A legal campaign has been launched to eradicate regional inequalities in the NHS that deny treatment to thousands who are facing blindness.

The challenge is being spearheaded by a former Labour MP, Alice Mahon, who has pledged to force health bosses to provide the drugs to save her own sight - and that of other sufferers.

The condition at the centre of the battle is age-related macular degeneration (AMD) which affects 500,000 people in the UK. Mrs Mahon suffers from the "wet" form, of which there are 27,000 new cases a year in the UK.

Mrs Mahon said she would go to the High Court to compel her local primary care trust (PCT) to pay for a new drug that could prevent her going blind after the trust refused her request to fund it.

Campaigners claim 50 people a day go blind because they are refused access to drugs that could save their sight. MPs rallied to Mrs Mahon's cause yesterday tabling an early day motion calling for the treatment to be funded.

She will be joined by other MPs in Parliament today to speak out against the refusal to fund treatment for patients suffering from wet AMD. A private member's Bill tabled by Linda Riordan, the Labour MP for Halifax, is to have its second reading next month.

Ms Mahon, aged 69, has lost most of the sight in one eye and is likely to lose it in the other if nothing is done. The condition is caused by overgrowth of the capillaries behind the retina leading to bleeding and scarring of the macula, the centre of the retina.

Her best hope is a new drug, Lucentis, which has been shown in trials to improve vision in a third of patients and to halt the deterioration in most of the rest. But a request by her consultant at Calderdale Royal Hospital, where she was diagnosed in November, to Kirklees and Calderdale PCT to fund the drug was turned down.

Mrs Mahon said: "I have been an ardent supporter of the NHS all my life and now feel totally let down. The excuses that PCTs are giving for not funding treatment are scandalously lame.

"Everyone has a right to free treatment on the NHS for a condition that results in blindness and devastates lives. Supporting people who are blind or partially sighted, who may need home help and suffer injuries from falls, is far more expensive than the treatment. The Chancellor must ensure the NHS budget is large enough to fund such a basic health care need."

Mrs Mahon said she had written personally to Gordon Brown but had, so far, received no reply.

Lucentis was hailed as a "miraculous" advance against a modern epidemic in the New England Journal of Medicine last year. It is given by injection directly into the eye and, in patients treated, it not only halted the gradual deterioration in sight but even regained some of that lost.

Lucentis is due to receive its European licence shortly. But many PCTs refuse to fund Lucentis and a rival, Macugen, licensed last year, in advance of an assessment by the National Institute for Clinical Excellence (Nice). Macugen costs about £500 a dose and Lucentis about £1,000. Nice is to consider both drugs together and expects to publish its report in October.

Even if both drugs are approved by Nice, and recommended for use on the NHS, there is no guarantee they will be available to all patients. There is wide variation across the NHS in the provision of Nice-recommended drugs to patients and those are set to grow as PCTs struggle to clear deficits.

The Royal National Institute for the Blind said almost 20,000 people in England and Wales could go blind during the next year without either drug. In Scotland, Macugen was approved for use by the Scottish Medicines Consortium last August.

Steve Winyard, head of campaigns at the RNIB, said: "Fifty people a day are being condemned to blindness because PCTs are refusing to fund a licensed treatment, even though it could save patients' sight. The actions of these PCTs are simply unacceptable."

Mr Winyard said consultants were experimenting with the number of doses needed. In some cases, as few as three are required for successful treatment.

Mr Winyard said: "It would save the NHS money, because the cost of supporting someone who is blind is greater than the cost of treatment. We are hearing of blanket bans on Macugen by PCTs, even though Andy Burnham, the Health minister, told the Commons that each case should be treated on its merits."

In its response to the request from Mrs Mahon's consultant for funding for Lucentis, Kirklees and Calderdale PCTs, said - in a letter dated 16 December - that Lucentis was not currently licensed and had not been approved by Nice.

"This means there is insufficient clinical evidence of the effectiveness of this treatment to enable approval for funding to be given," the letter said.

Novartis, which markets Lucentis, announced last week that it had received its licence for the drug to be used across Europe. A spokesman for Nice said yesterday that it had contacted the European Medicines Agency, but had not yet received notification of licensing approval.

Nice has a "fast-track" assessment process, introduced last year, which was used for the first time for the breast cancer drug Herceptin, which was approved in record time. A spokesman said the fast-track process would not be used for Lucentis because the Department of Health had requested it be assessed alongside Macugen.

However, the Nice spokesman added: "There is no restriction on the prescribing of any drug, within its licensed indications, whilst Nice is developing guidance. In the absence of Nice guidance, local NHS organisations should develop their own prescribing policies."

The Department of Health said last night that patients should not be refused a treatment simply because Nice guidance does not exist yet. A spokesman said: "Macugen and Lucentis are being assessed by Nice against each other to ensure NHS patients receive clinically and cost-effective treatments. But, even while that process is taking place, doctors can prescribe Macugen within its licensed indications without Nice guidance if they believe it is the right treatment for their patient.

"We have made it clear it is not acceptable to refuse a treatment simply because Nice guidance does not yet exist."

Macular degeneration

* Macular degeneration affects 500,000 people in the UK.

* The macula is at the centre of the retina and is essential for seeing colour. In affected individuals, the cells at the centre of the macula stop working. Most cases are of the slow progressing, dry kind for which there is no treatment.

* Wet macular degeneration, which progresses faster, affects 27,000 new patients each year. About 7,000 of these can be helped by laser treatment. Most others can be helped by drugs.

* Most patients have to pay privately for drug treatment because the National Institute for Clinical Excellence is not due to issue guidance on NHS use until October 2007.