Age-related macular degeneration is a disease of the eye that causes gradual vision loss and, ultimately, blindness. And few treatments have succeeded in halting its symptoms.
The situation appears to be changing for patients with a certain form of age-related macular degeneration (AMD), however, and an Irish doctor in Aberdeen, Scotland, is deeply involved in proving the new treatment's worth.
Dr Dara Kilmartin, a 1991 UCD medical graduate, has been based at the University of Aberdeen medical school in its department of ophthalmology since 1996. He is a clinical research fellow and specialist registrar in ophthalmology at Aberdeen Royal Infirmary and Aberdeen was chosen as one of two UK centres in a 22-centre international trial of the new treatment.
"AMD is the leading cause of blindness among people over the age of 50 in the Western world," Dr Kilmartin said. "We don't really know the exact cause." There are two forms, `dry' and `wet' AMD, and while dry AMD is more common, it is the wet form that causes 90 per cent of the severe central vision loss in the elderly.
This form of AMD is characterised by the uncontrolled growth of unnecessary blood vessels behind the retina. These vessels can grow through the retina's surface and leak both blood cells and fluids, eventually causing scarring of the retina. "Retinal function declines as a result," Dr Kilmartin said, and because scar tissue is involved, the damage to vision is permanent. If left unchecked, the scarring will cover the central area of the retina where vision is most acute. Peripheral vision can remain but without intervention this too will eventually be lost.
Treatments such as lasers don't help much in checking AMD's advance. "The problem with laser is it is non-selective and can burn the retina, causing scarring," Dr Kilmartin said. It does block the disease but causes immediate vision loss at the treatment site. Radiation-based and surgical treatments, also non-selective, also offer little benefit.
The new treatment, which has been under study for several years, does offer hope for a proportion of patients with wet AMD. Of the approximate 1,300 new cases seen in Ireland each year, about 300 are of a type that could be helped by the treatment, known as "photodynamic therapy".
It is based on injecting a special dye, verteporfin, which is taken up by the rapidly growing blood vessels associated with wet AMD. "A photosensitising dye is injected intravenously and selectively taken up by the new vessels. Then we shine a very low energy laser on to the area which activates the dye."
The dye releases oxygen radicals which damage the inside walls of the vessels, causing clots to form. This in turn stunts vessel growth for about three months, after which growth will resume and another treatment would be required.
"It is entirely outpatient-based and so is more acceptable," Dr Kilmartin said. "It is entirely painless." Laser exposure begins only 15 minutes after infusion begins so it is also a very quick treatment.
Disadvantages include the need for repeat treatments, Dr Kilmartin said, with five treatments over two years a typical regime. Treatments also cost about £1,500 each. These costs, however, must be set against the benefits. Of the 609 patients in the latest two-year trial, those receiving the photodynamic therapy did about twice as well in maintaining visual acuity as untreated patients.
There were limits, however. "It is only applicable to patients who have new disease. Also, the treatment will not restore lost vision, it can only maintain a patient at their current level of vision." Even so, it could serve to protect the vision of up to 300 patients a year here who would likely go blind.
The 22-centre international trials were sponsored by Ciba Vision of Switzerland and by QLT Phototherapeutics Inc of Canada.