The effect of topical beta-adrenoceptor blocking agents on pulsatile ocular blood flow

Peripapillary microvasculature in the retinal nerve fiber layer in glaucoma by optical coherence tomography angiography: focal structural and functional correlations and diagnostic performance

Purpose

To quantify peripapillary microvasculature within the retinal nerve fiber layer (RNFL) in primary open-angle glaucoma (POAG) and normal eyes, determine association of perfusion parameters with structural and functional measures, and report diagnostic accuracy of perfusion parameters.

Patients and methods

POAG and normal patients underwent 6×6 mm² optic nerve head scans (Angioplex optical coherence tomography angiography [OCTA]; Cirrus HD-OCT 5000) and Humphrey Field Analyzer II-i 24-2 visual field (VF) testing. Prototype software performed semiautomatic segmentation to create RNFL en face images and quantified vessel area density (VAD), vessel skeleton density (VSD), and vessel complexity index (VCI) in the optic nerve head globally and focally. Generalized estimating equations models assessed association of OCTA parameters with VF mean deviation (MD) and RNFL thickness.

Results

Thirty-eight POAG and 17 normal eyes were studied. Global VAD, VSD, and VCI were reduced in mild POAG vs normal (P<0.02) and moderate-severe vs mild POAG (P<0.04). Stepwise focal reductions across disease stage were demonstrated for OCTA parameters in the inferior hemisphere (P<0.05); reduction in OCTA parameters in mild POAG vs normal was demonstrated in inferior and superior quadrants (P<0.05). Reduced global VF MD was associated with reduced VAD, VSD, and VCI (P=0.0007, 0.0013, <0.0001; R²=0.449, 0.312, 0.399, respectively), and global RNFL thickness was associated with VAD, VSD, and VCI (P<0.0001; R²=0.499, 0.524, 0.542), superior and inferior hemifield MD were associated with corresponding VAD, VSD, and VCI (P≤0.001; R² from 0.208 to 0.513). RNFL thickness in all quadrants was associated with corresponding OCTA parameters (P<0.05; R² from 0.213 to 0.394), except temporal VAD and VCI. Area under curves for VAD, VSD, and VCI demonstrated good diagnostic ability (0.868, 0.855, 0.868; P<0.0001).

Conclusion

Glaucomatous eyes showed stepwise reductions in RNFL microcirculation across severity; focal reductions in the inferior hemisphere and inferior and superior quadrants were most significant. OCTA parameters had stronger associations with structural rather than functional measures of glaucoma.

Opposing effects of atropine and timolol on the color and luminance emmetropization mechanisms in chicks

This study analyzed the luminance and color emmetropization response in chicks treated with the nonselective parasympathetic antagonist atropine and the sympathetic β-receptor blocker timolol. Chicks were binocularly exposed (8h/day) for 4days to one of three illumination conditions: 2Hz sinusoidal luminance flicker, 2Hz sinusoidal blue/yellow color flicker, or steady light (mean 680lux). Atropine experiments involved monocular daily injections of either 20μl of atropine (18nmol) or 20μl of phosphate-buffered saline. Timolol experiments involved monocular daily applications of 2 drops of 0.5% timolol or 2 drops of distilled H2O. Changes in the experimental eye were compared with those in the fellow eye after correction for the effects of saline/water treatments. Atropine caused a reduction in axial length with both luminance flicker (-0.078±0.021mm) and color flicker (-0.054±0.017mm), and a reduction in vitreous chamber depth with luminance flicker (-0.095±0.023mm), evoking a hyperopic shift in refraction (3.40±1.77D). Timolol produced an increase in axial length with luminance flicker (0.045±0.030mm) and a myopic shift in refraction (-4.07±0.92D), while color flicker caused a significant decrease in axial length (-0.046±0.017mm) that was associated with choroidal thinning (-0.046±0.015mm). The opposing effects on growth and refraction seen with atropine and timolol suggest a balancing mechanism between the parasympathetic and β-receptor mediated sympathetic system through stimulation of the retina with luminance and color contrast.

Effects of antiglaucoma drugs on blood flow of optic nerve heads and related structures

An association between glaucoma development or progression and compromised ocular blood flow has been postulated as a result of population-based studies and prospective cohort studies. Blood flow in the optic nerve head (ONH) is of primary importance in the pathogenesis of glaucoma. The potential to modify the blood flow in the ONH and its related structures has been reported in various agents, including topical antiglaucoma drugs and systemic drugs such as calcium channel antagonists, which are reviewed in this manuscript. Clinical implications of the improvement in ocular blood flow on the treatment of glaucomatous optic neuropathy require further investigation.

Vasodilatory mechanism of levobunolol on vascular smooth muscle cells

Topical application of levobunolol hydrochloride, a beta-adrenergic antagonist used for treatment of glaucoma, is reported to increase ocular blood flow. We studied the mechanism of levobunolol-induced vasodilation in arterial smooth muscle. The effects of levobunolol or other agents on isolated, pre-contracted rabbit ciliary artery were investigated using an isometric tension recording method. The effects of the same agents on intracellular free calcium ([Ca(2+)](i)) in cultured human aortic smooth muscle cells were also studied by fluorophotometry. Levobunolol relaxed ciliary artery rings that were pre-contracted with either high-K solution, 1microM histamine, 10microM phenylephrine, or 100nM endothelin-1. The relaxation induced by levobunolol was concentration-dependent over the range of 10microM to 0.3mM. Inhibition of endothelial nitric oxide synthase or denudation of the endothelium did not affect this relaxation. Histamine-induced contractions were inhibited by the histamine H(1) antagonist pyrilamine. Radioligand binding experiments showed that levobunolol did not bind to the H(1) receptor. Further, histamine induced transient contraction in Ca(2+)-free solution, and levobunolol inhibited this contraction by 74.6+/-11.0%. In cultured smooth muscle cells in the presence of extracellular Ca(2+), levobunolol significantly inhibited the histamine-induced elevation of [Ca(2+)](i). However, it did not inhibit the increase of [Ca(2+)](i) in histamine-stimulated cells incubated in Ca(2+)-free solution. These results indicate that levobunolol may relax rabbit ciliary artery by two different mechanisms. First, the relaxation could be due to the blockade of Ca(2+) entry through non-voltage-dependent Ca(2+) channels. Second, levobunolol may change the Ca(2+) sensitivity of vascular smooth muscle cells.

High-resolution functional vascular assessment with ultrasound

In order to improve the resolution of contrast-assisted imaging systems, we have created a high-frequency destruction/contrast replenishment imaging system with a spatial resolution of 160 microm x 160 microm. The system utilizes a 1-MHz cylindrically focused transducer for destruction and a 25-MHz spherically focused transducer for pulse/echo imaging. Speckle tracking and a clutter filter are applied across frames to remove the challenging physiologic motion artifacts that are obtained when imaging with a mechanically scanned transducer. Using a new estimation technique, flow constants proportional to absolute flow rate were estimated from B-mode time-intensity curves (TICs). The in vitro results indicate a correlation between the actual flow velocity and the estimated rate constant. In vivo images are presented showing blood perfusion in the ciliary processes and iris of the rabbit eye. The regions of interest (ROIs) from the ciliary processes yielded slower perfusion compared with the iris, as expected from vascular casts of the microcirculation in this region. Potential applications of this system include high-resolution perfusion assessment in small animals.

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.

Pulsatile ocular blood flow in primary open-angle glaucoma and ocular hypertension

PURPOSE

To compare pulsatile ocular blood flow measurements in untreated ocular hypertensive (OHT) subjects and primary open-angle glaucoma (POAG) patients.

DESIGN

A prospective observational study in an institutional setting.

METHODS

A total of 97 subjects were recruited to the study (50 ocular hypertensives, 24 glaucoma patients, and 23 normal subjects). "High-risk" OHT had intraocular pressure (IOP) > 25 mm Hg; "low-risk" OHT had IOP <or= 25 mm Hg. Pulsatile ocular blood flow (POBF) measurements were made with a pneumotonometer in sitting, standing, and supine positions. Intraocular pressure was measured with Goldmann tonometry. Twenty-six patients were started on topical treatment to reduce intraocular pressure, and the measurements were repeated at a review visit.

RESULTS

Untreated POAG patients and high-risk OHT had reduced POBF (P <.001) and pulse volume (P <.001) compared with both normals and low-risk OHT. Women had higher POBF than men (P =.009, two-way analysis of variance). Subjects with pharmacologically lowered IOP had a significant increase in mean POBF (+80.9 microl/min, P =.02) and a significant reduction in mean arterial blood pressure (-11.0 mm Hg, P =.003). Postural reduction in POBF (from sitting to supine) increased and became statistically significant in POAG and OHT subjects on treatment (P <.0001).

CONCLUSION

High-risk ocular hypertensives have reduced POBF when compared with low-risk ocular hypertensives and normals and do not differ significantly from POAG patients. Our findings support the clinical impression that ocular hypertensive subjects with IOP of over 25 mm Hg should be monitored closely and may benefit from prophylactic treatment to lower intraocular pressure.

Evaluation of retinal haemodynamics and retinal function after application of dorzolamide, timolol and latanoprost in newly diagnosed open-angle glaucoma patients

PURPOSE

The purpose of this prospective, randomized, cross-over study was to investigate and compare the microcirculatory effects of timolol, dorzolamide and latanoprost in newly diagnosed primary open-angle glaucoma (POAG) patients. Haemodynamics were assessed using fluorescein angiography by means of a scanning laser ophthalmoscope (SLO). Visual function and visual field indices were evaluated during all drug treatment phases.

METHODS

Fourteen patients with newly diagnosed POAG (age 55 +/- 7 years; 10 male, four female) were recruited for the study. At baseline examination, blood pressure, heart rate, intraocular pressure (IOP), SLO angiograms, and contrast sensitivity (CS) were analysed. Patients then randomly received timolol, dorzolamide or latanoprost treatment for 4 weeks. Patients then returned and all procedures were repeated and assessed. Arteriovenous passage times (AVPs), peripapillary arterial and venous diameters were assessed from SLO angiograms, using digital image processing. Calculated ocular perfusion pressure was determined for each treatment phase.

RESULTS

Intraocular pressure was significantly lowered by each drug compared to baseline (p < 0.0001). Arteriovenous passage times were significantly shortened after dorzolamide application compared to baseline (p = 0.009), whereas neither timolol nor latanoprost treatment resulted in significant AVP changes. Peripapillary arterial and venous diameters, systolic and diastolic blood pressure, heart rate and ocular perfusion pressures were not significantly altered during any treatment phase. Contrast sensitivity testing at 6 cycles/degree (c.p.d.) revealed a significant rise after dorzolamide compared to timolol (p = 0.007).

CONCLUSION

Our results suggest that dorzolamide treatment significantly shortened AVP times in newly diagnosed open-angle glaucoma patients, whereas timolol and latanoprost had no significant effect. Given that prolonged AVP times have been associated with disease progression in glaucoma; dorzolamide treatment may benefit optic nervehead preservation by increasing ocular perfusion.

Evaluating pulsatile ocular blood flow analysis in normal and treated glaucomatous eyes

PURPOSE

To evaluate pulsatile ocular blood flow (POBF) analysis in normal subjects and glaucoma patients by comparison of POBF measurements with functional (as determined by visual field [VF]) and structural (as determined by optical coherence tomography [OCT]) measures.

DESIGN

Prospective, cross-sectional study.

METHODS

Forty-one eyes of 24 consecutive glaucoma patients and 20 eyes of 10 healthy subjects were studied; POBF analysis was performed on all subjects at the same visit as VF testing and OCT retinal nerve fiber layer (NFL) thickness measurement. The mean results of normal and glaucomatous eyes were compared for each method. Correlation between measurements obtained with each modality and the discriminating power using receiver operator characteristic curves was tested.

RESULTS

The mean POBF (standard deviation [SD]) in the normal group was 1,010.4 (292.8) microl/min and 989.3 (305.5) microl/min in the glaucoma group (P =.90). Significant differences between groups were found for VF mean deviation and pattern standard deviation (P =.02, P =.004, respectively) and OCT mean NFL thickness (P <.0001). No correlation was found between POBF parameters and intraocular pressure, VF, or OCT variables except for intraocular pressure in glaucoma group (r = -.43, P =.003). The area under the receiver operator characteristic curves was higher for VF indexes and OCT mean NFL thickness than POBF parameters for distinguishing between normal and glaucomatous eyes.

CONCLUSIONS

The wide range of normal values and the low discriminating power of POBF between normal and glaucomatous eyes limits the clinical use of the device for glaucoma patients.

The short-term effect of latanoprost on intraocular pressure and pulsatile ocular blood flow

PURPOSE

There is evidence that ocular blood flow plays a critical role in the clinical course of glaucoma. Any reduction in ocular blood flow due to topical antiglaucoma treatment should therefore be avoided. This study aimed to evaluate the short-term effect of local latanoprost application on ocular hemodynamics.

METHODS

Intraocular pressure (IOP), ocular pulse amplitude (OPA), ocular pulse volume (OPV), systemic blood pressure, heart rate and the pulsatile component of ocular blood flow (POBF) were recorded using a pneumotonometer linked to the Langham Ocular Blood Flow System in 24 patients in a prospective, open-label study before and after 1 week of topical latanoprost application in both eyes. Twenty of the subjects had primary open-angle glaucoma and four had ocular hypertension.

RESULTS

After 1 week of latanoprost treatment, IOP decreased significantly 6.2 +/- 2.9 mmHg in OD (P < 0.001) and 6.2 +/- 3.2 mmHg in OS (P < 0.001). Pulsatile OBF increased significantly by 201.2 +/- 167.4 microL/min in OD (P < 0.001) and 203.8 +/- 187.3 microL/min in OS (P < 0.001). Ocular pulse amplitude and OPV showed statistically significant increases (P < 0.05 and P < 0.001 respectively). Blood pressure and heart rate did not change significantly.

CONCLUSION

Our results indicate that 1 week after latanoprost application, POBF, OPA and OPV were significantly increased in the eyes treated. More information on the perfusion of the optic nerve head is needed before the relevance of these findings to optic nerve head blood flow can be interpreted correctly.

The effects of beta-blockers on ocular blood flow in patients with primary open angle glaucoma: a color Doppler imaging study

PURPOSE

To evaluate the effects of four commonly used beta-blockers on ocular blood flow in patients with primary open angle glaucoma (POAG).

METHODS

Eighty eyes of 40 subjects with POAG were included in the study. Subjects were randomly divided into four groups given timolol maleate 0.50%, betaxolol HCl 0.50%, carteolol 1% or levobunolol 0.50% drops, applied twice daily (one drug to each group). Before beginning the treatment and at the end of the first month ocular blood flow velocity was measured using the color Doppler imaging (CDI) method. In the ophthalmic artery (OA), central retinal artery (CRA) and temporal posterior ciliary artery (TPCA) the peak systolic (PS) and end-diastolic (ED) blood flow velocities were measured and resistive index (RI) values were calculated. The results within each group were analysed using the matched paired student's t-test. The data between groups was compared with one-way analysis of variance (ANOVA) and Tukey-Kramer multiple comparison tests.

RESULTS

The timolol group showed a significant increase in RI values of TPCA. In the betaxolol group RI decreased significantly in CRA and TPCA, whereas in the carteolol group there was a significant decrease only in CRA. In the levobunolol group there was no change in any artery. CONCLUSIONS. Betaxolol seemed to have a greater vasodilator effect than carteolol, and levobunolol had no effect on the retinal and choroidal vasculature. Timolol may have some vasoconstrictive effect in the ciliary vasculature.

The effect of once-daily latanoprost on intraocular pressure and pulsatile ocular blood flow in normal tension glaucoma

PURPOSE

To determine the effect of once-daily 0.005% latanoprost on intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) in patients with normal tension glaucoma (NTG).

METHODS

The diurnal IOP and sitting POBF were determined for 32 eyes of 19 NTG patients after a washout period. The subjects were treated with 0.005% latanoprost for 3-4 weeks and the measurements repeated. Statistical analysis was performed using the Wilcoxon signed rank test.

RESULTS

Median IOP before and after treatment were 19 and 15 mmHg respectively (p < 0.001). The IOP reduction correlated with the initial IOP before treatment (p < 0.01) and was accompanied by an increase in median POBF from 656 to 796 microliters/min (p < 0.001).

CONCLUSIONS

Once-daily treatment with 0.005% latanoprost provides a significant and stable IOP reduction in the majority of NTG patients after short-term treatment. This is accompanied by a significant increase in POBF.

Latanoprost 0.005% in POAG: effects on IOP and ocular blood flow

The scope of this work was to evaluate the effect on ocular pressure and on ocular blood flow of latanoprost 0.005% eyedrops. Included in the study were 12 patients (24 eyes) with POAG, aged between 37 and 48 years, non-smokers, refractions between +/- 3D. Haemorrheological parameters within normal, not in ocular or systemic vasoactive therapy. Each patient had one eye treated with latanoprost 0.005% and the other with timolol 0.05%. The choroidal perfusion was measured by Langham's POBF system during the first day of therapy and then after 7, 15, 30, 60, 90 and 180 days. The maximum pressure decrease after the first administration of latanoprost was at the twelfth hour; after 6 months of therapy, mean IOP reduction was 32.6%. POBF values increased up to 55.8% in the first day and then settled at 22.6% at the end of the study. Timolol showed a similar pressure progress, but its haematic perfusion values were distinctly lower. In conclusion, latanoprost is efficacious in POAG therapy since it unites a positive optic nerve head perfusion effect with hypotensive efficacy.

A comparison of ocular blood flow in untreated primary open-angle glaucoma and ocular hypertension

PURPOSE

To compare ocular blood flow in untreated primary open-angle glaucoma and ocular hypertension using scanning laser Doppler flowmetry and pulsatile ocular blood flow.

METHOD

Fourteen ocular hypertensive subjects and 10 patients with primary open-angle glaucoma were matched for intraocular pressure, mean arterial blood pressure, and age. They had scanning laser Doppler flowmetry images taken centered on the optic disk. Pulsatile ocular blood flow readings were performed in sitting, standing, and supine positions. No subjects were receiving topical antiglaucoma treatment, systemic beta-blockers, calcium antagonists, or nitrates at the time of measurement.

RESULTS

Laser Doppler flowmetry results showed a significant reduction in blood velocity, volume, and flow at the lamina cribrosa and the temporal neuroretinal rim in glaucoma compared to ocular hypertension (P < .05). No difference was found between the groups at the nasal neuroretinal rim or the nasal juxtapapillary retina. There was a significant increase in minimum velocity (P = .03) at the temporal juxtapapillary retina in glaucoma compared to ocular hypertension. The ocular pulse amplitude, pulse volume, and pulsatile ocular blood flow were significantly lower (P < .05) in the glaucoma group compared to ocular hypertension in sitting and standing positions.

CONCLUSION

Having controlled for factors known to affect perfusion pressure, we found evidence of reduced ocular blood flow in primary open-angle glaucoma compared with ocular hypertension. Our findings indicate a reduction in choroidal and short posterior ciliary artery circulation in primary open-angle glaucoma. Whether these changes in blood flow are a cause or a consequence of glaucomatous optic atrophy is still unknown.