Patients who had laser eye surgery at a clinic run by high street chain Boots are being contacted amid fears the equipment used could be faulty.
The company is investigating claims that one of their machines was part of a batch of lasers which could potentially malfunction.
Boots said it is looking into the claims "as a matter of urgency" but believes its equipment is safe.
The move follows reports of legal action in the US.
Laser eye surgery is performed on thousands
A lawsuit filed there claims some of the Autonomous Ladarvision Systems, which are used in Boots' nine eye treatment clinics across Britain, can develop faults leading to blurred vision.
The laser machine used in Boots' London eye surgery clinic in Regent Street was said to be from a batch identified in 2001 by Swiss-owned health
care company Alcon as potentially having a problem.
The machine was modified by the laser manufacturer after concerns were raised, a Boots spokeswoman said.
A statement from Alcon claimed the allegations made in the US lawsuit were "completely unsupported by scientific or legitimate evidence".
The statement added: "The Ladarvision is safe and effective. It has been extensively tested in clinical trials and was approved for its intended use by the US Food and Drug Administration and other regulatory bodies around the world."
Around 49 patients who were treated with the London laser before it was modified are being contacted by the company to discover if they have suffered any adverse effects.
No complaints have been received so far.
A Boots spokeswoman said: "There have been allegations that much older lasers may have been reported as having problems.
"We are looking for evidence of that from Alcon.
"However, we have no reason to suspect any problems with our lasers in the UK.
"There is no reason to worry."
The company is being sued in North Carolina District Court by EBW Laser, which acquired 10 of its lasers to lease to US clinics, and alleges that two of the
machines were "badly malfunctioning", The Times reported.
In its statement Alcon said it looked into the machines' success rate voluntarily to prevent potential misfunctions.
Laser surgery costs £1,250 an eye at Boots' clinics, and is performed on around 100,000 people each year in Britain.