A woman whose eyes clamp shut for three days at a time, then open up for the next three, has baffled medical specialists.

Natalie Adler, 21, of Melbourne, Australia, has been locked in the extraordinary routine for four years. Doctors believe she may be the only person in the world with a condition in which her eyes involuntarily shut for days at a time.

"I go to bed and I can open my eyes, and then when I wake up the next day I can't," Adler told the Daily Telegraph. "Nobody knows why."

Click here to see a photo of Adler.

Adler has undergone hundreds of tests since her life dramatically changed before she even graduated from school.

"I woke one Sunday and my eyes were swollen. It was the day before an English exam," she said.

Doctors believed the swelling was from a sinus and staph infection, Adler said.

"I just never got better," she continued. "My eyes started closing intermittently, really randomly, but within a few weeks they were closing for three days."

Associate Professor Justin O'Day, head of the neuro-ophthalmology unit at the Royal Victoria Eye and Ear Hospital, said: "Natalie's a mystery. She's a one-off, we don't have a diagnosis."

During "closed-eye days," Adler's eyes are completely shut, except for a small slit in her left eye. On "open-eye days," they function normally, though the left eyelid can droop. Adler crams as much as she can into good days, which are marked months ahead in her diary. But some things can't be scheduled.

"On my 18th birthday, my eyes were closed, but on my 21st they were open, so I had a party," she added.