Researchers at the University of Tokyo's
School of Medicine have shown for the first time that caffeine
intake can significantly increase the eye's ability to produce
tears, a finding that could improve treatment of dry eye syndrome.
For many, dry eye syndrome is simply
uncomfortable and annoying, but for others it escalates into a
vision-threatening disease. All of the 78 participants in the new
study produced significantly more tears after consuming caffeine
than after taking a placebo. The study is available in
Ophthalmology, the journal of the American Academy of Ophthalmology.
Dry eye syndrome involves malfunction of
the rate of tear production, the quality of tears, and/or the rate
of evaporate from the surface of the eye. Anyone can experience dry
eye, though it is more common among women. Symptoms can include
gritty, scratchy or burning sensations, excessive tearing, and/or
production of stringy mucus.
The research team, by Reiko Arita, MD,
PhD, was motivated by an earlier study that had shown a reduced risk
for dry eye in caffeine users: 13 percent of users had the syndrome
compared with nearly 17 percent of non-users. The team knew that
caffeine was likely to stimulate tear glands, since it is known to
increase other secretions, such as saliva and digestive juices. They
also knew that people respond differently to caffeine, so they
analyzed study participants' DNA samples for two genetic variations
that play important roles in caffeine metabolism. Tear production
proved to be higher in study subjects who had the two genetic
variations.
The study subjects were divided into two
groups: one received caffeine tablets in the first session and a
placebo in the second session, while the order was reversed for the
other group. Tear volume was measured within 45 minutes of consuming
the tablets. All sessions took place between 10 a.m. and noon, a
time of day when tear production is usually stable. No subjects knew
whether they received caffeine or the placebo. All abstained from
caffeine use for six days prior to each session and used no drugs
during the sessions. To be eligible for the study subjects had to be
free of high blood pressure, dry eye syndrome, allergies that affect
the eye, glaucoma, and other eye diseases and conditions that can
interfere with tear production. The study also found that tear
drainage rates were not affected by caffeine.
"If confirmed by other studies, our
findings on caffeine should be useful in treating dry eye syndrome,"
said Dr. Arita. "At this point, though, we would advise using it
selectively for patients who are most sensitive to caffeine's
stimulating effects."
For more information
American Academy of
Ophthalmology
http://www.aao.org/
(MDN) | 
