Sequential Staining: The Effects of Sodium Fluorescein, Osmolarity, and pH on Human Corneal Epithelium

Abstract

Previous reports have suggested that sequential applications of sodium fluorescein (NaF) to the ocular surface cause loss of epithelial cells. In those experiments the solutions were free of preservatives, but delivered a hypertonic and alkaline load. It is possible that either the hyperosmolarity, NaF, and/or alkalinity may have contributed to the epithelial cell loss. Our study explored the possible impact of these three factors on epithelial integrity. We used a paradigm in which we designed four test solutions to isolate the cytotoxic effects of the three factors. Fifteen subjects were exposed to one of the solutions on separate visits. One solution was instilled in both eyes, every 3 min, for a total of seven applications, and a slitlamp examination was performed. Staining was graded on a scale of 0 to 3 for each of five corneal sectors. Application of solution 1 (NaF, hyperosmotic, and alkaline) resulted in staining for all subjects. For the other three solutions (without NaF), insignificant staining occurred. The epithelium tolerates changes in pH and osmolarity between 7.2 to 7.8 and 290 to 350, respectively. However, NaF when applied in multiple doses may be cytotoxic.