Dana Reeve chairs the Christopher Reeve Paralysis Foundation

The 44-year-old actress spent nine years caring for the Superman star until he died in 2004.

She is having treatment and her doctors are "optimistic" about her progress, she said. "Now, more than ever, I feel Chris with me as I face this challenge.

"As always, I look to him as the ultimate example of defying the odds with strength, courage and hope in the face of life's adversities."

Dana Reeve has appeared in a string of stage plays and TV shows and became well-known for supporting her husband after he was paralysed in a horse-riding accident in 1995.