Concordance between SIVA, IVAN, and VAMPIRE Software Tools for Semi-Automated Analysis of Retinal Vessel Caliber

Abstract

We aimed to compare measurements from three of the most widely used software packages in the literature and to generate conversion algorithms for measurement of the central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE) between SIVA and IVAN and between SIVA and VAMPIRE. We analyzed 223 retinal photographs from 133 human participants using both SIVA, VAMPIRE and IVAN independently for computing CRAE and CRVE. Agreement between measurements was assessed using Bland–Altman plots and intra-class correlation coefficients. A conversion algorithm between measurements was carried out using linear regression, and validated using bootstrapping and root-mean-square error. The agreement between VAMPIRE and IVAN was poor to moderate: The mean difference was 20.2 µm (95% limits of agreement, LOA, −12.2–52.6 µm) for CRAE and 21.0 µm (95% LOA, −17.5–59.5 µm) for CRVE. The agreement between VAMPIRE and SIVA was also poor to moderate: the mean difference was 36.6 µm (95% LOA, −12.8–60.4 µm) for CRAE, and 40.3 µm (95% LOA, 5.6–75.0 µm) for CRVE. The agreement between IVAN and SIVA was good to excellent: the mean difference was 16.4 µm (95% LOA, −4.25–37.0 µm) for CRAE, and 19.3 µm (95% LOA, 0.09–38.6 µm) for CRVE. We propose an algorithm converting IVAN and VAMPIRE measurements into SIVA-estimated measurements, which could be used to homogenize sets of vessel measurements obtained with different software packages.

Assessments of Perfusion, Blood Flow, and Vascular Structure in Ambulatory Subjects: Guidance for Translational Research Scientists

“…Analysis of images from retinal fundus photography focuses on the determination of several quantitative metrics that characterize the following: vessel widths around the optic disc, including the central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and arteriovenous ratio (AVR); tortuosity, including curvature tortuosity (CVT); fractal dimension (Df); and branch angles. A variety of software packages have been developed and are available to process and analyze images obtained during retinal fundus imaging and perform the calculations to determine some or all of these metrics [73]. These analytic packages use a similar approach, be-ginning with outlining of all retinal vessels greater than 25 µm in diameter located from one-half to two-disc diameters from the optic disc margin.…”

The impact of the image conversion factor and image centration on retinal vessel geometric characteristics

“…Caliber or angle measurements can therefore always only be a proxy. Thus unsurprisingly, RVGC differ between different vessel assessment software (18,19). Secondly, even when the same analysis software is used, RVGC can vary for different cameras (due to resolution or field of view) (20) and, third, ocular magnification needs to be factored in to account for differences in axial length and refraction between eyes.…”

“…This ICF is commonly calculated by the ratio of a reference optic disk (OD) size (e.g., 1,800 µm (29,30) or 1,850 µm (31,32), derived by Littmann's method, based on the assumption of this being the average adult optic disk size) and the average optic disk size of a cohort. In studies where comparisons between different software packages have been attempted, the same conversion method should be used in both cases (19,28).…”

“…To allow comparison of different software or analysis methods to establish RVGC reference values (17, 19), a large public data set is needed, containing fundus images and medical characteristics. This would help determine if associations with systemic variables might be software-dependent.…”

“…This would help determine if associations with systemic variables might be software-dependent. None the less, large cross-sectional studies have shown that associations of RVGC measurements with medical characteristics persist despite a difference in software (18,19). However, an average ICF does not enable long term follow-up of individual patients, when camera settings change or individual refraction differs between measurements.…”