- The Observer,
- Sunday December 7 2003
Cell biologists in Canada have developed a synthetic cornea which they say could pave the way to restoring sight to many thousands of people who would otherwise go blind. The advance is exciting because the new 'smart' material which is used enables the body's own eye and nerve cells to regenerate and weave themselves into the artificial tissue.
Some of the most common forms of blindness are due to swelling or scarring of the cornea. This focuses light on to the retina, at the back of the eye, but if the cornea is damaged by disease or accident it may become swollen or scarred. Some diseases also cause it to scatter or distort the light, causing severe visual problems.
For the past 20 years, doctors have performed corneal transplants or grafts on patients when their vision cannot be restored in any other way, but there is a 25 per cent chance that the graft will be rejected or fail within five years of the procedure.
Scientists have been hunting for ways to produce an artificial material which the body would not reject, but which would also be sensitive enough to focus the light properly. An artificial cornea has now been developed at the Ottawa University Eye Institute, where cell biologist Dr May Griffith has used her tissue engineering skills to construct the small device.
It looks very like a contact lens, but is actually made of a mixture of collagen, the natural substance which comprises most of a human cornea, and a synthetic polymer which has the same kind of scaffolding as a normal organ.
Griffith's hope is that the mate rial provides a habitat in which the body's cells themselves can grow into the material, making it a permanent part of the eye.
'Scientists have been trying since the 1800s to make a cornea, but none has worked,' she said. 'But now we have these smart materials we think we'll be able to implant within the body to stimulate regeneration. The aim is to get the host cells to recognise the material, then grow into it.'
Her team has already begun to trial the artificial corneas on pigs. 'You can't do an eye test on a pig, but we did find that the light hit the back of the retina and that some host cells did grow into the construct. We were also surprised to find that some host nerve cells had been regenerated in the process.'
Around ten million people worldwide have blindness which could be cured through corneal transplants or grafts. Many are children in the Third World, who contract river blindness through a common infection or develop complications from measles. There are also many elderly people whose corneas become scarred or cloudy.
'It's early days yet, and we have to prepare for human clinical trials, but it's a very exciting time,' said Griffith, who is associate professor at the university's department of opthalmology. 'We are hoping what we put in would last a lifetime.'
In Britain, as in other countries, there is a growing shortage of corneas from donors to meet the demand for a transplant. Some people feel squeamish about the prospect of donating their eyes after their death, while others do not know about the existence of eye banks, where the organs are stored for use in patients who would otherwise lose their sight. The scandal over the Alder Hey Children's Hospital in Liverpool, where donor organs were stored illegally, has also affected the donations.
Bruce Allan, consultant opthalmic surgeon at London's Moor fields Eye Hospital, said there was great potential in Griffith's work: 'In the Third World, there is a huge burden of corneal disease and blindness and these people have no prospect of a donor transplant. It hasn't come to a human trial yet, but the creation of an artificial cornea which could be truly integrated, or embedded in the eye, would be a great step forward.'
One problem surgeons face is that donated corneas run the risk of being infected, so an artificial construct might be safer.
Tissue engineering is proving one of the most exciting areas of science, combining chemistry, biology and engineering to create new materials which can regenerate the body's own cells.
Designer polymers, such as ones with which Griffith works, can be formed into virtually any size or shape and mimic the body's own internal scaffolding.
Another team, at the University of Toronto, are working on polymers to make artificial tubes that mimic spinal cord tissue. The tubes, which look like a soft white straw, can be implanted across a break in the spinal cord, providing support along which new nerve cells can grow. Preclinical trials in rats suggest that new nerve tissue can be made to grow along the tubes and there is some restoration of movement in the animals.
