OBJECTIVE To determine the effect of dexamethasone on the phagocytic capacity of the human trabecular meshwork. A decrease in meshwork phagocytosis has been proposed in the pathogenesis of steroid glaucoma. METHODS The anterior segments of seven pairs of human eyes were placed in perfusion organ culture. One eye of each pair received dexamethasone, and the fellow eye served as control. After 21 days, latex microspheres labeled with fluorescein isothiocyanate and coated with antibodies were added to the culture medium. Twenty-four hours later, the eyes were fixed, the trabecular meshworks were treated with a rhodamine-labeled secondary antibody and sectioned, and the number of ingested beads was determined using a laser scanning confocal microscope. Nuclei were counted and used to calculate the phagocytic index of each anterior segment (number of ingested beads divided by number of nuclei). RESULTS Ingested beads appeared green and could be differentiated from noningested beads, which appeared red, using appropriate wavelengths of the laser. Bead ingestion was confirmed with electron microscopy and the use of secondary antibody labeled with horseradish peroxidase. Dexamethasone decreased phagocytosis by 57%, as shown by the fact that trabecular cells in dexamethasone-treated meshworks ingested significantly fewer beads than cells in fellow control meshworks (1.5 +/- 0.6 beads/cell versus 3.5 +/- 1.4 beads/cell; P = 0.008). No evidence of significant migration or loss of trabecular cells was noted; the number of trabecular cells appeared similar in dexamethasone-treated and control meshworks (144 +/- 36 versus 141 +/- 46). CONCLUSIONS Dexamethasone inhibits phagocytosis by human trabecular meshwork cells in perfusion organ culture.