Purposeto evaluate the morphology, distribution and density of Langerhans cells (LC) in human cornea Method:In vivoconfocal microscopy of the cornea (Rostock Cornea Module in combination with commercial available confocal laser scanning system (Heidelberg Retina Tomograph II, Heidelberg Engineering GmbH, Germany)) was performed in healthy volunteers (225 eyes of 129 healthy volunteers aged 16–81 yrs), contact lens wearers (99 eyes of 59 contact lens wearers; age: 13–76 yrs.), glaucoma patients with preservative holding therapy (25 eyes of 15 patients aged 41–77 yrs.) as well as in patients with inflammatory diseases or in grafted cornea.ResultsIn healthy volunteers,in vivoconfocal microscopy revealed LCs in 31% of all volunteers; 37 out of these 43 volunteers present LCs both in the center and the periphery of the cornea with densities of 34 ± 3 cells/mm²and 98 ± 8 cells/mm². In the group of contact lens wearers 55% of all probands presented with LCs and 11 out of these 33 probands revealed LCs at central and peripheral location. LC densities were significantly higher in both the central (78 ± 25 cells/mm²) and the peripheral cornea (210 ± 24 cells/mm²) of contact lens wearers (p < 0.03 and p < 0.001 vs. healthy volunteers), the gradient of LC density from peripheral to central cornea was found almost identical in both groups. In the central cornea, LC density significantly decreased with duration of contact lens wear. In glaucoma patients were revealed 25 eyes with LCs including 24 eyes presenting with both central and peripheral LC location. LC densities averaged 196 ± 22 cells/mm²in the central cornea and 304 ± 27 cells/mm²in the periphery, (p < 0,001 in both zones vs. healthy volunteers). Moreover, LC present as either large cells bearing long processes or smaller cells lacking cell dendrites, most supposedly indicating mature and immature phenotype, respectively. The identification and distribution of the LCs was performed immunohistochemically.ConclusionQuantitative evidence of LC in cornea could be of clinical relevance in evaluation of wound healing, graftversushost disease, allergic and toxic drug side effects, etc. Modern diagnostic possibilities ofin vivoconfocal microscopy und immunohistochemistry regarding LC distribution and density enable to compare thein vivoandex vivodata and open a new horizon for clinical practice as well as experimental studies not only in human but also in veterinary medicine.