[The influence of local anesthetics on corneal epithelium. A scanning electron microscopic study (author's transl)].

The effect of different local anesthetics (Cocain 4%, Lidocaine 2%, Proparacain) on the corneal epithelium in rabbits was examined under scanning electron microscope. The experiment was divided into three groups. Group 1 received one application of two drops of the given local anesthetic for a reaction time of 5 minutes. Group 2 received two drops of the given anesthetic after 0, 5 and 10 minutes. The cornea was excised after 15 minutes. Group 3 were measured after a single application of Proparacain using a Schiötz or hand applanation tonometer according to Draeger. After a single dose of a local anesthetic principally the same changes in the surface of the cornea were observed with all the preparations used: a distinct decrease in the number of microvilli and microplicae, disruption of the intercellular spaces and the prominence of the cell nuclei which under normal conditions are not visible. After several applications the greater toxicity of Cocain compared with the other preparations was clearly seen through the disruption of the plasma membrane and the cytoplasm. The damage effected several layers of cells. Tonometry when correctly performed causes no additional damage to the cell surface.- The effect of local anesthetics on the cell membrane can only take place after the disruption of the tear film. The results emphasize that local anesthetics should only be applied when absolutely essential.