Retinal Vessel Caliber Measurement Bias in Fundus Images in the Presence of the Central Light Reflex

PURPOSE: To investigate the agreement between a fundus camera and a scanning laser ophthalmoscope in retinal vessel caliber measurements and to identify whether the presence of the central light reflex (CLR) explains potential discrepancies. METHODS: For this cross-sectional study, we obtained fundus camera and scanning laser ophthalmoscope images from 85 eyes of 85 healthy individuals (aged 50–65 years) with different blood pressure status. We measured the central retinal artery equivalent (CRAE) and central retinal artery vein equivalent (CRVE) with the Knudtson–Parr–Hubbard algorithm and assessed the CLR using a semiautomatic grading method. We used Bland–Altman plots, 95% limits of agreement, and the two-way mixed effects intraclass correlation coefficient for consistency [ICC(3,1)] to describe interdevice agreement. We used multivariable regression to identify factors associated with differences in between-device measurements. RESULTS: The between-device difference in CRAE (9.5 µm; 95% confidence interval, 8.0–11.1 µm) was larger than the between-device difference in CRVE (2.9 µm; 95% confidence interval, 1.3–4.5 µm), with the fundus camera yielding higher measurements (both P < 0.001). The 95% fundus camera–scanning laser ophthalmoscope limits of agreement were –4.8 to 23.9 µm for CRAE and –12.0 to 17.8 µm for CRVE. The corresponding ICCs(3,1) were 0.89 (95% confidence interval, 0.83–0.92) and 0.91 (95% confidence interval, 0.86–0.94). The between-device CRAE difference was positively associated with the presence of a CLR (P = 0.002). CONCLUSIONS: Fundus cameras and scanning laser ophthalmoscopes yield correlated but not interchangeable caliber measurements. The CLR induces bias in arteriolar caliber in fundus camera images, compared with scanning laser ophthalmoscope images. TRANSLATIONAL RELEVANCE: Refined measurements could yield better estimates of the association between retinal vessel caliber and ophthalmic or systemic disease.