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Therese von Hanno, Geir Bertelsen, Anne K. Sjolie, Ellisiv B. Mathiesen; Hemoglobin in Retinal Vessel Analysis: The Tromsø Eye Study. Invest. Ophthalmol. Vis. Sci. 2012;53(14):984.
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Hemoglobin (Hb) in the erythrocytes is the oxygen carrier in the blood and there is also evolving evidence that the Hb molecule may have a role in local regulation of blood flow. As the regulation of blood flow is effectuated through vessel calibre in the resistance vessels, we wanted to analyze the effect of including Hb in the multivariable models of retinal vessel calibres.
Tromsø Eye Study is part of the Tromsø Study, being a population based multipurpose study from the municipality of Tromsø, Norway. The 6th survey of the Tromsø Study was conducted in 2007/2008 and retinal photography was performed on 6540 participants. Retinal vessel calibre was measured computer-assisted on digital retinal images of one eye and summarized as central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE) by using Knudtson’s revised formulae. The effect of Hb on retinal vessel calibres were analyzed by multivariable linear regression in two different models: Model 1: Adjusting for age, blood pressure, diabetes and daily smoking, and Model 2: Model 1 + fellow vessel equivalent. Women and men were analysed separately. Unit change in analysis for Hb was 1 standard deviation.
6353 had retinal vessel measurements that were usable, of whom 57% were women. Mean age was 63 years for both genders (sd 9.0, range 38-87years). Mean Hb for women was 13.7 (sd 1.0) g/dl and for men 14.9 (sd 1.1) g/dl (p<0.001). In Model 1, increased Hb was associated with an increase in CRAE in men (β-coeff.1.14 µm, p<0.001), but not in women (β-coeff.0.31 µm, p=0.3). Increased Hb was associated with increased CRVE in both genders, and more strongly in men (β-coeff.4.10µm, p<0.001) than in women (β-coeff.2.99µm, p<0.001). In Model 2, increased Hb was associated with a reduction in CRAE in men (β-coeff.-0.52 µm, p=0.04) and women (β-coeff.-0.91 µm, p<0.001) and an increase in CRVE in men (β-coeff.3.09, p<0.001) and women (β-coeff.2.72, p<0.001).
Hb was independently associated with retinal vessel calibres, most pronounced in men. The association between Hb and CRAE changed direction when CRVE was added to the model, and the reason for this needs to be further evaluated.
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