Observer sensitivity to retinal vessel diameter and tortuosity in retinopathy of prematurity: a model system.

BACKGROUND Abnormally increased diameter and tortuosity of retinal blood vessels in the posterior pole, or "plus disease," is recognized as a powerful predictor of poor outcome in eyes with retinopathy of prematurity (ROP). Although the diagnosis of plus disease depends upon the examiner's ability to examine retinal blood vessels, the ability of the human observer to identify changes in retinal blood vessel diameter and tortuosity accurately has not been studied. METHODS Using computer-aided analysis of fundus photographs from eyes with a wide range of ROP severity, we generated tracings of posterior pole blood vessels which varied by quintiles of mean vessel diameter and tortuosity. Subjects (23 naive and 12 expert observers) ranked groups of tracings in order of increasing mean vessel diameter and tortuosity. These ranking tests were performed on tracings derived from the same fundus and tracings derived from distinct fundi. In a similar fashion, subjects also compared one designated standard fundus tracing with 25 distinct fundus tracings. RESULTS Vessel diameter was assessed correctly more often than vessel tortuosity, both among similar (> 99% vs 92% of the time, respectively, P < 0.001), or among distinct (88% vs 78% of the time, respectively, P < 0.001) fundus images. The mean vessel diameter and tortuosity of 25 distinct fundus images were correctly ranked versus a standard image in 89% of attempts. Assessments of increments in vessel diameter and tortuosity were independent. Naive and expert subjects performed indistinguishably on all tests. CONCLUSIONS Intelligent human observers have considerable ability to discern clinically relevant increments in blood vessel diameter and tortuosity. This ability may facilitate standardization in the diagnosis of plus disease in ROP.