High pressure alone not the only risk
June 29, 2000 -- The more eye pressure fluctuates during the day, the higher the risk that a glaucoma patient will lose vision, according to a study by researchers at Johns Hopkins and two other academic medical centers.
"For years physicians have been focused on lowering high intraocular pressure associated with glaucoma," says Ran Zeimer, Ph.D., director of the Ophthalmic Physics Laboratory at Hopkins' Wilmer Eye Institute. "Our study shows that's not enough. They also must control the daily variation in pressure. This poses a new challenge in therapy."
Results of the study, supported by the National Institutes of Health, were published recently in the Journal of Glaucoma.
Zeimer's team found that large fluctuations in intraocular pressure during the day or over consecutive days are associated with greater risk of vision loss. These changes also are a good marker for predicting risk after accounting for glaucoma damage that already exists.
Glaucoma is a vision-threatening disorder characterized by a build-up of pressure within the eye that slowly damages optic nerve fibers. Susceptibility to the disease depends on genetics and older age. Glaucoma patients can have pressures up to more than 25 millimeters of mercury (mmHg); by contrast, normal pressures range from 12 to 21 mmHg.
For the study, ophthalmologists recorded the measurements of 105 eyes of 64 glaucoma patients. Because daily monitoring was more practical in the home, patients were taught to use a self-tonometer, a device invented by Zeimer that measures pressure in the eye. They recorded the pressure in their own eyes five times a day for five days, taking measurements in the morning when they woke, around noon, in mid-afternoon, in the evening after supper and at bedtime. After five days, they returned to their ophthalmologist's office for another recording.
During an average day, the pressures recorded at home fluctuated by 4.3 mmHg and ranged from 1.5 to 12.5 mmHg. Over a five-day period, fluctuation was even greater 10 mmHg and ranged from 4.4 mmHg to 18.5 mmHg.
The patients' test results were compared to their medical records and vision tests over the next eight years.
The study found that:
- The measures taken at home over the five days were the strongest indicator of further vision loss (after accounting for baseline visual field loss). After eight years, 43 percent of patients with low fluctuations remained stable, compared with only 12 percent of those with high fluctuations in pressure.
- Moderate and severe visual field loss at the start of the study was strongly associated with progression, increasing the risk of further vision loss by three to eight times.
- Whites had significantly less risk of vision loss than people of other races. By the end of two years, the risk of further vision loss was far higher for African-Americans compared with whites. However, the number of African-Americans studied was small and further study is needed, Zeimer says.
The other study authors were Susan Vitale, Ph.D., M.S., of Hopkins; Sanjay Asrani, M.D., of Duke University Eye Center, Durham, N.C.; Jacob Wilensky, M.D., David Gieser, M.D., and Kim Lindenmuth, M.D., of the University of Illinois at Chicago Eye Center. Gieser also has an appointment at the Wheaton Eye Clinic, Wheaton, Ill.
Zeimer is entitled to sales royalty from CDS Technology, L.L.C., which is developing the Zeimer self-tonometer used in this study. The terms of this arrangement have been reviewed and approved by The Johns Hopkins University in accordance with its conflict of interest policies.
Related Web sites:
Wilmer Eye Institute at Johns Hopkins: http://www.wilmer.jhu.edu
National Eye Institute: http://www.nei.nih.gov
American Optometric Association: http://www.aoanet.org
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Email: kinfeld@jhmi.edu
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Journal
Journal of Glaucoma