To the Editor.
—Pflugfelder and Murchison1 reported a case of corneal toxicity with a 12-hour collagen shield soaked in tobramycin sulfate (40 mg/mL), vancomycin hydrochloride (50 mg/mL), and dexamethasone sodium phosphate (4 mg/mL) in the January 1992 issue of the Archives. When reconstituted in water, vancomycin has a pH of 2.5 to 4.5. Topical application of a solution with such a low pH to the cornea is toxic, whether or not a collagen shield is used. A collagen shield soaked in anything with a pH of 2.5 is extremely toxic to the cornea. I have seen several cases of corneal toxicity from topical application of acidic vancomycin solution alone. A buffer should be used to raise the pH to an acceptable level whenever vancomycin eye drops are used.
Barron B. Corneal Toxicity From Acidic Vancomycin Solution. Arch Ophthalmol. 1993;111(1):18. doi:10.1001/archopht.1993.01090010020003