OCULAR PIGMENTATION PROTECTS THE RABBIT RETINA FROM GENTAMICIN-INDUCED TOXICITY

Purpose. This study was designed to investigate the possibility that g entamicin-induced retinal toxicity is dependent on ocular pigmentation by comparing the effects of the drug on the functional and morphologi c integrity of the retina in albino and pigmented rabbits. Methods. In each rabbit, a solution of gentamicin sulfate was injected into the v itreous of one eye, and saline was injected into the other eye. Retina l function was assessed by electroretinogram (ERG) at different time i ntervals after injection. Retinal structure was examined at the light microscopic level. Results. In albino and pigmented rabbits, functiona l retinal damage developed to a maximal level within the first week af ter gentamicin injection. Thereafter, gradual recovery could be seen i n eyes that suffered less than 80% maximal reduction in the ERG b-wave . For each dose >0.1 mg studied, retinal damage was more severe in the albino rabbits than in the pigmented ones. The degree of damage was n ot affected by the level of ambient illumination, nor was it reduced b y the administration of N-acetylcystein, a free radical scavenger, tog ether with gentamicin. Conclusions. Ocular pigmentation partially prot ects the rabbit retina from the toxic action of gentamicin. This prote ction probably reflects binding of the drug by the melanin, which ther eby reduces the concentration of the free gentamicin. When the initial gentamicin-induced retinal damage is expressed in <80% reduction in t he ERG, substantial recovery may occur in both strains of rabbits.