Understanding the Visual Flashes Experienced by People with Retinal Degenerative Disorders
Report from the annual ARVO (Association for Research in Vision and Ophthalmology) meeting
May 1, 2011 - People who have lost much of their vision due to retinal degenerative disorders, like retinitis pigmentosa or age-related macular degeneration, often report seeing flashes of light. A recent online survey of people with retinitis pigmentosa suggests that these flashes are very common. Until recently, we have known little about the causes of these flashes and most people with vision loss simply learn to accept them.
One approach to restoring vision after photoreceptors have degenerated is to create new ones and transplant them into the affected eye. However, despite significant progress in this direction (see our stem cell therapy fact sheet), success in this kind of therapy has not yet been achieved.
Another way of restoring lost vision could be to find a new way of detecting light and sending vision signals to the brain. One FFB-funded scientist, Dr. Gautam Awatramani of Halifax, has been studying the use of a light-sensitive molecule derived from plants to substitute for the detection of light by rod and cone photoreceptors. Listen to his presentation at our 2010 Vision Quest Conference to learn more about his work.
For scientists like Dr. Awatramani, the flashes blind people see pose a problem. These flashes, which are not experienced in people without retinal disease, are a source of distracting background “noise” in the system. This noise will make it harder for people to interpret the new signals generated by the therapy he is developing. He has been studying these flashes and presented his findings at the ARVO conference this week.
Dr. Awatramani has shown that the flashes are definitely due to the degeneration of photoreceptors. Both the damaged photoreceptors themselves and the amacrine nerve cells linked to them appear to generate waves of electrical signals, which people with photoreceptor loss see as flashes. These electrical signals do not come from one particular damaged cell; rather, they appear to emerge from spontaneous activity (activity not caused by light) in a person’s network of retinal nerve cells, when the photoreceptors have been damaged.
Dr. Awatramani’s work suggests that these flashes are due to imbalances in sodium levels between nerve cells, causing waves of electrical activity to move through the network of cells. While more work remains before scientists will be able to control this unusual and distracting activity, Dr. Awatramani’s work is the first to identify this mechanism. His finding will ultimately help sight-saving therapies to succeed, as understanding what causes those annoying flashes may suggest how to get rid of them!
ARVO Presentation
Emergent Pacemaker Activity in the AII Amacrine/cone Bipolar Cell Network In The RD1 Mouse Model for Retinal Degeneration Relies On Voltage-dependent Na Currents. Presented Sunday May 1, 2011.Gautam B. Awatramani, Joanna Borowska, Stuart Trenholm. Anatomy & Neurobiology, Dalhousie University, Halifax.