Retinal toxicity of gentamicin after subconjunctival injection performed adjacent to thinned sclera

Objective: To investigate the potential toxicity to the retina of gentamici n injected near surgically thinned scleral areas in a rabbit model. Design: Experimental study, Methods: Scleral scraping to half thickness was performed in the superotemp oral scleral area in both eyes of adult rabbits (n = 10). Gentamicin sulfat e was injected subconjunctivally to the right eye and saline to the left ey e, which always sewed as a control eye, Four weeks after the procedure, ele ctroretinography (ERG) was performed to assess retinal function. Then, the eyes were enucleated and prepared for histologic evaluation of structural d amage. In four eyes of two additional rabbits, vitreous gentamicin concentr ations were measured using a fluorescence polarization assay. Main Outcome Measures: Dark- and light-adapted ERG responses and histopatho logic damage. Results: Dark- and light-adapted ERG responses in all rabbits were similar in the experimental and control eyes. Gentamicin levels were more than 10 m ug/ml after subconjunctival injection of gentamicin with scraping and 0.29 mug/ml after subconjunctival injection of gentamicin with no scraping. Hist opathologic examination revealed significant local damage to the photorecep tors adjacent to the area of scraping and subconjunctival injection. A sign ificantly lesser degree of damage was seen if gentamicin was injected in pi gmented rabbits or in albino rabbits, but only 4 weeks after scleral scrapi ng. Conclusions: Increased penetration of gentamicin through thinned sclera may lead to toxic levels of the drug in a localized area adjacent to the site of injection, These toxic effects are also influenced by the degree of pigm entation and acute inflammation. (C) 2001 by the American Academy of Ophtha lmology.