A new therapy for glaucoma could revolutionise the way the sight-threatening disorder is treated. The treatment, developed by British doctors, is designed to keep the pressure in the eye down after surgery, greatly improving its chances of success.
Glaucoma is a chronic condition where the pressure in the eyeball increases, damaging the optical nerve and causing loss of vision. The increase in pressure can result either from too much fluid being produced in the eye or, much more commonly, from too little fluid draining away.
At first, only the extreme edges of the field of vision are affected. However, if left untreated, the impairment spreads and can cause blindness.
Although some cases of glaucoma can be controlled by medicines and eye drops, one in ten people with the condition – around 20,000 a year in Britain alone – eventually needs surgery.
The new treatment, based on an antibody, will improve success rates by dramatically reducing the risk of side-effects and failure. ‘Glaucoma is the commonest cause of irreversible blindness in the world, and it is increasing,’ says Professor Peng Tee Khaw, consultant surgeon at Moorfields Eye hospital.
‘Surgery is the best treatment, but the big problem we have is the healing process itself.’ During surgery, laser or microsurgery techniques can be used to cut out part of the iris to allow excess fluid in the eye to escape.
The risk of surgery is that the act of cutting triggers the body’s own repair mechanisms, which creates scar tissue at the sight of the cut. In many cases, the scar tissue continues to be generated, so that it reduces or closes the new drainage channel, which can eventually lead to loss of vision. It is estimated that in up to half of patients, the surgery can fail in some way so that pressure builds up again.
‘The main reason operating fails is because of the development of this excessive scar tissue,’ says Dr David Glover, medical director of Cambridge Antibody Technology, the British company pioneering the new treatment.
‘Our drug helps to prevent this from developing.’ Researchers have discovered that the main culprit is a growth factor – a molecule in the eye whose job is to orchestrate the repair process. An added problem is that people with glaucoma have higher levels of this growth factor, so every time fluid passes through the new drainage channel it deposits more of the factor, leading to more scar tissue.
The new therapy is based on a human antibody to the growth factor. More than 80 people in Britain have so far had the new treatment in clinical trials, and another 350 are scheduled for the therapy at a number of hospitals in Britain and Europe this autumn.
And researchers believe they have also found a second and unexpected benefit from the treatment. Doctors have known for some time that patients who have undergone surgery for glaucoma have a much higher risk of going on to develop cataracts.
They now suspect that the same growth factor may be involved. It is thought that once activated to repair the damage caused by surgery, the higher levels of growth factor need something to work on – and so cause the cataract to grow.
‘Theoretically at least, the antibody drug could prevent it from happening,’ says Professor Khaw. ‘That, of course, would also be a great step forwards.’