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Evelyn Moore, A. McGowan, C. C Patterson, Silvestri Giuliana, Vittorio Silvestri, A. P Maxwell, G. McKay; Association of Retinal Vessel Calibre and Iris Colour. Invest. Ophthalmol. Vis. Sci. 2014;55(13):195.
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© ARVO (1962-2015); The Authors (2016-present)
Previous reports have demonstrated association between retinal vessel calibre (RVC) and ethnicity, principally on the basis of darker iris colour (1). We sought to evaluate RVC with iris colour in a population of elderly white Irish nuns.
The Irish Nun Eye Study (INES) was a cross-sectional analysis of 1233 participants with associated demographic, medical and ophthalmic history. Retinal status was assessed by stereo retinal photography in 966 participants. Retinal arteriolar and venular calibres (central retinal arteriolar [CRAE] and central retinal venular [CRVE] equivalents) were measured from retinal photographs by a standardized computer-assisted method (IVAN). Multiple linear regression was used to compare mean CRAE and CRVE between iris colour with adjustment for potential confounders.
The mean age of the 966 participants included was 75.9 years (range: 56-100 years). Iris colour was characterised as blue (58.4%), brown (20.3%), hazel (14.6%) and green (6.7%). CRAE and CRVE were normally distributed, with means (SD) of 120.7 (12.5) µm and 169.5 (18.2) µm. Darker iris colour was associated with wider arteriolar and venular calibre following adjustment for age, BMI, smoking status, mean arterial blood pressure and medication. The CRAE comparison between blue (120.3 µm; SD 12.5) and brown eyes (122.3 µm; SD 12.5) was not significant (P adjusted = 0.092). The CRVE comparison between blue (168.3 µm; SD 18.0) and brown eyes (171.9 µm; SD 17.9) was significant (P adjusted = 0.021). No significant difference in CRAE was detected between brown eyes and hazel (119.8 µm; SD 12.7) or green (121.0 µm; SD 12.2). Similarly, no significant difference in CRVE was detected between brown eyes and hazel (169.6 µm; SD 18.2) or green (172.3 µm; SD 19.5).
Our results confirm a significant variation in CRVE between individuals with blue compared to brown iris colour. Whether, the variation observed reflects an anomaly in the contrast sensitivity of the software to delineate vessel edges as a consequence of higher retinal pigmentation levels (as approximated by iris colour) remains to be elucidated. Nevertheless, iris colour could be an important source of error in the measurement of retinal vessel calibre. Reference 1: Rochtchina et al. Invest Ophthalmol Vis Sci. 2008;49(4):1362-6
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