Myopia clues gleaned from Bounty mutineers

The descendents of sailors who took part in the infamous mutiny on the Bounty are helping unearth the causes of short-sightedness, say Australian researchers.

Dr. David Mackey from the Lions Eye Institute in Perth and colleagues have been studying the eyesight of people on Norfolk Island, where almost half of the population can trace their ancestry back to nine Bounty sailors and their Polynesian wives.

Over the past five years, they have found that rates of short-sightedness, or myopia, are lower among people related to the Bounty sailors, nine of whom settled at Pitcairn Island after the mutiny in 1789 and later moved to Norfolk Island, 1600 kilometres north-east of Sydney.

All 1,275 permanent residents of the island aged over 15 years were invited to participate in the Norfolk Island Eye Study. The most recent paper from the study is published this month in the journal Investigative Ophthalmology and Visual Science.

"We found the rate of Pitcairn group myopia is approximately half that of the Australian population, and as a result would be ranked among one of the lowest rates in the world," Mackey tells the Australian Broadcasting Corporation.

By contrast, other Norfolk Island residents had approximately the same rates of short-sightedness as the Australian population — around 16 per cent.

Genetics and environment

Mackey says these differences show that genetic factors contribute to short-sightedness. However, it is also becoming apparent that spending too little time outdoors also raises a person's risk of becoming short-sighted.

To untangle these genetic and environmental factors, Mackey and colleagues used an ultraviolet light fluorescence photograph to measure Sun exposure to the white of the eye.

In 10 per cent of the Norfolk Island population, this area develops raised, bloodshot growths on the front of the eyes called pterygia. Pterygia are sometimes called surfers' eye, and are thought to result from exposure to ultraviolet light.

On Norfolk Island, the researchers found that the amount of autofluorescence on a person's eye correlated with the amount of time they spent outdoors.

Comparing the eyes of Norfolk Island residents with Pitcairn ancestors and those without, Mackey and his colleagues could find no differences. "We couldn't show a sign difference in the outdoor activity between the two groups," Mackey says.

The researchers are now studying the genes of Norfolk Island residents to see if they can identify the genetic factors that affect short-sightedness, says Mackey.

"It's the ideal situation. With any disease that involves genes and environment, you can identify the people who are at high genetic risk, and intervene by reducing the environmental risk."

"In this case, the advice to people with high risk genes might be to get outdoors more in their teenage years to reduce their chances of myopia."