The 62-year-old was diagnosed with the incurable disorder - progressive supranuclear palsy (PSP) - several months ago, his US doctors said.

Moore found Hollywood fame after launching his comedy career in Britain

He has now started to experience vision problems as the disease progresses.

In a statement, Mr Moore said: "I have decided to come forward to tell my friends and the public that I am being treated for a disease closely related to Parkinson's.

"I hope that by revealing my illness I can bring attention to this rare malady that afflicts thousands of people, many of whom remain undiagnosed."

The BBC's John McIntyre: "He helped change the face of comedy"

Despite his illness, Mr Moore also retained his sense of humour.

He said: "I understand that one person in 100,000 suffers from this disease, and I am also aware that there are 100,000 of my union, the Screen Actors Guild, who are working every day.

"I think, therefore, it is in some way considerate of me that I have taken on this disease for myself, thus protecting the remaining 99,999 SAG members from this fate."

Problems with balance

Dr Thomas Galski, who has been working with Mr Moore at the Kessler Institute for Rehabilitation in West Orange, New Jersey, said the actor was undergoing physical and speech therapy, as well as experimental drug therapy.

The star of the films Arthur and 10 is said to have been suffering symptoms of the disease for more than five years.

He began experiencing problems with his balance early in 1998. An accomplished pianist, he also noticed a slowing and loss of co-ordination of his finger movements.

Early symptoms of PSP include falling, difficulty walking, imbalance, and slowed movements, and often are confused with other health disorders, his doctor said.

Mr Moore's condition was finally diagnosed when doctors determined he had slowed vertical eye movements, a tell-tale sign of PSP.

Heart surgery

The actor who lives in Los Angeles, is said to be able to walk short distances without help, but is using a cane.

Mr Moore turned to acting after attending Oxford on an organ scholarship, and rose to fame in the satirical revue Beyond the Fringe along with Peter Cook, Alan Bennett and Jonathan Miller.

In 1979 he appeared in 10 with actress Bo Derek, while in 1981 he starred in Arthur, appearing in its sequel, Arthur 2: On the Rocks in 1988.

In 1997 he had open heart surgery, while he has also suffered four strokes.