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October 1994

The Role of Gravity in Gentamicin-Induced Toxic Effects in a Rabbit Model

Author Affiliations

From the Department of Ophthalmology, Emory University School of Medicine, Atlanta, Ga. The authors have no commercial or proprietary interest in any of the products discussed in this report.

Arch Ophthalmol. 1994;112(10):1363-1367. doi:10.1001/archopht.1994.01090220113032

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 μg (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 gentamicintreated 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.

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