Purpose:
Plus disease is a critical marker for treatment-requiring retinopathy of prematurity (ROP) and is defined by a standard narrow-angle photograph that displays vessels extending less than 1.0 disc diameters (DD) from the optic disc center superiorly, and approximately 2.0 DD inferiorly. The purpose of this study was to examine vascular tortuosity as a function of distance from the optic disc center in infants with ROP.
Methods:
34 wide-angle retinal images from infants with ROP were reviewed by 22 experts. A reference standard for each image was defined as the diagnosis (plus vs. no plus) given by the majority of experts. Venules (n=145) and arterioles (n=169) were identified by author consensus. Tortuosity, defined as vessel length from starting point to end point divided by the straight line distance between the same points, was calculated using a computer-based image analysis system developed by the authors. Mean tortuosity was computed as a function of distance from the optic disc center in all images.
Results:
Among 13 images with plus disease, the mean arterial tortuosity was 1.08 from 0-1.0 DD (n=70 arteries), 1.17 from 0-2.0 DD, 1.19 from 0-3.0 DD, and 1.20 from 0-4.0 DD (p=0.0008 compared to 0-1.0 DD). The mean venous tortuosity was 1.04 from 0-1.0 DD (n=60 veins), 1.08 from 0-2.0 DD, 1.11from 0-3.0 DD, and 1.12 from 0-4.0 DD (p=0.0001 compared to 0-1.0 DD). Among 21 images with no plus disease, the mean arterial tortuosity was 1.05 from 0-1.0 DD (n=99 arteries), 1.09 from 0-2.0 DD, 1.10 from 0-3.0 DD, and 1.11 from 0-4.0 DD (p=0.0004 compared to 0-1.0 DD). The mean venous tortuosity was 1.04 from 0-1.0 DD (n=85 veins), 1.05 from 0-2.0 DD, 1.06 from 0-3.0 DD, and 1.07 from 0-4.0 DD (p=0.01 compared to 0-1.0 DD).
Conclusions:
There is a continuous increase in vascular tortuosity as a function of distance from the optic disc center from 0-4.0 DD, both in images with and without plus disease. This may have implications for clinical diagnosis, for standard photographic definitions of plus disease, and for the future development of computer-based image analysis systems.
Keywords: retinopathy of prematurity