Sep 7 2005
Many elderly people suffer from cataracts. When clouded vision impairs everyday tasks, an operation is the only remedy. Scientists engaged in the EU project MIRO are developing new plastics for thinner intraocular lenses to improve minimally invasive operating techniques.
Cataracts are one of the most common eye problems. The first signs usually appear after the age of 50 and include clouded vision or increased sensitivity to glare, particularly when driving at night. The gray clouding of the lens in the eye is caused by proteins slowly crystallizing. Doctors do not advise an operation until older persons are really handicapped by their diminished vision. The surgeon destroys the old, clouded lens with an ultrasound instrument and vacuums it out before implanting a new plastic lens in the eye. Some 670,000 such lenses are implanted every year in Germany alone.
If the incision in the cornea is small enough, there is no need to stitch it afterwards – it closes and heals by itself. “Surgeons are aiming to reduce the width of the incision for the operation from three millimeters to only one and a half,” explains Joachim Storsberg, a chemical engineer at the Fraunhofer Institute for Applied Polymer Research IAP in Golm near Potsdam. “Folding intraocular lenses made of high-performance polymers permit a type of micro-invasive surgery that can be performed on outpatients and is even more readily tolerated than the operating methods used until now.” Operating techniques using such small incisions do exist already, but no suitable intraocular lenses are yet available on the market. Storsberg is collaborating with European colleagues on the CRAFT project MIRO (Micro Incision Research in Ophthalmology) to develop new plastics for this purpose.
The refractive index of intraocular lenses is currently about 1.5. Its value reveals how strongly light is refracted at the interface of two different materials – in this case water in the eye and the plastic material. The greater the refraction index, the thinner the lenses can be made. The Fraunhofer researchers have already attained a value that is significantly greater than for any lenses available so far. The most promising materials are highly refractive acrylates with molecular cross-linkers, and polymers containing nanoparticles of titanium oxide. Both of these possess high optical transparency and flexibility – in other words, they can be folded and rolled up. They are non-toxic, biocompatible and durable in shape. When frozen they can be machine-worked or produced directly in the desired form by means of photochemical polymerization. “We hope that the new lenses will be available for surgery on patients by 2006,” says Dr. Wolfgang Müller-Lierheim, project coordinator for CORONIS GmbH in Martinsried near Munich. “The clinical trials are expected to be completed by next year too.”
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