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Various parts of the eye work to focus light, which is processed by a membrane called the retina. The light is then converted by cells into electrical signals that travel to the brain via the optic nerve. Diseases can damage the retina causing a person’s vision to decline and eventually be lost altogether. Retinal stem cell therapy is a technique that some researchers have been exploring in the early 21st century to reverse the damage to such tissues. A few scientists have claimed success in treating animals, as of 2011, and clinical trials on humans may seek to find treatments for eye conditions like macular degeneration and retinitis pigmentosa.
Embryonic stem cells are typically not characterized as belonging to any tissue type. Retinal stem cell therapy researchers often believe these can develop into the same tissues they are placed in. The retina is usually comprised of a few different types of cells. Scientists have found retinal progenitor cells that can develop into specific types that are needed by the eye, but these have to be injected. Cell types in the retina typically include ganglion cells and photoreceptors.
Different types of stem cells have been used in research. Scientists have worked with several of them to try to determine which are best for retinal stem cell therapy. One kind seems to be more suitable for treating injuries of the retina, while another is believed to less likely be rejected by the body’s immune system. Researchers in animal studies have claimed that these can integrate with other cells in the retina and nerve fibers. Adult bone marrow stem cells have also been analyzed; they are usually specific to certain organs, but some research suggests they can be used on the retina.
Retinal stem cell therapy can be accomplished through an injection with a needle. While typically the most non-invasive approach, success often depends on the cells migrating to the right place. A technique called subretinal injection is usually more difficult but the stem cells are generally placed closer to the selected area. Experiments have often shown that there is more likelihood of them differentiating as well. Cell death can be a concern in experiments, and some scientists have tried to deliver the stem cells on a polymer graft to get a maximum number to survive.
A challenge of stem cell treatment in the eye can be getting grafts to integrate with tissue. Sometimes cell division is inhibited as well, while immune system reactions can also prohibit successful treatment. Retinal stem cell therapy in animals has sometimes been successful at the beginning, but visual performance can degrade over time, as shown in some scientific studies.