Stem Cells in the Eye
By Gail Seigel, Ph.D
Stem cells exist in various regions of the eye, even into old age. So far, stem cells can be found at the outer edges of the cornea (the outer clear part of the eye covering the iris and pupil), the conjunctiva (the thin, moist membranes that cover the inner surface of the eyelids and the outer surface of the eyeball), as well as the ciliary margin (the tissue that lies just behind the iris).
From http://webvision.med.utah.edu, a Web site of the John Moran Eye Center at the University of Utah. | The Cornea:
The cornea is the clear outermost surface of the eye and is subject to trauma, injury, and every day wear and tear. The stem cells of the cornea are located at the limbus (the thin area between the clear cornea and the white sclera of the eye). The purpose of corneal, or limbal, stem cells is to maintain a healthy eye surface and replace cells that are lost and blinked away. Limbal stem cells can be transplanted for severe eye injuries. During this outpatient procedure, some limbal stem cells are taken from the healthy eye, or a donor's eye, and then transplanted to the affected eye.
In a successful transplant, limbal stem cells will produce a new healthy layer of cells in the patient's eye. The success rate varies from 25 percent to 70 percent, depending on the underlying condition of the affected eye. |
Limbal stem cell transplantation in the eye holds great promise for patients. Researchers are still working to determine the best source of cells to use, the best way to transfer the cells and better ways to decrease the risk of rejection between donor cells and the recipient. In a successful transplant, limbal stem cells will produce a new healthy layer of cells in the patient's eye. The success rate varies from 25 percent to 70 percent, depending on the underlying condition of the affected eye. Limbal stem cell transplantation in the eye holds great promise for patients. Researchers are still working to determine the best source of cells to use, the best way to transfer the cells and better ways to decrease the risk of rejection between donor cells and the recipient.
The Conjunctiva:
Another important component of the eye surface is the conjunctiva, the transparent tissue that covers the outer surface of the eye. The conjunctiva is nourished by tiny blood vessels that are nearly invisible to the naked eye and also secretes oils and mucous that moistens and lubricates the eye. The conjunctiva, like the corneal surface, undergoes constant renewal. Specific cells, called goblet cells, of the conjunctiva produce mucin, an essential ingredient in tears.
Diseases and injuries to the conjunctiva may lead to scarring, adhesions (scar tissue that joins normally unconnected parts of the eye), dry eye or mucin deficiency—all of which affect tear film. Grafts of conjunctiva, in which a healthy piece of conjunctiva is used to replace a damaged area, can be used as a means to treat diseased or damaged tissue. Although the existence of conjunctival stem cells is well-accepted, the precise location of these stem cells within the conjunctiva is still under debate.
The Ciliary Margin:
The ciliary body includes the group of muscles that allow the eye lens to contract and also produces that clear fluid that fills the front of the eye. There are primitive cells located in the ciliary margin of the eye that can develop into mature cells of the retina. Early on, it was shown that stem cells exist in the eyes of fish and amphibians that contribute to the retina throughout life. Under specific experimental conditions, these cells from fish can regenerate a complete retina. More recently, adult retinal stem cells, or retinal progenitor cells, have been identified in the mouse, rat, cow and human ciliary margin.
Further, researchers have recently demonstrated that the cells of the retina, called retinal pigment epithelial cells, could be derived from human embryonic stem cells. In animal studies, the transplantation of mouse embryonic stem cells has been tried as an experimental treatment to rescue dying cells of the retina (the photoreceptor cells) with some degree of success. This leads to the intriguing possibility that stem cells from more than one source have the potential to be used for transplantation in people with retinal degenerations such as retinitis pigmentosa and age-related macular degeneration.
Gail Seigel, Ph.D, is an eye stem cell specialist at the Ross Eye Institute, SUNY at Buffalo.
Back to Selected Topics
Updated:
February 2, 2005
|
