KEY POINTS:
Humans are starting to outlive their eyeballs, say Australian researchers working on slowing vision deterioration caused by age.
Each eyeball starts out with about 150 million light-catching "photoreceptors" at birth, says Professor Jonathan Stone, and these then wink out at a rate of several hundred each day.
This natural process is the underlying reason why a person's vision deteriorates over time.
And while many people still have 100 million-plus photoreceptors per eye in their 80s, for others it means a loss of night vision or even blindness.
Stone said people were now living longer as a result of improved health standards, so new techniques were needed to slow the shedding of photoreceptors which could not be regrown.
"We're exploring these environmental ways of stabilising these photoreceptors into the ninth and tenth decade.
"What this is all about is preserving that as long as possible into late age."
Stone is attached to The Vision Centre at the University of Sydney and Australian National University where research is being conducted to better understand how foods rich in antioxidants help to protect eyes from light damage.
The researchers are also investigating how the eye benefits from oxygen-rich environments - as people undergoing treatment in hyperbaric chambers 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 awhile," he said.
"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 are routinely exposed to.
Stone says people over 20 should always wear sunglasses when outdoors in bright light.
Conversely, adolescents need light exposure while their eyes are 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," Stone said.
"Knowing what I now do, as a result of years of work in this field, I never go outside without my sunnies."
- AAP
