[Response of retinal vessel diameter to flicker-light in vasospastics compared to healthy controls]. / Flickerlichtprovokation bei Vasospastikern verglichen mit gesunden Kontrollpersonen.

BACKGROUND: Vascular dysregulation is considered to be a risk factor in several ophthalmic diseases. The purpose of this study was to evaluate the reaction of retinal vessels to flicker light in otherwise healthy subjects with a vasospastic propensity. PATIENTS AND METHODS: Thirty healthy Caucasians, aged between 18-35 years were recruited for this study and grouped into vasospastics, based on a history of frequent cold hands, even in summer, with concordant findings in nailfold capillary microscopy, or as controls, if such a history was absent. The reaction of the retinal vascular diameter to flicker light was observed in a distance of two to three discs diameters away from the optic nerve head with the retinal vessel analyser. Three phases of flicker light of twenty seconds followed by baseline light phases of eighty seconds were recorded. The maximal vasodilatory amplitude of each flicker phase was determined and the results averaged. RESULTS: The maximal average dilatory amplitude at the arterial side reached (mean +/- SD) 2.9 +/- 1.7 % and 4.8 +/- 2.6 % of the baseline amplitude respectively in vasospastic subjects and in healthy controls (t = 2.34; p = 0.025). The reaction at the venous side was statistically comparable in both groups. CONCLUSIONS: Otherwise healthy, vasospastic subject disclosed an altered reaction of the retinal vasculature to flicker light in this study.

Influence of change in body position on choroidal blood flow in normal subjects.

AIM: To compare subfoveal choroidal blood flow (ChBF) in sitting and supine positions in normal volunteers. METHODS: ChBF was measured with laser Doppler flowmetry in 22 healthy volunteers of mean (SD) age 24 (5) years. Six independent measurements of ChBF were obtained in one randomly selected eye of each subject while seated. The subjects then assumed a supine position for 30 minutes and a new series of six measurements was obtained. The mean values of the two series were calculated. Systemic brachial artery blood pressure and intraocular pressure were measured in the sitting and supine positions. Ocular perfusion pressure (OPP) was calculated based on formulae derived from ophthalmodynamometric studies. The influence of changing OPP during change in body posture on the change in ChBF was assessed by linear regression analysis. RESULTS: ChBF decreased by 6.6% (p = 0.0017) in the supine position. The estimated ophthalmic blood pressure in the supine position was adjusted to obtain a result of no change in OPP for no change in ChBF, yielding a mean decrease in the estimate of OPP of 6.7% (p = 0.0002). The necessary adjustment for the estimate of OPP in the supine position suggested a marked buffering of the change in perfusion pressure by the carotid system. The relative decrease in OPP correlated significantly with the relative decrease in ChBF (R(2) = 0.20; p = 0.036) with a slope for the regression line of 1.04. CONCLUSIONS: The comparable degree of change in ChBF and OPP and the linear relationship between the two parameters suggest a passive response of the choroidal circulation to a change in posture. In contrast, the carotid system seems to control the gradient in perfusion pressure closely between the heart and its branches.

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.

Reduced response of retinal vessel diameters to flicker stimulation in patients with diabetes.

BACKGROUND/AIM: Stimulation of the retina with flickering light increases retinal arterial and venous diameters in animals and humans, indicating a tight coupling between neural activity and blood flow. The aim of the present study was to investigate whether this response is altered in patients with insulin dependent diabetes mellitus. METHODS: 26 patients with diabetes mellitus with no or mild non-proliferative retinopathy and 26 age and sex matched healthy volunteers were included in the study. Retinal vessel diameters were measured continuously with the Zeiss retinal vessel analyser. During these measurements three episodes of square wave flicker stimulation periods (16, 32, and 64 seconds; 8 Hz) were applied through the illumination pathway of the vessel analyser. RESULTS: In retinal arteries, the response to stimulation with diffuse luminance flicker was significantly diminished in diabetic patients compared to healthy volunteers (ANOVA, p<0.0031). In non-diabetic controls flicker stimulation increased retinal arterial diameters by +1.6% (1.8%) (mean, p<0.001 v baseline), +2.8% (SD 2.2%) (p<0.001) and +2.8% (1.6%) (p<0.001) during 16, 32, and 64 seconds of flicker stimulation, respectively. In diabetic patients flicker had no effect on arterial vessel diameters: +0.1% (3.1%) (16 seconds, p = 0.9), +1.1% (2.7%) (32 seconds, p = 0.07), +1.0% (2.8%) (64 seconds, p = 0.1). In retinal veins, the response to flicker light was not significantly different in both groups. Retinal venous vessel diameters increased by +0.7% (1.6%) (16 seconds, p<0.05), +1.9% (2.3%) (32 seconds, p<0.001) and 1.7% (1.8%) (64 seconds, p<0.001) in controls during flicker stimulation. Again, no increase was observed in the patients group: +0.6% (2.4%), +0.5% (1.5%), and +1.2% (3.1%) (16, 32, and 64 seconds, respectively). CONCLUSION: Flicker responses of retinal arteries and veins are abnormally reduced in patients with IDDM with no or mild non-proliferative retinopathy. Whether this diminished response can be attributed to altered retinal vascular reactivity or to decreased neural activity has yet to be clarified.

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.

Response of retinal blood flow to CO2-breathing in humans.

PURPOSE: To investigate the effect of systemic hypercapnia on retinal hemodynamics in humans. METHODS: We studied the effect of breathing a mixture of normal air with 5% CO2 for 13 minutes in ten healthy young male volunteers, using the Zeiss retinal vessel analyzer for continuous measurement of retinal vessel diameter and the blue-field entoptic technique to quantify retinal white blood cell flux. In eight other subjects the effect of hypercapnia was measured with the Zeiss retinal vessel analyzer and by laser Doppler velocimetry to establish retinal blood flow velocity. RESULTS: Retinal arterial and venous vessel diameters increased by a maximum of 4.2% and 3.2%, respectively. Peak effect was observed after 3 minutes of breathing the mixture of normal air with 5% CO2. During hypercapnia red blood cell velocity increased 11.7% and, accordingly, retinal blood flow increased 19.1%. White blood cell density and velocity rose significantly during hypercapnia, resulting in an increase in white blood cell flux (19.2%). CONCLUSIONS: Our data indicate that CO2 induces vasodilation in retinal arteries and retinal veins. Retinal blood flow and perimacular white blood cell flux increased to the same extent in subjects breathing a mixture of normal air with 5% CO2.