Buffering capacity of bovine vitreous.

PURPOSE: To measure the buffering capacity of bovine vitreous to HCl, NaOH, and triamcinolone acetonide. METHODS: Vitreous was dissected from 10 bovine globes, homogenized, and divided into 5.0-mL aliquots. The carbonate/bicarbonate buffer of the vitreous was maintained by performing all subsequent titrations under an atmosphere of 5% CO2/95% air. The pH was monitored during the addition of 0.1 N HCl, 0.1 N NaOH, or 40 mg/mL triamcinolone acetonide to the vitreous sample; 0.9% NaCl was used as control. RESULTS: The buffering capacity of bovine vitreous to HCl was 10 times greater than that of 0.9% NaCl. The buffering capacity of vitreous to NaOH was four times greater than that of 0.9% NaCl. Bovine vitreous was able to resist pH changes from addition of triamcinolone acetonide at levels 20 times greater than commonly injected intravitreally. CONCLUSION: Vitreous had a greater buffering capacity than 0.9% NaCl, indicating a greater capacity to remain stable when acidic or alkaline pharmaceuticals are injected in microliter amounts.

Intravitreal toxicity of levofloxacin and gatifloxacin.

BACKGROUND AND OBJECTIVE: To assess the retinal toxicity of varying concentrations of intravitreally injected gatifloxacin and levofloxacin. MATERIALS AND METHODS: In this experimental, controlled study, levofloxacin (initial concentration = 25 mg/mL) and gatifloxacin (initial concentration = 2 mg/mL) were titrated using 5% dextrose solution to concentrations of 2,500 to 156 microg/0.1 mL and 400 to 50 microg/0.1 mL, respectively. Each concentration was injected intravitreally into two rabbit eyes (one eye per animal); two control eyes were injected with 0.1 mL of 5% dextrose solution. All animals were examined and electroretinography was performed before and 14 days after injection. The animals were killed at 14 days; the eyes were enucleated and prepared for light microscopy. RESULTS: The levofloxacin group exhibited significant decreases in electroretinography in the eyes injected with 1,250 and 2,500 microg. No signs of retinal toxicity were observed on slit-lamp examination, indirect ophthalmoscopy, or light microscopy in all eyes injected intravitreally with 625 microg or less of levofloxacin or in any eyes given gatifloxacin. CONCLUSION: Intravitreally injected concentrations of 625 microg or less of levofloxacin and 400 microg or less of gatifloxacin appeared nontoxic.