Response of the Ocular Surface to Histamine

Abstract

Eye rubbing results in ocular surface changes, such as irregular epithelial cell morphology, alterations in microprojections, and increased cellular exfoliation. It is unknown whether such changes are related entirely to the mechanical trauma of eye rubbing or manifest secondary to the effects of histamine released from degranulated mast cells associated with eye rubbing. To distinguish between these effects, the present study examines the effects of topical histamine application in the absence of applied mechanical trauma. The bulbar and tarsal conjunctiva of rabbits (n=10) exposed to 25 μl of histamine (25 mg/ml) for 10 minutes were examined using scanning electron microscopy. Contralateral untreated eyes served as controls. Regions studied included the bulbar and tarsal conjunctivae. The bulbar conjunctiva was divided into two regions, the interpalpebral bulbar conjunctiva and that portion unexposed to the environment. In contrast to control eyes, the interpalpebral bulbar conjunctiva of treated eyes had surface cells with irregular morphology and elevated apices. The goblet cell intercellular crypt openings in treated eyes had minimal mucus, while in control conjunctiva most intercellular openings contained mucus. The upper tarsal conjunctiva of treated eyes had an irregular surface and empty intercellular crypt orifices when compared to the smooth tarsal conjunctival surface and mucus-con- taining crypts of control eyes. The lower tarsal conjunctiva had minimal differences in surface cell morphology and did not appear notably altered, in contrast to the upper tarsal conjunctiva. In summary, topical histamine resulted in alteration of the exposed bulbar conjunctiva and upper tarsal conjunctiva, whereas the unexposed bulbar conjunctiva and lower tarsal conjunctiva surfaces exhibited only subtle changes. Perhaps the changes observed in the upper tarsal conjunctiva resulted from the blinking (wiping) action of the upper lid over the chemotic exposed bulbar conjunctiva. The paucity of mucus in the goblet cell orifices after histamine exposure was unexpected.