An interesting review article in the July 2015 issue of Stem Cells looks at using stem cell therapy to prevent the progression of myopia ("Concise Review: Using Stem Cells to Prevent the Progression of Myopia - A Concept", by M. Janowski, et. al.). The authors, a team from Johns Hopkins University School of Medicine, discuss the prevalence of myopia and how different mechanisms might be amenable for stem cell treatments.
Myopia, or nearsightedness, is basically the condition where objects that are near are seen clearly while far objects are blurry. There are a couple of causes, either the eyeball being too long or the cornea being overly curved. Both scenarios cause light entering the eye to not focus appropriately. This leads to the blurred vision of distant objects.
This condition is rather common, affecting about 30% of the population in the US. However, it is becoming an increasingly more common disorder throughout the world. There are both hereditary and environmental influences that lead to the condition, and as the world becomes more industrialized the environmental effect is increasing. It seems that this is due to strain on the eyes caused by educational stressors along with a decrease in sunlight exposure. In areas of the world with minimal education, the incidence is rather low; however, in those regions with more advanced educational systems the rate of myopia is rapidly increasing, possibly towards pandemic levels.
The authors propose a couple of ways in which stem cells might be useful in treatment of myopia and its progression. The first is in use of stem cells to support the sclera of the eye, as the myopic sclera is commonly characterized as being weak, thinned, and less rigid than normal. This theory is based on applying stem cells to an area in the back of the eye in a region known as the subscleral space, between the sclera and the choroid. These cells would then differentiate into fibroblasts that can produce extracellular matrix, strengthen and reinforce the sclera itself, and prevent elongation of the eyeball. In this case, the stem cells have a direct effect on the eye.
The second proposed method of treatment with stem cells is in the area of dopaminergic signaling. Dopamine is a neurotransmitter, a type of chemical produced by certain cells to send signals to other cells. There is significant cross-talk between the sclera and the retina, and a proposed cause of myopia is a disruption or dysfunction in that signaling process. Dopamine is secreted in the retina to specifically enhance the activity of cone cells while also suppressing activity of rods. This occurs only during daylight hours as a way to increase sensitivity to contrast and color during the conditions of bright light. It also seems that dopamine plays a role in the eye's growth and potentially in control of myopia. Various animal studies have already shown that dopamine and dopamine-agonists can slow myopic changes. Thus, stem cells could be used to obtain highly functional dopaminergic cells which could then be used to treat myopia. In this instance, the stem cells are contributing an indirect effect.
The take-away is that stem cell treatments could be formulated to provide both direct and indirect help for this particular medical issue. Once again, the potential applications for stem cells continues to expand!
