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Niacin is a B vitamin well-known for causing vasodilation and flushing. The purpose of this study was to investigate its effect on the retinal vasculature of patients with age-related macular degeneration (AMD).Twelve patients with AMD were enrolled in a double-blind, randomized, placebo-controlled, crossover trial. Fundus photographs of the posterior pole were taken at baseline, 30 min, and 90 min after a single dose of niacin or placebo. The protocol was repeated after a washout period using the alternate study drug. The diameters of two veins and one artery on each image were measured.An analysis of variance for repeated measures comparing the effects of niacin with those of placebo demonstrated a significant increase in the inferior temporal retinal artery diameter (p = 0.01), with a 5.3 +/- 7.7% increase at 30 min (p = 0.05) and 5.8 +/- 5.0% increase at 90 min (p = 0.003). No significant changes were observed in the temporal retinal veins.Our results suggest that niacin produces vasodilatation of retinal arterioles. Further studies are needed to ascertain whether niacin treatment may be beneficial in retinal ischemic diseases.

To evaluate the relationship between extent of glaucoma damage and optic nerve blood flow, we investigated optic nerve head bloodflow in patients with asymmetric glaucoma damage between their two eyes and also in glaucomatous eyes with asymmetric damage inferiorly versus superiorly.From our institutional practice, 16 subjects with asymmetric glaucoma damage between their two eyes and 25 eyes of 20 patients with asymmetric damage superiorly versus inferiorly were included in the study. Determinations of relative optic nerve head blood flow, velocity, and volume were obtained with laser Doppler flowmetry in the superotemporal and inferotemporal neuroretinalrim and in the cup. Means of flow (Flow(3)), velocity (Vel(3)), and volume (Vol(3))were calculated from these three measurement sites, and eyes or hemidisks with greater glaucomatous damage were compared to eyes or hemidisks with less damage.For subjects with asymmetric glaucoma damage between eyes, Flow(3) and Vel(3) were significantly lower in the eyes with worse glaucoma damage(mean difference = 2.09, p = 0.005, and mean difference = 0.05, p = 0.002,respectively). When comparing optic disks displaying within-eye asymmetry, the hemidisk with greater damage showed significantly lower blood velocity than the hemidisk with less damage (mean difference = 0.05, p = 0.013); however,no difference in blood flow or volume was detected.This study provides additional evidence that impaired optic nerve circulation is associated with the extent of glaucomatous pathology.

The purpose of this randomized double-masked cross-over study was to determine the effects of 20 mg of 5-isosorbide mononitrate (ISMO) on the retinal hemodynamics of young healthy subjects.Monochromatic fundus photography and bidirectional laser Doppler velocimetry (BLDV) were used to determine vascular diameters (D), and blood velocity (V(max)) and flow (Q) in retinal veins, respectively. The diameter of the vein [D((vein))] at the same location where BLDV measurements were made, and the diameter of a neighboring artery [D((art) )], were determined from the fundus photographs. Measurements were carried out one and three hours after ISMO dosing, on twelve and six subjects, respectively. Mean blood pressure (BP(m)) and intraocular pressure (IOP) were also monitored, and ocular perfusion pressure (PP) was calculated. Results are expressed in percentage changes (+/- the standard error of the mean).On average, we observed a moderate increase of Q one hour after ISMO dosing (+8.2 +/- 5.4%), but not after placebo (+2.7 +/- 1.6%). This effect of ISMO, which displayed remarkable interindividual variability (95% confidence interval: -3.9%, +20.4%), did not attain statistical significance. D((vein)) and D((art)) were not appreciably affected. No effect was observed three hours after either ISMO or placebo dosing. PP was reduced one hour following ISMO administration, mainly as a function of reduced BP(m), although this variation was not statistically significant. IOP did not change appreciably throughout the duration of the study.Our findings suggest that, in contrast to the optic nerve head, in which we previously documented consistent and significant increases in blood flow following ISMO administration at both one and three hours, retinal hemodynamics are not equally responsive to a single dose of ISMO at these time points. Marked interindividual variability to the effects of this long-acting nitric oxide donor was documented one hour after administration, but not at three hours. This study further suggests that distinct vascular tissues of the ocular microcirculation respond differently to identical pharmacological challenges.

To determine the effect of one week of topical treatment with levobunolol HCl 0.5% on the retinal circulation of normal subjects.Fifteen healthy volunteers with no history of ocular disease were included in this study. In a double-masked, randomized, cross-over design, one eye of each subject was treated, for one week, with one drop of either levobunolol or placebo, administered twice daily. Following a washout period of at least three weeks, the same eye received the alternate treatment for one week. Before the beginning of therapy and then two hours after the last drop, vessel diameter (D), maximum erythrocyte velocity (Vmax), and volumetric blood flow rate (Q) were determined in one major retinal vein of the treated eye, using bidirectional laser Doppler velocimetry and monochromatic fundus photography. Statistical analysis was performed using two-tailed, paired Student's t-test, linear regression, and correlation analysis.The average percentage change from baseline in intraocular pressure was statistically significant following levobunolol (-15% +/- 13% (+/-1 SD), P.001), but not following placebo (-3% +/- 11%, P.05). No significant changes in average D, Vmax, or Q were observed after levobunolol treatment (-1% +/- 4%, 5% +/- 11%, 4% +/- 15%, respectively) or placebo treatment (-1% +/- 4%, -2% +/- 9%, -5% +/- 10%, respectively). The average difference between the changes in Q from baseline after levobunolol and placebo treatments (9% +/- 17%) achieved a significance level of P = 0.06. Furthermore, following levobunolol treatment, Q was 7% +/- 14% higher than following placebo treatment (P = 0.05).A comparison of the effects of placebo and levobunolol treatments suggests that levobunolol has a variable effect on the retinal circulation with a tendency to show an overall slight increase in flow.

The noninvasive Laser Doppler velocimetry technique was applied in normal volunteers and in patients with background diabetic retinopathy to determine retinal blood flow during pure oxygen breathing at atmospheric pressure. In normal subjects, five minutes of oxygen breathing produced a 63 +/- 6% decrease in retinal blood flow. In the diabetic patients blood flow decreased by only 36 +/- 15%. A significant correlation between the decrease in blood flow and that of the diameter of the veins was found in the diabetic patients. This was not the case for the normal subjects.