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MEDICINE | IN THE LAB

A better faux teardrop

Dry eyes afflict millions. Scientists are cooking up new eyedrops to better match nature.

February 12, 2007|Karen Ravn | Special to The Times

TO most of us, tears are those wet, salty drops that come out of our eyes when we cry. To scientists who study them, they're those wet, salty, oily, mucous, protein-filled drops that lubricate our eyes and protect them from dust, debris and infection.

For the most part, tears go unnoticed -- until something goes wrong. Eyes sting, burn, itch or turn red. They feel like they're full of sand or being poked with a stick.

These symptoms, grouped under the general label "dry eye," can develop when a person doesn't make enough tears, when tears evaporate too fast, or their intricate chemical balance is knocked out of kilter.

Scientists are working to find more -- and more effective -- approaches to treating the problem. Several new products have entered the market in recent years and are jockeying for position with older remedies, sometimes with only unpublished trials to support them. More strategies are under development.

The task is tricky, because tears are more complex than pure water. The lacrimal glands, just below the eyebrow, produce them continuously. Salty water forms the middle -- aqueous -- layer of a three-layered tear film that lubricates and protects our eyes.

Below it lies the sticky mucous layer, secreted by the conjunctiva, a transparent membrane covering the surface of the eyeball. Mucus "glues" the film in place. Third is the lipid, or oily, layer produced by tiny sebaceous glands, the meibomians, lined up along the edges of the eyelids. The lipids get squirted onto the eye surface when we blink, and float on the top of the aqueous layer, like oil on a puddle, minimizing evaporation.

The tear film is constantly being renewed. The old batch drains out into our nose and throat through tiny holes called puncta, and the eyelids spread a new batch smoothly and evenly across the surface of our eyes. This happens every time we blink -- and we blink 12,000 to 15,000 times a day.

There are many causes of dry eye, including an autoimmune disease called Sjogren's syndrome that attacks the tear-producing glands of the eye, side effects of Lasik surgery, taking antihistamines or spending too much time at a computer. Women and older people are most prone.

Experts estimate that 20 million Americans have mild symptoms, while for 6 million women and 3 million men, the symptoms are moderate to severe.

"Our aging population of baby boomers is resulting in a very significant increase in the number of people who suffer from dry eye," says Doug MacHatton, vice president investor relations and strategic communications for Alcon Laboratories in Fort Worth.

Because dry eye is becoming more prevalent, over-the-counter treatments are big business and getting bigger.

Among the recent entrants into the market is Optive, introduced in January, designed to fight the problem of over-salty tears. It contains two key ingredients in addition to water -- carboxymethylcellulose, a lubricant with a unique binding effect, and glycerin, which helps keep the eye hydrated.

"The glycerin goes into cells, takes water with it and keeps it there," says Joe Vehige, Allergan's senior director of consumer eye care research and development. In an unpublished, 90-day study of about 300 subjects with dry eye symptoms, he says, Optive outperformed two other popular artificial tear products: Refresh, also made by Allergan, and Systane, made by Alcon. Performance was measured on six common measures, including needed frequency of use and comfort rating. MacHatton's company's product, Systane, introduced in 2003, improves comfort by increasing lubrication between the eyelid and the cornea. It does so by combining a substance called hydroxypropol guar (HP-Guar), a gelling agent that works to hold Systane on the eye surface, with polyethylene glycol 400 and propylene glycol, two lubricants.

Kim Fisher, Alcon's senior product manager for dry eye, says that several controlled, double-blind studies have shown that Systane outperforms other solutions on four of the main patient symptoms -- namely, burning, dryness, grittiness and the feeling that something is in the eye.

New developments came also from a better understanding of what happens to eyes when they're dry. In the late 1980s, Stephen Pflugfelder, professor and director of the ocular surface center in the department of ophthalmology at Baylor College of Medicine in Houston, discovered high levels of inflammatory mediators in the tear film of dry eye patients -- chemicals, that is, involved in the inflammation process. One of the first he identified was Interleukin-1, part of the body's response in fighting infection.

"This showed there was inflammation going on in dry eye," Pflugfelder says. Indeed, scientists now believe that dry eye can be caused by inflammation of the lacrimal and meibomian glands, resulting, respectively, in insufficient tear production or too much tear evaporation. Three treatments intended to fight inflammation have either come on the market recently or are in clinical trials.

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