the mouse retinitis pigmentosa models have the potential not only to survive, but also to differentiate, organize into and function as photoreceptor cells. Furthermore, there is early evidence that these transplanted cells provide improved visual function. These groundbreaking studies provide proof of concept that stem cell therapy is a viable method of visual rehabilitation among eyes with retinitis pigmentosa. Further studies are required to optimize these techniques in human application. This review focuses on stem cell therapy as a new approach for vision restitution in retinitis pigmentosa.
A potential target disease for stem cell therapy is retinitis pigmentosa (RP). RP is the most commonly inheritable eye disease that causes progressive loss of photoreceptor cells resulting in gradual visual decline. While the onset of RP may occur during infancy, the first symptoms are usually observed in early adulthood, beginning with nyctalopia or night blindness followed by loss of peripheral vision and eventually, as the central photoreceptors in the macula are damaged, loss of fine central vision. Morphologically, these retinas are characterized by centripetal proliferation of bone spicule-like pigmentation, attenuation of retinal blood vessels and optic nerve pallor. At least 50 genetic mutations have been associated with the disease. The Beijing Eye Study reported a prevalence rate of 1 in 1000 and estimates about 1.3 million people are afflicted in China alone.
Previously, RP was considered a devastating and untreatable condition. These pioneering animal studies provide hopeful evidence for the hypothesis that stem cell therapy is a viable means for visual rehabilitation of RP patients. What is now known is that stem cell therapy can potentially replace degenerate photoreceptors and outer retinal cells. When placed in the appropriate tissue niche, these stem cells not only survive but differentiate into critical retinal cells, develop a retina-like organizational structure and exhibit functional characteristics of full-fledged photoreceptors and outer retinal cells. Further studies are needed to optimize techniques and validate these findings before proceeding to human trials.