Effect of Bicubic Image Interpolation on Retinal Vascular Caliber Measurement

Aim: To assess whether retinal vascular caliber measurement from digital fundus photographs using IVAN software (University of Wisconsin, Madison, WI) is affected by bicubic image interpolation using image processing software (Photoshop version 5.5, Adobe Systems Inc., San Jose, CA). Material and methods: 32 good quality optic disc centered retina photos (slides) acquired in healthy volunteers were used for the analysis. The slides were scanned twice to create two groups of digital photos of different size (the first 432x288 pixels and the second 1800x1200 pixels). Using Photoshop image processing software, the bicubic image interpolation protocol was used to resize the first group of photos to the size of 1800x1200 pixels – thus a third group of photos was created. Retinal vessel diameters of the second and third group were measured by a trained grader using the IVAN software according to the proposed protocol. The intra-class correlation coefficient was calculated following that. Results: The intra-class correlation coefficient for central retinal artery equivalent, for central retinal vein equivalent and for arteriole to venule ratio for the second and third group of photos were 0.883, 0.979 and 0.939 respectively. Conclusions: The use of bicubic image interpolation to resize optic disc centered retina photos with the protocol described does not affect retinal vessel diameter measurement. A high reproducibility was observed for the retinal vessel diameter measurements. Keywords— Bicubic image interpolation, non-adaptive techniques, retinal vessel diameters