Effect of Nifedipine and Glyceryl Trinitrate on Retinal Blood Flow in Normal Subjects

The retinal vasculature is an accessible region of the microcirculation in humans which undergoes change in essential hypertension. In this study we have examined the effect of nifedipine and glyceryl trinitrate (GTN) on retinal blood flow velocities. Retinal blood flow was measured in 11 subjects using colour Doppler ultrasound. Nifedipine (10 mg orally) or glyceryl trinitrate (0.3 mg, GTN) was given after 30 minutes recumbancy. Systolic retinal arterial blood flow velocity (SRV), diastolic retinal arterial blood flow velocity (DRV), retinal resistive index (RI), SBP, DBP were measured at -10, 0, 5, 10, 15, 20 and 25 minutes following drug administration. Nifedipine significantly increased SRV (peak effect at 15 minutes) but by 25 minutes SRV did not differ significantly from pre-drug values. Nifedipine did not significantly affect DRV, RI, SBP or DBP. GTN significantly increased both SRV and DRV, although both tended to fall towards pre-drug values by 25 minutes. RI, SBP nor DBP were not significantly altered by GTN. Both nifedipine and GTN transiently increase blood flow velocity in the central retinal artery although at the doses used neither agent affected BP or RI. Doppler ultrasound measurement of retinal arterial blood velocity may be a useful technique in the investigation of the retinal microcirculation in essential hypertension.