A woman who is virtually blind today won a unique court victory for compensation to help bring up her child, who was born after a failed sterilisation operation.

Lawyers acting for Karina Rees, 30, convinced two out of three Court of Appeal judges that her case broke the accepted legal principle that healthy children are always "a blessing" and parents cannot be compensated even if the birth resulted from medical negligence.

Lady Justice Hale, in a judgment given today, said the law had limited the doctor's responsibility because of the incalculable benefit the child was presumed to bring.

"But if that incalculable benefit is put at risk by the very fact which led the parent to ask for the sterilisation, there is nothing unfair, unjust or unreasonable in holding that the surgeon assumes a more extensive responsibility for the consequences, at least where he knew of the disability and that this was the reason why she wished to avoid having a child."

She allowed the appeal from a ruling of the High Court sitting in Newcastle, which had to award Miss Rees any money to cover the cost of bringing up her son, Anthony, who was born in 1997.

Lady Justice Hale said the mother was entitled to claim the extra costs of raising her child which were attributable to her disability.

Her views were endorsed by Lord Justice Robert Walker.

But Lord Justice Waller, dissenting, said: "I believe that ordinary people would think that it was not fair that a disabled person should recover when mothers who may in effect become disabled by ill-health through having a healthy child would not."

Miss Rees, of St Paul's Place, Darlington, County Durham, who was born with the genetic disorder retinitis pigmentosa, is blind in her left eye and has only one sixth of normal vision in her right.

She underwent a sterilisation at the Darlington Memorial Hospital in 1995 but one of her fallopian tubes was not fully tied, and she discovered in October the following year that she was pregnant.

Since the birth of her son, she has cared for him with the help of her parents and social workers the child's father has played no part in the upbringing.

The hospital admitted the sterilisation was negligently performed but disputed the level of compensation, which it said should be limited to a modest sum for pain and suffering and losses caused by her unwanted pregnancy and labour.

Her counsel, Robin de Wilde, had told the appeal judges she was "adamant" that she wanted the operation because her visual handicap made her doubt her ability to cope with a baby.

Miss Rees had great difficulty in doing many everyday things for her son, he said.

In previous cases, damages have been awarded for the "wrongful birth" of handicapped children to cover the extra costs of caring for them because of their disabilities.

Until today's judgment, the law had stuck to the principle that healthy children were a blessing and that their parents could not be compensated even if the birth was wrongful.

Mr de Wilde argued that Miss Rees faced many extra child care costs because of her handicap, and was in a different position to a healthy parent.

Neither Miss Rees nor her solicitors were in court today Lady Justice Hale said there was no difference between a high-flying career woman whose sterilisation fails or a poor single mother.

She said: "It is probably safe to assume that the ordinary person would be more sympathetic to the hard-pressed single parent than to the high-flying career woman. "But they differ from one another only in their financial circumstances and the law does not usually regard this as relevant.

"There is, however, a crucial difference between them and a seriously disabled parent."

She said a handicapped parent would need help feeding, bathing, clothing, training, supervising, playing with, reading to and taking their child to school if they were to avoid the risk of having the child taken away by the social services.

"That is the distinction between an able-bodied parent and a disabled parent who needs help if she is to be able to discharge the most ordinary tasks involved in the parental responsibility which has been placed upon her as a result of the defendant's negligence."

The amount of damages are to be assessed.