observation of corneal langerhans cells by in vivo confocal microscopy in thyroidassociated ophthalmopathy purpose to examine the density and morphology of langerhans cells lcs in the cornea of patients with thyroidassociated ophthalmopathy taomethods forty patients with tao and 20 healthy volunteers were studied all subjects underwent a thorough ophthalmic examination of both eyes the ocular surface status was assessed by ocular surface disease index osdi symptom questionnaires tear breakup time but fluorescein staining and the schirmer test laser scanning in vivo confocal microscopy was applied to evaluate the lc density and morphology in both central and peripheral cornea the correlations between confocal microscopy data and clinical data were also analyzedresults the osdi and fluorescein staining values were significantly higher while but and schirmer test scores were lower in both active and inactive tao patients compared to the controls central lc densities of patients with active tao 7638 6777 cellmm2 and inactive tao 4749 3858 cellmm2 were both significantly higher than those of the controls 2146 2174 cellmm2 the number of lcs in the peripheral cornea was also significantly increased in the active tao group 13153 7418 cellmm2 compared to the control group 7021 3776 cellmm2 central lc morphology lcm values were significantly higher in both active 177 063 and inactive 151 063 tao groups compared to the control group 101 080 whereas peripheral lcm scores of the two tao groups were increased without statistical significance there were significant correlations between both central lc density and central lcm scores and clinical data including clinical activity score osdi and schirmer test scores and between peripheral lc density and osdi and schirmer test scores no significant correlations were found between peripheral lcm scores and clinical dataconclusions the increase of corneal lcs in density and maturation in patients with tao reflects an activated state of the local immune system which indicates an inflammatory process in the cornea of tao