RESUMO
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.
