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Julie L. Morrison, Joo Hoe Koh, Rachel McIntosh, Carol Y. Cheung, Tien Y. Wong, Jie Jin Wang; Age, Blood Pressure and Retinal Fractal Dimension: The Singapore Malay Eye Study. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3603.
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Retinal vascular fractal dimension (Df) is a global measure of complexity of the vascular structure, and has been shown associated with blood pressure (BP), stroke and other cardiovascular diseases. Previous studies suggest that the influence of BP on retinal arteriolar caliber narrowing is weaker in older than younger persons, we aimed to assess if age had a similar effect modification on the association between BP and Df..
The Singapore Malay Eye Study (SiMES) is a population-based survey of persons aged 40-80 years. Disc-centred photos of the right eye of 2678 (81.6%) SiMES participants were graded for Df, using International Retinal Imaging Software (IRIS-Fractal) following a standardized protocol. Multiple linear regression analysis was performed to determine the associations of Df with age and mean arterial BP (MABP), adjusting for gender, body mass index, blood glucose, diabetes and smoking status and mean arteriolar and venular caliber. The BP and Df association was further assessed in subgroups stratified by age and gender.
The mean (SD) age was 57 (10) years, mean MABP 101 (14) mmHg and mean Df 1.452 (0.023). After adjustment, age and MABP were both significantly and inversely associated with Df (β = -0.00014 and -0.00096, respectively). There was a significant interaction between age and MABP in the MABP-Df association (p=0.015). The association of MABP and Df was weaker in younger persons aged <60 years (β =-0.00014) than in those aged ≥60 years (β =-0.00018) (p=0.009). The different magnitude of this association was similar in men and women.
In this Asian population we documented an association between higher BP and reduced retinal vascular Df. This association was slightly stronger in older aged persons. This suggests that in older people, higher BP is associated with reduced retinal vascular complexity. This age effect modification contrasts to that observed for BP and retinal arteriolar caliber, where the effect of BP on retinal arteriolar caliber narrowing was weaker in older aged persons. Thus, retinal fractal dimensions may measure different microvascular characteristics than vascular caliber.
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