Researchers Discover Relationship Between Visual Function and Symptoms of Cardiovascular Disease
09/06/00 Portland, Ore.
For years pressure in the eye called intraocular pressure has been measured by physicians attempting to identify patients at risk for glaucoma. More recently aspects of cardiovascular dysfunction have been shown to be involved in the development of glaucoma. Now new research conducted by researchers at Oregon Health Sciences University suggests that modest cardiovascular compromise may lead to subtle visual processing changes even for people without eye disease. Researchers believe this discovery may be useful in evaluating the next generation of glaucoma medications, which are expected to act by altering the neurochemistry of the eye. Alvin Eisner, Ph.D., an associate scientist at OHSU's Neurological Sciences Institute, and John Samples, M.D., a professor of ophthalmology in OHSU's School of Medicine, conducted this research.
To uncover the relationship between cardiovascular and visual function, Eisner and his colleagues evaluated the visual system's ability to adapt to light by measuring visual sensitivities across a range of lighting conditions. They measured subjects' sensitivities for detecting flicker, that is rapid periodic changes of light intensity at about 20 times per second. In the past, flicker sensitivity tests have been used to investigate glaucoma-related visual change, but not under stimulus conditions expressly designed to tax the visual system's light-adaptation capabilities, and not in conjunction with measures of blood pressure and heart rate.
Research subjects for the study were between 40 to 68 years of age. All had 20/20 vision and no evidence of glaucoma or other eye disease. A total of 18 subjects were tested. None were using medication to lower blood pressure or otherwise alter cardiovascular function. After the flicker sensitivity data were obtained from all subjects, statistical analysis was used to factor out the effects of aging and intraocular pressure. These two variables already have been shown to affect flicker sensitivity. By removing the effects of these two variables, Eisner and Samples were able to reveal a significant and quantifiable relation between flicker sensitivity, blood pressure and heart rate. They found that high blood pressure/heart-rate ratios were associated with low flicker sensitivities. This association was highly stimulus-dependent, being evident only for the condition chosen expressly to tax the visual system's response and adaptation capabilities. Eisner and Samples believe more work is needed to fully interpret and determine the generality of these results.
"'Based on the work of many investigators, it has become apparent that glaucoma is a complex disease, often involving factors other than elevated intraocular pressure,"' said Eisner, who is principal author of the study. "'Not only can glaucoma involve cardiovascular compromise, but effects of glaucoma are not always limited to peripheral vision. Visual processing in the center of a person's field of view can be affected relatively early in the disease process. By quantifying relations between visual response and cardiovascular function, we hope to provide new means for understanding glaucoma and other age-related diseases."'
The research was funded by the National Eye Institute, an institute of the National Institutes of Health. The conclusions are printed in the August edition of the Archives of Ophthalmology.