IT IS not surprising that Leonardo da Vinci had the earliest sketches of contact lenses. But as with the helicopter and his other prescient ideas, a prototype for vision-correcting lenses had to wait. In this case, it was almost 400 years after Da Vinci that the first transparent vision-correcting contact lens was developed. At this time, however, these bulky, full-eye caps could not compete with the comfort of the standard spectacle. It was only in 1961 that a Czechoslovak chemist called Otto Wichterle brought the world the first soft plastic lenses.

Since its inception, the soft contact lens has held promise as a way of transporting antibiotics and other drugs to the eye. The concept is simple enough: apply a drug to a contact lens, and then apply the lens to the eye. Unfortunately the technical hurdles proved difficult to surmount, and current treatments for infections and diseases such as glaucoma still come in the form of pills or, more commonly, eye drops.

Recent advances in contact-lens fabrication at the Institute of Bioengineering and Nanotechnology in Singapore are, however, giving drug-loaded lenses a new look. Edwin Chow, the leader of the group and inventor of the medicated lenses, used a well-known nanotechnology fabrication method for making small channels that, for the first time, has been modified to transport drugs successfully to the eye through contact lenses.

The benefits of loading contact lenses with medication are many. When someone applies an eye drop, almost 95% of the solution is washed away with tears. Some of the medicine even drains into the nasal cavity, where it can enter the bloodstream and thus, potentially, cause side-effects. For example, a drug called Timolol, which is used to treat glaucoma, has been known to result in heart problems. In addition, the dose of medicine in drops can be inconsistent and difficult to control, since drops give an initial burst of medication when they are applied, rather than a steady, controlled dose.

Dr Chow's lenses aim to solve these problems, and they do so in a surprisingly straightforward way. When an ordinary contact lens is made, the steps are fairly simple: mix the lens solution, pour it into a mould and let it harden. The same type of process is used to make medicated lenses. It is only the lens solution that makes the medicated variety different. First, the drugs are added to the solution. Second, the solution contains a mixture of molecules that, when they set, create a network of tiny channels that are 100,000 times smaller than the width of a strand of hair. These channels act as conduits for a drug to be released when the lens comes in contact with eye fluid. Dr Chow claims that by adjusting the channel size, medicine can be administered over the course of hours or days.

Other recent research in this field has explored the idea of soaking a lens in a drug-laden solution, but this results in an uncontrolled release of medicine that is depleted after only a few hours. Another approach, now being pursued by Anuj Chauhan at the University of Florida, involves incorporating drug-filled nano-particles into a lens mixture. While this research would, in theory, produce a timed-release system like Dr Chow's, it is still in its early design stages.

The idea of using channels also allows for flexibility in the type of medicine that can be incorporated into the lenses. Some drugs are water-soluble, and these would be trapped within the water-filled channels. Others, however, are water-insoluble, and would be kept in the nanoscale spaces between the channels. In either case, the rate of leaking into the eye can still be controlled.

Dr Chow also made sure that his lenses do not suffer from one of the most important problems that confronts this sort of research: being incompatible with an actual human eye. Dr Chow has tested his lenses successfully with human cells, and the solution that he uses for fabrication allows the final lenses to be 'nanoporous', thereby letting gases and tear-fluid cross into and out of a lens. Dr Chow claims that this new form of drug delivery could both reduce drug waste and result in higher patient compliance with treatment. That would be a welcome sight to ophthalmologists.