Effect of timolol on optic nerve head autoregulation

Effect of changing from concomitant timolol pilocarpine to bimatoprost monotherapy on ocular blood flow and IOP in primary chronic angle closure glaucoma

The aim of the present prospective masked study was to assess the effect of bimatoprost monotherapy on ocular blood flow and intraocular pressure (IOP) in eyes of primary chronic angle closure glaucoma patients already on concomitant timolol and pilocarpine. Thirty two patients of bilateral primary chronic angle closure glaucoma (PCACG) on topical timolol 0.5% twice a day and pilocarpine 2% three times daily were switched over to bimatoprost 0.03% once daily in both eyes. Intraocular pressure (IOP) and pulsatile ocular blood flow (POBF) were recorded before and after starting bimatoprost and were followed up every four weeks for three months. Bimatoprost had statistically significant (p < 0.05) mean IOP reduction from 19.3 +/- 6.6 to 13.5 +/- 4.5 mmHg (30.5%) and there was improvement from 858 +/- 260 to 1261 +/- 321 microL/min (46.8%) in mean pulsatile ocular blood flow (p < 0.05). Conjunctival hyperemia (32%) was the most common adverse effect of bimatoprost. Bimatoprost 0.03% monotherapy improved ocular blood flow and provided a better diurnal IOP control than concomitant timolol-pilocarpine in eyes with primary chronic angle closure glaucoma and was found to be well tolerated.

Changes in optic nerve head blood flow after therapeutic intraocular pressure reduction in glaucoma patients and ocular hypertensives

PURPOSE

To detect and quantify changes in optic nerve head (ONH) and peripapillary retinal blood flow by scanning laser Doppler flowmetry (SLDF) in open-angle glaucoma (OAG) and ocular hypertension (OHT) after therapeutic intraocular pressure (IOP) reduction.

DESIGN

Prospective, nonrandomized, self-controlled trial.

PARTICIPANTS

Twenty patients with OAG and 20 patients with OHT with clinical indications for therapeutic IOP reduction were prospectively enrolled.

INTERVENTION

IOP reduction was achieved by medical, laser, or surgical therapy. All patients had IOP reductions more than 20% and a minimum of 4 weeks follow-up.

MAIN OUTCOME MEASURES

Blood flow measurements were performed by SLDF analysis software (version 3.3) using Heidelberg Retina Flowmeter images. Statistical evaluations were performed on both groups using a two-tailed distribution paired t test.

RESULTS

Twenty patients with OAG had a mean IOP reduction of 37% after treatment. In these patients, mean (+/- standard deviation) rim blood flow increased by 67% (from 158 +/- 79 arbitrary units to 264 +/- 127 arbitrary units, P = 0.001), whereas mean temporal peripapillary retinal flow decreased by 7.4% (P = 0.24), and mean nasal peripapillary retinal flow increased by 0.3% (P = 0.96). Twenty OHT patients had a mean IOP reduction of 33% after treatment. In contrast to the OAG group, neither the mean rim blood flow (7.5% increase from 277 +/- 158 arbitrary units to 298 +/- 140 arbitrary units, P = 0.41) nor the mean temporal (P = 0.35) or nasal (P = 0.88) peripapillary retinal flow changed significantly.

CONCLUSIONS

For a similar percentage of IOP reduction, OAG patients had a statistically significant improvement of blood flow in the neuroretinal rim of the ONH, whereas OHT patients did not demonstrate such a change. Peripapillary retinal blood flow, expected to be affected less in glaucoma, remained stable in both groups. In addition to indicating a response to therapy in OAG patients, the reported changes in rim perfusion suggest that ONH autoregulation may be defective in OAG while intact in OHT.

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.

Ocular blood flow measurement

Images

Colour Doppler velocimetry of the arterial vasculature of the optic nerve head and orbit

Blood flow in the orbital vasculature can be investigated by colour Doppler velocimetry which allows simultaneous imaging of B-scan and Doppler ultrasound. In this paper we review the results of our recent studies on the arterial vasculature of the orbit and optic nerve head. A control study is described in which reliable measurements were obtained from the ophthalmic artery at the orbital apex, the medial orbit, and the complex of the central retinal artery and posterior ciliary arteries. Patients with occlusion of the central retinal artery and posterior ciliary arteries were examined. The results indicate that readings at the optic nerve head primarily represent blood flow in the central retinal artery. A study of the effects of posture on velocimetry demonstrated no change in the measurements obtained. Finally, topical timolol 0.5% was found to reduce the resistive indices of flow in the central retinal artery.

Vasoconstrictive effect of topical timolol on human retinal arteries

Timolol is widely used in glaucoma treatment without sufficient knowledge of its vascular retinal effects. In this study, we measured the retinal vessel diameters before and after instillation of 0.5% timolol twice daily in one eye for 1 week, using photographic enlargements (x44). A total of 12 normal, caucasian subjects aged 25-39 years (average, 30.6 +/- 4.2 years) participated in this study. In all, 75% of the subjects had a diminution of retinal arterial size in the treated eye. The mean arterial diametric decrease was 4.1% in treated eyes compared with both untreated eyes and pretreatment values of treated eyes. These diminutions were statistically significant according to Student's paired t-test (P less than 0.05). No statistical difference was found in venous diameters (t = -0.065). Results showed that 0.5% timolol may have a vasoconstrictive effect on the retinal arteries of normal human subjects after 1 week of unilateral instillation twice daily. We suggest that this arterial vasoconstriction could be caused by the effect of timolol on the vascular beta-2 receptors. Further investigations are warranted to determine whether timolol also acts on ciliary arteries and whether arterial vasoconstriction participates in lowering intraocular pressure.

Effect of different antiglaucomatous drugs on ocular perfusion pressures

In an attempt to elucidate whether antiglaucomatous drugs, especially beta-blockers, affect systemic and/or ocular blood flow, we measured ocular perfusion pressures (PP), systemic blood pressure (BP) and heart rate in 50 healthy subjects before and after topical instillation of the following eye drops: timolol 0.5% (n = 10), betaxolol 0.5% (n = 10), carteolol 2% (n = 10), pilocarpine 2% (n = 10) and acetazolamide 750 mg per os (n = 10). The ocular perfusion pressures were measured by OODG as described by Ulrich. By means of this method--retinal and ciliary perfusion pressure can be recorded separately and simultaneously. Our results indicated that, in spite of a statistically significant decrease in IOP in all 5 groups, there was no change in retinal or ciliary perfusion pressure, heart rate or blood pressure in any of the groups except the carteolol subjects. The ocular perfusion pressures should be increased with reduction of the IOP when the systemic parameters remain unchanged. This was not the case in our experiments and therefore it can be suggested that a relative reduction in ocular perfusion pressure occurs with all agents and, in this respect, timolol and betaxolol did not affect ocular perfusion pressure more than pilocarpine and acetazolamide. Carteolol, however, produced a slight decrease (alpha less than 0.02) in ocular perfusion pressure, in spite of lowering of the IOP.