Ocular toxicity of subconjunctival gentamicin.

The subconjunctival injection of commercial gentamicin, given either as a single dose or as repeated injections, caused a hyperemic conjunctival response. Simultaneously there was a toxic myopathy induced in the extraocular muscles. The overall response, followed with light microscopy, occurred as a focal infiltrate of polymorphonuclear leukocytes with progression over a few days to a mononuclear cell infiltrate that accompanied fiber degeneration. Injections of each ingredient of commercial gentamicin individually showed that only gentamicin caused the muscle response; methylparaben, EDTA, and sodium bisulfite were without effect. The pH of the solution was eliminated as a contributing factor as was osmolarity of the injection. Increasing recognition is being given to post-operative complications caused by the prophylactic subconjunctival injection of gentamicin following cataract, and other intraocular surgery. The present data offer a mechanistic explanation for many of these toxic findings.