LASER EYE SURGERY MAY HARM NIGHT VISION, STUDY SUGGESTS

Louise Elliott, The Canadian Press, Toronto

Laser eye surgery, which was performed on almost one million patients worldwide last year, may do long-term damage to the eye's ability to see at night, a British study has found.

Of patients who had undergone the two most common types of surgery - LASIK and photo-refractive keratectomy - 58 percent failed a night vision test, said ophthalmalogist Dr. William Lory of the London Centre for Refractive Surgery in England.

Jory, who presented his findings at the May meeting of the American Society of Cataract and Refractive Surgeons in Boston, said even patients who responded well overall showed a decrease in night vision.

'What really concerned me was that 41 per cent had gained day time vision, but some of those lost night time vision.'

Jory tested 38 people who underwent surgery two to seven years ago. He said his study was inconclusive because it looked at patients with moderate to severe corrections, who may be more prone to developing night vision problems after surgery.

But Dr. Evanne Casson, a researcher at the University of Ottawa Eye Institute, said Jory's figures were consistent with tests she did on PRK patients between 1996 and 1998. Sixty per cent showed reduced contrast sensitivity- a leading indicator of night vision- in tests covering presurgery to two years later.

Early results of another study show 30 per cent are affected, Casson said. But even that figure is alarming because doctors don't know how surgery will affect the eye as patients age and night vision naturally decreases, she said.

'What happens if 30 per cent of the population is myopic, and half of them get laser surgery? That means 15 per cent of people attempting to drive on the road at night (having had laser surgery)- that's pretty scary.'

Jory said an independant, international study of LASIK patients should be launched immediately.

The LASIK procedure, which overtook PRK as the surgery of choice about five years ago, is now used by up to 95 per cent of patients.

Already, more than 100,000 Canadians have had the procedure, which costs between $1,000 and $3,000, and involves cutting a small flap in the cornea to remove underlying tissue.

Some experts said Jory's numbers were too high.

Dr. Michael Pop, who does the surgery in Montreal, siad he published a study of 1,300 patients that found 50 per cent had night vision problems in the first month after surgery, but only five per cent had problems a year later.

There are different theories about why the surgery reduces night vision. Some say lasers can't adjust to the unique shape of each patients cornea. Others say the surgery can inhibit light's flow through the cornea.