SEQUENTIAL STAINING - THE EFFECTS OF SODIUM FLUORESCEIN, OSMOLARITY, AND PH ON HUMAN CORNEAL EPITHELIUM

Background. Previous reports have suggested that sequential applicatio ns of sodium fluorescein (NaF) to the ocular surface cause toss of epi thelial cells. In those experiments the solutions were free of preserv atives, but delivered a hypertonic and alkaline load. It is possible t hat either the hyperosmolarity, NaF, and/or alkalinity may have contri buted to the epithelial cell loss. Our study explored the possible imp act of these three factors on epithelial integrity. Methods. We used a paradigm in which we designed four test solutions to isolate the cyto toxic effects of the three factors. Fifteen subjects were exposed to o ne of the solutions on separate visits. One solution was instilled in both eyes, every 3 min, for a total of seven applications, and a slitl amp examination was performed. Staining was graded on a scale of 0 to 3 for each of five corneal sectors. Results. Application of solution 1 (NaF, hyperosmotic, and alkaline) resulted in staining for ail subjec ts. For the other three solutions (without NaF), insignificant stainin g occurred. Conclusions. The epithelium tolerates changes in pH and os molarity between 7.2 to 7.8 and 290 to 350, respectively. However, NaF when applied in multiple doses may be cytotoxic.