Objectives: Our objective is to study the relationship between vitamin D status and ON recovery by RNFL measures at 6 months using OCT. The hypothesis is that vitamin D sufficiency will be associated with better RNFL outcomes and axonal preservation. Primary outcomes include affected eye RNFL and inter-eye RNFL difference (IED, a measure of RNFL difference between the unaffected and ON eye) at 6 months between vitamin D sufficient and insufficient groups. We will also examine the relationship between vitamin D status and ON features at onset.
Methods: In this prospective cohort study, patients with acute ON undergo OCT to assess mean RNFL thickness, macular volume (MV) and IED, visual acuity and evoked potentials, and vitamin D (serum 25(OH)D) status testing at baseline, months 3 and 6. Vitamin D insufficiency is defined as 25(OH)D < 80 nmol/L.
Results: Forty-two of 50 patients have been enrolled (32 women, 10 men), 30 having completed the study. Thus far, 62% of patients were vitamin D insufficient at baseline, which was associated with greater baseline edema seen in mean RNFL (132.4 vs 95.5 µm, p=0.0219) and MV (10.25 vs 9.83 mm3, p=0.0134). At month 6, edema is still subtly present, but IED is significantly greater in vitamin D insufficient vs sufficient patients (11.6 vs 3.7 µm, p=0.16) as is the proportion of vitamin D insufficient patients with a 6 month IED > 10 µm (58% vs 25% of sufficient patients).
Conclusions: Our results suggest that vitamin D insufficiency at ON onset is associated with greater edema with greater baseline RNFL and MV in ON eyes. At 6 months, ON eye RNFL thickness in vitamin D insufficient patients, as evaluated by IED, drops below the RNFL value of the unaffected eye, while this does not appear to occur in sufficient patients. Vitamin D insufficient patients also make up a greater proportion of those with an IED > 10 µm. As we near the end of this study, it appears that vitamin D sufficiency may protect against both the acute inflammatory and late degenerative/axonal loss associated with optic nerve demyelination.