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Doped lenses counteract cataracts

01 Jul 2003

Polymer lenses doped with light-activated drugs may ease treatment of secondary cataracts.

A new optical treatment for secondary cataracts may ultimately eliminate the need for further invasive surgery to correct the problem, according to scientists in Germany. A team from the Philipps Universität Marburg has developed polymer-lens implants that are doped with light-activated drugs that inhibit the growth of cataracts.

Cataract surgery, where the clouded lens of the eye is surgically removed and replaced with a clear polymer version, is now a routine operation. Unfortunately, a few years after surgery, cells often migrate and start to grow on the surface of the lens, distorting vision once again.

"In Germany, there around 400,000 cataract operations each year," Norbert Hampp from the University's Institute for Physical Chemistry told delegates at the European conference on Biomedical Optics which took place at LASER 2003. "While the surgery has a very high success rate, within 5 years secondary cataracts can occur in up to 50% of cases."

Hampp's team hope that its new Polymer Attached Drug Intraocular Lens (PADIOL) may help the problem. The idea is that green light pulses from a Nd:YAG laser stimulate two-photon absorption in the polymer lens. This severs a chemical bond, releasing the drug 5-fluoruracil (5FU) -- a clinically tested cell toxin.

"The drug is photoloaded into the polymer using ultraviolet light," said Hampp. "Upon interaction with UV again it diffuses out of the polymer into the surrounding water and becomes active."

The team's calculations suggest that the drug-release process requires 50 mJ green light pulses which corresponds to an intensity of the retina of 500 kW/cm2. Although this is much higher than an acceptable value, Hampp is confident that by optimizing the lens material is can be reduced by a factor of ten. "Proof of principle has been shown," he concluded.

Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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