Abstract / Summary
Background The optic nerve (ON), as an extension of the central nervous system, reflects multiple sclerosis (MS) pathological processes. Transorbital sonography (TOS) is emerging as a novel technique to detect ON changes. Our aim was to investigate retrobulbar ON morphometric changes in MS and their relationship with prior history of optic neuritis. Methods 122 MS subjects were enrolled, 68 with and 54 without history of optic neuritis. ON diameters without and with sheath were measured at 3 mm (OND3 and ONSD3) and 5 mm (ONSD5) posterior to the optic disc; myelination index (MI=ONSD3/ONSD5) was calculated. To account for intrasubject dependencies, linear mixed models (LMMs) for repeated measures were employed, adjusting for age at onset and body mass index. Results ONs with history of inflammation (I-ON) exhibited significantly reduced diameters versus companion nerves in both measurements with and without sheath (OND3: p = 0.002 ; ONSD3: p = 0.010 ; ONSD5: p = 0.046 ). All ONs diameters progressively decreased with increasing neuritis frequency, demonstrating a dose-response effect. Significant measurement reductions in OND and ONSD3 were observed in I-ON of patients with Expanded Disability Status Scale >3, whereas no significant differences emerged for progression index (PI) > 0.20 among ONs with and without history of optic neuritis. Conclusions TOS reliably captures ON morphometric changes related to inflammatory history and chronic neuroaxonal injury in MS, supporting its role as a promising biomarker of disability burden and progression independent of relapse activity (PIRA).