CONTACT SOLUTION
Tech researchers are working to determine if coating contact lenses with selenium will make daily cleaning unnecessary.
Written by Andrea Watson
Imagine wearing contact lenses for months without worrying about cleaning and disinfecting them. Ted Reid, Ph.D., and Steven Mathews, O.D., Ph.D., both faculty members in the Texas Tech University Health Sciences Center’s Department of Ophthalmology and Visual Sciences, and Julian Spallholz, Ph.D., a professor of nutrition in the College of Human Sciences at Texas Tech University, are working to determine if coating contact lenses with selenium will make the hassle of daily cleaning unnecessary.
“The coating is only one molecule thick,” Reid said. “It’s not something that can affect the clarity of the lens or even be noticed by the wearer. The coating is a permanent part of the lens.”
The coating is designed to keep bacteria from accumulating on the lens, causing biofilm formation, which causes a major class of eye problems for contact lens wearers.
“Bacteria are constantly floating around looking for places to attach themselves,” Reid said. “The problem is that when they attach themselves, they grow and form these films that are very resistant to antibiotics and even bleach. These films take on a tissue-like structure. One layer attaches to the lens and then the next layers form a tissue-like structure which is finally covered with a layer that acts like a skin. It’s this tissue or film that causes the wearer to have problems with their lenses.”
Some of these bacterial biofilms also can be very dangerous because the bacteria can produce toxins that damage the cornea, often leading to ulcers and infections, which is why Reid and Mathews believe the selenium also will help make the lenses safer.
“That may be the primary benefit,” Mathews said. “Evidently the selenium either sheds the bacteria or it kills it. Either way, if the material doesn’t allow the biofilms to form, it will reduce the problems some wearers have with acute red-eye reaction or infections. These problems are all about bacterial load and if the coating reduces that bacterial load, then it will make it less likely that these conditions can develop. On its own, a healthy eye can fight off small numbers of bacteria very effectively, but a large number of bacteria can create their own environment and that makes them very difficult to fight off.”
For decades, selenium has been recognized as an essential element, necessary for the body to function properly, but its medical uses have only been recognized within the last 20 years. Previously, selenium’s main applications were commercial in nature, from being used to transfer images within copiers to tinting auto glass.
Spallholz, who has been researching selenium’s effect on cells for more than three decades, believes the coating is effective because it kills the bacteria.
Without Selenium: with average wear, bacteria builds up on the contact lense, endangering the cornea.“My original interest was in attaching selenium to antibodies to use as drugs,” he said. “These experiments showed that the selenium could kill cells. The selenium coating on the contact lenses works the same way. The selenium acts as a catalyst on the surface of the lens and helps create a molecular barrier to the growth of cells.”
The catalytic reaction continues unimpeded, Spallholz said, because the elements used and created are present in all biological fluids.
The reaction is created when oxygen molecules collide with the selenium, which has a negative charge. During the collision, the oxygen molecules pick up electrons from the selenium, creating superoxide radicals, which then collide with something, typically bacteria, and oxidize, or kill, them. To keep the selenium stable and to keep the reaction going, a sulfur compound in the tear film gives an electron back to the selenium, starting the process again, Reid said.
“There’s nothing to stop the reaction,” Spallholz added. “That’s why this permanent coating continues to be effective at stopping biofilm formation.”
While the idea of putting a contact lens coated with a cell-killing chemical into the eye seems strange, the practice seems to be perfectly safe, Reid said, because the lens doesn’t actually sit directly on the eye.
“The lens actually rests on the tear film on the surface of the eye,” he said. “There is no direct contact with the cornea and even if there were, the half-life of the superoxide radicals created is less than 65 nanoseconds. There simply isn’t enough time for the radicals to reach the eye.”
In fact, Reid said, the distance the superoxide radicals can travel is barely half the distance of one bacterium.
“This is important because this is what prevents damage to the cornea,” he said. “Even if these compounds could reach the cornea, there is no danger of damage because the top surface of the cornea is dying cells. The cornea resurfaces itself every three to four days anyway, minimizing the potential for damage.”
The initial research on the selenium-coated lenses was funded by a $25,000 Vistakon Research Grant from the American Optometric Foundation. This original grant allowed the researchers to examine the effects of the selenium coating on lenses in both test tubes and in animal models using PureVision silicon-hydrogel lenses manufactured by Bausch & Lomb.
“Now we’re waiting on approval for human trials,” Reid said. “But, I’m ready to put them in my own eyes right now. We put the lenses in rabbits for two months solid and there was no evidence of damage to the cornea. We examined the corneal surface, the histology and thickness and there were no effects from the selenium. But, it’s all conjecture at this point really. We need to get these into humans to see how they perform.”
Human trials are important at this stage, Mathews said, because the animal trials didn’t show any significant change in protein or lipid deposit build-up on the lenses, which would be necessary to dramatically increase the length of time the lenses can be worn without cleaning.
“It may be that rabbit tears are so different from human tears that they overwhelm the selenium,” he said. “It’s still possible that the selenium could have a favorable effect on deposition in humans. Protein deposits are still a major problem for contact lens wearers. That’s why we’ve gone to disposables in the first place. Even the best cleaning can still leave up to 60 percent of deposits on the lens. It would be nice if the lens could actually reject deposits so you wouldn’t have to throw them away. Ultimately, the best scenario would be to put these lenses on and not have to take them out for a year and to have them resist all the bacteria and deposits that currently cause problems.”
While safety may actually be the main benefit of the selenium-coated lenses, the idea of wearing contacts for months at a time is what draws the attention of contact wearers. This prospect also has drawn media attention from across the world and the nation, Reid said.
The research, which was first presented at the annual meeting of the Association for Research in Vision and Ophthalmology in May 2002, also was presented recently at a meeting of the American Chemical Society, and has since been highlighted in newspapers in England, the Netherlands, Japan and Australia, as well as across the United States.
With Selenium: in the same conditions, contact lenses treated with selenium remain almost completely free of bacteria.Spallholz admitted that while creating a safer contact lens is the current focus, he sees bigger applications for this technology.
“You don’t die because you can’t see clearly,” he said. “However, bacteria on things like heart valve replacements can be very dangerous. This may provide a way to prevent that. There are probably other applications that we haven’t even thought of.”
Reid said selenium coatings may be used to keep biofilms from forming on many other things that are surgically placed in the body, including glaucoma shunts, stents used to keep blood vessels open, ear tubes and catheters.
“This can be used on anything you don’t want bacteria on in relation to the body,” he said. “Bacteria are the single biggest problem with anything you put inside the body. When you surgically implant something within the body, you give high doses of antibiotics to fight infection, but in time, the bacteria will still find a way to this surface. This may give us a permanent way to treat that bacterial threat.”
Spallholz said he believes selenium also may represent a breakthrough in the future of treating diseases by harnessing the chemical reaction produced within the body. He said researchers have done some interesting research using bacterial viruses to transport the selenium directly to the bacteria, creating a new treatment for numerous infections.
“This may present a whole new type of anti-bacterial drugs,” he said. “This work with contact lenses proves that this can work. We can use what we’ve learned about selenium’s ability to kill bacteria to treat drug-resistant strains of bacteria in the body. This is very promising, but it’s going to take time, research and a lot of money.”
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