What is it about losing our vision that scares us so much?
The slow loss of vision associated with eye diseases is difficult to think about. When you are personally connected to those who suffer from vision loss or blindness, you feel the loss keenly.
But now there is a glimmer of hope. Researchers at the University of Southern California have engineered an eye implant that has reportedly stabilized the vision of four patients with advanced age-related macular degeneration.
Approximately 10-20% of adults above the age of 65 will develop age-related macular degeneration (AMD), a degenerative eye disease that progressively leads to blindness. AMD comes in two varieties: wet and dry. While wet AMD has a number of available treatments, dry AMD is currently untreatable.
Dry AMD is associated with loss of a specialized layer of cells in the back of the eye called the retinal pigment epithelium, or RPE. The RPE is the main support system for the cells that are responsible for detecting light and transmitting the information to the brain to form an image. These cells are called the photoreceptors. If anything happens to the RPE, the photoreceptors can degenerate and die, resulting in progressive vision loss.
Since the RPE is a critical factor in our ability to see, scientists seeking treatments for dry AMD have focused their efforts on healing or replacing damaged RPE.
But how can a layer of cells in the back of the eye be regrown?
Here's where the cool science comes in. The University of Southern California researchers, led by Mark Humayun, M.D., Ph.D., have designated their eye implant the California Project to Cure Blindness-Retinal Pigment Epithelium 1, or CPCB-RPE1.
The CPCB-RPE1 is a solid 3.5 mm x 6.25 mm scaffold on which about 100,000 RPE cells are grown on a synthetic material. When the device is implanted into the eye, these RPE cells can incorporate into the area of the damaged RPE and restore the normal behavior of the RPE.
Images from the April 2018 report illustrating the relative position of the CPCB-RPE1 implant (black dotted lines) in the eyes of two patients.
The RPE cells used for this implant were derived from human embryonic stem cells. Embryonic stem cells are a very special cell type and have great promise for treating disease. They are sort of like a primordial cell that has no specific identity, unlike a skin cell or a muscle cell. However, they can become ANY type of cell in the body depending on the environment they are exposed to.
Researchers have been hard at work identifying the conditions that specify the ultimate identity of a stem cell. This work has incredible potential for treating different types of human disease. For example, we can now direct stem cells to become insulin-secreting β cells that might help cure type I diabetes or, in this case, RPE cells to treat patients with vision loss.
Before testing in humans, the group first tested their implant on rats with a form of retinal dystrophy that mimics AMD. Not only were the implanted RPE cells still alive and well 21 weeks after the surgery, there were more photoreceptors in the eye with the implant. The researchers also confirmed the safety of the implant in pigs, whose eye structure is more similar to that of the human eye. Importantly, these preclinical animal studies showed the surgical procedure and implant were safe, and the RPE on the implant was doing its job.
The group then took the next step and was approved for a clinical trial for patients with advanced AMD and severe vision loss. The results from four patients who received the implant were published in April in Science Translational Medicine.
The implant was safely surgically inserted into patients’ eyes with no unexpected adverse effects. Because only one eye received the implant, the other eye was used to monitor progression of vision loss without treatment over the course of the study. Excitingly, the vision in the implanted eyes of all four patients stabilized compared to their untreated eye. And even better, one patient even experienced vision improvement.
While there is still a lot more to do, including studying more patients over longer time periods, these results are heartening as the implant stabilized the vision of patients with advanced AMD, those who have low chances of recovery.
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Additional Resources:
Link to original study