Retrobulbar Arterial Hemodynamic Effects of Betaxolol and Timolol in Normal-Tension Glaucoma

β-Adrenergic blocking drugs lower intraocular pressure. The question of whether these drugs also alter, either directly or indirectly, orbital hemodynamics is potentially of great importance for patients with normal-tension glaucoma who may have some degree of reversible vasospasm. We compared the effect of selective (betaxolol) and nonselective (timolol) β-adrenergic blocking drugs on flow velocities (as determined by color Doppler imaging) in orbital vessels in 13 patients with normal-tension glaucoma (mean age, 62 ± 3 years; mean intraocular pressure, 15 ± 2 mm Hg). A one-month drug treatment double-masked crossover design, with a three-week washout before each drug, was used. Neither drug changed peak systolic velocity in any of the four vessels studied (ophthalmic, nasal and temporal posterior ciliary, and central retinal arteries). Additionally, timolol did not alter end-diastolic velocity or resistance index (defined as [peak systolic velocity minus end-diastolic velocity] divided by peak systolic velocity) in any of the vessels measured. In contrast, betaxolol tended to increase end-diastolic velocity and to decrease resistance index: the four-vessel average end-diastolic velocity increased 30% (P = .08), and the four-vessel average resistance index decreased significantly (P = .04). These reductions in resistance index occurred despite that betaxolol, in contrast to timolol, did not significantly decrease intraocular pressure. These results suggest that, in patients with normal-tension glaucoma, selective β-adrenergic blockade (betaxolol) may have ocular vasorelaxant effects independent of any influence on intraocular pressure, whereas nonselective blockade (timolol) lowers intraocular pressure without apparently altering orbital hemodynamics.