P-Score: A Reference-Image-Based Clinical Grading Scale for Vascular Change in Retinopathy of Prematurity

Purpose The International Classification of Retinopathy of Prematurity Third Edition (ICROP3) acknowledged that plus-like ROP vascular changes occur along a spectrum. Historically, clinician-experts demonstrate variable agreement for plus diagnosis. We developed a 9-photo reference-image set for grading plus-like changes and compared intergrader agreement of the set to standard grading with no-plus/pre-plus/plus. Design Retinal photographic grading and expert consensus opinion Participants Development: 34 international ICROP3 committee members. Validation: 30 ophthalmologists with ROP expertise (15 ICROP3 committee members, 15 non-ICROP3 members) Methods Nine ROP fundus images (P1 through P9) representing increasing degrees of zone I vascular tortuosity and dilation, based on ICROP3-committee's 34 members' gradings and consensus image review, were used to establish standard photographs for the “Plus (P) Score.” Study participants graded 150 fundus photographs two ways, separated by a 1-week washout period: (1) no-plus/pre-plus/plus disease, (2) choosing the closest P-Score image. Main Outcome Measures Intergrader agreement measured by intraclass correlation coefficient (ICC) Results Intergrader agreement was higher using P-Score (ICC 0.75, 95% CI 0.71-0.79) than no-plus/pre-plus/plus (ICC 0.67, 95% CI 0.62-0.72). Mean P-Scores for images whose mode gradings were no-plus, pre-plus, and plus, were 2.5 (SD 0.7), 4.8 (SD 0.8), and 7.4 (SD 0.8), respectively. Conclusions Intergrader agreement of plus-like vascular change in ROP using the P-Score is high. We recommend incorporation of this 9-image reference set into ICROP3 and clinician daily practice alongside zone/stage/plus. P-score is not yet meant to replace plus diagnosis for treatment decisions, but its use at our institutions has permitted better comparison between examinations for progression and regression, communication between examiners, and documentation of vascular change without fundus imaging. P-score also could provide more detailed ROP classification for clinical trials, consistent with the spectrum of plus-like change that is now formally part of ICROP.