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. Author manuscript; available in PMC: 2008 Dec 1.
Published in final edited form as: J AAPOS. 2007 Oct 29;11(6):532–540. doi: 10.1016/j.jaapos.2007.09.005

Figure 1. Parameters of computer-based Retinal Image multiScale Analysis (RISA) system.

Figure 1

(A) Tortuosity index (TI) is defined as the length of a vessel divided by a line segment connecting the end points. (B) Integrated curvature (IC) is computed by forming vectors along the vessel, calculating cumulative sum of angles θ between vectors, and normalizing by vessel length. If a vessel is perfectly straight, then IC has a minimum value of zero and TI has a minimum value of one. (C) TI vs. IC. Departures from linearity, such as the vessel depicted on right, are captured both by IC and TI. However, multiple changes in vessel depicted on left are better captured by IC. TI is similar for the two shapes (5% difference), whereas IC is higher for the vessel depicted on left (50% difference).