Fed: Humans outliving their eyeballs, Australian scientist says
By Danny Rose, Medical Writer07 Jan 2009 3:19 PM
SYDNEY, Jan 7 AAP - Humans are starting to outlive their eyeballs, say Australian researchers working on ways to slow the way vision deteriorates with 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 every 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 into their 80s, for others it means a loss of night vision or even blindness.
Prof 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 cannot be regrown.
"The clinical evidence is the retina goes well really into your eighth decade (80 years), depending on how fast you've lost your photoreceptors and that changes because of genetic factors," Prof Stone says.
"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."
Prof Stone is attached to The Vision Centre (University of Sydney and Australian National University) where research is now underway 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 Prof Stone says people aged over 20 should always wear sunglasses when outdoors in bright light.
Conversely, he says adolescents need 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," Prof Stone says.
"Knowing what I now do as a result of years of work in this field, I never go outside without my sunnies."
