Age-related macular degeneration (AMD) affects between 30 and 50 million people around the globe, and it is the number on reason for vision loss in developed countries. It is most common in those over 60. Around 90% of those with AMD have dry AMD. Unfortunately, there is no real effective treatment for it yet.
What Is AMD?
AMD affects the retina, which is the tissue inside of the eye that is responsible for converting the light received into vision. At the back of the retina, in the center, is the macula, which providess central vision. Central vision is needed for things like facial recognition, driving, and reading. Inside the macula, you will find photoreceptor cells, and behind those is the retinal pigment epithelium (RPE). In people with AMD, the RPE cells no longer support the eye properly, and central vision is loss. Usually, with dry AMD, it takes several years for total loss of vision. With wet AMD, on the other hand, central vision can be lost in just a few days. The table below highlights some of the main differences between wet and dry AMD.
|Wet AMD||Dry AMD|
|Rarity||Very rare||Very common|
|How it happens||Blood vessels sprout in the choroid, leading to a cluster.||The RPE cells stop being able to support the photoreceptor cells.|
|Development time||Days or weeks||Years|
There are a number of drugs and surgical treatments that can be used for wet AMD. However, dry AMD, which is so much more common, cannot be treated. Additionally, most people with wet AMD also have dry AMD, and the medication to treat wet AMD could make the dry version worse. Most people with dry AMD are asked to take vitamin supplements, which helps slow down progression.
Stem Cells for AMD
Thanks to stem cell research, scientists are beginning to understand the cells in the retina, and how they work in synergy. It is hoped that this can help in improving the support the RPE cells are able to give. RPE cells don’t connect to the fibers of the nerves, which means that it may be easier to integrate them with existing cells. New ones could simply replace the damaged ones and support them. If this is done before the cones and rods in the eye are lost, which happens in advanced AMD, then the new cells may prevent the disease from progressing at all. Furthermore, it is reasonably easy to create new RPE cells from stem cells.
Stem cells are also used to discover new drugs. Scientists put healthy RPE cells under stress so that they start to behave as if AMD is present. These can then be studied and tested to help with earlier diagnosis and perhaps even to find a permanent cure.
Stem cell research is still in its infancy but scientists believe that, if used properly, stem cells could halt or perhaps even reverse AMD vision loss. There is particular excitement about induced pluripotent stem cells (iPS cells), which can be programmed to behave in an embryonic way. Human embryonic stem cells are also being used, while others are using those from organ donations such as the eyes.
One of the things researchers are trying to determine is the optimal maturation of the cells. The more mature the cells, the less likely it will be for them to grow beyond what is needed, or to migrate to other parts of the body. If they are not mature enough, however, they may be ineffective.
Scientists are also looking into how the stem cells can be delivered to the eye. Currently, research into patches seems to be the most promising. When placed on a material that allows waste materials and nutrients to pass through when implanted in the eye, the patch has shown some very promising results in animal tests. It seems that the cells are stable and do not migrate.
Cell suspension is also being tested. Here, the cells are actually injected under the retina itself. They are injected as part of a harmless fluid.
The critical question, however, is whether integration into a human host will be successful, and whether the cells will be able to do their job.
There are numerous studies currently taking place in stem cells for AMD, as the table below highlights.
|Moorfields Eye Hospital, London, United Kingdom||An 18 month clinical trial in which 10 people will receive stem cell treatment to study the effects on their wet AMD||The first woman to take part, a 60 year old, has shown promising results.|
|Ocata Therapeutics||Early stage clinical trials using human embryonic stem cells (hESC) for Stargardt disease and dry AMD||Early results have been positive.|
|University of California Davis||Phase 1 clinical trial where patients are injected with CD34+ stem cells from the patient’s own bone marrow. This will look at feasibility and safety concerns. After treatment, participants will be monitored for six months.||Currently recruiting.|
|SCOTS Clinical Trial||Different cell injections will take place, comparing the results. Patients will be monitored for 12 months.||Currently recruiting.|
|StemCells, Inc. C||Phase I/II study to determine the preliminary effect and safety of HuCNS-SC cell transplantation for dry AMD.||More patients to be recruited before results are to be revealed.|
While there is no real cure for AMD yet, it appears that stem cell research looks promising. In theory, it should be able to halt the disease and, if caught early enough, even reverse it. Further studies are required to understand if and how this would be possible.