The harmonic content of the envelope waveform of the blood flow velocity in the ophthalmic artery was analyzed in aging and arterial hypertension. The case-control study enrolled 98 healthy men (age: 44.0+/-15.6 years), 100 healthy women (age: 44.5+/-19.1 years), which is group 1, and overall 199 hypertensive patients with increased systolic and diastolic blood pressure (in millimeters of mercury) before registration of the blood flow velocity using pulsed Doppler sonography. Group 2 was sufficiently treated (<or=140/<or=90), group 3 (>140/<or=90) and group 5 (>140/>90) were insufficiently treated, and group 4 (>140/<or=90) and group 6 (>140/>90) were untreated. Cronbach-alpha reliability of the calculated spectral coefficient and SI (SI) was 0.88 and 0.93, respectively. In control subjects, the SI was influenced by age (men: 45.1%; women: 50.2%; P<0.001 each) and in women additionally by mean arterial pressure (13.1%; P<0.001). The SI differed in subjects >43 years of age (men: 0.37+/-0.11; women: 0.26+/-0.08; P<0.001 each) as compared with subjects <or=43 years of age (men: 0.60+/-0.18; women: 0.48+/-0.13). All of these changes were lacking for the resistance index. In both men and women with hypertension, the SI decreases, whereas the mean arterial pressure increases, but the resistance index did not change. The SI of the ophthalmic artery allows an assessment of the ocular circulation in consideration of age and arterial blood pressure in contrast to the resistance index.