Ocular rosacea. A histologic and immunopathologic study. Acne rosacea is an idiopathic dermatologic disease that frequently produces conjunctival inflammation. The authors studied the histology and immunopathology of epibulbar conjunctival biopsy specimens from eight patients with ocular rosacea and compared the findings with those from conjunctiva from 13 normal individuals. The conjunctival epithelium in ocular rosacea was attenuated and infiltrated by inflammatory cells, mainly T-helper/inducer (CD4) cells, phagocytic cells, and antigen-presenting (CD14, Mac-1) cells. The difference between the normal control group and the rosacea group in the number of mononuclear cells forming these populations was statistically significant (P less than 0.01). The substantia propria of the rosacea specimens contained large subepithelial infiltrates of chronic inflammatory cells, and in some cases frank granuloma formation was evident. There was an overall mean increase of nearly all cell types, but especially of T-helper cells in the rosacea specimens compared with the controls. Interestingly, T-helper/inducer (CD4) cells, which were outnumbered by the T-suppressor (CD8) cells in the normal conjunctival epithelium (CD4/CD8 = 0.85), outnumbered the CD8-positive cells in the rosacea specimens (CD4/CD8 = 1.6). There also was a 3.5-fold increase of the CD4/CD8 ratio in the rosacea conjunctival stroma compared with the normal specimens. The mechanism involved in rosacea conjunctival inflammation resembles a type IV hypersensitivity reaction. 