Revised formulas for summarizing retinal vessel diameters

Abstract

Background/Purpose. Recent findings suggest that an objective assessment of retinal vessel caliber from fundus photographs provide information about the association of microvascular characteristics with macrovascular disease. Current methods used to quantify retinal vessel caliber, introduced by Parr(1,2) and Hubbard,(3) are not independent of scale and are affected by the number of vessels. To improve upon these methods we introduce revised formulas for quantifying vessel caliber. Methods. Revised formulas were estimated using retinal vessel measurements from 44 young adults free of hypertension and diabetes. Comparisons between the two methods were done using digitized photographs from 4926 participants at the baseline examination of the Beaver Dam Eye Study (BDES), an ongoing population-based cohort study initiated in 1987. Individual arterioles and venules were measured using semi-automated computer software from which summary measures were calculated. Results. Correlation coefficients between the Parr-Hubbard and revised formulas were high (Pearson correlation coefficients ranging from 0.94 to 0.98). Both arteriolar and venular caliber significantly increased with an increasing number of vessels measured using the Parr-Hubbard formulas (p < 0.001), which in turn affected the relationship to mean arterial blood pressure. To the contrary, the revised formulas were not affected by the number of measured vessels (p > 0.50). Conclusions. We describe revised formulas for summarizing retinal vessel diameters measured from fundus photographs to be used in future studies and analyses. The revised formulas correlate highly with the previously used Parr-Hubbard formulas, but offer the advantages of being more robust against variability in the number of vessels observed, being independent of image scale, and being easier to implement.

The relationship between aortic stiffness and changes in retinal microvessels among Asian ischemic stroke patients

“…The calibers of retinal arterioles and venules passing through a zone between 0.5 and 1.0 disc diameters from the optic disc margin were measured using a validated computer-assisted method (IVAN, University of Wisconsin-Madison, Madison, WI, USA), described previously in detail. 31 These measurements were then summarized using the Parr-Hubbard formula, 32 modified by Knudtson 31 to compute the central retinal artery equivalent (CRAE) and the central retinal vein equivalent (CRVE), representing the average internal caliber of retinal arterioles and venules, respectively. Intragrader reliability was high, with intraclass correlation coefficients 0.99 and 0.94 for CRAE and CRVE, respectively.…”

“…Intragrader reliability was high, with intraclass correlation coefficients 0.99 and 0.94 for CRAE and CRVE, respectively. 31 Generalized arteriolar narrowing was defined as the lowest tertile of CRAE. The arteriovenous ratio (AVR) was computed as the quotient of CRAE over CRVE.…”

“…The arteriovenous ratio (AVR) was computed as the quotient of CRAE over CRVE. 31 We also assessed the presence of focal arteriolar narrowing, arteriovenous nicking and enhanced arteriolar wall light reflex in comparison with standard photographs following Blue Mountains Eye Study protocols. 18,24 Focal arteriolar narrowing could be assessed in 132 patients, arteriovenous nicking in 134, enhanced arteriolar light reflex in 130 and CRAE/CRVE in 141 patients.…”

Body mass index and its effects on retinal vessel diameter in 6-year-old children

“…Details of this method have been described. 10,11 Average retinal arteriolar or venular diameters were calculated with the Knudtson-Hubbard formula 12 and are termed the central retinal arteriolar equivalent (CRAE) or central retinal venular equivalent (CRVE).…”

The relationship of retinal vascular calibre to diabetes and retinopathy: the Australian Diabetes, Obesity and Lifestyle (AusDiab) study

“…Once the diameters of all arterioles and venules within zone B had been assessed, the measurements were summarised into a central retinal arteriolar equivalent (CRAE) and central retinal venular equivalent (CRVE), according to formulas given by Hubbard et al [21] and modified by Knudtson et al [22]. The formula allows individual vessel diameters to be combined into summary indices reflecting the average arteriolar and venular diameters of that eye.…”