Thanks to biomedical research, our understanding of the human body is evolving and this has led to treatments that improve health outcomes. This includes vision research and as a result, more is being learned about what leads to amblyopia and a possible treatment for age-related macular degeneration (AMD).
Amblyopia, also known as lazy eye, is a condition that occurs in children where vision weaker in one eye, as opposed to the other. Left untreated it can lead to partial blindness. Research done at the Picower Institute at the Massachusetts Institute of Technology shows that when you look for one type of outcome, sometimes you find something else.
In order to do the research, the lab of Professor Mark Bear knocked out the N-methyl-D-aspartate (NMDA) receptors in the excitatory neurons in layer 4 of the visual cortex of mice. NMDA are ion channel receptors found at excitatory synapses in the brain. The lab then investigated what happened to the mice’s visual recognition memory and how they reacted to monocular deprivation. The idea was to knock out the NMDA receptors to see if that would prevent an increase in the strength of the stimulus-selective response nerve impulses. They thought that this would also prevent degradation of vision in the deprived eye and the subsequent strengthening of the unaffected eye.
As it turned out, amblyopia didn’t happen to the mice and two forms of plasticity remained. It will take more research to find out where the NMDA receptors are triggering stimulus-selective response nerve impulses. This study also focuses on the need to identify the components that leads to visual enhancement, which could lead to treatments not just for amblyopia but for other visual disorders.
Age-Related Macular Degeneration
Age-related macular degeneration (AMD) is the leading cause of vision loss in persons 65 and older. AMD occurs when the retinal pigment epithelial (RPE) cells waste away and die. Currently there is no treatment for AMD. A clinical trial is taking place that is looking into utilizing a person’s stem cells to replace the RPE cells.
The RPE cells support the development of photoreceptors in the retina and when the RPE cells die, the photoreceptors die and the end result is blindness. Researchers at the National Eye Institute (NEI) are using patient-derived induced pluripotent stem cells (iPSC) to bolster the health of the remaining RPE cells by replacing the dying cells with RPE cells made from the patient’s stem cells.
Before a transplant can take place, the RPE cells are grown in sheets one-cell thick, duplicating their natural structure in the eye. The cells are grown in a biodegradable scaffold that promotes the synthesizing of the cells in the retina. Doctors place the sheet of cells between the RPE and photoreceptors using a tool designed for this purpose.
The clinical trial involves 12 people who will receive the stem cell derived RPE implant in one eye and they will be monitored for a year to confirm the safety of the procedure. A big concern in using stem cells is the potential for tumors to grow. Thankfully, researchers found no mutations that would lead to tumors in the animal models that were used. Of course, the upside of using a person’s stem cells is that the risk of the body rejecting the implanted tissue is reduced.
Research doesn’t always follow a straight path and sometimes researcher can find what they need in a patient’s body. What scientists learn as a result of their work is for the benefit of all.