July 7 (HealthDay News) -- A study of people who suffer the mini-strokes called silent cerebral infarcts could help explain the medical mystery of normal-tension glaucoma, Hong Kong ophthalmologists report.
Glaucoma is the progressive loss of vision caused by deterioration of the optic nerves, which carry signals from the eyes to the brain. It is customarily attributed to abnormally high pressure of the fluid in the eye. But glaucoma can occur in some people who have normal intraocular pressure, a phenomenon that puzzles eye doctors.
The Hong Kong study of 286 people with normal-tension glaucoma found a high incidence of silent cerebral infarcts among those whose loss of vision progressed more rapidly. The finding is in the July issue of Ophthalmology.
"We feel that our study does cast light on the pathogenesis of normal-tension glaucoma," said the study's lead author, Dr. Dexter Y.L. Leung, deputy coordinator of the glaucoma service at Hong Kong Eye Hospital. "We postulate that vascular [blood vessel] risk factors may be interacting with intraocular pressure in causing glaucoma optic neuropathy."
The study found that 29.6 percent of people with silent cerebral infarcts -- symptomless blockages of small brain arteries -- experienced steady deterioration of their vision, whereas such infarcts occurred in only 15.3 percent of those whose glaucoma-caused vision loss did not progress.
All study participants were Chinese, Leung noted. "We feel that a similar silent cerebral infarct-glaucoma relationship is likely to be applicable to other ethnic groups than the Chinese, but more studies are needed to confirm that," he said.
Doctors treating people with normal-tension glaucoma should consider obtaining brain images to determine whether silent infarcts have occurred, Leung said. There has been a debate about whether doing neuroimaging to detect abnormal growths within the brain is worthwhile, he said.
The next step in the Hong Kong research program will be to determine whether the severity of the silent infarcts correlates with the degree of vision loss in glaucoma, Leung said. Such a relationship would confirm the role of silent infarcts in normal-tension glaucoma, he said.
Dr. Andrew Iwach, executive director of the Glaucoma Center of San Francisco and a spokesman for the American Academy of Ophthalmology, said that while the Hong Kong study adds evidence that there might be a vascular effect in normal-tension glaucoma, "at the moment, the only parameter that has been clearly shown to affect patients is lowering eye pressure."
That applies even to people with normal-tension glaucoma, Iwach said. A study done several years ago by the Glaucoma Research Foundation found that lowering eye pressure reduced visual field loss in such cases, he said.
But sudden changes in vision were seen in some study participants, Iwach said, "and one characteristic of a vascular process is that you can have such sudden changes." Though eye pressure remains the dominant factor in glaucoma, "we are continuing to look for other contributing factors, and high on our list has been the vascular component," he said.
Because glaucoma-caused vision loss can be insidious, the American Academy of Ophthalmology recommends that a comprehensive eye examination, with careful checking of the optic nerve, be done no later than age 40, Iwach said.
SOURCES: Dexter Y.L. Leung, M.D., deputy coordinator, glaucoma service, Hong Kong Eye Hospital; Andrew Iwach, M.D., director, Glaucoma Center of San Francisco; July 2009, Ophthalmology