An investigation was launched following the incident at Glan Clwyd hospital in Bodelwyddan, Denbighshire, last week.

A surgeon and his assistant were also injured when the lamp slipped from its bracket.

Betsi Cadwaladr University Health Board apologised and said checks were being carried out at all its hospitals.

The lamp, weighing between 11 and 13kg, became detached from its support as it was being manoeuvred into position during an operation.

The patient, who was under anaesthetic, suffered a cut lip and has since received an apology.

One of the surgeons suffered concussion and was sent off duty for several days as a precaution.

A health board spokesperson said an investigation found that a retaining screw on a swivel bracket holding the lamp had worked loose.

Checks have been carried out in operating theatres at hospitals across the region, but no similar problems have been found.

The health board said routine maintenance is carried out on all theatre lamps.

Following the incident, an expert from the Medicines and Healthcare products Regulatory Agency (MHRA) has been to Glan Clwyd to see if any lessons can be learned for the wider NHS.

The health board said in a statement: "We are very sorry that this incident occurred and that one of our patients suffered an injury as a result."

"The surgeon has since contacted the patient at home to explain what occurred and offer our sincere apologies."

"All theatre lamps are subject to routine maintenance. No previous concerns had been raised regarding the light, however investigations revealed that a retaining screw on the swivel bracket that holds the lamp had worked loose."

"As a precautionary measure, all similar fittings in the theatres in Glan Clwyd have been checked and the same checks are being carried out in the operating theatres in all our other hospitals. No similar problems have been found."

The lamp has now been "refitted onto its mounting and tightened into place to the satisfaction of the agent for the manufacturer".