Influence of OSCAR-IB Criteria on Test-Retest Reliability of Cirrus HD-OCT Retinal Thickness Measurements in People With Multiple Sclerosis

Optical coherence tomography (OCT) allows evaluation of inter-eye differences (IEDs) in macular ganglion cell-inner plexiform layer (GCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thicknesses to identify unilateral optic nerve involvement (UONI). UONI supports dissemination in space (DIS) as part of the 2024 revised McDonald diagnostic criteria for multiple sclerosis (MS). The OSCAR-IB quality control (QC) criteria identify suboptimal-quality OCT scans, which could potentially result in false-positive or false-negative UONI identification. We aimed to determine the influence of scans fulfilling OSCAR-IB criteria (SFO) and not fulfilling (SNFO) on test-retest reliability of pRNFL and GCIPL thicknesses/IEDs, with a commonly used OCT platform (Cirrus HD-OCT). A total of 509 participants, including 397 people with MS, underwent Cirrus HD-OCT, with acquisition of 2 macular and optic disc scans per eye. Each scan was classified as either SFO or SNFO. There were no clinical or demographic exclusions in order to reflect a real-world clinical setting. Reproducibility was evaluated with intravisit intraclass correlation coefficients (ICCs) and coefficients of variation (COVs). IED consistency was assessed with difference-in-differences (DiDs) and probabilities of agreement (POA) for specific IED thresholds (GCIPL </≥4; pRNFL </≥6 μm). A total of 1,143 macular scan pairs (1,100 SFO and 42 SNFO) for GCIPL and 1,108 optic disc scan pairs (1,003 SFO and 105 SNFO) for pRNFL were analyzed. SFO demonstrated superior reliability, as compared to SNFO for GCIPL (SFO: ICC = 0.998, COV = 0.40%; SNFO: ICC 0.353, COV 10.14%) and pRNFL (SFO: ICC = 0.989, COV = 1.18%; SNFO: ICC = 0.852, COV = 3.94%) thicknesses. DiDs were lower for SFO (GCIPL 0.64 ± 0.67 μm, pRNFL: 2.00 ± 1.72 μm), as compared to SNFO (GCIPL: 10.17 ± 13.87 μm, pRNFL: 4.78 ± 5.51 μm). POA of IED thresholds (GCIPL: </≥4; pRNFL: </≥6 μm) was higher for SFO than for SNFO (GCIPL: 95.58% vs 47.83%; pRNFL: 86.89% vs 71.67%). GCIPL and pRNFL thicknesses/IEDs demonstrated markedly inferior reliability in SNFO, relative to SFO. Failure to fulfill OSCAR-IB criteria influenced pRNFL measurements and, in particular, GCIPL measurements, highlighting the importance of thorough QC in the interpretation of OCT to correctly identify UONI and accurately support DIS for the diagnosis of MS.