Each eyeball starts out with about 150 million light-catching ''photoreceptors'' at birth, Professor Jonathan Stone said, and these then winked out at a rate of several hundred every day.

This natural process was the underlying reason why a person's vision deteriorated over time.

And while many people still have 100 million-plus photoreceptors per eye into their 80s, for others it means a loss of night vision or even blindness.

Professor Stone said people were now living longer as a result of improved health standards, so new techniques were needed to slow the shedding of these photoreceptors which could not be regrown.

''The clinical evidence is the retina goes well really into your eighth decade [70-80 years], depending on how fast you've lost your photoreceptors and that changes because of genetic factors,'' Professor Stone said.

''We're exploring these environmental ways of stabilising these photoreceptors into the ninth and 10th decade.

''What this is all about is preserving that as long as possible into late age.''

Professor Stone works for the Vision Centre run jointly by the Australian National University and University of Sydney where research is now under way to better understand how foods rich in antioxidants help to protect eyes against light damage.

The work also includes finding out how the eye benefits from oxygen-rich environments, as people undergoing treatment in hyperbaric chambers can report a temporary side-effect of improved vision.

''Acute high oxygen is protective to photoreceptors and tends to make them respond better, so that people coming out [of hyperbaric chambers] notice their vision is better for a while,'' he says.

''We're just beginning to untangle that.''

Aside from genetics, the rate at which a person loses their photoreceptors is determined by how much light they were routinely exposed to and Professor Stone said people aged over 20 should always wear sunglasses when outdoors in bright light.

Conversely, adolescents needed light exposure while their eyes were developing to prevent the onset of near-sightedness.

''So it is a case of striking the correct balance between more outdoor exposure in youth, to prevent myopia, and greater use of light protection in the form of sunglasses to prevent age-related degeneration,'' Professor Stone said. AAP