The direct vascular relaxing action of betaxolol, carteolol and timolol in porcine long posterior ciliary artery

The Effect of Betaxolol on Ocular Blood Flow and Visual Fields in Patients with Normotension Glaucoma

Purpose

This study investigated the effect of ophthalmic betaxolol, a ß, selective adrenoceptor antagonist, on ocular blood flow and visual function in patients with normotension glaucoma (NTG).

Methods

Thirty-six eyes of eighteen patients with NTG, but otherwise free of systemic disease, were included. Blood fibrinogen, sedimentation rates, Goldmann intraocular pressure, Humphrey automated perimetry, and color Doppler imaging were done at baseline and after one year of twice-daily bilateral topical ocular dosing with 0.5% betaxolol HCl.

Results

After treatment, the resistivity index of the ophthalmic artery was significantly reduced, and visual fields were significantly improved. The resistivity indexes of the central retinal artery and posterior ciliary artery were also reduced but did not achieve statistical significance. Intraocular pressure was significantly reduced. There was no change in blood fibrinogen and sedimentation rates.

Conclusions

These findings indicate that long-term treatment with ophthalmic betaxolol improves ocular hemodynamics by lowering the resistivity index of the ophthalmic artery and results in an improvement in the visual fields of patients with NTG. In view of this positive effect on blood flow and visual function, betaxolol is recommended in the management of patients with NTG.

Effects of Betaxolol and Latanoprost on Ocular Blood flow and Visual Fields in Patients with Primary Open-Angle Glaucoma

Purpose

To evaluate the effects of betaxolol and latanoprost on ocular blood flow and visual fields in patients with primary open-angle glaucoma (POAG) by means of an obseiver-masked, prospective clinical study.

METHODS

Thirty-two patients with newly diagnosed POAG were included in the study. The patients were randomized into two groups. The first group was treated with betaxolol 0.50% twice daily and the second group with latanoprost 0.005% once daily. Baseline and post-treatment examinations on the first and third months of treatment included intraocular pressure (IOP) measurement, automated visual field testing, and ocular blood flow assessment. For evaluation of visual fields, mean defect and pattern standard deviation indices were used. Ocular blood flow was assessed by means of color Doppler imaging of the central retinal artery (CRA) and the temporal short posterior ciliary artery (PCA). For each vessel, peak systolic (PSV) and end-diastolic (EDV) blood flow velocities were measured and resistivity index (RI) calculated.

Results

After exclusion of one noncompliant patient, the study was completed with 31 eyes of 31 patients. Both drugs significantly reduced IOP (p<0.05). The mean IOP lowering effect of latanoprost was significantly higher than that of betaxolol (p=0.03). Visual field indices exhibited no significant changes in either group (p>0.05). There were no significant changes in PSV or EDV measurements of CRA or PCA in either group (p>0.05). RI decreased in both CRA and PCA with both drugs. The mean changes between baseline and 3 month blood flow measurements were not significantly different between betaxolol and latanoprost (p>0.05).

CONCLUSIONS

Over a treatment period of 3 months, both betaxolol and latanoprost tended to improve ocular blood flow without one of them being superior to the other. The results suggest that the direct (non IOP-dependent) influence on ocular circulation is better for betaxolol than for latanoprost. In addition, neither drug caused significant generalized improvements in visual fields during this period.

Calcium channels and their blockers in intraocular pressure and glaucoma

Several factors besides high intraocular pressure assumed to be associated with the development and progression of glaucoma, and calcium channel blockers (CCBs) have been an anticipated option for glaucoma treatment by improving ocular perfusion and/or exerting neuroprotective effects on retinal ganglion cells with safety established in wide and long-term usage. Decrease in IOP has been reported after topical application of CCBs, however, the effect is much smaller and almost negligible after systemic application. Various CCBs have been reported to increase posterior ocular blood flow in vivo and to exert direct neuroprotection in neurons in vitro. Distribution of the drug at a pharmacologically active concentration in the posterior ocular tissues across the blood-brain barrier or blood-retina barrier, especially in the optic nerve head and retina where the ganglion cells mainly suffer from glaucomatous damage, is essential for clinical treatment of glaucoma. Improved visual functions such as sensitivity in the visual field test have been reported after administration of CCBs, but evidences from the randomized studies have been limited and effects of CCBs on blood flow and direct neuroprotection are hardly distinguished from each other.

Neurodegenerative diseases of the retina and potential for protection and recovery

Recent advances in our understanding of the mechanisms in the cascade of events resulting in retinal cell death in ocular pathologies like glaucoma, diabetic retinopathy and age-related macular degeneration led to the common descriptive term of neurodegenerative diseases of the retina. The final common pathophysiologic pathway of these diseases includes a particular form of metabolic stress, resulting in an insufficient supply of nutrients to the respective target structures (optic nerve head, retina). During metabolic stress, glutamate is released initiating the death of neurones containing ionotropic glutamate (N-methyl-D-aspartat, NMDA) receptors present on ganglion cells and a specific type of amacrine cells. Experimental studies demonstrate that several drugs reduce or prevent the death of retinal neurones deficient of nutrients. These agents generally block NMDA receptors to prevent the action of glutamate or halt the subsequent pathophysiologic cycle resulting in cell death. The major causes for cell death following activation of NMDA receptors are the influx of calcium and sodium into cells, the generation of free radicals linked to the formation of advanced glycation endproducts (AGEs) and/or advanced lipoxidation endproducts (ALEs) as well as defects in the mitochondrial respiratory chain. Substances preventing these cytotoxic events are considered to be potentially neuroprotective.

Topical Drug Therapy in Glaucoma

Glaucoma is defined as a progressive optic neuropathy involving characteristic structural changes in the optic nerve head and corresponding visual field defects. Elevated intraocular pressure (IOP) is a major risk and causative factor for glaucomatous optic neuropathy. Although mechanisms other than elevated IOP may contribute to the underlying pathophysiology of glaucoma, reducing IOP remains the primary goal of therapy. Recent clinical studies have shown that decreasing the IOP can delay, or in some cases prevent progression of this chronic ocular disease. Over the past decade, several new medical therapies have become available for the treatment of glaucoma. In this article a review of topical glaucoma therapy is presented.

Changing therapeutic paradigms in glaucoma management

Glaucoma is a family of diseases commonly characterised by progressive optic neuropathy with associated visual field deficits for which elevated intraocular pressure (IOP) is one of the primary risk factors. For more than a century the main goal of glaucoma management has been to eliminate the risk associated with elevated IOP. In recent years, accumulating evidence of pressure-independent causes of glaucomatous optic neuropathy has led to the recognition that lowering IOP alone may often be insufficient for the long-term preservation of visual function. An innovative therapeutic approach is now emerging to prevent progression of glaucomatous optic neuropathy and preserve vision, irrespective of disease aetiology: direct protection of the optic nerve. In addition to reducing the risk associated with elevated IOP, this neuroprotective approach will augment the overall goal of preserving the optic nerve through direct promotion of retinal ganglion cell (RGC) survival and/or prevention of RGC death. Although no currently available compounds have been clinically demonstrated to provide neuroprotective benefit in glaucoma, recent preclinical studies have shown that alpha-adrenergic agonists, such as brimonidine, provide neuroprotective benefits, as well as excellent IOP lowering efficacy. In addition, new agents with promising neuroprotective utility that are emerging from other studies are now being investigated for efficacy in glaucoma. The review discusses recently introduced compounds and new drugs in development with regard to their potential value in conventional and/or neuroprotective strategies for vision sparing in glaucoma.

Inhibition of endothelin-1 and KCL-induced increase of [CA2+]i by antiglaucoma drugs in cultured A7r5 vascular smooth-muscle cells

Over contraction of vascular smooth muscle may result in ischemia to ocular neuronal cells and deteriorate the glaucoma. The purpose of this study was to investigate the inhibitory effects of various commercial antiglaucoma drugs including brimonidine, dipivefrin, betaxolol, timolol, levobunolol, carteolol, brinzolamide, dorzolamide, unoprostone, latanoprost, pilocarpine, and preservative benzalkonium chloride on endothelin-1(ET-1) and KCl-induced increase of intracellular free Ca2+ ([Ca2+]i) in cultured rat A7r5 vascular smooth muscle cells. These drugs were diluted from original concentrations to 1/100, 1/1000, and 1/10000. [Ca2+]i mobility was analyzed by spectrofluorometry after loading with fura-2-AM. Betaxolol, timolol, levobunolol, and carteolol were found to inhibit KCl-induced release of [Ca2+]i in a dose-dependent manner. High concentrations of betaxolol, timolol, levobunolol, carteolol, and unoprostone also inhibited ET-1-induced increase of [Ca2+]i in A7r5 cells. However, ET-1- and KCl-induced increase of [Ca2+]i was not diminished by other drugs including brimonidine, dipivefrin, brinzolamide, dorzolamide, latanoprost, pilocarpine, and benzalkonium chloride. These results indicate that high concentrations of unoprostone and beta-adrenergic blocking agents including betaxolol, timolol, levobunolol, and carteolol may inhibit ET-1-induced increase of [Ca2+]i. The mechanism may be mediated by inhibition of extracellular calcium influx via blocking of L-type voltage-dependent Ca2+ channel in A7r5 cells.

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.

Randomized clinical trial of topical betaxolol for persistent macular edema after vitrectomy and epiretinal membrane removal

PURPOSE

To report the efficacy and safety of topical betaxolol for treatment of persistent macular edema.

DESIGN

Randomized clinical trial.

METHODS

Thirty-seven eyes (37 patients) with best-corrected visual acuity between 20/200 and 20/50 and macular edema that remained for 3 months after vitrectomy and removal of epiretinal membrane were prospectively, randomly assigned to receive betaxolol or placebo. Nineteen eyes of 19 patients received betaxolol twice daily, and 18 eyes of 18 patients received placebo as a randomized comparison group. The patients were followed up for 6 months. This study evaluated the effect of betaxolol on best-corrected visual acuity and area of macular edema, which was digitally measured on serial fluorescein angiogram. Calculations of mean best-corrected visual acuity were based on logarithm of the minimal angle of resolution (logMAR). To assess changes in area of edema, the initial (pretreatment) size of the edema was set to 100%, and all posttreatment measurements were normalized relative to the initial size.

RESULTS

Mean best-corrected visual acuity at baseline was 0.216 (20 of 92.6) and 0.244 (20 of 82.0) in the treatment and control group, respectively. Mean area of macular edema was 2.271 +/- 1.629 mm(2) and 2.273 +/- 1.209 mm(2) in the treatment and control group; there was no significant difference. The visual acuity at 6 months after the start of the follow-up was 0.471 (20 of 42.5) in the treatment group and 0.236 (20 of 84.7) in the control group. Mean changes in logMAR of visual acuity for 3- and 6-month follow-up were -0.282 +/- 0.191 and -0.337 +/- 0.197 in the treatment group, and -0.016 +/- 0.186 and +0.015 +/- 0.267 in the control group; a significant difference was found (P <.0001; P <.0001). Areas of macular edema at 6 months after the start of the follow-up were 1.492 +/- 1.357 mm(2) in the treatment group and 2.125 +/- 1.434 mm(2)in the control group. Mean change in area of the edema for 6 months were 76.5% +/- 24.1% and 63.4% +/- 28.3% in the treatment group and 92.9% +/- 15.4% and 87.4% +/- 25.6% in the control group; treated patients showed a significantly larger reduction than untreated patients at each examination (P =.0193; P =.0102). No complication associated with treatment or placebo was found.

CONCLUSIONS

Topical betaxolol appeared to have a favorable treatment effect in eyes with macular edema that remained after vitrectomy and removal of epiretinal membrane. Further investigation of more cases and longer follow-up are needed.

Effects of commercial antiglaucoma drugs to glutamate-induced [Ca2+)]i increase in cultured neuroblastoma cells

Over releasing of glutamate and cellular calcium influx always results in neuronal death. In the present study, we investigated various commercial antiglaucoma drugs including timolol (0.58 microM to 58 microM), betaxolol (1.62 microM to 162 microM), carteolol (6.8 microM to 680 microM), pilocarpine (4.08 microM to 408 microM), latanoprost (0.01 microM to 1.1 microM), dorzolamide (6.16 microM to 616 microM), brinzolamide (2.6 microM to 260 microM), brimonidine (0.68 microM to 68 microM), dipivefrin (0.28 microM to 28 microM) and preservative benzalkonium chloride on their effects to inhibit glutamate-induced intracellular free Ca(2+) ([Ca(2+)](i)) increase in cultured N1E-115 neuroblastoma cells. These drugs were diluted from original concentrations to 1/100, 1/1000 and 1/10000. The [Ca(2+)](i) mobility was studied after loading with fura-2-AM and analyzed by spectrofluorometry. It was found that betaxolol, dipivefrin and brimonidine have remarkable effects not only to inhibit the glutamate-induced [Ca(2+)](i) increase but also to decrease the basal [Ca(2+)](i). In the case of other drugs, only high concentration of timolol (58 microM) exhibited significant effect to completely prevent glutamate-induced [Ca(2+)](i) increase. Moreover, benzalkonium chloride did not exhibit any inhibitive effect. These results indicate that betaxolol, dipivefrin and brimonidine may have neuroprotective effects to inhibit the glutamate-induced over Ca(2+) influx damage.

Results of the betaxolol versus placebo treatment trial in ocular hypertension

PURPOSE

To determine whether treatment with betaxolol can delay or prevent the conversion from ocular hypertension to early glaucoma on the basis of visual field criteria, by means of a prospective, randomised, placebo-controlled trial.

METHODS

Three hundred and fifty-six ocular hypertensives were randomized to treatment with either betaxolol drops or placebo drops during the period 1992-1996. Each patient was followed prospectively with 4-monthly visits. Examination at each visit included visual field testing, intra-ocular pressure (IOP) measurement and optic disc imaging. Conversion to early glaucoma was defined on the basis of visual field change by AGIS criteria. An intent-to-treat analysis compared visual field conversion after 3 years in the treatment and placebo arms. Normal visual field survival analysis was also performed. The IOP characteristics of the two treatment groups were compared.

RESULTS

Two hundred and fifty-five patients completed the study, which ended in 1998, with a range of follow-up of 2-6 years. Sixteen (13.2%) of 121 patients in the placebo group converted to glaucoma, compared with 12 (9.0%) of 134 patients in the betaxolol group. The intent-to-treat analysis demonstrated no evidence of any difference in conversion rates between the betaxolol and placebo groups after 3 years. Visual field survival analysis demonstrated no significant difference between the betaxolol and placebo groups. The betaxolol-treated group had significantly lower post-treatment IOP values. Converters had significantly higher pre- and post-treatment IOP values than non-converters.

CONCLUSIONS

Betaxolol significantly lowered the IOP level compared with placebo. Conversion to glaucoma was found to be related to both the baseline and post-treatment IOP levels. However the intent-to-treat analysis did not demonstrate a statistically significant reduction in the conversion rate in the betaxolol-treated group.

Betaxolol, a beta1-adrenoceptor antagonist, protects a transient ischemic injury of the retina

In the present study, we investigated the protective effects of the topical beta-adrenoceptor antagonist Betoptic((R)) (0.25% betaxolol) in the rat retina following the ischemic injury induced by a transient increase of intraocular pressure (IOP). Like other areas of the central nervous system, the retina is highly vulnerable to ischemic-induced injury. Ischemia was induced in the rat retina by raising the IOP above the systolic blood pressure for 60min. After an ischemia/reperfusion, the thickness of the retinal layers and the immunoreactivities of choline acetyltransferase (ChAT), gamma-amino butyric acid (GABA) and tyrosine hydroxylase (TH) were examined. After a reperfusion period of 7 days, the thickness of both the inner plexiform layer and inner nuclear layer was much decreased. After a reperfusion period of 14-28 days, the thickness of the outer nuclear layer decreased markedly. Moreover, the ChAT and TH immunoreactivity had almost completely disappeared in the retinas after 7 days, while GABA immunoreactivity remained for 28 days. These results suggest that the inner retinal layers are more susceptible to ischemic-induced injury than the outer retinal layer.Histological examination demonstrated protective effects of betaxolol on ischemic-induced retinal damage, which was more substantial in the inner retinal layer. When two drops of betaxolol, once before ischemic injury and twice daily for 28 days after ischemia, were continuously administered, the reductions in the retinal ChAT, GABA and TH immunoreactivities were significantly attenuated. The present study suggests that topically applied betaxolol is an efficient neuroprotective agent and prevents the retinal cell damage induced by ischemic injury in rats.

Effect of betaxolol on aspartate aminotransferase activity in hypoxic rat retina in vitro

We investigated the effect of betaxolol on the decrease of mitochondrial aspartate aminotransferase (mAAT) activity in rat retinas induced by hypoxia in vitro. It is reported that mAAT decreases in ischemic or hypoxic retina and that the decrease is caused by Ca(2+)-dependent proteases such as calpain. Betaxolol is a compound that has beta(1)-adrenergic receptor blocking and voltage-dependent calcium channel blocking properties. The rat eye cups were maintained with Locke's solution saturated with 95% air - 5% CO(2). The eye cups were immersed in glucose-free Locke's solution saturated with 95% N(2) / 5% CO(2) (hypoxic solution). Ninety minutes of hypoxia caused a 20% decrease in mAAT activity. The eye cups incubated with the hypoxic solution containing 1 mM EGTA, 10 micro M MK-801 or 100 micro M betaxolol were protected from the decrease in mAAT activity, so that the residual mAAT activity was 50%, 45% or 40%, respectively, compared to the eye cups incubated in hypoxic solution alone, which had a 100% decrease in mAAT activity. In addition, co-incubation with EGTA and betaxolol had a greater protective effect against the mAAT decrease than a single application. This additive effect of betaxolol was dose-dependent. These results suggested that betaxolol had a protective effect against the decrease of mAAT caused by hypoxia and indicated that betaxolol might inhibit the Ca(2+) release from intracellular Ca(2+) stores.

Progression of retinal nerve fibre layer damage in betaxolol- and timolol-treated glaucoma patients

PURPOSE

It has been suggested that there are differences between selective and non-selective beta-blocking agents in their ability to protect glaucomatous eyes. The purpose of this study was to follow glaucoma patients treated with either betaxolol 0.5% or timolol 0.25% ophthalmic solutions and to compare the rate and degree of progression in retinal nerve fibre layer (RNFL) defects between the groups.

METHODS

A total of 64 patients were prospectively recruited in a double-masked study and randomly divided into two treatment groups. Retinal nerve fibre layer photographs were analysed. The incidence and total amount of progression in each group were recorded. The rate of impairment was demonstrated using Kaplan Meier survival curves.

RESULTS

The analysis included 27 patients treated with betaxolol and 28 patients treated with timolol. Of these, 30% of betaxolol-treated patients and 46% of timolol-treated patients had RNFL damage progression (p = 0.20). The total amount or rate of progression did not differ significantly between the two groups. There was no significant difference in intraocular pressure (IOP) levels between the groups (p = 0.68) during follow-up. The degree of RNFL deterioration did not correlate to the amount of IOP reduction.

CONCLUSION

The group treated with betaxolol 0.5% and the group treated with timolol 0.25% did not differ significantly in RNFL damage progression.

Nitric oxide synthase expression in the transient ischemic rat retina: neuroprotection of betaxolol

Betaxolol is a beta-adrenergic blocker but its neuroprotective action is generally thought to be due to its calcium channel blocking properties. In this study, we investigated neuronal cell damage and changes in the expression of neuronal nitric oxide synthase (nNOS) immunoreactivity in the ischemic retina and its relationship to the neuroprotection of betaxolol treatment after ischemic injury. Using the retina after ischemia, the expression of nNOS was studied by immunocytochemistry. In control retinas, two types of amacrine cells and a class of displaced amacrine cells were nNOS-labeled. After ischemia/reperfusion, the number of nNOS immunoreactive cells increased in both the ganglion cell layer and the inner nuclear layer compared to the control retinas. However, when experiments were carried out on animals that had been treated with betaxolol twice daily after ischemia/reperfusion, the number of nNOS immunoreactive cells decreased compared to the untreated ischemic retinas. These results suggest that an increase in nNOS expression could be associated with the degenerative changes in the ischemic retina, and that betaxolol treatment appears to play a role in protecting retinal tissue from ischemic damage.

Effect of betaxolol on impaired choroidal blood flow after intravitreal injection of endothelin-1 in albino rabbits

We investigated the effect of topical betaxolol on impaired choroidal blood flow (CBF) induced by endothelin-1 (ET-1) injection into the vitreous of albino rabbits. Betaxolol (n = 7) or balanced salt solution (BSS) (n = 6) was instilled in the right eyes before and 12 hrs after the intravitreal injection of ET-1 (10(-6) M, 10 microl), and BSS was instilled in the right eyes before and 12 hrs after the intravitreal injection of BSS (n = 6). Blood pressure, intraocular pressure and CBF were measured prior to the instillation of betaxolol or BSS, and just before and 2 hrs, 12 hrs and 24 hrs after ET-1 or BSS injection. CBF was measured by scanning laser Doppler flowmetry. Intravitreal injection of ET-1 decreased CBF. Compared with topical BSS, topical betaxolol significantly inhibited the decrease in CBF at 2 hrs (p = .022), 12 hrs (p = .046) and 24 hrs (p = .015) after the intravitreal injection of ET-1. There was no significant change of blood pressure or intraocular pressure after the topical administration of betaxolol or the intravitreal injection of ET-1. The decrease in CBF after the intravitreal injection of ET-1 was partially inhibited by topical betaxolol.

Levobetaxolol-induced Up-regulation of retinal bFGF and CNTF mRNAs and preservation of retinal function against a photic-induced retinopathy

Betaxolol (racemic), a beta-adrenoceptor antagonist that is used to lower intraocular pressure in the treatment of glaucoma, has been shown to protect inner retina cells from various insults. To determine if such protection could be afforded to retinal photoreceptors and retinal pigment epithelial cells (RPE), levobetaxolol (S-betaxolol) was evaluated in a photic-induced retinopathy model. Rats were dosed (IP) with vehicle or levobetaxolol (10 and 20 mg kg(-1)) 48, 24 and 0 hr prior to exposure for 6 hr to fluorescent blue light. The electroretinogram (ERG) and retinal morphology were assessed after a 3 week recovery period. Evaluation of the ERG demonstrated significant protection of retinal function in levobetaxolol (20 mg kg(-1))-dosed rats compared to vehicle-dosed rats. Similarly, the RPE and outer nuclear layer were significantly thicker in levobetaxolol (20 mg kg(-1))-dosed rats compared to vehicle-dosed rats. To elucidate potential mechanism(s) of the neuroprotective activity of levobetaxolol, bFGF and CNTF mRNA levels in normal rat retinas were evaluated 12 hr after a single i.p. injection. Northern blot analysis of levobetaxolol treated retinas demonstrated a 10-fold up-regulation of bFGF and a two-fold up-regulation of CNTF mRNA levels, trophic factors that have been shown to inhibit retinal degeneration in a number of species. These studies suggest that levobetaxolol can be used as a novel neuroprotective agent to ameliorate retinopathy.

Ocular and retrobulbar blood flow in ocular hypertensives treated with topical timolol, betaxolol and carteolol

The purpose of this study was to evaluate the effect of topical timolol 0.5%, betaxolol 0.5% and carteolol 2% on the blood flow velocity of the central retinal artery (CRA), the posterior ciliary artery (PCA) and the ophthalmic artery (OA) in patients with ocular hypertension. A group of 14 patients with ocular hypertension and a group of 11 normals were studied. The color Doppler was used to measure the peak systolic flow velocity (PSFV) and the end diastolic flow velocity (EDFV) of the CRA, the PCA and the OA in the normals and in the patients. The normals were under no treatment, while the patients were studied before and after treatment with topical timolol 0.5%, betaxolol 0.5% and carteolol 2%. In the systolic phase, there was a significant increase in the flow velocity of the CRA with all three drugs. In the diastolic phase of the CRA, the increase was significant for timolol 0.5% and carteolol 2% but not for betaxolol 0.5%. The flow velocity of the PCA and OA remained unchanged. In this study of 14 patients with ocular hypertension, topical timolol 0.5%, betaxolol 0.5% and carteolol 2% led to a significant increase in the flow velocity of the CRA without creating a steal or decrease in the flow velocity of the PCA.

Vasorelaxant effects of racemic betaxolol and its R- and S- isomers on bovine retinal vessels

PURPOSE

RS-Betaxolol (equimolar R- and S- isomers) lowers intraocular pressure and dilates precontracted retinal and posterior ciliary arteries in vitro. Betaxolol's vasorelaxant effect is thought to involve the inhibition of calcium influx into vascular smooth muscle and is unrelated to its stereoselective beta-adrenergic blocking action. The authors assessed the vasodilatory effect of RS-betaxolol on different diameters of bovine retinal arterioles and venules, and these responses were compared with the responses induced by R- and S-betaxolol isomers in vitro.

METHOD

In-vitro preparations of the bovine retinal microcirculatory system were perfused continuously with oxygenated, heparinized physiological salt solution at 37 degrees C. Diameters of retinal arterioles and venules were measured using video imaging. The retinal vessels were preconstricted with 40 mM KCl, and concentration-response curves for vasodilation were obtained for RS-betaxolol, R-betaxolol, and S-betaxolol.

RESULTS

Baseline diameters of first-order (A1) and second-order (A2) branches of retinal arterioles were 50 +/- 0.6 microm and 39 +/- 1 microm, respectively (n = 20), whereas diameters of first-order (V1) and second-order (V2) branches of venules were 75 +/- 0.8 microm and 50 +/- 0.4 mM, respectively (n = 20). The diameters of all sizes of retinal arterioles and venules were significantly reduced (i.e., vasoconstricted) in the presence of 40 mM KCl (n = 20). These preconstricted vessels were relaxed in a dose-dependent manner by cumulative additions of RS-betaxolol, R-betaxolol, and S-betaxolol. The dose-response curves of these compounds were not significantly different.

CONCLUSION

RS-Betaxolol, R-betaxolol, and S-betaxolol were equiactive and produced concentration-dependent vasodilatation of all sizes of retinal arterioles and venules studied.

Influence of betaxolol and timolol on the venous tone in glaucoma patients

The aim of this study was the assessment of physiological venous reflexes in 40 glaucoma patients treated with topically applied timolol maleate 0.50% and betaxolol HCL 0.50%. They were divided into two groups of twenty each; one group being given timolol and the other betaxolol. The assessment of the venous tone was performed by testing venous reflexes. We found no statistically significant difference between timolol and betaxolol; however, when the influence of circulating catecholamines and the other vasoactive substances was excluded by suprasphygmatic insufflation of a pediatric cuff, a significant difference was found in the Valsalva's maneuver (125.5 +/- 8.1 vs 85.0 +/- 34.3 venoconstrictive units VCUs, p = 0.03). The IOP was significantly decreased in both treatment group, although the pressure reduction effect was more pronounced in the timolol group. Our study suggests that timolol and betaxolol have a slightly different mode of action on the venous side of circulation under topical medications. It is possible that the use of betaxolol topically may reduce a systemic venoconstriction.

Endothelium-dependent vasoactive modulation in the ophthalmic circulation

The vascular endothelium is strategically located between the circulating blood and the vascular smooth muscle cells. Different agonists or stimuli transported by the circulating blood can trigger the endothelium to release potent relaxing (nitric oxide, prostacyclin, endothelium-derived hyperpolarizing factor) or contracting factors (endothelin, cycloxygenase products). These endothelium-derived vasoactive factors can modulate blood flow locally. Heterogeneity exists from one vascular bed to the other, or even between vessels, in the agonists able to stimulate the release of endothelium-derived vasoactive factors. In the ophthalmic circulation, nitric oxide and endothelin are strong vasoactive modulators. In many vascular diseases that are of importance in ophthalmology (hypercholesterolemia, arteriosclerosis, hypertension, diabetes, vasospastic syndrome, ischemia and reperfusion, etc) the function of the endothelium can be impaired. There exist different drugs that can modulate the vasoactive function of the vascular endothelium. In other words, it appears that the vascular endothelium plays an important role in both the physiology and pathophysiology of the regulation of blood flow. The modulation of this regulatory system by different drugs might open new therapeutical approaches to treat vascular disorders in ophthalmology.

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.

Suppressive actions of betaxolol on ionic currents in retinal ganglion cells may explain its neuroprotective effects

Betaxolol, a beta 1-selective adrenoceptor antagonist, is widely used in the treatment of glaucoma. In addition to its ocular hypotensive effects, betaxolol has been suggested to act as a retinal neuroprotective agent (Osborne et al., 1997). To investigate possible mechanisms underlying the neuroprotective effects, we tested the actions of betaxolol on ion channels and calcium signaling in isolated retinal ganglion cells. Betaxolol (50 microM) reduced by about 20% the high-voltage-activated (HVA) Ca channel currents in ganglion cells isolated from tiger salamander retina. In contrast, the beta 1-adrenoceptor antagonists propranolol (10 microM) and timolol (50 microM) had no inhibitory actions on HVA Ca channel currents. The L-type Ca channel antagonist, nisoldipine, blocked the HVA Ca channel current partially and the remaining current was not inhibited by betaxolol. Outward current was inhibited in the presence of betaxolol. Both iberiotoxin (IBTX; 10 nM), a selective inhibitor of large-conductance Ca-activated K channels, and Cd2+ (100 microM), which suppresses Ca-activated K channels subsequent to its block of Ca channels, reduced outward current and the remaining current was not blocked significantly with betaxolol. In the presence of betaxolol, Na channel currents were reduced by about 20%, as were currents evoked by glutamate (10 mM) and GABA (1 mM). Current clamp recordings from isolated ganglion cells showed that betaxolol had several effects on excitability: spike height decreased, repetitive spike activity was suppressed, spike width increased and hyperpolarization following spikes was reduced. Calcium imaging in isolated rat retinal ganglion cells revealed that betaxolol inhibited glutamate-induced increases in [Ca2+]i. These results suggest that betaxolol has a diversity of suppressive actions on ganglion cell ion channels and that, as a consequence, one of the net actions of the drug is to reduce Ca2+ influx. The subsequent reduction in [Ca2+]i may contribute to the apparent neuroprotective actions of betaxolol in promoting ganglion cell survival following ischemic insult, as may occur in glaucoma and retinal disease.

Topically applied betaxolol attenuates NMDA-induced toxicity to ganglion cells and the effects of ischaemia to the retina

The present results show that topically applied Betoptic(R)(0.5% betaxolol) to the rabbit or rat eye reaches the retina and can counteract the detrimental effects caused by ischaemia/reperfusion or N -methyl- d -aspartate (NMDA)-induced insults to the retina. Betaxolol is a beta(1)-adrenergic blocker but its neuroprotective action is generally thought to be due to its calcium channel blocking properties. Support for this view comes from studies on cultures of cortical neurones where it was found that betaxolol attenuated the NMDA-induced influx of(45)Ca(2+)while beta-adrenoreceptor agonists were ineffective. Topically applied Betoptic(R)to the rabbit eye was observed to reach the retina in maximal amounts within 60 min. Some of the substance was also found in the contralateral retina of the untreated eye suggesting that the agent reaches the retina by local systemic and retinal circulation. Concurrent treatment with Latanoprost(R)did not result in a greater amount of betaxolol reaching the retina. An ophthalmodynamometric procedure, which raises the intraocular pressure, was used to apply an ischaemic insult to the rabbit retina. After three days of reperfusion the b-wave of the electroretinogram was reduced by an average of 59% and the choline acetyltransferase immunoreactivity in the retina was almost obliterated. However, when experiments were carried out on animals which had been treated with one drop of Betoptic(R) twice daily for 4 weeks before ischaemia and also during the reperfusion phase, the reductions in both the b-wave of the electroretinogram and retinal choline acetyltransferase immunoreactivity due to ischaemia/reperfusion were greatly attenuated. Intravitreal injection of NMDA into the rat eye caused a decrease in the immunostaining for Thy-1 antigen which is associated with ganglion cells. The Thy-1 mRNA level was also reduced as was the mRNA for the common subunit of the NMDA receptor, the NR1 subunit. However, in animals subjected to a topical Betoptic(R)regime, before and after intravitreal injection of NMDA, the decreases in the mRNA levels of Thy-1 and NR1 were significantly attenuated.

Betaxolol, a beta1-adrenoceptor antagonist, has an affinity for L-type Ca2+ channels

The effect of betaxolol on the specific binding of [3H]diltiazem and [3H]nitrendipine to rat cortical membranes was examined. Betaxolol inhibited specific [3H]diltiazem and [3H]nitrendipine binding with IC50 values of 19.7 and 46.3 microM, respectively. The effect of betaxolol on L-type Ca2+ channels showed little stereospecificity, since similar inhibitions of radioligand binding were observed with both racemic betaxolol and L-betaxolol. The dissociation kinetics of [3H]diltiazem were unaffected by 30 microM betaxolol, whereas it increased the [3H]nitrendipine dissociation rate, thus suggesting that betaxolol directly interacts with the benzothiazepine binding site and allosterically modulates the dihydropyridine binding site. Carteolol, propranolol and timolol were also found to inhibit both specific [3H]diltiazem and [3H]nitrendipine binding to rat cortical membranes, but with less potency than betaxolol. The ability of betaxolol to interact with L-type Ca2+ channels may have a role in its therapeutic effects in the management of systemic hypertension and in reducing neuronal death as occurring in glaucoma.

Effect of topical betaxolol on tissue circulation in the human optic nerve head

There have been no reports to date on long-term betaxolol instillation effects on the human optic nerve head (ONH) tissue circulation. The purpose of this study was to study the effect of topical 0.5% betaxolol on tissue blood velocity in the human ONH. Using a laser-speckle tissue blood flow analyzer, normalized blur (NB; a quantitative index of tissue blood velocity) was measured every 0.125 seconds at a temporal ONH site free of visible surface vessels. Measurements were averaged for 3 cardiac cycles (NB(ONH)). For baseline comparison (day 0), recordings of bilateral NB(ONH) and intraocular pressure (IOP), blood pressure (BP) and pulse rate (PR) were recorded in healthy volunteers before, and 2, 4.5, and 7 hr after, instillation of 30 microL of betaxolol vehicle, and again on day 21; IOP was also recorded on days 7 and 14. On day 1 (the day after baseline measurements), and twice daily for 3 weeks, 30 microL of 0.5% betaxolol into one eye and 30 microL vehicle was instilled into the other in a double-blind study. Measurements as on day 0 were again recorded on day 21; IOP was also recorded on days 7 and 14. During baseline recordings, no significant changes were noted in any parameters. After administration of topical betaxolol, IOP was significantly reduced, bilaterally, with greater reduction in the betaxolol-treated eyes on day 21. Also on day 21, the NB(ONH) of the betaxolol-treated eyes was significantly higher 4.5 hr after instillation than that of the comparable baseline recording (p = 0.035 with Bonferroni's correction); BP, PR, and NB(ONH) in the eye which received only the vehicle showed little change. Tissue blood velocity in the human ONH was increased at least temporarily by instillation of topical betaxolol twice daily for 3 weeks. Although the obtained increase is small and may be clinically insignificant, the potential of betaxolol that can affect the ONH tissue circulation in humans after 21 days of instillation is thought to deserve further investigation.

Systemic and ocular vascular roles of the antiglaucoma agents beta-adrenergic antagonists and Ca2+ entry blockers

This review addresses whether the antiglaucoma agents beta-adrenergic antagonists and Ca2+ entry blockers cause vasoactive effects in the retinal and other ocular vasculatures, as they do in other tissues. The potent vasodilating effects of Ca2+ entry blockers on ocular vessels have recently been demonstrated in in vivo and in vitro studies, implying that the maintenance of ocular vascular tone relies almost exclusively on extracellular Ca2+. Ca2+ entry blockers may potentially play a role in relaxing the retinal, long posterior ciliary, and ophthalmociliary arteries to improve the ocular circulation in vascular diseases in which there is considerable vascular tone present. The beta-adrenergic antagonists are discussed with reference to their antihypertensive role, their effect on other vascular beds, and finally what is known of their effect in the ocular vasculature. The emerging evidence that particular selective beta-adrenergic antagonists, such as betaxolol, are also potent Ca2+ channel entry blockers in other vascular beds is presented. Betaxolol has been shown to induce vasodilatation in the retinal and other ocular vascular beds, although studies have shown that beta1-adrenergic receptors are sparse in these vascular beds. This implies that an alternative mechanism must be responsible for betaxolol-induced vasodilatation. Evidence is presented that betaxolol vasodilates via its potent Ca2+ channel entry blocking properties, and its potency and ability to vasodilate are compared with those of nimodipine and timolol, as well as with those of other Ca2+ channel entry blockers. Important areas for future research in this area are discussed.

In vitro studies of the effects of beta-adrenergic drugs on retinal and posterior ciliary microarteries

The small-vessel myograph allows for precise measurements of physiopharmacologic responses of the ocular microarteries under controlled conditions. Studies using the myograph have shown that beta-adrenergic agonists are unable to induce significant relaxation in retinal and posterior ciliary microarteries, indicating that these microarteries have very few or no functional beta-adrenoceptors. Thus, beta-blockers would not be expected to have important adverse vasoconstrictory effects in the posterior part of the eye that are caused by their beta-adrenoceptor binding capacities. On the contrary, some beta-blockers, such as propranolol (the standard beta-blocker in pharmacology) and betaxolol (a beta-blocker used in ophthalmology), have vasorelaxant effects, probably a result of their Ca2+ channel-blocking activity. This activity shows no stereospecificity. Betaxolol could thus act as a vasodilator in glaucoma patients, on the condition that it penetrates in the posterior part of the eye after topical application. If so, it could also induce vasodilatation in circumstances of vascular endothelium injury, because this effect is endothelium-independent.

Periocular accumulation of timolol and betaxolol in glaucoma patients under long-term therapy

PURPOSE

To determine if betaxolol or timolol is present in measurable concentration in the Tenon capsule in patients under long-term topical therapy.

METHODS

Small (1-cc) specimens of Tenon capsule were removed at the time of filtering surgery from 15 glaucoma patients under long-term preoperative topical therapy, nine of whom had been treated with timolol and six of whom had been receiving betaxolol. Methanol extracts of these tissue samples were analyzed quantitatively for the presence of either beta-adrenergic antagonist by high-performance liquid chromatography.

RESULTS

Drug was detected in every specimen. A mean total of 2.6 (range, 0.1-30.0) microg of betaxolol was detected per 1-cc specimen.

CONCLUSION

Timolol and betaxolol penetrate the conjunctiva and accumulate in the Tenon capsule. In patients under long-term therapy, the periocular tissue can accumulate a greater quantity of beta-antagonist than is present in a daily dosage of applied eyedrops, manyfold higher than the maximal intraocular concentration.

Neuroprotection in relation to retinal ischemia and relevance to glaucoma

Management of glaucoma is directed at the control of intraocular pressure (IOP), yet it is recognized now that increased IOP isjust an important risk factor in glaucoma. Therapy that prevents the death of ganglion cells is the main goal of treatment, but an understanding of the causes of ganglion cell death and precisely how it occurs remains speculative. Present information supports the working hypothesis that ganglion cell death may result from a particular form of ischemia. Support for this view comes from the fact that not all types of retinal ischemia lead to the pathologic findings seen in glaucomatous retinas or to cupping in the optic disk area. Moreover, in animal experiments in which ischemia is caused by elevated IOP, a retinal abnormality similar to that seen in true glaucoma is produced, whereas after occlusion of the carotid arteries a different pattern of damage is found. In ischemia, glutamate is released, and this initiates the death of neurons that contain ionotropic glutamate (NMDA) receptors. Elevated glutamate levels exist in the vitreous humor of patients with glaucoma, and NMDA receptors exist on ganglion cells and a subset of amacrine cells. Experimental studies have shown that a variety of agents can be used to prevent the death of retinal neurons (particularly ganglion cells) induced by ischemia. These agents are generally those that block NMDA receptors to prevent the action of the released glutamate or substances that interfere with the subsequent cycle of events that lead to cell death. The major causes of cell death after activation of NMDA receptors are the influx of calcium into cells and the generation of free radicals. Substances that prevent this cascade of events are, therefore, often found to act as neuroprotective agents. For a substance to have a role as a neuroprotective agent in glaucoma, it would ideally be delivered topically to the eye and used repeatedly. It is, therefore, of interest that betaxolol, a beta-blocker presently used to reduce IOP in humans, also has calcium channel-blocking functions. Moreover, experimental studies show that betaxolol is an efficient neuro protective agent against retinal ischemia in animals, when injected directly into the eye or intraperitoneally.

The potential of neuroprotection in glaucoma treatment

Visual field loss in glaucoma is due to death of retinal ganglion cells. Reducing or slowing down the loss of ganglion cells in glaucoma, a concept known as neuroprotection, would appear to be the only way forward. This does not imply that treatment of risk factors, such as elevated intraocular pressure, must not be continuously implemented. In this paper we point out that very little is known about the mechanisms of ganglion cell death in glaucoma and that data derived from studies on the "ideal animal model for glaucoma" must not be overemphasized. We also propose that the death processes of neurones in various diseases are fundamentally the same but vary in cause. Experimental data show that the death rate of neuronal populations is dependent on the impact of the insult and that neuroprotectants are more likely to benefit a patient in diseases in which the neurones die slowly, as in glaucoma, than in a disease in which the death of a set of neurones is rapid. We conclude that if a putative neuroprotectant can be administered in such a way that it reaches the retina in appropriate amounts and has insignificant side effects, it is likely to attenuate ganglion cell death and thus benefit the glaucoma patient.

Comparison of short- and long-term effects of betaxolol and timolol on human retinal circulation

PURPOSE

To determine the short- and long-term effects of betaxolol and timolol on human retinal circulation.

METHODS

In a double-masked, randomised, placebo-controlled study we evaluated the effects of both a one-drop application and a twice-daily 2-week application of either topical 0.5% betaxolol hydrochloride or topical 0.5% timolol maleate on the retinal circulation in 12 healthy volunteers. Laser Doppler velocimetry was used to detect changes in the retinal venous blood flow.

RESULTS

In both betaxolol- and timolol-treated eyes, intraocular pressure decreased significantly compared with baseline values after both 90 min and 2 weeks. In betaxolol-treated eyes, retinal blood flow did not change significantly after 90 min, but increased significantly (14 +/- 9%; p = 0.02) compared with baseline after 2 weeks. In timolol-treated eyes, retinal blood flow decreased significantly (18 +/- 5%: p = 0.04) compared with baseline after 90 min, and also decreased significantly (14 +/- 6%; p = 0.04) compared with baseline after 2 weeks.

CONCLUSIONS

Retinal blood flow increases as a long-term effect of betaxolol and decreases as both a short- and long-term effects of timolol.

Ca2+ channel-blocking activity of propranolol and betaxolol in isolated bovine retinal microartery

The relaxant action of the standard beta-blocker propranolol was compared with betaxolol, a beta-blocker with established vasorelaxant properties. Ring segments of bovine retinal microartery (n=36, theta=237 microm), which lacks adrenergic nerves and beta-adrenoceptors, were mounted in an organ bath for isometric force recording. l-, d-, dl-Propranolol and betaxolol were equally effective in relaxing tonic K+-induced contractions. The median effective dose (ED50) value was approximately 10(-5) M for both beta-blockers. The relaxation by both beta-blockers was unaffected by endothelium removal. Like verapamil, both beta-blockers induced smaller relaxation of tonic prostaglandin F2alpha (PGF2alpha)-induced force, which depended less on Ca2+ influx than did K+-induced force: K+-, but not PGF2alpha-induced contractions were abolished in Ca2+-free medium. The minor betaxolol-induced relaxation of tonic PGF2alpha-induced force was blocked in Ca2+-free medium. With repeated exposures to PGF2alpha in Ca2+-free medium, initial phasic PGF2alpha-induced force declined less with every exposure than did subsequent tonic force. When the preparations were briefly equilibrated with K+- and Ca2+-rich solution before every exposure to PGF2alpha phasic force did not decline, indicating that phasic force primarily depended on Ca2+ released from intracellular stores. Both beta-blockers failed to relax phasic PGF2alpha-induced force. Thus propranolol and betaxolol are equipotent vasorelaxant drugs in retinal microartery, both probably acting via Ca2+ channel blockade. This activity (that shows no stereospecificity) thus appears to be a more general property of beta-blockers. Microarteries might be more sensitive to this activity than are conductance arteries.

Effect of topical betablockers on human retinal vessels diameters

PURPOSE

To measure the effect of topical betaxolol 0.5% and timolol 0.5% on retinal vessels diameters by means of photographic enlargement.

METHODS

Thirteen glaucomatous patients (primary open angle glaucoma (POAG) and ocular hypertensive (OH)) were treated twice daily with betaxolol 0.5% for one year. These same patients were subsequently treated with timolol 0.5% during the following year. Fundus photographs were taken with Canon camera 30 degree angle at baseline and two hours after instillation at 3, 6 and 12 months of treatment for each drug. The diameters of the superior and inferior temporal vessels (arteries and veins) were measured at one and two disc radii from the margin of the disc using photographic enlargement (x 66.7) of the right eye and were analysed under double masked fashion during the same session.

RESULTS

A significant increase of the mean arterial diameter (+ 7.4% p = 0.000 paired t) was found after 12 months of betaxolol treatment, while no persistent further difference (+ 1.3% NS) was found after 12 months of timolol treatment. No modification was found in venous diameter.

CONCLUSION

Betaxolol treatment is associated with a beneficial effect on retinal arteries width whereas Timolol does not yield the same amplitude of benefit.

Effect of betaxolol, timolol and nimodipine on human and pig retinal arterioles

This study tested the hypothesis that the beta-adrenergic antagonists betaxolol and timolol, cause retinal arteriolar vasodilatation in addition to their ability to reduce intraocular pressure (IOP), and compared their vasodilatory ability with that of a known Ca2+ channel entry blocker nimodipine in donor human and pig isolated perfused retinal arterioles. This study was performed using a microperfusion technique specifically established to allow investigations in arterioles as small as the first order human and pig retinal arterioles (approximately 100 microns diameter). The scarcity of viable human tissue was overcome by the successful development of controlled rate freezing and cryopreservation techniques which were able to preserve the vascular responsiveness of the retinal arterioles, thus enabling multiple experiments to be performed on segments of retinal arterioles from each individual donor eye. Furthermore, relaxation by acetylcholine in noradrenaline contracted pig retinal arterioles showed that endothelial cell function was well maintained after cryopreservation (n = 8). Baseline diameters of retinal arterioles used in the main studies were: cryopreserved human 92.3 +/- 3.4 microns (n = 44), fresh pig 94.7 +/- 2.2 microns (n = 42), and cryopreserved pig 94.3 +/- 2.3 microns (n = 30). Precontraction with extraluminal endothelin-1 (ET-1) 10(-9) M reduced the diameters to 74.3 +/- 0.9%, 71.6 +/- 1.6% and 72.5 +/- 0.9% respectively. Intraluminally applied nimodipine and betaxolol caused a significant dose dependent dilatation (P < 0.001) in human retinal arterioles with a threshold of 10(-12) M. Timolol did not produce a significant dilatation in human arterioles. Timolol produced a small but significant dilatation in fresh and cryopreserved pig arterioles but the dilatation with betaxolol and nimodipine was significantly larger. The nimodipine and betaxolol dose response curves were not significantly different in human arterioles, but nimodipine produced significantly greater dilatation than betaxolol (P < 0.001) in fresh and cryopreserved pig arterioles. Both nimodipine and betaxolol were significantly more effective vasodilators than timolol (P < 0.001) in human and pig retinal arterioles.

Effects of topical adrenergic agents on tissue circulation in rabbit and human optic nerve head evaluated with laser speckle tissue circulation analyzer

The effects of topical adrenergic agents on the tissue circulation of the optic nerve head (ONH) were studied in animal and human eyes with use of a laser speckle tissue circulation analyzer. Drugs studied were nipradilol, a beta1-2-blocker with weak alpha-blocking and nitroglycerinlike activities; bunazosin, a selective alpha1-blocker; carteolol, a beta1-2-blocker with intrinsic sympathomimetic activity; and betaxolol, a selective beta1-blocker. In the animal experiment, one eye each of nine albino rabbits received 0.25% nipradilol (N = 9) twice daily for 15 days or 0.01% bunazosin (N = 10) twice daily for 20 days; the fellow eye received the vehicle of each drug in a randomized masked design. Normalized blur (NB) in an area of ONH free of visible surface vessels, a quantitative index of peripheral blood velocity in ONH, was measured under general anesthesia before treatment and 2 hours after the last instillation on the 15th or 20th day. At 15 days, intraocular pressure and NB in the nipradilol-treated eyes decreased by 4.3 mm Hg (P < 0.01) and increased by 15.9% (P < 0.01), respectively, while those in the vehicle-treated eyes showed little change. At 20 days NB in both bunazosin- and vehicle-treated eyes showed little change, while intraocular pressure decreased only in the bunazosin-treated eyes (P < 0.01). In the human volunteer experiment NB was averaged over five pulses (mean NB) in both eyes before and 1.5, 3.0 and 4.5 hours after a 30 microL instillation of the vehicle of carteolol or betaxolol to serve as a control. Intraocular pressure, blood pressure and pulse rate were also measured. One week later a 30 microL drop of 2.0% carteolol (N = 6) or 0.5% betaxolol (N = 10) was instilled in one randomly chosen eye and the vehicle for each drug in the other eye, and those parameters were measured as above in a double-masked manner. In the carteolol experiment, mean NB in both eyes was significantly higher at 3 hours than it was in the control experiment (P < 0.05), while intraocular pressure was significantly lower in both eyes and blood pressure and pulse rate showed little change. In the betaxolol experiment, intraocular pressure at 1.5 hours and blood pressure at 4.5 hours were significantly lower than those in the control experiment (P < 0.05), while mean NB and pulse rate showed little change. In summary, using the laser speckle method we found that topical nipradilol and carteolol increase ONH blood velocity in rabbits and humans, respectively. This finding suggests that some topical beta-blockers used clinically may influence the ONH tissue circulation in patients and that this method may be used in clinical situations to assess the effect of various drugs on ONH circulation.

Association of retinal capillary perfusion with visual status during chronic glaucoma therapy

PURPOSE

The purpose of the study is to determine whether retinal microcirculation is associated with the degree of visual function in glaucomatous eyes receiving chronic bilateral medical therapy with topical beta-blockers.

METHODS

A nonrandomized, 3-year prospective clinical study was undertaken on 37 patients with glaucoma and normal visual acuity receiving symmetric topical medication in both eyes. Humphrey 30-2, Henson CFA 2000, and Vistech 3 and 6 cycles/degree contrast sensitivity were obtained bilaterally at multiple visits, along with Oculix 1000 blue-field estimates of perimacular leukocyte velocity. The mean asymmetry of measurements obtained throughout the treatment period for each pair of eyes was determined, and correlations were obtained to assess visual function asymmetry circulatory asymmetry.

RESULTS

Significant associations were observed between blue-field entoptic capillary leukocyte velocity measurements and those for all three visual function testing methods, the eye with the superior vision typically having the higher mean leukocyte velocity (P < 0.001 for both Humphrey mean deviation and Henson perimetry, P < 0.002 for Humphrey corrected pattern standard deviation, and P < 0.02 for contrast sensitivity at both 3 and 6 cycles/degree).

CONCLUSIONS

Central retinal microcirculation is associated with various measures of central and peripheral visual function in glaucomatous eyes receiving beta-adrenergic blocker therapy.

Effects of antiglaucoma drugs on ocular hemodynamics in healthy volunteers

BACKGROUND AND PURPOSE

There is evidence that ocular blood flow plays a critical role in the clinical course of glaucoma. Hence a reduction in ocular blood flow due to topical antiglaucoma treatment should be avoided. The purpose of this study was to characterize the effect of antiglaucoma drugs on ocular hemodynamics.

METHODS

In a double-blind, placebo-controlled, randomized crossover study, we investigated the effects of single topical doses of five beta-blocking agents (befunolol, betaxolol, levobunolol, metipranolol, and timolol), two adrenergic agents (clonidine and dipivefrin [INN, dipivefrine]), and a parasympathomimetic agent (pilocarpine) on ocular and systemic hemodynamics in healthy subjects (n = 10). Fundus pulsation amplitudes in the macula and the optic disc were measured to characterize pulsatile choroidal and optic disc blood flow, respectively. Moreover, central retinal and ophthalmic artery blood flow velocities were measured by Doppler ultrasound.

RESULTS

Befunolol, metipranolol, timolol, clonidine, and dipivefrin reduced fundus pulsations in the macula and the optic disc (-9% to -14% versus baseline). In contrast, betaxolol, levobunolol, and pilocarpine had no effect on fundus pulsations. Antiglaucoma drugs had no effect on either blood flow velocities in the central retinal or the ophthalmic artery or systemic hemodynamics.

CONCLUSIONS

Our results indicate that befunolol, metipranolol, timolol, clonidine, and dipivefrin reduce choroidal and optic disc blood flow. This could be caused by drug diffusion to the choroid, which may cause vasoconstriction. Ocular blood flow reduction was not observed with betaxolol, levobunolol, or pilocarpine. The lack of effect of all drugs under study on central retinal blood flow velocity might partially be the result of autoregulative mechanisms. Because optic nerve head blood flow likely plays a critical role in the clinical course of glaucoma, the use of antiglaucoma drugs, which reduce blood flow, should be reconsidered.

In vivo and in vitro experiments show that betaxolol is a retinal neuroprotective agent

The aim of the study was to determine whether betaxolol is a neuroprotective agent and can therefore slow down the changes seen in the retina following ischaemia/reperfusion. Ischaemia was induced in one rat eye by raising the intraocular pressure for 45 min. Three days later electroretinograms were recorded from both eyes and the retinas were examined immunohistochemically for the localisation of calretinin and choline acetyltransferase (ChAT) immunoreactivities. The effect of glutamate agonists, hypoxia or experimental ischaemia was examined on the GABA immunoreactivity, lactate dehydrogenase (LDH) and internal calcium levels ([Ca2+]i) of the isolated rabbit retina, rat cortical cultures and chick retinal cell cultures respectively. Betaxolol was tested to see whether it can attenuate the influence of the glutamate agonists, hypoxia or experimental ischaemia. Ischaemia for 45 min causes a change in the nature of the normal calretinin immunoreactivity, an obliteration of the ChAT immunoreactivity and a drastic reduction in the b-wave of the electroretinogram after 3 days of reperfusion. When betaxolol was injected i.p. into the rats before ischaemia and on the days of reperfusion the changes to the calretinin and ChAT immunoreactivities were reduced and the reduction of the b-wave was prevented. Rabbit retinas incubated in vitro in physiological solution lacking oxygen/glucose or containing the glutamate agonists kainate or NMDA caused a change in the nature of the GABA immunoreactivity. Inclusion of betaxolol partially prevented the changes caused by NMDA and lack of oxygen/glucose. Rat cortical cultures exposed to glutamate or hypoxia/reoxygenation resulted in a release of LDH. The release of the enzyme was almost completely attenuated when betaxolol was included in the culture medium. Kainate increased the [Ca2+]i in chick retinal cultures, as measured with Indo-1. In a medium with sodium, this kainate-induced elevation of [Ca2+]i was significantly reduced by betaxolol. The combined data show that betaxolol is a neuroprotective agent and attenuates the effects on the retina induced by raising the intraocular pressure to simulate an ischaemic insult as may occur in glaucoma.

Optic nerve vasomotor effects of topical beta-adrenergic antagonists in rabbits

PURPOSE

To examine the anterior optic nerve vasomotor effects of nonselective and relatively beta-1-selective beta-adrenergic antagonists in rabbits, because different influences on optic nerve blood flow with these medications have been suggested.

METHODS

After topical therapy for 30 days with either timolol maleate 0.5% (six rabbits), betaxolol hydrochloride 0.5% (six rabbits), or placebo (two rabbits), the microvasculature of the optic nerve was examined with an intraluminal microvascular corrosion casting technique. The investigators were masked to both the medication group and the treated eye. The constriction, in percent of the downstream vessel caliber, was measured at the vascular branching point of arterioles supplying the anterior optic nerve. An average constriction was calculated and compared between the medication groups and between the treated and the contralateral, untreated eyes.

RESULTS

Constriction values from a total of 218 arterioles supplying the anterior optic nerve were obtained for the 14 rabbits. The means of the average constriction on the treated side were comparable between the groups treated with timolol maleate, betaxolol hydrochloride, and placebo (one-way analysis of variance, P = .64), as well as between the treated and untreated eyes (two-tailed t-test for paired variables, P = .68 for timolol maleate and P = .42 for betaxolol hydrochloride). The statistical power to find a difference of 5% or more average constriction was at least 90%.

CONCLUSIONS

Both relatively selective and nonselective beta-adrenergic antagonists produce no observable optic nerve vasomotor effects in the rabbit eye.

Doppler ultrasonography of the central retinal artery in patients with diabetes and vascular disease treated with topical timolol

Using high-resolution duplex scanning it is possible to evaluate the blood flow velocity in the central retinal artery of the eye. Four different patient groups were studied with this technique: normals, diabetics with a decreased flow, diabetics with an increased flow and vascular patients with a decreased flow. The eyes of these patients were then treated with topical timolol and the flow measured again. An increase in the flow was found in three of the four groups. This increased flow velocity may be due to a vasodilatory effect of timolol. The results are presented and discussed.

Effect of betaxolol on the retinal circulation in eyes with ocular hypertension: a pilot study

This study investigated the effect of betaxolol, a beta 1 selective blocker, on the retinal circulation in 10 patients with ocular hypertension. In a masked randomised fashion, one eye of each subject received betaxolol and the fellow eye received placebo (hypromellose). Retinal blood flow (RBF) was determined in a major temporal vein of each eye just prior to instillation of drops and 2 h later, using laser Doppler velocimetry and monochromatic fundus photography. There was an increase of 15.0% in RBF (p = 0.03) in the betaxolol-treated eyes. No significant change was observed in the placebo-treated eyes. Intraocular pressure was reduced by 27.7% in the treated eyes, resulting in an increase of 16.9% in perfusion pressure (p = 0.02) compared with an 8.4% increase in placebo-treated eyes (p = 0.15). This study demonstrated that betaxolol increases RBF in eyes with ocular hypertension; this increase is probably related to the increase in perfusion pressure.