Auckland scientists have made important discoveries in the eye, which they hope will lead to the development of the world's first drugs to prevent blindness after an eye stroke.
The findings also have implications for other conditions, such as stroke in the brain.
"At the moment, if you get a stroke of the eye, there is no treatment. As clinicians, we are helpless. We just have to watch the patient go blind," said Professor Helen Danesh-Meyer, co-leader of the research with Professor Colin Green.
The rare but catastrophic condition, in which a blocked blood vessel cuts the blood supply to an eye, is likely to afflict up to 40 patients a year in New Zealand.
The loss of blood causes damage to neurons - nerve cells - in the retina, the structure at the back of the eye which sends visual signals to the brain as nerve impulses.
This damage spreads between neurons.
In their paper in the world's leading neurology journal, Brain, the Auckland University researchers have shown that, following an eye stroke, there are increases in the amount of the protein connexin43 in the astrocyte helper cells of the retina and in the activation of the cells themselves.
Groups of connexin43 molecules form communication portals, called gap junctions, between cells. This allows harmful products of neuron damage to pass to other neurons, expanding the original injury.
Connexin43 is also produced in cells lining blood vessels and the researchers found leakage from blood vessels involved in an eye stroke.
In their study involving rats which had an eye stroke, followed by re-establishment of the blood supply, the researchers injected an experimental connexin43 blocker drug into the abdomen of some.
Blood vessel leakage and loss of astrocytes were less in those given the treatment. Loss of the retina's light-sensitive cells was dramatically lower, at around 10 per cent, compared with expected losses of around 35 per cent.
Professor Danesh-Meyer, an ophthalmologist, said, "We know that the connexin43 doesn't have any direct effect on the neuron ... Previous research has focused on how you modulate the neuron once it's injured, but now we're not actually touching the neuron, we're just saving its environment, modulating and making it a better environment. That's the new direction that's unique."
The research paper says the findings can be extrapolated to brain strokes, chronic inflammatory diseases and trauma. It also notes that the retinal cell death that occurs in an eye stroke is implicated in other eye diseases, such as glaucoma and the retinal problems associated with diabetes, both of which can cause blindness.
Professor Danesh-Meyer said research had begun on developing the Connexin43 blocker as a human drug that could possibly be injected into the eye after an eye stroke. If it proved safe and effective in clinical trials, she expected it would take only a few years to become available commercially.
A CLOSER LOOK
* Eye stroke: Caused by blockage in a blood vessel of the retina.
* Light-sensitive nerve cells on the retina die.
*Leads to blindness.
*No effective treatment available.
*An animal study has found an experimental drug greatly reduces nerve-cell death.