Morphological changes of the corneal epithelium after application of topical anaesthetic ointments

The effect of topical anaesthetic ointments (4% cocaine, 4% xylocaine, 0.5% proparacaine, 0.2% oxybuprocaine) on the corneal epithelium of rabbits was examined using a scanning electron microscope. Even after a single application, the more toxic effect of cocaine compared to the other topical anaesthetics was evident. Cocaine caused disruption of both the plasma membrane and the cytoplasm. After a single application, the other preparations caused a marked decrease in the microvilli and microplicae, disruption of the intercellular spaces and the prominence of the cell nucleus which under normal condition is not visible. Repeated applications caused regular cell desquamation and damage to the plasma membrane and cytoplasm. The damage also affected several cell layers. The cell reactions described are clearly a consequence of the topical anaesthetics, as the ointment base itself produced no essential cell damage. The scanning electron microscope findings were supported by results from the transmission electron microscope.