The role of gravity in gentamicin-induced toxic effects in a rabbit model
J. I. Lim, C. T. Anderson, A. Hutchinson, R. R. Buggage and H. E. Grossniklaus
Department of Ophthalmology, Emory University School of Medicine, Atlanta, Ga.
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.
