Effect of oral felodipine on ocular circulation

Remodeling of retinal small arteries in hypertension

Vascular dysfunction due to elevated blood pressure constitutes an early step in the pathogenesis of atherosclerotic disease. A better understanding of the pathophysiology and of clinical correlates of vascular remodeling in retinal arteries and arterioles offers the opportunity for a better risk stratification and treatment. In vivo vascular changes can be best detected by direct imaging techniques. In this review, we summarize the main findings of several recent studies analyzing retinal-arteriolar parameters, such as outer diameter (OD) and lumen diameter (LD), retinal capillary flow (RCF), wall-to-lumen-ratio, and wall cross-sectional area by using scanning laser Doppler flowmetry (SLDF). Blood pressure emerged as an independent determinant of the wall-to-lumen ratio (WLR) of retinal arterioles. Retinal arterioles and small arteries of hypertensive subjects showed eutrophic inward remodeling as indicated by increased WLR, decreased LD and almost unchanged wall cross-sectional area compared to normotensive subjects. These findings are in accordance with those observed in small-resistance vessels analyzed ex vivo. In hypertensive patients, an increased retinal vascular resistance has been documented and basal nitric oxide activity emerged as an independent determinant of early arteriolar remodeling. Thus, SLDF emerged as a noninvasive research tool to assess early vascular changes in the retinal circulation.

Effects of bisoprolol and cilazapril on the central retinal artery blood flow in patients with essential hypertension--preliminary results

BACKGROUND

A growing body of evidence suggests that effective blood pressure reduction may inhibit the progression of microvascular damage in patients with essential arterial hypertension. However, the potential influence of anti-hypertensive drugs on ocular circulation has not been studied sufficiently.

PURPOSE

The aim of our study was to evaluate the effects of anti-hypertensive therapy on blood flow in the central retinal artery in patients with systemic arterial hypertension.

MATERIAL AND METHODS

Twenty patients with essential arterial hypertension, aged 32-46 years, were examined with Doppler ultrasonography (10 MHz ultrasound probe). Blood flow velocities, pulsatility, and vascular resistance were determined before and 3 hours after systemic application of either bisoprolol 5 mg or cilazapril 2.5 mg.

RESULTS

Administered bisoprolol significantly decreased maximum (9.8 ± 0.5 cm/s versus 8.5 ± 0.6 cm/s; P < 0.05) and minimum (2.75 ± 0.19 cm/s versus 1.75 ± 0.27 cm/s; P < 0.02) velocity, increased the Pourcellot's index (0.71 to 0.79; P < 0.05) in central retinal artery. There were no statistically significant changes in central retinal artery blood flow after administration of cilazapril.

CONCLUSION

Systemic application of beta-blockers may unfavourably disturb the ocular blood flow.

Influence of macular microcirculation and retinal thickness on visual acuity in patients with branch retinal vein occlusion and macular edema

PURPOSE

To investigate perifoveal capillary blood flow velocity and retinal thickness at the central fovea in patients with branch retinal vein occlusion (BRVO) and macular edema and to assess their relation with visual acuity and visual prognosis.

METHODS

Eighteen patients with BRVO and 16 healthy volunteers were compared. Perifoveal capillary blood flow velocity was measured on fluorescein angiograms with a scanning laser ophthalmoscope by the tracing method. Retinal thickness was measured at the central fovea by optical coherence tomography. Best-corrected visual acuity (BCVA) was determined.

RESULTS

BCVA differed significantly between patients and controls (P < 0.0001). Among patients, BCVA was negatively correlated with perifoveal capillary blood flow velocity by univariate analysis (r = -0.7916, P < 0.0001), and positively correlated with retinal thickness at the central fovea (r = 0.8970, P < 0.0001). Multivariate analysis showed that retinal thickness at the central fovea was the only independent determinant of BCVA (P < 0.0001).

CONCLUSIONS

In patients with BRVO, BCVA was more strongly influenced by retinal thickness at the central fovea than by perifoveal capillary blood flow velocity.

Macular microcirculation in hypertensive patients with and without branch retinal vein occlusion

PURPOSE

Our purpose was to determine whether a reduction in blood flow velocity (BFV) in the perifoveal capillaries is involved in the pathogenesis of branch retinal vein occlusion (BRVO) in patients with hypertension.

METHODS

Subjects included hypertensive patients with (n = 12) and without (n = 16) BRVO and healthy volunteers (n = 16). Perifoveal BFV was measured by the tracing method using fluorescein angiography and a scanning laser ophthalmoscope. Logistic regression analysis was performed to assess factors that influenced the presence or absence of BRVO.

RESULTS

Mean BFV showed a significant decrease across the three groups (healthy controls: 1.49 +/- 0.11 mm/second; hypertensive patients without BRVO: 1.36 +/- 0.12 mm/second; hypertensive patients with BRVO: 1.16 +/- 0.24 mm/second; p(trend) < 0.001). Multivariate logistic regression analysis showed that BFV was a significant risk factor for the presence of BRVO.

CONCLUSIONS

Perifoveal capillary BFV is reduced in hypertensive patients with and without BRVO. It is possible that a decrease in BFV may be involved in the occurrence of BRVO. Measurement of perifoveal capillary BFV may be useful for investigating the pathogenesis and progression of BRVO.

Effect of nimodipine on ocular blood flow and colour contrast sensitivity in patients with normal tension glaucoma

AIM

To investigate the effects of oral nimodipine on ocular haemodynamic parameters and colour contrast sensitivity in patients with normal tension glaucoma (NTG).

DESIGN

The study was performed in a randomised, placebo controlled, double masked, crossover design.

PARTICIPANTS

Nimodipine (60 mg) or placebo was administered to 14 consecutive NTG patients.

METHODS

The effects or oral nimodipine or placebo on ocular and systemic haemodynamic parameters and colour contrast sensitivity along the tritan axis were studied two hours after administration. Optic nerve head blood flow (ONHBF) and choroidal blood flow (CHBF) were assessed with laser Doppler flowmetry. Ocular fundus pulsation amplitude (FPA) was measured with laser interferometry. Colour contrast sensitivity (CCS) was determined along the tritan colour axis.

MAIN OUTCOME MEASURES

ONHBF, CHBF, FPA, intraocular pressure and CCS were assessed in patients with NTG.

RESULTS

Mean ocular FPA increased by 14% (SD 14%) (p = 0.0008), ONHBF by 18% (SD 16%) (p = 0.0031), and CHBF by 12% (SD 14%) (p<0.001) after administration of nimodipine. Nimodipine also decreased the threshold of colour contrast sensitivity along the tritan colour axis (-14% (SD 12%); p = 0.048). However, individual changes in FPA, ONHBF, or CHBF were not correlated with changes in threshold of CCS along the tritan colour axis.

CONCLUSIONS

The results indicate that nimodipine increases ONH and choroidal blood flow in NTG patients and improves CCS. The latter effect does not, however, seem to be a direct consequence of the blood flow improvement.

Effect of hypertension on foveolar choroidal haemodynamics

AIMS

To assess the effect of systemic hypertension on the choroidal circulation in subjects with a normal eye examination.

METHODS

Laser Doppler flowmetry was used to determine relative choroidal blood velocity (Ch(vel)), volume (Ch(vol)), and flow (Ch(flow)) in the centre of the fovea. Measurements were obtained in 15 eyes of 15 subjects with systemic hypertension. The mean average duration of hypertension was 11 (SD 6) years. Findings obtained in these patients were compared with those of 15 eyes of 15 age matched healthy controls. All subjects had normal eye examinations.

RESULTS

No significant differences in Ch(vel), Ch(vol), and Ch(flow), were found between the subjects with and without systemic hypertension despite a 17% higher perfusion pressure (PP) in patients with hypertension. No significant correlation was found between mean arterial pressure or PP and the choroidal circulatory parameters. It was estimated that there is a 90% power to detect a 35% difference in Ch(flow) between the two groups.

CONCLUSION

Systemic hypertension does not seem to have a large effect on the choroidal circulation in hypertensive patients that are controlled by antihypertensive therapy. Further studies are needed to elucidate whether systemic hypertension has an effect on the choroidal circulation in patients with ocular diseases.

Adenylyl and guanylyl cyclase activity in the choroid

The choroid, a low-resistance vascular structure provides nourishment to and removal of potential toxic waste products from the adjacent non-vascularized outer layers of the retina, macula, and optic disc region and may be involved in the pathology of normal tension glaucoma. This study is aimed at delineating the biochemical pharmacology of vascular tone control in this tissue. By using a procedure to harvest fresh choroidal tissue, we studied some basic characteristics of the adenylyl (AC) and guanylyl cyclase (GC) enzyme systems in this tissue using the 3H-cAMP/32P-ATP tracer method. Compared to respective baseline measurements (100+/-SEM%), AC activity was stimulated (p < 0.05) by forskolin (FSK, 477+/-59%), fluoroaluminate (AlF(4), 360+/-10.3%), isoproterenol (ISO, 129+/-5.5%), vasoactive intestinal peptide (VIP, 132+/-6.1%), calmodulin (CAM)+Mn2+ (196+/-69%), and dose-dependently by prostaglandin (PG) E2 (up to 162+/-3.6%). The antagonist drug calmidazolium inhibited the CAM-dependent increase but also blocked basal activity (47+/-2.0%) without affecting the FSK response. Other CAM blockers (TFP, W5) produced similar results but were not completely selective for CAM-activated cyclase. GDPbetaS, a blocker of G-protein coupling to AC did not affect AC responses to FSK, ISO, and AlF4, but decreased the response to PGE2. N-ethyl-carboxamido adenosine (NECA), which activates adenosine A2 receptors, did not synergize with FSK or add to ISO responses and did not activate AC by itself. In the GC system activity was stimulated (p< 0.05) by CAM+Mn2+ (239+/-27%), by atrial natriuretic peptide (ANP, up to 143+/-1.4%) and sodium nitroprusside (SNP, up to 179+/-1.6%). These results show that choroidal tissue has significant activities of the adenylyl and guanylyl cyclase second messenger systems potentially responsive to hormones/neurotransmitters that may control the degree of relaxation in this vascular tissue.

The effects of antiglaucoma and systemic medications on ocular blood flow

Based on the body of evidence implicating ocular blood flow disturbances in the pathogenesis of glaucoma, there is great interest in the investigation of the effects of antiglaucoma drugs and systemic medications on the various ocular vascular beds. The primary aim of this article was to review the current data available on the effects of antiglaucoma drugs and systemic medications on ocular blood flow. We performed a literature search in November 2002, which consisted of a textword search in MEDLINE for the years 1968-2002. The results of this review suggest that there is a severe lack of well-designed long-term studies investigating the effects of antiglaucoma and systemic medications on ocular blood flow in glaucomatous patients. However, among the 136 articles dealing with the effect of antiglaucoma drugs on ocular blood flow, only 36 (26.5%) investigated the effects of medications on glaucoma patients. Among these 36 articles, only 3 (8.3%) were long-term studies, and only 16 (44.4%) were double-masked, randomized, prospective trials. Among the 33 articles describing the effects of systemic medications on ocular blood flow, only 11 (33.3%) investigated glaucoma patients, of which only one (9.1%) was a double-masked, randomized, prospective trial. Based on this preliminary data, we would intimate that few antiglaucoma medications have the potential to directly improve ocular blood flow. Unoprostone appears to have a reproducible antiendothelin-1 effect, betaxolol may exert a calcium-channel blocker action, apraclonidine consistently leads to anterior segment vasoconstriction, and carbonic anhydrase inhibitors seem to accelerate the retinal circulation. Longitudinal, prospective, randomized trials are needed to investigate the effects of vasoactive substances with no hypotensive effect on the progression of glaucoma.