Fig 1. Measurement of retinal vascular calibre using color fundus photographs.

SIVA software automatically identified and traced the retinal vessels (arteries and veins) on the digital colour fundus photographs. To further ascertain the accuracy of the automated vessel tracing generated by the software, trained graders examined the traced vessels and made manual corrections as necessary. Central retinal arteriolar and vascular caliber were summarized as CRAE and CRVE, respectively based on the revised Knudtson–Parr–Hubbard Formula.