A Proposed 1 to 9 Severity Scale for Vascular Abnormalities in Retinopathy of Prematurity

Abstract

Purpose : Retinopathy of Prematurity (ROP) remains one of the leading causes of childhood blindness. Retinal vascular abnormalities in ROP are classified as plus, pre-plus, or neither. Previous studies found that there is a continuous spectrum of vascular abnormality in ROP and that the inter-expert discrepancy in plus disease diagnosis is largely due to the systematic bias based on subjective cut-point differences among experts regarding the amount of vascular abnormality required to distinguish between plus and pre-plus disease. This suggests consideration of a more granular severity scale for vascular abnormalities in ROP. The purpose of this study is to develop 1 to 9 severity scale for vascular abnormalities and to validate the severity scale by correlating with expert graders’ classifications.

Methods : We defined a scale to represent a continuous spectrum vascular abnormality from 1 to 9, where 1-3 are intended to represent normal findings (e.g. no plus), 4-6 are intended to represent borderline findings (e.g. “pre-plus”), and 7-9 are intended to represent severe disease (e.g. “plus”) (Figure 1). As part of a multicenter ROP cohort study, Imaging and Informatics in ROP (i-ROP) study, retinal images of 499 eye exams from 279 eyes of 192 infants were independently graded as 1 to 9 by 5 expert graders. Absolute agreement (difference of 1 grade or less was considered as agreement), weighted kappa, and Pearson correlation coefficient between pairs of expert graders were calculated.

Results : Mean 1 to 9 grade by 5 graders was 7.7 ± 1.0, 4.7 ± 1.1, and 2.4 ± 0.8 in images with plus (n=31), pre-plus (n=96), and normal (n=372), respectively. Absolute agreement between pairs of 5 graders ranged from 0.86 to 0.97. In addition, 9 of 10 paired comparisons between 5 graders showed strong agreement (kappa between 0.6 and 0.8). Pearson correlation coefficient between pairs of 5 graders ranged from 0.82 to 0.92.

Conclusions : We proposed a 1 to 9 severity scale system for vascular abnormalities in ROP, which showed high agreement among the expert graders. This quantitative classification system may be helpful in clinical practices (e.g. monitoring disease progression) and clinical trials. Moreover, with quantitative assessment of vascular features with deep learning, the 1 to 9 severity scale may be used in an automated and objective diagnosis of vascular abnormalities in ROP.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.