Image-level tortuosity estimation in wide-field retinal images from infants with Retinopathy of Prematurity.

Tortuosity and dilation of retinal vessels are considered of primary importance for the diagnosis and follow-up of the Retinopathy of Prematurity (ROP) disease. We developed an algorithm to estimate vessel tortuosity in images acquired with a wide-field fundus camera in ROP subjects, offering clinicians a quantitative, objective, and reproducible diagnostic parameter. Vessels were manually traced in 20 images to provide error-free input data for the tortuosity estimation. At first we investigated different vessel-level measures, some including also caliber information. Then we used them to obtain different imagelevel tortuosity measures, which were eventually combined in a supervised approach to provide a tortuosity index capable to reproduce the clinical experts assessment.To provide manual assessment, the 20 images were independently ordered by increasing tortuosity by three clinical graders and three retinal imaging experts. The proposed tortuosity index obtains a Spearman’s correlation coefficient of 0.95 with ground truth, a performance comparable to the clinical graders’ one and better than the retinal imaging experts’ one.