Statistical analysis

Statistical analysis was performed with R version 3.1.2 and geepack 1.2-0. To account for within-subject inter-eye effects, generalized estimating equation models (GEE) with working correlation matrix “exchangeable“ were used for all group comparisons and correlations involving corneal, retinal, and visual function measurements. GEE Results are given with regression coefficient (B) and standard error (SE). In HC, higher corneal nerve fibre density and DC density showed a trend to an association with higher age (B=107.9, SE=57.2, p=0.059 and B=0.8, SE=0.4, p=0.052, respectively), which is why we included age as a covariate in all analyses. Demographic group differences between patients and healthy controls were analysed using a non-parametric Mann-Whitney-U test (MWU) for age and Pearson’s Chi² test for sex. TN-related symptom frequency comparisons between patients with and without history of such symptoms were calculated with Pearson’s χ² statistics. Statistical significance was established at p<0.05. No a priori sample size calculation was performed and significance levels were not corrected for multiple comparisons. The study should therefore be considered exploratory.