A woman who was been blind for more than 20 years has regained her sight – after falling over and hitting her head at her home in Florida.

Mary Ann Franco, 70, gradually became blind after injuring her spine in a car accident in 1993.

Then, more than two decades later, another accident and a subsequent operation appears to have led to the recovery of her sight, although doctors are still trying to work out how exactly this could have happened.

“I was fully blind – all I could see was blackness,” she told The Independent.

“I was in my living room, going over to the door. My foot caught on a tile, and it flipped me. I hit my head in the back, and hit it on something else, maybe the fireplace,” she said.

After the fall, which took place in August 2015, Ms Franco was incapacitated and had to wear a neck brace until an operation a few weeks ago.

She was in hospital recovering from four hours of surgery on her neck when she came round from the anesthetic and realised her sight had returned.

However, in her confused state, she didn’t realise what had happened straight away.

“I looked towards the foot of my bed and said, ‘Hey, lady in purple, get me something for pain'. I was in so much pain, I wasn’t nice – and I’m always nice,” she said.

“My niece said: ‘what did you say?’ and I realised I could see. They gave me more medication, and the next morning I could see all the trees, and white houses below from my small window on my side in hospital.

“I was the happiest woman in the whole world. It was wonderful. Everyone came in and said: ‘You’re the miracle lady’.”

Neurosurgeon Dr John Afshar, who performed the operation, told ABC News that he had not expected Ms Franco's vision to be affected.

“The restoration of Mary Ann Franco's vision is a true miracle,” he said. “I really don't have a scientific explanation for it.“

He said that one theory for the exceptional story was that the accident could have affected an artery and restricted blood flow to the part of the brain which controls vision.

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“It could have been a result of the artery being kinked, and then when we performed the surgery itself, we unknowingly probably unkinked that vessel re-establishing blood flow and, therefore, she could have regained her vision,” he said.

Ms Franco is a firm believer in God and attributes the extraordinary return of her sight to her faith.

She spoke of how happy she was to be able to see her family once again, and added that regaining her sight had changed how she thought of the world.

“Everything seems so much smaller to me, since I can see. I felt like the room was bigger than it was ... but they weren’t as big as I thought,” she said.