Dissociation Between Progressive Retinal Nerve Fibre Layer Thinning and Perimetric Change in Multiple Sclerosis-Associated Uveitis

Background and Objective: Uveitis occurs more frequently in multiple sclerosis (MS) than in the general population and is often clinically silent. We determined the anatomical types and visual field defect patterns of MS-associated uveitis, and compared the 24-month course of peripapillary retinal nerve fibre layer (pRNFL) thickness and perimetric mean defect (MD) between symptomatic and asymptomatic patients. Methods: Retrospective longitudinal study of 32 MS patients with uveitis diagnosed by SUN criteria, none with prior optic neuritis. Cirrus HD-OCT and Octopus 900 N1 perimetry were performed at three annual visits. Linear mixed models accounted for inter-eye correlation; annualized rates of change were calculated. Results: Uveitis was identified in 32 of 852 referred patients (3.8%). Intermediate uveitis predominated (59.4%). Fourteen patients (43.8%) were asymptomatic, yet visual field defects were present at baseline in 84.4% of the full cohort, despite generally preserved visual acuity. pRNFL declined in every subgroup (p < 0.0001), including non-inflamed fellow eyes. Within the bilateral uveitis subgroup (n = 24), thinning was faster in asymptomatic than symptomatic patients (−2.75 vs. −1.40 µm/year; Mann–Whitney p = 0.033), persisting in direction and magnitude after exclusion of three patients with cystoid macular oedema, although significance in that restricted sample was test-dependent (Mann–Whitney p = 0.054); the corresponding MD difference did not persist (p = 0.292). These symptom-based comparisons were exploratory. Conclusions: MS-associated uveitis is frequently asymptomatic but accompanied by subclinical perimetric loss, supporting examination irrespective of symptoms. pRNFL thinning was not confined to inflamed eyes; without an MS-without-uveitis or healthy comparator its origin cannot be attributed to a single mechanism. Structural and functional change dissociated.