Comparison of Common Retinal Vessel Caliber Measurement Software and a Conversion Algorithm

PURPOSE To compare three commonly used retinal vessel caliber measurement software systems, and propose an algorithm for conversion between measurement systems. METHODS We used 120 retinal photographs to evaluate the agreement between three commonly used software (Retinal Analysis [RA], Integrative Vessel Analysis [IVAN], and Singapore I Vessel Assessment [SIVA]). Bland-Altman plots were used to evaluate agreement of retinal arteriolar (central retinal artery equivalent, CRAE) and venular (central retinal vein equivalent, CRVE) calibers. Pearson's correlation was used to assess the associations between systemic factors and retinal vessel calibers, and Z-test was used to compare the strength of the correlation coefficients across the three software systems. An algorithm was created to convert measurements, with paired t-test performed to evaluate the differences between SIVA-measured retinal calibers and SIVA-approximates converted from RA- and IVAN-measurements using the algorithm. RESULTS Differences between SIVA- and RA-measured calibers (CRAE: mean difference [MD] = -21.8 μm, 95% limits of agreement [LOA], -47.3 to 3.7 μm; CRVE: MD = -7.7 μm, 95% LOA, -28.0 to 12.6 μm), SIVA- and IVAN-measured calibers (CRAE: MD = -6.7 μm, 95% LOA, -23.8 to 10.4 μm; CRVE: MD = -18.2 μm 95% LOA, -36.7 to 0.4 μm) were large. However, the strength of correlations between systemic factors with SIVA-measured retinal calibers was not significantly different to that measured using RA and IVAN (P ≥ 0.332). SIVA-approximates converted from RA and IVAN measurements using the proposed algorithm was not significantly different from SIVA-measured calibers (P ≥ 0.20). CONCLUSION Absolute measurements of retinal vessel calibers vary between three common software systems but associations with systemic factors were similar. TRANSLATIONAL RELEVANCE The proposed algorithm allowed conversions of RA and IVAN measurements to SIVA-approximates. This conversion is important for future data pooling and establishment of normative values for retinal vascular caliber measurements.