Relationship Between Renal Resistive Index and Retinal Vascular Density in Individuals with Hypertension

Background/Objectives: Considering the physiological analogies between the eye and the kidney, this study aimed to investigate the potential relationship between retinal vascular density, assessed using Optical Coherence Tomography Angiography (OCT-A), and the renal resistive index (RRI) in patients with arterial hypertension. Methods: A total of 82 hypertensive patients (mean age 48 ± 13) were enrolled in the study. Participants underwent routine biochemical evaluations, office-based blood pressure measurement, 24 h ambulatory blood pressure monitoring, OCT-A imaging, and renal Doppler ultrasound examinations. Results: The mean RRI in the study population was 0.616 ± 0.06. Participants were divided into two groups based on the 75th percentile threshold of the RRI distribution (0.66, 95% CI 0.64–0.68). The group with RRI > 75th percentile, which appeared to have a higher number of smokers, exhibited significantly higher mean triglyceride and urinary albumin excretion (UAE) levels and a significantly reduced estimated glomerular filtration rate (eGFR) as compared to the group with RRI < 75th percentile. Among the hemodynamic parameters, 24 h pulse pressure (PP), daytime and nighttime PP, and nighttime systolic blood pressure (SBP) were significantly higher in the group with RRI > 75th percentile. Regarding retinal vascular density indices, the only significant difference was observed in the deep foveal vascular plexus, which displayed a reduced density in the group with RRI > 75th percentile. Logistic regression analysis revealed that RRI > 75th percentile was independently associated with increased nighttime mean pulse pressure (OR = 1.13, 95% CI: 1.049–1.221, p = 0.0014) and reduced deep foveal vascular density (OR = −0.5026, 95% CI: 1.0493–1.2211, p = 0.0044). Conclusions: Our findings demonstrate that ocular microvascular alterations are associated with RRI, a marker with a well-established prognostic value for renal disease progression and systemic macrovascular dysfunction. These results further substantiate the close relationship between renal and ocular microcirculation.