THURSDAY, March 13, 2003 (HealthDayNews) -- Vision is a very complicated process, requiring many steps to occur in rapid succession so that people, animals and even insects can see the images around them.
Remarkably, though, it only takes one chemical to abruptly stop the whole process, says a new study.
Researchers from the National Cancer Institute report that in fruit flies a chemical called ceramide accumulates with exposure to light and when enough ceramide collects, it triggers light-sensitive cells in the eyes to die. When too many of these cells die off, blindness occurs.
In an accompanying editorial to the researach appearing in the March 14 issue of Science, Dr. Rama Ranganathan, an associate investigator at the Howard Hughes Medical Institute in Dallas, explains that many diseases of the eye that affect humans, such as macular degeneration, retinitis pigmentosa, cone dystrophy and Oguchi's disease, may be caused by the death of these light-sensitive cells, known as photoreceptor cells.
"Photoreceptor cells translate light energy to electrical signals," says Ranganathan. Those electrical signals are then sent to the brain, which interprets the signals as an image.
Ranganathan says photoreceptor cells are remarkable because they work in very low light conditions and in very intense light as well. Additionally, he notes that photoreceptor cells have to work at incredible speeds to send information to the brain, so images are seen as they are encountered.
In many retinal diseases, Ranganathan explains, photoreceptor cells work normally for a period of time, but, "as light accrues, they start dying and lead to blindness." If scientists could understand the mechanism that causes these cells to die off, they might be able to develop therapies to prevent it.
That's exactly what the current study was attempting to do.
Led by researchers at the National Cancer Institute, scientists looked at photoreceptor cells in fruit flies and found that ceramide accumulated in photoreceptor cells over time and that, somehow, it was triggering these cells to die off.
The researchers then genetically engineered the fruit flies to produce an enzyme called ceramidase that disposes of ceramide and found that photoreceptor cells were saved. Also, according to Ranganathan, the researchers discovered that if you blocked the production of ceramide, photoreceptor cells could be saved.
Ranganathan says this study makes an important contribution to the understanding of how cells die, but there is still a long way to go before any potential therapies could be developed.
Dr. Robert Cykiert, an ophthalmologist at New York University Medical Center, agrees: "This is interesting research, but it's very preliminary and very far away from being of any value for treatment."
More information
Go to the National Library of Medicine to learn more about diseases that affect the retina, such as macular degeneration or retinitis pigmentosa.
