Effect of timolol on human retinal, choroidal and optic nerve head circulation

Changes in spectral parameters of corneal pulse following canaloplasty

PURPOSE

To ascertain whether changes in the spectral content of the corneal pulse (CP) signal, measured in vivo in primary open-angle glaucoma (POAG) patients, indirectly reflect changes in corneal biomechanics after canaloplasty.

METHODS

Fifteen eyes of 15 POAG patients who underwent canaloplasty combined with phacoemulsification were enrolled. Standard ophthalmic examinations were conducted before washout, pre-operatively, at days 1, 7, and 1, 3, 6, and 12 months after surgery. Non-contact measurements of the CP signal were performed at pre-washout, pre-operatively, and at 3, 6, and 12 months post-operatively. Then, amplitudes of the CP first five harmonics associated with the heart rate were estimated. Temporal changes of all considered parameters were tested at a Bonferroni-adjusted significance level set to 0.005.

RESULTS

A decrease in the amplitude of the first harmonic and an increase in the normalized amplitude of the third harmonic (A_CP3n) of the CP signal were noticed between the pre-washout and the pre-operative stages (p = 0.003 and p = 0.004, respectively). This corresponds to an increase in median intraocular pressure (IOP) values by 6.0 mmHg (p = 0.0045). After surgery, A_CP3n reached the highest value at 3 months post-operatively, compared with pre-washout level (p = 0.0045).

CONCLUSIONS

Alterations in corneoscleral stiffness caused by surgery are reflected in changes in the A_CP3n value. Hence, post-operative corneal biomechanics could be monitored indirectly by this supporting indicator that can be used to estimate the time at which measures of IOP are no longer biased by the changed cornea boundary conditions caused by canaloplasty.

CLINICAL TRIALS REGISTRATION

NCT02908633.

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.

Retinal oximetry

ABSTRACT.:

PURPOSE

Malfunction of retinal blood flow or oxygenation is believed to be involved in various diseases. Among them are retinal vessel occlusions, diabetic retinopathy and glaucoma. Reliable, non-invasive technology for retinal oxygen measurements has been scarce and most of the knowledge on retinal oxygenation comes from animal studies. This thesis describes human retinal oximetry, performed with novel retinal oximetry technology. The thesis describes studies on retinal vessel oxygen saturation in (1) light and dark in healthy volunteers, (2) central retinal vein occlusion, (3) branch retinal vein occlusion, (4) central retinal artery occlusion, (5) diabetic retinopathy, (6) patients undergoing glaucoma surgery and (7) patients taking glaucoma medication.

METHODS

The retinal oximeter (Oxymap ehf., Reykjavik, Iceland) is based on a fundus camera. An attached image splitter allows the simultaneous capture of four images of the same area of the fundus. Two images are used for further analysis, one acquired with 586 nm light and one with 605 nm light. Light absorbance of retinal vessels is sensitive to oxygen saturation at 605 nm but not at 586 nm. Measurement of reflected light at these wavelengths allows estimation of oxygen saturation in the main retinal vessels. This is performed with custom-made analysis software.

RESULTS

LIGHT AND DARK: After 30 min in the dark, oxygen saturation in retinal arterioles of healthy volunteers was 92 ± 4% (mean ± SD, n = 15). After 5 min in 80 cd/m(2) light, the arteriolar saturation was 89 ± 5%. The decrease was statistically significant (p = 0.008). The corresponding values for retinal venules were 60 ± 5% in the dark and 55 ± 10% in the light (p = 0.020). Similar results were found after alternating 5 min periods of darkness and light. In a second experiment (n = 19), a significant decrease in retinal vessel oxygen saturation was found in 100 cd/m(2) light compared with darkness but 1 and 10 cd/m(2) light had no significant effect. CENTRAL RETINAL VEIN OCCLUSION: In patients with central retinal vein occlusion, the mean saturation in affected retinal venules was 49 ± 12%, while the mean value for venules in the fellow eye was 65 ± 6% (mean ± SD, p = 0.003, n = 8). The retinal arteriolar saturation was the same in affected (99 ± 3%) and the unaffected (99 ± 6%) eyes. The venous oxygen saturation showed much variation between affected eyes. BRANCH RETINAL VEIN OCCLUSION: Median oxygen saturation in venules affected by branch retinal vein occlusion was 59% (range, 12-93%, n = 22), while it was 63% (23-80%) in unaffected venules in the affected eye and 55% (39-80%) in venules in the fellow eye. The difference was not statistically significant (p > 0.05). There was a significant difference between affected arterioles (median 101%; range, 89-115%) and unaffected arterioles (95%, 85-104%) in the affected eye (p < 0.05, n = 18). CENTRAL RETINAL ARTERY OCCLUSION: In a patient with a day's history of central retinal artery occlusion due to temporal arteritis, the mean arteriolar saturation was 71 ± 9% and 63 ± 9% in the venules. One month later, after treatment with prednisolone, the mean arteriolar saturation was 100 ± 4% and the venous saturation 54 ± 5%. DIABETIC RETINOPATHY: When compared with healthy volunteers (n = 31), patients with all categories of diabetic retinopathy had on average 7-10 percentage points higher saturation in retinal arterioles (p < 0.05 for all categories, n = 6-8 in each category). In venules, the saturation was 8-12 percentage points higher (p < 0.05 for all categories). GLAUCOMA SURGERY: Oxygen saturation in retinal arterioles increased by 2 percentage points on average (p = 0.046, n = 19) with surgery, which lowered intraocular pressure from 23 ± 7 mmHg (mean ± SD) to 10 ± 4 mmHg (p < 0.0001). No other significant changes were found (p ≥ 0.35). DORZOLAMIDE: A significant reduction of 3 percentage points was found in arterioles (p < 0.01) and venules (p < 0.05) when patients with glaucoma or ocular hypertension changed from dorzolamide-timolol combination eye drops to timolol alone (n = 6). No change was found in patients, who started on timolol and switched to the combination therapy (p > 0.05, n = 7).

CONCLUSIONS

Dual wavelength oximetry can be used to non-invasively measure retinal vessel oxygen saturation in health and disease. The results indicate that retinal vessel oxygen saturation is (1) increased in the dark, (2) lower in venules affected by central retinal vein occlusions, (3) variable in branch retinal vein occlusion, (4) lower in retinal arterioles in central retinal artery occlusion, (5) increased in diabetic retinopathy, (6-7) mildly affected by glaucoma surgery or dorzolamide.

The effects of a fixed combination of 0.5% timolol and 1% dorzolamide on optic nerve head blood circulation

PURPOSE

The purpose of the present study is to evaluate the effects of a fixed combination of 0.5% timolol maleate (TM) and 1% dorzolamide hydrochloride (DZ) (FCTD(1%)) on optic nerve head (ONH) blood circulation.

SUBJECTS AND METHODS

A drop of 0.5% TM, 1% DZ, or FCTD(1%) was topically administered to the right eyes of 15 healthy Japanese subjects, and a drop of saline was likewise administrated to their left eyes. Systemic blood pressure, heart rates (HRs), intraocular pressures (IOPs), ocular perfusion pressures, and blood circulation by a laser speckle flowgraphy at the ONH were measured before administration, and again at 1.5 and 6 h afterward.

RESULTS

FCTD(1%) caused a significant increase in ONH blood circulation 6 h after the administration, while 0.5% TM and 1% DZ had no significant effect. The IOPs were significantly decreased in 0.5% TM (P<0.01) and FCTD(1%) (P<0.05) when compared with the saline-treated eyes at 1.5 and 6 h after administration, while 1% DZ did not show a statistically significant decrease. There were no significant changes in other systemic parameters except for a significant transient decrease in the HRs observed in 0.5% TM (P<0.01) when compared with the baseline at 1.5 h after the administration.

CONCLUSION

Our current results suggest that FCTD(1%) caused a significant increase in ocular blood circulation on the ONH in healthy Japanese subjects, presumably by a synergistic effect of 0.5% TM and 1% DZ, although neither 0.5% TM nor 1% DZ on their own had a significant effect.

Changes in optic nerve head blood flow induced by the combined therapy of latanoprost and beta blockers

PURPOSE

To assess the effects of combined therapy with latanoprost and beta blockers on optic nerve head (ONH) blood flow in normal-tension glaucoma (NTG) patients.

METHODS

Intraocular pressure (IOP), ONH blood flow (laser speckle flowgraphy) and blood pressure were measured in 15 eyes of 15 NTG patients (41-76 years old) before treatment or after a 1-month washout period. Similar measurements were performed at 2 months after the commencement of treatment with latanoprost and at 3 months after the start of combined therapy of latanoprost with 0.5% timolol or 2% carteolol in a crossover study using the envelope method. Measurement was carried out 2-3 hr after the morning application of eyedrops.

RESULTS

Latanoprost decreased IOP with no significant change in ONH blood flow. Concomitant use of timolol or carteolol further decreased IOP with no significant difference between these two drugs. Only the combined therapy of latanoprost with carteolol significantly (p < 0.01) increased ONH blood flow by approximately 10%, compared to initial levels. There was no significant change in mean blood pressure, ocular perfusion pressure or pulse rate as a result of these therapies.

CONCLUSION

Topical latanoprost-carteolol combined therapy increased ONH blood flow in NTG patients, unlike latanoprost-timolol therapy. Because ocular perfusion pressure was unchanged, direct vasodilative effects were suspected as the mechanism.

Decrease of optic disc cupping and pallor of ocular hypertensives with timolol therapy

PURPOSE

The purpose of this study was to determine whether timolol drops compared to placebo drops had a significant effect on optic disc cupping and pallor in ocular hypertensives.

METHODS

Thirty-seven ocular hypertensives were randomly assigned to placebo or 0.5% timolol drops to both eyes in a double masked clinical trial. Measurements of ocular pressure and photographs of the optic disc for cupping by photogrammetry and pallor by computerized image analysis were made at about 3 month intervals, for 18 to 24 months of follow-up.

RESULTS

None of the subjects developed visual field loss when tested with the Goldmann perimeter by kinetic and static means at six month intervals. Subjects treated with timolol developed a significant decrease in ocular pressure and a significant decrease in optic disc cupping with a smaller decrease in pallor compared to subject treated with placebo. Multivariate analyses indicated that the decrease of optic disc cupping and pallor was not associated with the ocular pressure on treatment or the decrease in ocular pressure during the trial.

CONCLUSION

Timolol treatment was associated with a decrease in optic disc cupping and pallor. The effect of timolol appears to be related to mechanisms other than the decrease in ocular pressure.

Increase of retinal nerve fiber layer thickness in ocular hypertensives with timolol therapy

PURPOSE

The purpose of this study was to determine whether timolol drops compared to placebo drops had a significant effect on retinal nerve fiber layer thickness in ocular hypertensives.

METHODS

Thirty-seven ocular hypertensives were randomly assigned to receive placebo or 0.5% timolol drops to both eyes for 18 to 24 months in a double masked clinical trial. Measurements of ocular pressure and photographs of retinal nerve fiber layer using stereophotogrammetric techniques were made at about 3 month intervals for 18 to 24 months of follow-up.

RESULTS

None of the subjects developed visual field loss when tested with the Goldmann perimeter by kinetic and static means at six month intervals. Subjects treated with timolol had a significant decrease in ocular pressure and developed a significant increase in retinal nerve fiber layer thickness compared to subjects treated with placebo. Multivariate analyses indicated that the increase of retinal nerve layer thickness was not associated either with the ocular pressure on treatment or the decrease in ocular pressure on treatment.

CONCLUSION

Timolol treatment was associated with an increase of retinal nerve fiber thickness. The effect of timolol appears to be related to mechanisms other than the decrease in ocular pressure.

Increase of retinal vessel width in ocular hypertensives with timolol therapy

PURPOSE

The purpose of this study was to determine whether timolol drops compared to placebo drops had a significant effect on retinal vessel width in ocular hypertensives.

METHODS

Thirty-seven ocular hypertensives were randomly assigned to receive placebo or 0.5% timolol drops to both eyes for 18 to 24 months in a double masked clinical trial. Measurements of ocular pressure and retinal vessel width by computerized image analysis from fundus photographs were made at about 3 month intervals for 18 to 24 months of follow-up.

RESULTS

None of the subjects developed visual field loss when tested with the Goldmann perimeter by kinetic and static means at six month intervals. Subjects treated with the placebo showed no change in ocular pressure and a significant decrease in retinal vessel width over time especially in the right eye. Subjects treated with timolol had an increase in retinal vessel width compared to the placebo group significant especially for the superior temporal vein. Multivariate analyses indicated that the increase of retinal vessel width was not associated mainly with the ocular pressure on treatment or decrease in ocular pressure on treatment.

CONCLUSION

Timolol treatment was associated with an increase of retinal vessel width. The effect of timolol appears to be related primarily to mechanisms other than the decrease in ocular pressure.

Effect of dorzolamide and timolol on ocular blood flow in patients with primary open angle glaucoma and ocular hypertension

BACKGROUND

There is evidence that perfusion abnormalities of the optic nerve head are involved in the pathogenesis of glaucoma. There is therefore considerable interest in the effects of topical antiglaucoma drugs on ocular blood flow. A study was undertaken to compare the ocular haemodynamic effects of dorzolamide and timolol in patients with primary open angle glaucoma (POAG) or ocular hypertension (OHT).

METHODS

One hundred and forty patients with POAG or OHT were included in a controlled, randomised, double blind study in two parallel groups; 70 were randomised to receive timolol and 70 to receive dorzolamide for a period of 6 months. Subjects whose intraocular pressure (IOP) did not respond to either of the two drugs were switched to the alternative treatment after 2 weeks. Scanning laser Doppler flowmetry was used to measure blood flow in the temporal neuroretinal rim and the cup of the optic nerve head. Pulsatile choroidal blood flow was assessed using laser interferometric measurement of fundus pulsation amplitude.

RESULTS

Five patients did not respond to timolol and were changed to the dorzolamide group, and 18 patients changed from dorzolamide treatment to timolol. The effects of both drugs on IOP and ocular perfusion pressure were comparable. Dorzolamide, but not timolol, increased blood flow in the temporal neuroretinal rim (8.5 (1.6)%, p<0.001 versus timolol) and the cup of the optic nerve head (13.5 (2.5)%, p<0.001 versus timolol), and fundus pulsation amplitude (8.9 (1.3)%, p<0.001 versus timolol).

CONCLUSIONS

This study indicates augmented blood flow in the optic nerve head and choroid after 6 months of treatment with dorzolamide, but not with timolol. It remains to be established whether this effect can help to reduce visual field loss in patients with glaucoma.

Optic nerve oxygenation

The oxygen tension of the optic nerve is regulated by the intraocular pressure and systemic blood pressure, the resistance in the blood vessels and oxygen consumption of the tissue. The oxygen tension is autoregulated and moderate changes in intraocular pressure or blood pressure do not affect the optic nerve oxygen tension. If the intraocular pressure is increased above 40 mmHg or the ocular perfusion pressure decreased below 50 mmHg the autoregulation is overwhelmed and the optic nerve becomes hypoxic. A disturbance in oxidative metabolism in the cytochromes of the optic nerve can be seen at similar levels of perfusion pressure. The levels of perfusion pressure that lead to optic nerve hypoxia in the laboratory correspond remarkably well to the levels that increase the risk of glaucomatous optic nerve atrophy in human glaucoma patients. The risk for progressive optic nerve atrophy in human glaucoma patients is six times higher at a perfusion pressure of 30 mmHg, which corresponds to a level where the optic nerve is hypoxic in experimental animals, as compared to perfusion pressure levels above 50 mmHg where the optic nerve is normoxic. Medical intervention can affect optic nerve oxygen tension. Lowering the intraocular pressure tends to increase the optic nerve oxygen tension, even though this effect may be masked by the autoregulation when the optic nerve oxygen tension and perfusion pressure is in the normal range. Carbonic anhydrase inhibitors increase the optic nerve oxygen tension through a mechanism of vasodilatation and lowering of the intraocular pressure. Carbonic anhydrase inhibition reduces the removal of CO2 from the tissue and the CO2 accumulation induces vasodilatation resulting in increased blood flow and improved oxygen supply. This effect is inhibited by the cyclo-oxygenase inhibitor, indomethacin, which indicates that prostaglandin metabolism plays a role. Laboratory studies suggest that carbonic anhydrase inhibitors might be useful for medical treatment of optic nerve and retinal ischemia, potentially in diseases such as glaucoma and diabetic retinopathy. However, clinical trials and needed to test this hypotheses.

Adenylyl and guanylyl cyclase activity in the choroid

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

Optic nerve oxygen tension: the effects of timolol and dorzolamide

BACKGROUND/AIMS

The authors have previously reported that carbonic anhydrase inhibitors such as acetazolamide and dorzolamide raise optic nerve oxygen tension (ONPO(2)) in pigs. The purpose of the present study was to investigate whether timolol, which belongs to another group of glaucoma drugs called beta blockers, has a similar effect. In addition, the effect of dorzolamide and timolol in combination was studied.

METHODS

Polarographic oxygen electrodes were placed transvitreally over the optic disc in anaesthetised pigs and ONPO(2) was recorded continually. Drugs were administered intravenously either as 100 mg timolol followed by 500 mg dorzolamide (n = 5), 500 mg dorzolamide followed by 100 mg timolol (n = 5), or 100 mg timolol and 500 mg dorzolamide given simultaneously (n = 5). Arterial blood pressure, blood gasses, and heart rate were recorded.

RESULTS

ONPO(2) was unaffected by administration of 100 mg timolol as an intravenous injection (n = 5). Administration of 500 mg dorzolamide by itself significantly increased ONPO(2) from 2.96 (SD 0.62) kPa to 3.69 (SD 0.88) kPa (n = 4, p = 0.035). The dorzolamide induced ONPO(2) increase was not significantly different from the ONPO(2) increases were seen when dorzolamide was administered simultaneous with (n = 5) or 35 minutes (n = 5) after 100 mg timolol.

CONCLUSION

Systemic administration of timolol does not affect the optic nerve oxygen tension despite its lowering effect on the intraocular pressure. Additionally, timolol does not affect the ONPO(2) increasing effect of dorzolamide.

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.

Changes in choroidal blood flow during light/dark transitions are not altered by atropine or propranolol in healthy subjects

It has recently been reported that light/dark transitions lead to changes in choroidal blood flow. Several observations indicate that these changes in choroidal perfusion are triggered at least in part by neural mechanisms. In the present study we hypothesised that the choroidal blood flow response to changes in retinal illumination may be modified by either the muscarinic receptor antagonist atropine or by the beta-receptor antagonist propranolol. In 15 healthy subjects the response of choroidal perfusion was studied in a randomised placebo-controlled three way cross-over study using laser Doppler flowmetry and laser interferometric measurement of fundus pulsation amplitude. Before drug administration a transition from light to dark reduced both choroidal haemodynamic parameters by 8%-12%. Neither propranolol nor atropine altered basal choroidal blood flow or choroidal blood flow responses to light/dark transitions. Our data indicate that neither muscarinic nor beta-receptors are involved in the choroidal blood flow response to changes in retinal illumination. Further studies are required to elucidate which mechanisms contribute to this blood flow behaviour of the choroid.

Drug delivery to the posterior segment from drops

The published evidence that instilled drugs can affect the blood supply to the retina and optic nerve head in humans is examined. As a background, seven techniques that have been used to measure flow are briefly described and criticized. For timolol, the corresponding measurements, obtained by a number of investigators are evaluated. The outcome is very erratic and does not allow any conclusion as to the effect of this drug on flow. Consideration is then given to the possible mechanism whereby a drug could affect blood flow; directly, by diffusion to receptors on the vessels, or indirectly, through more anterior receptors. The question is raised whether the small changes in circulation induced by drugs would not be swamped by those resulting from natural alterations in the ambient light level. The literature was analyzed in the hope of identifying discrete entry pathways, for example, through the lens or the suprachoroidal space, that are sufficiently permeable to allow a significant quantity of drug to pass. There was an indication that a drug might diffuse through the lens cortex in sufficient quantity to cause a measurable rise in its concentration in the vitreous. In general, however, there was insufficient quantitative data to allow any meaningful predictions to be made. Stimulated by recent evidence, it is suggested that drug penetration from the tear fluid takes place by direct diffusion across the conjunctiva into the sclera and orbit when the head is supine.

Short-term effect of beta-adrenoreceptor blocking agents on ocular blood flow

PURPOSE

In this study the acute effect of the topically-delivered non-selective beta-blockers timolol and carteolol, and the selective beta-blocker betaxolol, were evaluated with respect to ocular blood flow, intraocular pressure (IOP) and vessel resistance in rabbits' eyes.

METHODS

In a double masked randomized design, one eye of each subject (n = 9) received two drops of 0.5 % timolol or 2 % cartelol or 0.5 % betaxolol ophthalmic solution and a separate group of nine rabbits received two drops of placebo consisting of physiological saline in both eyes to serve as control. Using hydrogen clearance method, ciliary body blood flow (CiBF), choroidal blood flow (CBF), and retinal blood flow (RBF) were measured. IOP and systemic mean arterial pressure (MAP) of each subject were measured under same condition before and after the administration of respective drugs to calculate the ocular perfusion pressure (OPP) and vessel resistance.

RESULTS

In timolol- and carteolol-treated eyes significant reduction was observed in IOP (p < 0.01), CiBF (p < 0.01), CBF (p < 0.01) and RBF (p < 0.01) compared to control eyes. However, in betaxolol-treated eyes a marginal reduction in IOP was observed accompanied by significant increase in CiBF (p < 0.01) and RBF (p < 0.05). The non-selective beta-blocker-treated eyes tended to have increased vessel resistance, whereas, selective beta-blocker-treated eyes tended to have decreased vessel resistance.

CONCLUSIONS

Our current results comparing non-selective and selective beta-blockers suggest that the selective beta-blocker betaxolol may be more appropriate for maintenance of retinal blood flow in situations with low perfusion. Currently the mechanism for regulation of IOP is unclear; however, the findings from this study indicate that decreased CiBF may contribute to reduction in IOP.

The impact of glaucoma medication on parameters of ocular perfusion

Whereas intraocular pressure is considered a major risk factor in glaucoma, growing evidence now indicates that ocular ischemia plays a major role too. By virtue of this and because many existing medications are able to interact with vasculature, altering ocular blood flow, it is essential that current and future medications for glaucoma be evaluated for their effect on ocular circulation. The authors review published papers examining the effect of topical and some systemic medications on ocular blood flow, focusing mostly on data from the human eye. The authors provide a comprehensive review on the effect of subclasses of medications (eg, carbonic anhydrase inhibitors, beta-blockers, alpha-adrenergic agonists, and prostaglandin analogues on optic nerve head, and on retinal, choroidal, and retrobulbar circulation. The various claims for enhancements or reduction of ocular circulation within each class of medication are reviewed and evaluated.

A comparative study on the effects of apraclonidine and timolol on the ophthalmic blood flow velocity waveforms

PURPOSE

To evaluate the effects of topical timolol and apraclonidine on retrobulbar blood flow velocity waveforms in a group of healthy volunteers.

METHODS

Apraclonidine 1% and timolol maleate 0.5% single dose administrations were crossed over double masked in 12 healthy volunteers. The intraocular pressure measurements were followed by Doppler examination of the ophthalmic artery and the central retinal artery.

RESULTS

Intraocular pressure was reduced significantly on both treated and fellow eyes after timolol (p = 0.003, p = 0.04 respectively) and after apraclonidine (p = 0.002, p = 0.01 respectively). After apraclonidine administration end diastolic velocity, mean velocity decreased and pulsatility index increased in the ophthalmic artery of both treated and fellow eyes. Resistivity index increased and peak systolic velocity decreased only in the ophthalmic artery of treated eyes. All Doppler indices remained nonsignificant for central retinal artery of both eyes. After timolol administration there were no significant changes of the Doppler indices in the ophthalmic artery and central retinal artery of the treated and fellow eyes.

CONCLUSION

Topical timolol and apraclonidine significantly reduced the intraocular pressure. Single dose administration of apraclonidine 1% increased the vascular impedance distal to the ophthalmic artery. On the other hand, timolol 0.5% had no effect on vascular impedance.

Effect of timolol on anterior optic nerve blood flow in patients with primary open-angle glaucoma as assessed by the Heidelberg retina flowmeter

PURPOSE

To evaluate the effect of 0.5% timolol maleate on the capillary circulation of the anterior optic nerve head in patients with primary open-angle glaucoma and to compare the results with those obtained in a healthy control group.

PATIENTS AND METHODS

Twelve patients with nonprogressive glaucoma and 12 age- and sex-matched healthy volunteers were included in this prospective study. Optic nerve head perfusion was examined by the Heidelberg Retina Flowmeter (HRF) in both groups. A 3-week washout period preceded the baseline measurement in the glaucoma group, and ONH blood flow was assessed again after 3 weeks of bilateral topical timolol treatment and 2 hours after timolol application.

RESULTS

Intraocular pressure decreased significantly with timolol (P < 0.001). The HRF flow values for patients with glaucoma were comparable to those for a control group at baseline (P = 0.25), 3 weeks after timolol therapy (P = 0.09), and 2 hours after timolol instillation (P = 0.15). The glaucoma group showed no statistically significant change in the HRF parameter flow as compared with baseline, either after 3 weeks of timolol treatment or 2 hours after timolol instillation (P = 0.40). The heart rate and arterial systolic and diastolic blood pressure values showed no alteration after timolol therapy.

CONCLUSIONS

Patients with nonprogressive glaucoma seem not to have an altered optic nerve blood flow as assessed by the HRF, and timolol treatment does not seem to alter the latter blood flow parameter in such patients.

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.

Sympathetic vasodilation in the rat anterior choroid mediated by beta(1)-adrenoceptors

Electrical stimulation of the preganglionic superior cervical nerve produced a frequency-dependent vasoconstrictor response in the anterior choroidal blood vessels of the eye of anesthetized rats. Systemic administration of phentolamine (5 mg kg(-1)) reversed the vasoconstriction to a vasodilator response. This sympathetic-evoked vasodilation was not antagonized by inhibition of nitric oxide synthase with N(G)-nitro-L-arginine methyl ester (L-NAME) (20 mg kg(-1)) or by inhibition of cyclo-oxygenase with indomethacin (20 mg kg(-1)). Intravenous administration of propranolol (1 mg kg(-1)), as well as selective beta(1)-adrenoceptor antagonists atenolol (3 mg kg(-1)), timolol (0.3 mg kg(-1)), and betaxolol (0.1 mg kg(-1)), totally abolished the sympathetic nerve evoked ocular vasodilation. In contrast, the selective beta(2)-adrenoceptor antagonist, ICI-118, 551 ((+/-)-1-[2, 3-(Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2- butanol) (0.3 mg kg(-1), i.v.), was without effect. These results support the conclusion that the residual sympathetic ocular vasodilation observed in the rat anterior choroid after alpha-adrenoceptor blockade is mediated exclusively by neurogenic release of norepinephrine acting on vascular beta(1)-adrenoceptors.

Progress in measurement of ocular blood flow and relevance to our understanding of glaucoma and age-related macular degeneration

New technologies have facilitated the study of the ocular circulation. These modalities and analysis techniques facilitate very precise and comprehensive study of retinal, choroidal, and retrobulbar circulations. These techniques include: 1. Vessel caliber assessment; 2. Scanning laser ophthalmoscopic fluorescein angiography and indocyanine green angiography to image and evaluate the retinal circulation and choroidal circulation respectively; 3. Laser Doppler flowmetry and confocal scanning laser Doppler flowmetry to measure blood flow in the optic nerve head and retinal capillary beds; 4. Ocular pulse measurement; and 5. color Doppler imaging to measure blood flow velocities in the central retinal artery, the ciliary arteries and the ophthalmic artery. These technique have greatly enhanced the ability to quantify ocular perfusion defects in many disorders, including glaucoma and age-related macular degeneration, two of the most prevalent causes of blindness in the industrialized world. Recently it has become clear, in animal models of glaucoma, that retinal ganglion cells die via apoptosis. The factors that initiate apoptosis in these cells remain obscure, but ischemia may play a central role. Patients with either primary open-angle glaucoma or normal-tension glaucoma experience various ocular blood flow deficits. With regard to age-related macular degeneration, the etiology remains unknown although some theories include primary retinal pigment epithelial senescence, genetic defects such as those found in the ABCR gene which is also defective in Stargardt's disease and ocular perfusion abnormalities. As the choriocapillaris supplies the metabolic needs of the retinal pigment epithelium and the outer retina, perfusion defect in the choriocapillaris could account for some of the physiologic and pathologic changes in AMD. Vascular defects have been identified in both nonexudative and exudative AMD patients using new technologies. This paper is a comprehensive update describing modalities available for the measurement of all new ocular blood flow in human and the clinical use.

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.

Effects of timolol and betaxolol on choroidal blood flow in the rabbit

This study evaluated the effects of the topical beta1-adrenergic antagonist betaxolol and the non-selective beta-adrenergic antagonist timolol on the choroidal pressure-flow relationship. Pentobarbital-anesthetized rabbits were instrumented with hydraulic occluders on the aorta and inferior vena cava to control MAP, an ear artery cannula to measure mean arterial pressure (MAP), and two vitreous cannulas to control and measure intraocular pressure (IOP). Choroidal blood flow was measured by laser Doppler flowmetry with the fiber-optic probe tip positioned over the posterior pole. Choroidal pressure-flow curves were obtained before and 30 min after topical application of 0.1 ml of betaxolol (Betoptic, 0.5%, n=10), timolol (Timoptic, 0.5%, n=10) or saline (n=8) by varying the MAP without controlling the IOP and by raising IOP while holding the MAP constant at 70 mmHg. The IOP was significantly reduced by betaxolol and timolol but not by saline. MAP was also slightly, but significantly, reduced after betaxolol but not after timolol or saline. However, the systemic hypotensive response to isoproterenol (8 microgram/kg, i.v.) was blunted after betaxolol and timolol indicating appreciable systemic absorption of both drugs. Timolol, but not betaxolol or saline, caused a significant, small increase in baseline choroidal vascular resistance. Timolol also attenuated the IOP response to MAP; however, none of the treatments had a significant effect on the choroidal pressure-flow relationship. We conclude that both drugs reach the systemic circulation after topical application, but neither betaxolol nor timolol alter the choroidal response to acute changes in perfusion pressure.

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.

Acute effect of metipranolol on the retinal circulation

AIM

To assess the effect of topical and systemic application of a beta adrenergic receptor blocker on retinal haemodynamics.

METHODS

24 healthy subjects were included in this double masked, randomised, placebo controlled crossover study. Metipranolol, a non-selective beta adrenergic receptor blocking agent was used as test drug. In all subjects arm-retina time, arteriovenous passage time, arterial mean dye velocity, the arterial vessel diameters, and capillary flow velocity were quantified from digital video fluorescein angiograms.

RESULTS

A significant effect was observed on the arteriovenous passage time (p < 0.05), the arterial mean dye bolus velocity (p < 0.05), and capillary blood velocity (p < 0.05), but not on the arterial vessel diameter. The arterial mean dye bolus velocity and capillary blood velocity increased after application of the test drug (topical and systemic). In tandem with this a decrease of the arteriovenous passage time was observed. The perfusion pressure increased after topical application and remained unchanged after systemic application of metipranolol.

CONCLUSIONS

This study shows that systemic as well as topical application of metipranolol leads to increased retinal blood flow velocities. The implications of these results for treatment with beta adrenergic receptor blockers is not clear. However, in view of these data it is very unlikely that treatment with metipranolol has a negative effect on retinal blood flow.

Assessment of human ocular hemodynamics

Vascular abnormality and altered hemodynamics play important roles in many ophthalmic pathologies. Much of our knowledge of ocular hemodynamics was gained from invasive animal research, although a number of noninvasive methods suitable for in vivo use in humans have been developed. Data from these methods now produce a significant literature of their own. Understanding the origins of the data and appreciating their limitations can be difficult. Modern hemodynamic assessment techniques each examine a unique facet of the ocular circulation. No single facet provides a complete description of the hemodynamic state of the eye. These methods have contributed a great deal to our understanding of normal hemodynamics. More importantly, they continue to add to our understanding of altered hemodynamics found in disease. Some have found their way into limited clinical practice. The predominant ocular hemodynamic assessment techniques are reviewed with the aims of introducing the fundamental principles behind each, highlighting their inherent advantages and limitations, highlighting their contributions to understanding ocular physiology, and considering their potential to provide signs for diagnosis.

Short-term effects of topical levobunolol on the human retinal circulation

PURPOSE

The effect of topical levobunolol HCl 0.5% on the retinal circulation was studied on 15 normal volunteers aged 21-54 years (32 +/- 10 years).

METHODS

In a double-masked, randomised design, one eye of each subject received a drop of levobunolol HCl 0.5% (LEV) and the fellow eye received a drop of artificial tears (TEAR). Leucocyte velocity (VBFS) and density in the retinal macular microcirculation were measured by the blue-field simulation technique. Venous diameter (D), maximum erythrocyte velocity (Vmax) and volumetric blood flow rate (Q) were measured in a major temporal vein by laser Doppler velocimetry and monochromatic fundus photography.

RESULTS

The following average changes from baseline were observed 2 hours after treatment: heart rate, -4.6 +/- 8.3% (p = 0.04); intraocular pressure, -31.7 +/- 10.6% (p = 0.0001); and perfusion pressure, 15.4 +/- 14.4% (p = 0.02) in LEV eyes; no statistically significant changes in IOP and perfusion pressure were seen in TEAR eyes. When each eye was compared with its own baseline, there were no significant changes in VBFS, density, D, Vmax and Q in LEV eyes. In TEAR eyes, there were no significant changes in VBFS, density, Vmax and Q, but a significant change in D (-1.8 +/- 2.6%; p = 0.02) was observed. A significant average percentage increase in Q of 10.9 +/- 19.2% (paired t-test between the change after LEV and the change after TEAR, p = 0.044) was seen in LEV eyes when compared with TEAR eyes. Twelve of the 15 subjects demonstrated a relative increase in Q in the LEV eyes in comparison with the TEAR eyes, while 3 subjects showed the opposite.

CONCLUSION

A significant difference in the effect of levobunolol between the two eyes was detected, even though there was no statistically significant effect when each eye was compared with its baseline.

Effect of topical beta-blockers on tissue blood flow in the human optic nerve head

PURPOSE

To study the effect of topical 0.5% timolol and 2% carteolol on tissue blood flow in the human optic nerve head (ONH).

METHODS

Using a laser speckle tissue blood flow analyzer, normalized blur (NB), a quantitative index of tissue blood velocity, was measured every 0.125 s in the temporal site of the ONH free of visible surface vessels and averaged over 3 cardiac pulses (NBONH). To serve as a baseline, NBONH and intraocular pressure (IOP) in both eyes, blood pressure (BP) and pulse rate (PR) were recorded in healthy volunteers before, 1.5, 3 and 4.5 hrs after a 30L instillation of the vehicle of timolol or carteolol. From the following day and twice daily for 3 weeks, 30L of either 0.5% timolol or 2% carteolol was instilled into one eye and the respective vehicle into the fellow eye in a masked manner. NBONH, IOP, BP and PR were again recorded on the 21st and last experiment day. IOP was also recorded on the 7th and 14th days. Carteolol concentration in the plasma was also recorded after instillation of carteolol on the 21st day.

RESULTS

During the baseline experiments, all the parameters recorded showed no significant change. After topical timolol, IOP was significantly reduced bilaterally with more reduction in the timolol-treated eye. Bilateral NBONH, BP and PR showed little change on the 21st day. After topical carteolol, IOP was significantly reduced bilaterally with more reduction in the carteolol-treated eyes on the 21st day. NBONH in the carteolol- and vehicle-treated eyes was significantly higher on the 21st day than recorded in the same eye in the baseline experiment (P = 0.013 and 0.047), while BP and PR showed little change. The maximum carteolol concentration in plasma at 3 hrs on the 21st day averaged 1294 pg/ml.

CONCLUSIONS

Results indicated that 3-week twice daily topical timolol treatment had no deleterious effect on the ONH tissue blood flow in the human eye, and that 3-week twice daily topical carteolol treatment may increase the tissue blood flow in the human ONH.

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.

Effect of one week of levobunolol HCl 0.5% on the human retinal circulation

PURPOSE

To determine the effect of one week of topical treatment with levobunolol HCl 0.5% on the retinal circulation of normal subjects.

METHODS

Fifteen healthy volunteers with no history of ocular disease were included in this study. In a double-masked, randomized, cross-over design, one eye of each subject was treated, for one week, with one drop of either levobunolol or placebo, administered twice daily. Following a washout period of at least three weeks, the same eye received the alternate treatment for one week. Before the beginning of therapy and then two hours after the last drop, vessel diameter (D), maximum erythrocyte velocity (Vmax), and volumetric blood flow rate (Q) were determined in one major retinal vein of the treated eye, using bidirectional laser Doppler velocimetry and monochromatic fundus photography. Statistical analysis was performed using two-tailed, paired Student's t-test, linear regression, and correlation analysis.

RESULTS

The average percentage change from baseline in intraocular pressure was statistically significant following levobunolol (-15% +/- 13% (+/-1 SD), P < .001), but not following placebo (-3% +/- 11%, P > .05). No significant changes in average D, Vmax, or Q were observed after levobunolol treatment (-1% +/- 4%, 5% +/- 11%, 4% +/- 15%, respectively) or placebo treatment (-1% +/- 4%, -2% +/- 9%, -5% +/- 10%, respectively). The average difference between the changes in Q from baseline after levobunolol and placebo treatments (9% +/- 17%) achieved a significance level of P = 0.06. Furthermore, following levobunolol treatment, Q was 7% +/- 14% higher than following placebo treatment (P = 0.05).

CONCLUSIONS

A comparison of the effects of placebo and levobunolol treatments suggests that levobunolol has a variable effect on the retinal circulation with a tendency to show an overall slight increase in flow.

A comparative study of the effects of timolol and latanoprost on blood flow velocity of the retrobulbar vessels

PURPOSE

To examine the effects of topical timolol and latanoprost on retrobulbar vessel blood velocity in patients with glaucoma or ocular hypertension.

METHODS

Nine patients with primary open-angle glaucoma and six patients with ocular hypertension were enrolled for this study. All patients were treated topically with 0.5% timolol or 0.005% latanoprost, using a double-masked crossover design with a 3-week washout before administration of each drug. Each patient had a baseline color Doppler imaging ultrasound of the central retinal artery, short posterior ciliary arteries, and ophthalmic artery and two other ultrasound examinations during the 1-week treatment with each drug, performed 12 hours after the first dose of the drug and 12 hours after the last dose, 7 days later.

RESULTS

Both topical timolol and topical latanoprost significantly reduced the intraocular pressure. The only significant change observed in the retrobulbar blood velocity with timolol was a reduction of end diastolic velocity in the ophthalmic artery 12 hours after the first dose, accompanied by a trend toward a decrease in the peak systolic velocity and an increase in the resistance index in the same vessel. No change in blood velocity was observed with latanoprost.

CONCLUSION

Topical timolol and latanoprost significantly reduced the intraocular pressure in ocular hypertensive and glaucoma patients without creating substantial hemodynamic changes in the retrobulbar vessels.

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

Thirty-three ocular hypertensive patients (21 with primary open angle glaucoma and 12 glaucoma suspects) were randomly assigned to receive either timolol, levobunolol or betaxolol in one eye. Pulsatile ocular blood flow (POBF) was measured before treatment (baseline) and 2 hours after drop administration. After 1 week of regular twice-daily dosage, POBF was measured again both immediately before and 2 hours after drop instillation. All measurements were made by an investigator masked to treatment. POBF increased by 11% (p = 0.09) at week 0 after levobunolol administration, and by 22% (p = 0.20) at week 1 before drop administration compared with baseline. It dropped by 23% and 25% (p = 0.04 and 0.06, respectively) before and after betaxolol administration at week 1. Although POBF was reduced in the timolol group, this change was not significant. These results can not be explained uniformly by changes in intraocular pressure or blood pressure. The relevance of these measurements to visual function in glaucoma is not known.

Ocular and cerebral blood flow measurements in healthy subjects. A comparison of blood flow velocity and dynamic tonometry measurements before and after acetazolamide

The ocular and cerebral blood flow was studied in 15 healthy subjects using transcranial Doppler ultrasonography (2 MHz). The blood flow velocity in the precerebral carotid arteries, in the ophthalmic artery and in the middle cerebral artery was measured under baseline conditions and after i.v. administration of 1 g acetazolamide. To measure the intraocular pressure and the corneal indentation pulse amplitude, a dynamic tonometer was used. Pulsatile ocular blood volume was calculated from these values. After one single dose of acetazolamide a significant decrease in ophthalmic artery flow velocity, and a significant increase both in internal carotid and in middle cerebral artery velocity was found. A significant decrease in intraocular pressure and in pulsatile ocular volume after acetazolamide was also demonstrated. These findings suggest that the acute effect of acetazolamide may be associated with a reduced ocular blood flow, explaining some of the reduction in IOP.

Longterm effect of topical beta-blockers on intraocular pressure and visual field sensitivity in ocular hypertension and chronic open-angle glaucoma

In a prospective, randomized study, nineteen patients with ocular hypertension (n = 14) or chronic open-angle glaucoma (n = 5) were treated with either betaxolol 0.5% or timolol 0.5% in both eyes twice daily. Visual field sensitivity and intraocular pressure were assessed with the Octopus perimeter (program G1) and applanation tonometry, respectively, at 3, 6, 12, 24, 36, and 48 months during treatment. Four of the nineteen patients (two timolol-treated and two betaxolol-treated) were lost to follow-up after the 36-month examination. Whereas both drugs reduced the intraocular pressure, the decrease in the timolol-treated group was statistically more pronounced than in the betaxolol-treated group at month 3, 6, and 48 (p < 0.03). In both treatment groups, the visual field mean sensitivity (MS) index decreased slightly during the first six months of treatment, but remained so only in the timolol-treated group at all subsequent examinations. In the betaxolol-treated group, there was a statistically significant increase in MS at the 12, 24, 36, and 48 month visits (p < 0.01). These findings suggest that factors other than IOP alone may determine visual field outcome.

Ocular blood flow and vision in healthy and glaucomatous eyes

The differential light sensitivity (DLS) in healthy, but not glaucomatous eyes, is stable and unaffected by substantial loss of the ocular perfusion pressure resulting either from increased intraocular pressure (IOP) or from moderate to severe stenosis of the internal carotid arteries. Results of pulsatile ocular blood flow measurements provide evidence that this stability of vision in healthy eyes is dependent on autoregulation of blood flow to the retinal ganglion cell axons. The onset and progression of glaucoma is shown to be associated with instability of the DLS at discrete retinal points, which develops prior to visual loss, and with an abnormal sensitivity of the DLS to increased IOP. The abnormal fluctuation of the DLS in glaucomatous eyes and the loss of DLS induced by increased IOP and decreased ocular blood flow provides evidence of a microvascular impairment to discrete areas of the optic nerve.

Differences in the longterm effect of timolol and betaxolol on the pulsatile ocular blood flow

In the past several years the effect of longterm glaucoma therapy on ocular hemodynamics has taken on increased interest. This interest has been sparked by studies demonstrating differential effects of various beta-blockers on visual function, and the possible contributory role of ocular blood flow. In the present study, the pulsatile ocular blood flow (POBF), as derived by the Langham OBF system, was measured prior to treatment and then tracked throughout a one-year period of beta-blocker therapy (betaxolol 0.5% or timolol 0.5%) in 25 glaucoma patients. Results of the two treatments were compared, and indicated that, whereas both betaxolol- and timolol-treated patients had similar significant reductions in the IOP, the effect of the two treatments on the POBF differed. In timolol-treated patients, the POBF decreased significantly over the 12-month observation period, whereas in betaxolol-treated patients it remained stable.

Diurnal variation in pulsatile ocular blood flow in normal and glaucomatous eyes

Ocular blood flow, in particular to the optic nerve head, is considered important in determining the extent of glaucomatous damage. The 24-hour variation in the pulsatile component of ocular blood flow (POBF) was measured using a pneumotonometer linked to the Langham Ocular Blood Flow System. Intraocular pressure (IOP), ocular pulse amplitude, POBF, systemic blood pressure and heart rate were recorded at three-hourly intervals over a 24-hour period in 10 ocular hypertensives, eight patients with primary open angle glaucoma (POAG) treated with timolol eyedrops (G timolol 0.25%), and eight ocular normotensive control subjects. The POAG subjects were readmitted for a second set of 24-hour measurements after temporarily discontinuing G timolol for two weeks. The POBF showed no significant diurnal variation in any of the patient groups, the POAG values being taken from the "off treatment" period. By contrast, there were overnight falls in IOP, ocular pulse amplitude, blood pressure and heart rate, which reached significance in some groups. This suggests that overall there are compensatory changes in IOP, blood pressure, heart rate, and perhaps ocular vascular resistance, to preserve POBF overnight. Within all groups there was much individual variation, with some subjects showing an overnight fall in POBF, suggesting a lack of autoregulation in these cases who might prove to be at greater risk of developing nocturnal glaucomatous damage. When timolol was withdrawn from POAG subjects, there was no change in POBF despite an increase in IOP, implying that timolol, though effective as ocular hypotensive, did not alter POBF.

Blood flow rate in the microvasculature of the optic nerve head in primary open angle glaucoma. A new approach

In order to evaluate the optic nerve head perfusion in patients with primary open-angle glaucoma (POAG), we measured the velocity of the red blood cells (RBCs) in the capillaries of the optic nerve head with a laser-Doppler velocimeter and evaluated the blood viscosity by determining the capacity of the RBCs to disaggregate with an erythroaggregameter. Our results showed that in POAG patients optic nerve blood velocity was reduced and that the aggregability of the RBCs was increased. The two parameters were not significantly correlated, possibly because of local papillary autoregulation and anatomical variability in the papilla vessels. These two factors could explain why the same rheological anomaly in two subjects could lead to different responses in blood velocity. The RBC hyperaggregability cannot be explained by quantitative modifications of the plasma proteins. Modifications in the membrane of the RBCs could indeed be responsible for hyperaggregability, since our data suggest that deformability of the RBCs is impaired in glaucoma.

Short-term effects of levobunolol on ocular pulsatile flow

In a randomized, double-masked, placebo-controlled study, we evaluated the effect of levobunolol 0.5%, a nonselective beta-blocker, on intraocular pressure, volume amplitude, and ocular pulsatile flow in healthy individuals and patients with glaucoma. Volume amplitude and ocular pulsatile flow were derived from measurements of pulse amplitude with a pneumatonometer. Two hours after instillation of levobunolol, intraocular pressure decreased from 26.0 +/- 5.1 mm Hg to 17.8 +/- 3.9 mm Hg (28.3%) (P less than .001) in glaucomatous eyes and 20.2 +/- 3.6 mm Hg to 14.5 +/- 4.2 mm Hg (29.6%) (P less than .001) in healthy eyes. Ocular pulsatile flow was increased after treatment with levobunolol from 482.1 +/- 133.3 microliter/minute to 548.5 +/- 180.3 microliter/minute (13.3%) (P less than .006) in glaucomatous eyes and 457.6 +/- 178.2 microliter/minute to 528 +/- 223.8 microliter/minute (12.3%) (P greater than .05) in healthy eyes. There was no significant change in intraocular pressure, volume amplitude, or ocular pulsatile flow in placebo-treated eyes. The implication of these data for glaucoma therapy is not clear. Although we used an instrument that supposedly measures total pulsatile flow, it may be that optic nerve blood flow is dependent on total, both pulsatile and nonpulsatile, flow. Further, even though retinal blood flow is a small component of total ocular blood flow, it may be equally or more important than choroidal flow because of the necessity to maintain the perfusion of the retinal ganglion cells.

Effects of timolol on visual-field mean retinal sensitivity in normal subjects

This single-blind, randomized study investigated the effects of unilateral instillation of 0.5% maleate timolol twice a day for 7 days on visual-field parameters of both eyes. Twelve normal, young subjects (30.6 +/- 4.2 years) participated in this study. Using program G1 of the Octopus 500 automated perimeter, the visual fields were measured one week and one day before therapy and a third time one week after beginning therapy. The paired T-test was used for statistical analysis, where a P-value < or = 0.05 indicated significance. Whereas nothing statistically significant was found in the treated eyes, the contralateral, untreated eyes showed a statistically significant decrease of mean sensitivity between the first visual fields and the third ones (P < 0.01) This diminution of mean sensitivity in the untreated contralateral eyes may be due to statistically significant lowering of blood pressure (P < 0.01) and slowing of cardiac frequency, which were not compensated by a local decrease of intraocular pressure. If confirmed, these findings could be of clinical importance in the management of glaucoma patients, since some authors have, in some cases, recommended a unilateral therapy.