Scientists at the Veterans Affairs (VA) Hospital and Washington University School of Medicine in St Louis are developing a gel-like material that could eventually be used to replace diseased and ageing lenses in the eyes of patients with cataracts.
The material also might eventually mean the end of bifocals and contact lenses for millions of people who suffer from presbyopia, a condition that makes it difficult for people over 40 to read without magnification.
‘This could represent a totally different approach to the treatment of cataracts and presbyopia,’ says Nathan Ravi, MD, Ph.D., principal investigator, associate professor of ophthalmology and visual sciences and professor of chemical engineering at Washington University in St Louis. ‘As we age, the lens of the eye gradually loses its ability to adjust its focus. We have demonstrated that this gel has similar mechanical properties to the lens of the eye, and we hope it also will be able to perform the visual functions of the natural lens.’
Ravi has been working with various synthetic polymers, looking for those that compare favourably with the natural lens. His research centres on understanding the biomechanics of the lens and the causes of presbyopia.
The tissues in our eyes tend to lose their flexibility as we age. The lens also becomes cloudy if cataracts form. The current treatment for cataracts is to remove the old lens material and replace it with a flexible plastic lens.
The new strategy would be to carefully remove the ageing and clouded lens material from the lens’ capsular bag (the part of the eye that holds the lens), while leaving that structure intact. Then, the surgeon would replace the extracted lens material with the clear, flexible polymer that Ravi’s lab has developed by carefully injecting it into the empty capsular bag.
Such a strategy would help not only cataract patients but also could be used to treat presbyopia. While not a life-threatening condition, presbyopia affects nearly everyone by the time they are 40 to 45. After that age, less flexible lenses make it more difficult for the eyes to focus on nearby objects. The current solution for most people involves reading glasses or contact lenses. Even those who undergo corrective laser surgery often need glasses for reading and focusing on objects close up when corrected to give clear vision at distance.
‘Our idea is that if we can remove the lens and replace it with a material that is soft, like a young healthy lens at age 20, many people would have their accommodative ability restored,’ says Madalene Fetsch, a graduate assistant in biomedical engineering at Washington University who works with Ravi. ‘Such a material would allow people to focus both on objects that are distant and those that are close.’
The polymer material being tested is called a hydrophobically modified hydrogel. This type of material is currently used in many extended wear contact lenses.
‘The gel material is soft to the touch, and it has elastic properties similar to those found in the natural human lens,’ Fetsch says. ‘It also looks as if it has the potential to be injectable, which would mean it could be delivered with less invasive surgery.’
Ravi and Fetsch say that using molecular techniques, it’s possible to change the artificial lens material from a gel to a liquid. That liquid then can become a gel again in the presence of oxygen in the body after it is injected into the capsular bag. The hope would be that only a very small injection hole would be required during cataract or other lens replacement surgery so those patients undergoing the operation would not require stitches.
The researchers expect to begin animal testing early next year. Before testing the hydrogel in animals, the researchers hope to improve the material’s refractive index – the degree at which it refracts light – a key to how well the eye can focus once the material is implanted.
‘Currently, in this particular system, the refractive index has been a little low,’ Fetsch says. ‘It’s not good enough to be able to provide much more than blurry vision.’
But other researchers in Ravi’s group, particularly research associates Hyder Ali Aliyar, Ph.D., and Paul Hamilton, Ph.D., have successfully formed several soft gels with the appropriate refractive index. ‘It’s a very significant breakthrough,’ Ravi says.
The researchers admit there is still much work ahead before an injectable lens could be used in human patients, but Fetsch and Ravi expect it would be introduced into cataract patients first.