A simple way to reduce falls in elderly people who spend regular time outdoors is to switch their multifocal glasses to single lens distance glasses, say Australian researchers.
Fall prevention expert Dr Stephen Lord of the Prince of Wales Medical Research Institute in Sydney and colleagues report their study today online in the British Medical Journal
"If you are old and fit and you're going outside a lot, multifocal glasses are in effect an elective disability," says Lord. "You're walking around with part of your visual field blurred.
"People should just wear a single lens pair of glasses in those circumstances."
Most people over the age of 50 need glasses, especially for reading, and the most convenient solution is a single pair of multifocal glasses, which contain multiple lenses for focusing at different distances.
"You don't have to change your glasses. If you look up you can see into the distance and if you look down you can see closer up," says Lord.
This is great for tasks such as driving where you switch between scanning the road ahead and looking at the speedometer, for walking down a supermarket aisle occasionally reading food labels, or knitting while watching TV.
But these advantages come at a cost.
Lord says, when we walk along we tend to lower our gaze and scan the ground in front for obstacles.
But, if you are wearing multifocal glasses, the lower part of our visual field is focused on 'reading' distances of up to 50 centimetres.
This means our vision of the path a few steps in front of us will be blurred and this might make it hard to notice, for example, a dangerous tree root or a crack in the pavement.
"That crack is in the bottom part of your visual field so you don't see it, it's blurred. You hit it and if you can't react in time you'd fall," says Lord.
While people in their 50s may be able to react in time, people in their 70s and 80s are more likely to fall because their strength, balance and reaction time is not as good, he says.
Lord and colleagues studied 606 elderly people with a mean age of 80, who wear multifocal glasses.
One half of the group was told about the potential dangers of multifocal glasses, provided with two different pairs of single lens glasses, and asked to wear the distance pair when they went outside. The other half of the group kept using their multifocal glasses.
Over a period of 13 months, the participants in the randomised controlled trial, marked on a calendar whenever they had a fall.
Lord says overall those who wore single lens glasses had 8% less the number of falls than those who wore multifocal glasses.
While this finding was in the direction expected, it was not statistically significant, he says.
Lord says the most significant finding was that in elderly people who spent regular time outside - two or three times a week - single lens distance glasses was associated with 40% fewer falls.
This did not hold for participants who spent more time inside, who had more outside falls when using single lens distance glasses.
Lord says this group of people tended to be frailer and were probably less able to cope with the two pairs of glasses.
Lord says while switching to single lens glasses may be a bit inconvenient for elderly people who spend time outdoors, it's worth the reduction in falls.
Falls are a major problem in older people, with 1 in 3 suffering a fall every year, he says.
Those who fall have a 5 to 7% chance of a fracture, a 3% chance of a hip fracture, a 1 in 3 chance of never regaining their original mobility, and 1 in 4 chance of not surviving a year, says Lord.
In an accompanying editorial, Professor John Campbell and colleagues at the Dunedin School of Medicine in New Zealand say any changes to glasses should be introduced carefully so that people are not overwhelmed.
They also say doctors and optometrists should have good communication when considering vision, glasses and the risk of falls.