UH Optometry Professor's Research Focuses on Retinal Diseases

Hundreds of thousands of Americans have degenerative retinal diseases, which cause the light-sensitive photoreceptor cells of the retina to die, leading to permanent visual impairment and eventually blindness. There are currently no effective treatments to restore lost vision due to these diseases. But if Dr. David Sherry has his way, his basic research will help bring effective transplant therapies to restore vision one step closer to reality.

Dr. Sherry, an assistant professor at the University of Houston College of Optometry, has been awarded a $10,000 grant from the Lions Eye Bank Foundation to study the survival and growth of regenerating adult photoreceptors and the key factors that regulate these processes. Dr. Sherry's studies of the basic biological processes underlying photoreceptor growth will help pave the way for improving the ability of transplanted photoreceptors to restore vision in patients with degenerative retinal disease.

When the light-sensitive photoreceptors in the retina - the delicate lining of nervous tissue at the back of the eye - detect light, they signal other nerve cells in the retina, which process the information. These nerve cells then signal the brain, eventually leading it to form an image of the light pattern, which is what we see when looking at an object. The photoreceptors are the only cells in the entire visual system that respond directly to light. If these cells die, the input to the visual system is lost, resulting in loss of visual function.

Retinal diseases such as retinitis pigmentosa (a group of hereditary diseases of the retina) and diabetic retinopathy (a common complication of diabetes that causes changes in the blood vessels nourishing the retina) cause photoreceptors to die and disrupt the input to the visual system, leading to vision loss.

"One potentially promising approach to restoring vision is to transplant new photoreceptors to replace the photoreceptors that have died in the retinas of these patients," says Dr. Sherry. "Despite their promise, photoreceptor transplants remain highly experimental and have provided little functional improvement to date, due in part to the poor integration of the transplanted photoreceptors with the other nerve cells in the host retina.

"It is possible to transplant photoreceptors and get them to survive, but they do not seem to regenerate the circuits needed to communicate with the host retina so that the visual information can get to the brain to form an image. Regenerating the proper circuits is crucial to developing functional transplants anywhere in the nervous system, but we don't understand how the regeneration process works very well, particularly for photoreceptors. If we can understand how photoreceptors regenerate and the factors that control it, we might be able to help transplanted photoreceptors regenerate circuits with the host retina to restore visual function."

Dr. Sherry's research focuses on the fundamental processes underlying development and regeneration by photoreceptors. The project, sponsored by the Lions Eye Bank Foundation, investigates regeneration by isolated photoreceptors in cultures using time-lapse microscopy to visualize the dynamic process of growth. This experimental approach is necessary because it is impossible to visualize the dynamic interactions between transplanted photoreceptors and the host retina directly.

"Time-lapse microscopy is basically making a movie of a regenerating photoreceptor as it grows over the span of several days or weeks," says Dr. Sherry. "This approach allows us to visualize the dynamic process of photoreceptor growth so that we can determine when critical events occur. For example, we need to determine when photoreceptors show the most growth after isolation, so that transplants of isolated photoreceptors from the donor can be timed to maximize growth and increase the chances of regenerating circuits with the host retina.

"Another critical event that we can visualize is the dynamic interaction between regenerating photoreceptors and other retinal nerve cells that determine if new circuits will form or fail to form," he adds. "The ultimate goal of the project is to generate information that can be applied to transplantation therapies to improve circuit formation between the transplanted photoreceptors and the host."

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©2006 Texas Medical Center

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