"Medicine has an eye-opening side effect"
A new type of drug to battle vision-stealing glaucoma works significantly better than standard therapy - but has the startling side effect of sometimes turning blue eyes brown.
Despite not understanding the cause or significance of the eye color change, which is apparently irreversible, the Food and Drug Administration should approve Latanoprost, a panel of scientific advisers decided. But the FDA panel insisted that manufacturer Pharmacia & Upjohn Inc. continue to study the drug's long-term safety and clearly state on the label that it can cause the eye color change, so doctors and patients understand the risk.
"This could turn out to be a major public-health hazard for glaucoma patients", said Dr. A. Brucker of the University of Pennsylvania, who opposed approving the drug. But "it is very effective", Dr. Emily Chew of the National Eye Institute said before the panel approved the drug by a vote of 4-2. The FDA is not bound by advisory panel decisions but it usually follows them.
Glaucoma blinds 80,000 Americans a year and steals some sight from 900,000 others. It is caused when fluid builds up inside the eyeball and causes dangerous pressure. Over time that pressure pushes against the delicate optic nerve until it is damaged and the person begins to lose eyesight. Standard therapy is a drug called Timolol, made by Pharmacia competitor Merck & Co. This eye drop makes the eye produce less fluid, thus keeping the pressure down. But the drug has numerous side effects, from breathing problems to irregular heartbeat. And people with hearing or respiratory problems cannot use it.
Latanoprost is the first of a new class of drugs based on a natural chemical called prostaglandin, which helps the eye drain off its fluid. In a study of 829 patients, those who took Latanoprost had a 37% greater drop in inner-eye pressure than Timolol patients. They also had significantly fewer side effects.
But some had a startling side effect: Blue eyes turned brown, as did green, hazel, and even yellowish ones. The color change hit 15.5% of patients after a year of Latanoprost use.
"This is a very strange side effect", acknowledged Dr. J. Stjernschantz, the company's lead researcher. "There is no other drug or agent that can cause this side effect". And it is apparently not a reversible change even when patients stop taking the drug. The question is whether the change is cosmetic or dangerous.
The company theorizes that Latanoprost increases the amount of melanin in people's eyes. Melanin is a chemical that gives people skin color, and everybody's eyes have some. But lighter-colored eyes don't produce as much of the pigment, allowing light to better diffuse through the eye and reflect back. The company gave high levels of Latanoprost to monkeys for a year and counted the number of melanin-producing cells, finding no increase. But these cells were producing more of the kind of melanin that causes a dark color than the kind that causes yellow colors. The company notes that 10% of the population experience an unexplained eye color change by adulthood anyway. But critical panelists asked whether the melanin-producing cells would eventually get so full that they burst. And they noted that 90% of the people studies were white. Black glaucoma patients naturally have more eye pigment, and nobody knows how their eyes would be affected.
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