Introduction: The relationship between a non-dipping blood pressure profile and retinal vessel calibre is not well established. A sustained increase in nocturnal arterial pressure may induce changes throughout the vascular tree, including the retinal microvasculature. We therefore explored the relationship between retinal vessel calibre and dipping status in a cohort of African and Caucasian teachers.

Methods: 68 African and 81 Caucasian men were selected from those taking part in the follow-up phase of the SAPBA study. 24hr Ambulatory blood pressure measurements and dipping status were determined. The percentage mean arterial pressure (% MAP) dipping was calculated as: (diurnal MAP - nocturnal MAP)/diurnal MAP x 100. Retinal images were captured and the central retinal artery equivalent, central retinal vein equivalent (CRVE) and subsequent arteriolar-venular ratio (AVR) determined.

Results: African men demonstrated higher 24hr MAP and poorer % MAP dipping compared to Caucasian men. When sub-divided into non-dippers and dippers, African non-dippers demonstrated a reduced AVR and an increased CRVE (p<0.001) compared to their dipper counterparts. The AVR was positively (R²=0.34, β=0.38; p=0.001) while the CRVE was negatively (R²=0.24, β=−0.50; p<0.001) associated with % MAP during dipping. CRVE maintained a negative association with dipping status (non-dipper, yes/no) (R²=0.21, β=−0.38; p=0.001). These associations were independent of 24hr MAP. No associations were observed in the Caucasian men.

Conclusion: In this group of African men, a non-dipping blood pressure profile was associated with a reduced AVR and larger CRVE, reflecting microvascular deterioration as a result of prolonged periods of increased arterial pressure.