The role of gravity in gentamicin-induced toxic effects in a rabbit model.

OBJECTIVE

To define the role of gravity in gentamicin sulfate-induced retinal toxic effects by injecting the drug into vitrectomized rabbit eyes oriented in one of two positions.

METHODS

Ten right eyes of New Zealand white rabbits underwent a two-port pars plana vitrectomy and were positioned with traction scleral sutures to rotate the medullary ray superiorly (five eyes) or nasally (five eyes). Six eyes received a pars plana intravitreal injection of 400 micrograms (0.1 mL) of gentamicin, and four eyes received 0.1 mL of balanced salt solution only. All eyes were kept in position for 30 minutes after the injection. Unoperated-on fellow eyes served as controls. Three or 5 days later, the eyes were enucleated and histopathologic examination was performed.

RESULTS

Light and electron microscopy of gentamicin-treated eyes showed inner-retinal edema and disruption of the nerve-fiber and ganglion-cell layers within the more dependent retina vs sparing of the less dependent half of the retina. Eyes that received balanced salt solution showed rare inflammatory cells along the inner-retinal surface but essentially no inner-layer disruption. Examination of unoperated-on control eyes showed no inflammatory cells, edema, or necrosis.

CONCLUSION

Gravitational effects and positioning contribute to the location of gentamicin-induced retinal toxic effects in vitrectomized eyes.