Purpose: To investigate the possible effects of topical cyclosporine eye drops 2% (CsA) on conjunctival immune cells obtained by impression cytology technique and to determine the clinical relevance of this effect if present. Methods: Ten consecutive patients with severe, resistant, and active vernal keratoconjunctivitis (VKC) were included in this study. All of them were treated with 2% of topical CsA drops. Symptom and clinical scores and conjunctival impression cytology specimens were obtained both before and following treatment. Impression cytology specimens were stained with anti-CD8+, CD4+, CD45RA+, and CD23+ antibodies and the percentages of positive cells were counted. The results were compared and correlation analyses were performed between clinical and laboratory data. Results: Significant reductions were observed with respect to the percentages of CD4+ and CD23+ cells in the conjunctival impression cytology specimens and clinical and symptom scores following treatment with topical CsA, while no change occurred in the percentages of CD8+ and CD45RA+ cells. The percentages of CD4+ and CD23+ cells showed good correlations with symptom and clinical scores. Conclusion: Topical CsA treatment is a very effective alternative in severe VKC cases in clinical ground and clinical efficacy of topical CsA treatment in severe, resistant VKC cases can be (at least partly) related to reduction of the CD23+ and CD4+ cell populations on the conjunctival surface. Copyright (C) 2001 S.KargerAG, Basel.