Mast cells in human optic nerve.

PURPOSE Mast cells are classically found in ocular tissues within the conjunctiva, choroid, and iris. The aim of this study was to examine their distribution in the optic nerve and its meninges. METHODS Sixty-six human optic nerves were studied from normal subjects at autopsy, fetuses aborted for chromosomal abnormalities, and from enucleation specimens of patients with a variety of inflammatory, traumatic, neoplastic, and vascular disorders. Mast cells were identified using a stain for the enzyme chloroacetate esterase, and confirmed using toluidine blue, revealing metachromatic cytoplasmic granules. RESULTS Mast cells were found scattered in the meninges of almost all optic nerves examined, frequently in perivascular locations, with densities up to 2325 mast cells/mm3 (mean 269.7 +/- 64.1 cells/mm3 in normal nerves). Mast cells were found in the optic nerve parenchyma in nerves from four eyes that had severe abnormality, often associated with neovascularization. Normal nerves, as well as nerves from fetuses aborted for congenital defects, had significantly fewer meningeal mast cells than those from eyes with inflammatory or vascular diseases. Degranulation of mast cells was observed more often in eyes with recent severe trauma. CONCLUSIONS Based on their work and the work of others suggesting an association between mast cells and nervous system autoimmune disorders, the authors hypothesize a role for optic nerve mast cells in certain ocular inflammatory conditions.