The Public Services Ombudsman for Wales said the man, referred to only as Mr L, will need life-long treatment as a result of the failures by the Betsi Cadwaladr University Health Board.

The patient complained that staff had failed to identify and treat a blockage of blood vessels in his neck when he went to hospital in January 2018 and again in March later that year.

It took until September 2018 before Mr L had an appropriate scan, and even then the surgery he needed was delayed until November.

The ombudsman found that the health board, the largest in Wales, had failed to consider the possibility Mr L had suffered from a watershed stroke, which occurs when the flow of the body's blood supply is restricted.

If Mr L undergone had been offered a scan it in January, he would likely have been offered treatment as a matter of urgency, the review found.

Ombudsman Michelle Morris, said: "As a result of the repeated missed opportunities to identify and treat his vascular condition, Mr L suffered multiple strokes, ongoing discomfort, and blurred vision.

"Despite the irreversible nature of the condition affecting his eyesight, there still appeared to be no sense of urgency to offer treatment."

She added: "These missed opportunities amount to significant service failures - they caused significant and ongoing injustice to Mr L because he continues to experience debilitating symptoms."

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Mr L was left with permanent sight loss and will require life-long treatment to manage his "ongoing pain", the ombudsman added.

Ms Morris also said she was "shocked" that it took until February this year for the health board to recognise any failings - despite Mr L first launching a complaint back in June 2019.

The health board was placed back into special measures earlier this year by the Welsh government following a damning report into its services.

Health minister Eluned Morgan refused to resign, telling Sky News that the board's officials had to "take responsibility".

The Welsh Conservatives' shadow health minister, Russell George, said the case was a "symptom of wider Labour failure to run our Welsh NHS properly".

Sky News has contacted Betsi Cadwaladr Health Board for a response.