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Concern has been raised about the long-term effects of laser eye surgery after a new study has shown that tens of thousands of Kiwis are likely to suffer defective vision from the surgery in their later years.

Studies from Otago and Oxford Universities have shown that laser surgery for short-sightedness could cause haze, glare and blurred vision as people reach their 60s and 70s.

Given that around 25,000 New Zealanders have had the surgery, Otago University head of ophthalmology Anthony Molteno said there could be significant legal class actions in the future, an issue that is causing major concern among eye surgeons.

"When we presented this work at the local conference, there was a stunned silence and some anxious questions," said Molteno.

In the procedure the central cornea is flattened. That provides better eyesight, but research shows that it seriously affects the movement of corneal cells, which affect sight. In a normal eye, the cells start at each end of the eye and migrate towards the centre. The top cells move quicker and meet the lower cells below the pupil. Where they meet, called the Hudson-Stahli Line, they create pigment, scattering light and causing glare, haze and blur.

As people age, that area increases and moderately affects eyesight but isn't a real problem, as the line is below the pupil.

"But after the surgery, the top cells move slowly down the flattened cornea, meeting the lower cells in front of the pupil. That causes haziness immediately, and most people who have the surgery see as though they're "looking through hazy spectacles", according to Molteno.

The new findings show the new location of the Hudson-Stahli Line will cause haze and glare in front of the pupil as people age. "The question is, is this permanent, and is it going to increase in the normal manner with age? If so, a lot are going to have a hazy, soft, fuzzy view of society as they get older. This is a long-term effect, and we are following these people. If this turns out to be a major effect, I presume it will one day see a major class action suit."

Molteno said the problems could be serious, with people unlikely to be able to drive. "Anybody who's had their cornea planed would be eaten by a lion at the water hole... If there was serious break-down of law and order, they would probably get shot before the others because they couldn't see so well."

At present, the process cannot be fixed. "The issue is really this: if you pay the private sector to do this, they do it at a profit and pay taxes. The question is how much of those taxes come to the public sector, and how much is it going to cost to clean up the mess? We don't know."

Molteno said the surgery was still full of unknowns, and it should be given serious consideration. There have been 11 claims lodged with ACC over complications since 2000.

"It's not risk-free, make no mistake about that. I wouldn't have them done myself or let my family. But it depends on what it's worth to you."

The research was first raised by a caller to Kerre Woodham on her talkback show for NewstalkZB.

But Malcolm McKellar, an eye surgeon in Canterbury, said that while the technique had risks, these outweighed bad eyesight. "Overall, the risk is very low, but it's not zero. However you do it, it's a surgical procedure. The technology in New Zealand is all cutting edge. Across the board every single centre has got a very new laser. It's one of the most precise surgeries on the planet."

Even though the technology was still evolving and new problems are uncovered, McKellar said, the technique was safe. "There's been animal research and evolving technologies, and we've now got 15 years of the surgery. Given that everything so far has been very good, we're prepared to take the small risk in order to trade poor vision now for good vision."

Worth the risk?

Laser eye surgery may have its risks but for most people it brings huge relief.

Katie Stow, a public relations consultant, had laser surgery eight months ago and she's delighted with the results. From being nearly blind, she now has almost perfect eyesight.

"It was really good and my eyesight is pretty much perfect."

The only problem she has had is to do with night vision.

"My night vision looking at lights, there's a bit of a halo around it. But it's definitely deal-with-able."

Stow said her surgeons were helpful and she had confidence in them.

"They went though all the risks involved. They were pretty cautious about the whole thing. I was thinking, 'just do it'."

And when she was told of the new research saying she may have problems in the future she wasn't unduly worried.

"Anything is better than what I had before. I might be concerned about that if my eyesight was bad.

"But having the next 30 years of proper eyesight is fine for me."