Response of retinal vessel diameters to flicker stimulation in patients with early open angle glaucoma.

INTRODUCTION: Diffuse luminance flicker increases retinal vessel diameters in animals and humans, indicating the ability of the retina to adapt to different metabolic demands. The current study seeks to clarify whether flicker-induced vasodilatation of retinal vessels is diminished in glaucoma patients. METHODS: Thirty-one patients with early stage glaucoma (washout for antiglaucoma medication) and 31 age- and sex- matched healthy volunteers were included in the study. Retinal vessel diameters were measured continuously with a Retinal Vessel Analyzer. During these measurements three episodes of square wave flicker stimulation periods (16, 32, and 64 secs; 8 Hz) were applied through the illumination pathway of the retinal vessel analyser. RESULTS: Flicker-induced vasodilatation in retinal veins was significantly diminished in glaucoma patients as compared with healthy volunteers (ANOVA, P < 0.01). In healthy volunteers, retinal venous vessel diameters increased by 1.1 +/- 1.8% (16 seconds, P < 0.001), 2.0 +/- 2.6 (32 seconds, P < 0.001), and 2.1 +/- 2.1% (64 seconds, P < 0.001) during flicker stimulation. In glaucoma patients, venous vessel diameters increased by 0.2 +/- 1.7% (16 seconds, P < 0.6), 1.1 +/- 2.1% (32 seconds, P < 0.01), and 0.8 +/- 2.5 (64 seconds, P < 0.09). In retinal arteries, no significant difference in flicker response was noticed between the two groups (ANOVA, P < 0.6). In healthy controls, flicker stimulation increased retinal arterial vessel diameters by 1.0 +/- 2.4% (P < 0.03), 1.6 +/-3.2% (P < 0.004) and 2.4 +/- 2.6% (P < 0.001) during 16, 32, and 64 seconds of flicker, respectively. In glaucoma patients, flickering light changed arterial vessel diameters by 0.3 +/-2.6% (16 seconds, P = 0.4), 1.3 +/-3.1% (32 seconds, P = 0.03), and 1.8 +/- 3.8% (64 seconds, P = 0.005). CONCLUSION: Flicker-induced vasodilatation of retinal veins is significantly diminished in patients with glaucoma compared with healthy volunteers. This indicates that regulation of retinal vascular tone is impaired in patients with early glaucoma, independently of antiglaucoma medication.

Diffuse luminance flicker increases blood flow in major retinal arteries and veins.

It has been shown that diffuse luminance flicker increases optic nerve head blood flow. The current study has been performed to quantify changes in retinal blood flow during flicker stimulation. In a group of 11 healthy volunteers, red blood cell velocity and retinal vessel diameters were assessed with bi-directional laser Doppler velocimetry and the Zeiss retinal vessel analyzer before, during and after stimulation with diffuse luminance flicker. Retinal blood flow was calculated for each condition. Flicker stimulation increased retinal blood flow by +59 +/- 20% (p<0.01) in arteries and by +53 +/- 25% (p<0.01) in retinal veins. These results demonstrate that diffuse luminance flicker increases retinal blood flow in the human retina.

Influence of diffuse luminance flicker on choroidal and optic nerve head blood flow.

PURPOSE: In the retina there is general agreement that blood flow adapts in response to different conditions of light and darkness including diffuse luminance flicker. By contrast, regulation of choroidal blood flow in response to different light conditions is still a matter of controversy. Thus, we investigated the effect of diffuse luminance flicker on choroidal and optic nerve head blood flow. METHODS: In a group of 14 healthy volunteers, choroidal blood flow and ocular fundus pulsation amplitude were assessed with laser Doppler flowmetry and laser interferometry, respectively. Measurements were done before, during and after stimulation with diffuse luminance flicker. Furthermore, the response of optic nerve head blood flow (ONHBF) to flicker stimulation was measured. Flicker stimuli were generated by a Grass PS2 photostimulator, stimulating at a frequency of 8 Hz. Flicker light consisted of light flashes at a wavelength below 550 nm and produced a retinal irradiance of 140 microW/cm( 2). Blood pressure and pulse rate were measured non-invasively. Paired t-test was used for statistical analysis. RESULTS: ONHBF increased immediately after onset of flicker stimulation. The maximum increase in ONHBF was 30% +/- 10% (mean +/- SEM, p < 0.008). Both choroidal perfusion parameters were only slightly increased during flicker stimulation, by 2 +/- 2% (laser Doppler flowmetry, p < 0.5) and by 4 +/- 1% (laser interferometry, p < 0.12). After the end of stimulation all values returned to baseline levels. CONCLUSION: Our study clearly demonstrates that diffuse luminance flicker increases optic nerve head blood flow. In contrast, increased neural activity in the retina has no effect on choroidal blood flow. Thus, choroidal blood flow appears to be largely independent of alterations in retinal metabolism.

Cardiovascular, endocrine, and receptor measures as related to sex and menstrual cycle phase.

OBJECTIVE: The present study was undertaken to elucidate possible mechanisms underlying sex differences in cardiovascular measures or reactivity to challenge. Because there is vastly diverging literature on the issue, we tried to control for endocrine and psychological factors, which might contribute to some of the apparent discrepancies. METHODS: Blood pressure, heart rate, adrenaline, and noradrenaline in women (N = 24) and men (N = 14) were examined during baseline and challenge (Stroop Test and Cold Face Test). Adrenoceptor density on lymphocytes (beta 2) and platelets (alpha 2) were determined to examine possible sex differences in underlying cardiovascular mechanisms. Gender effects were controlled by assessing gender role orientation and task appraisal. Women were tested during either the follicular (N = 12) or the luteal (N = 12) phase of the menstrual cycle (verified by estradiol, progesterone, and luteinizing hormone). RESULTS: Follicular and luteal phase women did not differ in any parameter except progesterone. We observed sex-related differences in absolute levels of physiological parameters, the male group having higher systolic blood pressure levels, higher adrenaline plasma concentrations, and significantly more alpha 2-adrenergic receptors. Both challenges elicited pronounced cardiovascular and endocrine responses. Men and women did not differ in response magnitude, in task appraisal, or gender role orientation. CONCLUSIONS: The assumption that female sex hormones reduce reactivity to challenge is not supported by our data. The frequently reported male/female differences in reactivity may be caused by an interaction of gender and task characteristics.

Working with new technologies: hormone excretion as an indicator for sustained arousal. A pilot study.

Effects of working with new technologies (visual display units) on hormone levels were investigated in a pilot study. The relationship between subjective strain and hormone levels was also assessed. Twenty subjects participated in the study reported here, which is a part of a comprehensive longitudinal study, in which 279 employees participated. Measurements were taken two months before the new technology was installed (baseline: work with conventional technology), during the implementation phase of the new technology, and at a 12-month interval. Fourteen complete data sets were analysed. The introduction of new technologies was accompanied by enhanced levels of catecholamines (epinephrine and norepinephrine). Levels also remained high one year after the implementation. Similar values were found on work days and rest days. Cortisol changes were less evident; excretion tended to increase after the implementation had been completed. The relationship was weak between hormone levels and subjective strain measurements. The results indicate that working with new technologies was accompanied by enhanced physiological arousal of the employee. Reactivity was related more to a particular occupational setting than to scales of subjective assessment.