This is the VOA Special English Health Report.

The retina is the sensory tissue in the back part of the eye. It gathers light and captures images from the lens, much like film in a camera. The retina processes these images into signals that travel through the optic nerve to the brain.

Diseases of the retina can cause vision loss over time.

A thirty-year-old listener in Vietnam says he cannot see well and doctors have told him he has retinal degeneration. This is the loss or destruction of the sensory tissue of the retina. Trinh Phuong Bac says he first developed problems in his right eye when he was a child. He would like to know more about this disease.

Doctor Emily Chew is a deputy division director at the National Eye Institute, one of the National Institutes of Health in the United States. She says it is true what doctors have told our listener: there is no cure for retinal degeneration.

She says most cases are considered genetic. Scientists have been trying to develop gene treatments for it, and in recent years there have been some reports of possible progress. But Doctor Chew says these studies of experimental gene therapies have so far only involved animals.

Recently, the National Eye Institute reported the findings of a study of diet and a disease called retinopathy. It says the omega-three fatty acids EPA and DHA, both found in fish, protected mice against the development and progression of retinopathy. The study showed that decreasing omega-six fatty acids in the diet also helped. The study was published this month in Nature Medicine.

The findings could be useful to research into retinopathy in humans, including a common cause of vision loss in diabetics. A separate form can lead to permanent blindness in babies born too early. Doctor Chew, however, says this study may have no connection to treating retinal degeneration.

She also says there is disagreement about whether taking high levels of vitamin A could reduce the severity of the disease. She says there was a study which suggested that vitamin A helped some people with retinitis pigmentosa. But she notes that other investigators have disputed these findings.

Retinitis pigmentosa, or R.P, is a form of retinal degeneration. R.P. is the name for a group of diseases that can be found as early as when a person is a teenager. People with R.P. have genes that give incorrect orders to cells that receive light. As a result, the retina can begin to self-destruct.

And that's the VOA Special English Health Report, written by Caty Weaver. I'm Mario Ritter.