Flicker sensitivity and cardiovascular function in healthy middle-aged people

Objective: To establish normative relations between measures of visual function and cardiovascular variables that are important for age-related disease, including various forms of glaucoma. Methods: Foveal flicker sensitivities, resting blood pressures and heart rates, and intraocular pressures were measured in 18 individuals aged 40 to 68 years. All subjects had 20/20 or better visual acuity in the test eye and no evidence of eye disease or glaucoma suspicion on clinical evaluation and medical history. No subjects were using medication to lower blood pressure. Flicker sensitivity was measured by increasing the illuminance of a fully modulated 20-Hz test stimulus until flicker was perceived. Two test-background stimulus combinations were used: a 570-nm ("yellow") test on a predominantly long-wavelength ("magenta") background and a 580-nm ("yellow") test on a 580-nm ("yellow") background. The illuminance of the yellow background was dimmer than that typically used for short-wavelength automated perimetry, whereas the illuminance of the magenta background was greater. Results: The 2 flicker sensitivity measures were distinguished by the strong dependence of the magenta background measure on the ratio of mean arterial blood pressure to heart rate. Log flicker sensitivity on this background generally could be modeled as a linear combination of age, intraocular pressure, and ratio of mean arterial blood pressure to heart rate. The optimal model accounted for 84% of the variance (R=0.92) from all but 2 outlying individuals, After age and intraocular pressure effects were partialed out, an increasing ratio of mean arterial blood pressure to heart rate was strongly associated with decreasing flicker sensitivity. Conclusions: Reduced cardiovascular function impacts the ability of the normal visual system to adapt and regulate flicker sensitivity. Elevated intraocular pressure and increased age reduce flicker sensitivity relatively uniformly across a range of stimulus conditions. Because the ratio of mean arterial blood pressure to heart rate equals total peripheral vascular resistance multiplied by cardiac stroke volume, and because total peripheral resistance is determined largely at the arterioles, it is likely that even modest changes in arteriolar function are associated with measurable alterations of visual function.