I can tolerate reading glasses. What I'm afraid of is developing a degenerative eye disease, like many older Americans, and eventually losing my sight.

No kidding, yet it is a reality for many seniors. Degenerative eye diseases that lead to blindness are caused by the death of photoreceptor cells, which are nerve cells in the retina that allow us to see.

For years scientists have experimented with ways to repair or replace these cells and finally, in a recent, landmark study, researchers transplanted immature photoreceptor cells in mice and restored their vision.

They first engineered mice with rods that didn't work. Rods and cones are the two types of photoreceptor nerve cells. The cells convert light energy into signals that travel from the optic nerve to the brain. Cones detect color and detail, while rods pick up black and white, peripheral, and low-light vision.

In these mice with non-working rods, researchers injected their retinas with immature rod receptor cells from young healthy mice. Within four to six weeks, one in six of these transplanted rod precursor cells were close to functioning normally. They formed nerve connections and generated signals that were transmitted to the brain for visual processing.

This is the first time transplanted photoreceptor cells have been shown to integrate into the circuitry of the retina and improve vision.

To test their results, researchers placed treated mice and diseased mice into a dimly lit water maze. The treated mice with new rods could see well enough in low light to find a platform and climb out. The diseased mice took much longer, proving the implants work.

Researchers say the study's success was due to the large number of photoreceptor cells they implanted. A clinical trial is already underway.