Cataract surgery: The eyes have it

The Economist online, October 23rd, 2007
Replacing worn-out eye lenses has never been simpler or better

Replacing worn-out eye lenses has never been simpler or better

PAUL URSELL, an ophthalmic surgeon who works at St Helier hospital, just outside London, is one of the first people in Britain to use a new piece of equipment called the Stellaris. This is an all-in-one lens removal and replacement kit intended to treat those whose natural lenses are going cloudy and thus making them blind. It is the latest in a series of improvements to the technology of replacing damaged eye lenses with artificial substitutes. These improvements are simplifying and speeding up the surgery involved.

The ability to remove lenses darkened by cloudy imperfections, known as cataracts, and substitute them with artifical lenses, is more than half a century old. It started with the chance observation during the second world war, by Harold Ridley, a British eye doctor, that pilots whose eyes had been penetrated by perspex shrapnel from cockpit canopies did not suffer an immune reaction.

Perspex lenses have long since been replaced by silicone ones. But now the whole process of inserting those lenses is changing as well. One of the biggest innovations has been the introduction of microsurgery. Originally, inserting a new lens meant cutting a flap in the eyeball some 11mm across. Today’s microsurgery requires a cut of less than 2mm. Such small wounds heal by themselves, and do not need to be stitched. The whole process is thus less traumatic, and patients are often able to return to work the day after an operation.

Two technologies in particular have helped to reduce the size of the incisions needed. The first, phakoemulsification, uses a tiny ultrasound probe to remove the lens. An ageing lens goes yellow, cloudy and hard. Mr Ursell likens its texture to that of a gravy cube. Exposing such a lens to high-frequency sound waves breaks it up into an emulsion that can then be sucked out of the eyeball. The second innovation is injectable lenses. Progressive improvements in the design and material of artificial lenses mean it is now possible to roll them up, inject them into position in the eye through a narrow slit, and then have them unfold, naturally into place.

The tools to perform these tricks have been available for a while. The novelty of Stellaris—which is made by Bausch & Lomb, a firm based in Rochester, New York—is that all the pieces of kit are pulled together into one snazzy little box. The system can extract lenses, keep the eyeball inflated, and inject lenses in several different ways. Stellaris has options to use an older or a newer surgical technique, depending on the surgeon’s preference.

The newer form of surgery splits the instruments into two tools which enter the eye through identical tiny slits. One provides the ultrasound to break down the cataract, and also contains a vacuum to hoover out the pieces. The other tool provides fluid to keep the pressure while the lens is being extracted. That prevents the eyeball collapsing.

In short, a useful innovation. But lens replacement is not yet perfected, largely because replacement lenses themselves still have room for improvement. Standard replacement lenses have no ability to focus, so the wearer is often stuck with excellent distance vision but must use glasses for reading. That can be addressed with multifocal lenses, which have concentric rings of material that offer alternate bands of near and distant vision, but these can cause problems with a person’s night vision and his sensitivity to contrast.

What excites ophthamologists most, however, and what every lens-making company wants to achieve, is a lens that can change its focal length in the way that a natural lens does. A few such “accommodating” lenses are already on the market. The Crystalens from Eyeonics in Aliso Viejo, California, is one example. The Tetraflex by Lenstec of St Petersburg, Florida, is another. These products use the eye muscles to change the shape of the lens and move it backwards and forwards in the eye during focusing. Such products are soon likely to replace multifocal lenses. After that, light-sensitive silicone lenses may arrive. These can be customised after surgery by playing a low-intensity beam of light onto the photosensitive material. That causes the material to polymerise, and thus change shape, which means the ophthamologist can tweak the lens to alter its power. Raging against the dying of the light now has powerful technological allies.