The effect of beta blockers on retinal blood flow in diabetic patients

The effect of a single oral dose of propanolol 80 mg, dilevalol 200 mg, salbutamol 4 mg, and placebo on the systolic (BPs), diastolic blood (BPd), intraocular pressure (IOP), on retinal vessel diameter (D), blood velocity (Vmax) and volumetric retinal blood flow (RBF), was measured at baseline, 90 minutes and three hours after administration in normotensive diabetic volunteers. These drugs were chosen to demonstrate a range of beta receptor activity. Propanolol is a non-specific beta blocker, affecting beta 1 and beta 2 receptors, dilevalol has beta 1 antagonist and beta 2 agonist effects and salbutamol has beta 2 agonist effects. Retinal blood flow was measured by bidirectional laser Doppler velocimetry (BLDV) and red free photography. Dilevalol reduced the mean BPs by 10.4 mmHg (SD 4.2, P less than 0.05), the mean BPd by 7 mmHg (SD 3.8, P less than 0.05), whereas propanolol, salbutamol and placebo had no significant effect. Propanolol reduced the mean intraocular pressure by 4.88 mmHg (SD 1.8, P less than 0.01). No treatment had a significant effect on retinal perfusion pressure. In all treatments the vessel diameter and volumetric flow remained unchanged, and there was no significant difference between the treatments. The mechanisms of action of these drugs are analysed and the possible implications of their use in patients with retinal disease are discussed.