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

Abstract

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). 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. 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. 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.