Stem cells: new opportunities to treat eye diseases.

The recent identification and characterization of neural progenitors with stem cell properties has opened new avenues that may be useful for treating functional impairments caused by the death of specific neural cell populations. Neuronal degeneration is the cause of debilitating visual impairment associated with prevalent ocular diseases, such as retinitis pigmentosa (RP), age-related macular degeneration (AMD), retinal detachment, and glaucoma. Neural stem cells may help to restore vision in patients who have these diseases, by repopulating the damaged retina and/or by rescuing retinal neurons from further degeneration. In addition, understanding the molecular and cellular biology of neural stem cells will shed light on developmental mechanisms that regulate their maintenance, differentiation, and survival. Insights into these developmental mechanisms are likely to provide additional therapeutic approaches. This review provides an overview of the progress made in the area of neural stem cell research with emphasis on the eye. First, neural stem cells are defined and described. Second, their location and characterization in the mammalian eye is outlined. Third, progress in therapeutic usage of neural stem cell is discussed. And finally, the current barriers to neural stem cell therapy are assessed in an attempt to provide a balanced view of these exciting new opportunities in treating degenerative eye diseases. This review does not include corneal stem cells; the reader is referred to an excellent review by Schwab and Isserhoff on the therapeutic uses of corneal stem cells.