Retinal Blood Vessels Tortuosity Measurement

The degree of retinal blood vessels' tortuosity may indicate the progression of various diseases, such as hypertension or diabetic retinopathy. Therefore, observing the changes in tortuosity levels in retinal fundus images can be an effective biomarker for diagnosing diseases. However, tortuosity assessments performed by ophthalmologists are usually subjective and time-consuming. Thus, there is a need for a universally accepted tortuosity measurement standard. Several studies have proposed parameters or methods to measure blood vessel tortuosity, but these methods still have some drawbacks that can be improved to better describe tortuosity both in retinal arteries and veins. For that reason, this study aims to propose tortuosity measurement parameters that can increase the correlation between tortuosity assessments from ophthalmologists and automatic tortuosity measurement results. This research led to the development of a combined parameter incorporating some features that are included in previous studies, such as the comparison of arc length and chord length, as well as the angle values at the critical points of the curve structure. The proposed parameter has been applied to a retinal blood vessels dataset that consists of 60 fundus images (30 artery images and 30 veins images with similar length and caliber). The automatic measurement of each image's tortuosity level are compiled, ranked, and compared to the ground truth tortuosity ranks of each image provided in the dataset. The proposed parameter for retinal blood vessels tortuosity measurement achieved a Spearman rank correlation coefficient of 0.886 for arteries and 0.884 for veins.