Response to Are Narrower or Wider Retinal Venules Associated With Incident Hypertension?
We read with interest the letter by Liew et al1 concerning the question of whether narrower or wider retinal venules are related to hypertension. We agree with the suggestion made by Liew et al1 that the counterintuitive association between retinal venular narrowing and hypertension observed in the Rotterdam Study may be because of the confounding effect of arteriolar and venular diameters,2 because persons with narrower arterioles are more likely to have narrower venules. As was the case in the Blue Mountains Eye Study, in our study, the Pearson’s correlation coefficient between arteriolar and venular diameters was also 0.59. We repeated our analyses by constructing the models as suggested by Liew et al1: first, by including arteriolar or venular diameters separately; second, by taking arteriolar and venular diameters simultaneously in the same logistic regression model.
After a follow-up of 6.6 years, incident hypertension, defined as systolic blood pressure ≥140 mm Hg, diastolic blood pressure ≥90 mm Hg, or use of antihypertensive medication, was diagnosed in 808 of 1900 participants without hypertension at baseline. In model I, incident hypertension was associated with not only narrower arteriolar diameters, but also narrower venular ones, albeit weaker (Table). In contrast, in model II, where arteriolar and venular diameters were included simultaneously, retinal venular narrowing was not related to an increased risk of hypertension (odds ratio, 1.11; 95% CI, 0.98 to 1.26). Additional adjustments for other cardiovas-cular risk factors did not affect these associations. The data presented in model II confirm the confounding effect of arteriolar and venular diameters that was not accounted for in model I. In conclusion, these findings further support the explanation provided by Liew et al.1
Liew G, Mitchell P, Wong TY, Wang JJ. Are narrower, or wider, retinal venules associated with incident hypertension? Hypertension. 2006; 48: e10.
Ikram MK, Witteman JC, Vingerling JR, Breteler MM, Hofman A, De Jong PT. Retinal vessel diameters and risk of hypertension: the Rotterdam Study. Hypertension. 2006; 47: 189–194.