The Effect of Refrigeration on the Osmolality and pH of Nonpreserved Artificial Tears Containing Carboxymethylcellulose

Introduction Nonpreserved artificial tears (NPAT) are a recommended treatment for dry eye. The manufacturers’ instructions state to discard the container after initial opening and use. Some clinicians advocate the use and storage of NPAT in a zip‐lock bag in a refrigerator for up to 12 h. The purpose of this study was to evaluate whether refrigeration of opened NPAT over a 12‐h period had any effect on the pH or osmolality. Methods Forty individual carboxymethylcellulose NPAT samples were used in this study. The initial osmolality and pH of each sample were measured with a vapor pressure osmometer and electronic pH meter. The samples were refrigerated (4°C) in closed zip‐lock plastic bags for 12 h. After storage, the pH and osmolality of the samples were measured. The data were statistically analyzed for significant differences using a paired t‐test. Results The mean initial pH and osmolality before refrigeration were 6.46 pH units and 304.10 mmol/kg, respectively. After refrigeration, the mean pH was 6.44 units, and mean osmolality was 305.87 mmol/kg. Paired t‐tests revealed a nonsignificant difference (p > 0.05) for both pH and osmolality. Conclusion Refrigeration of opened carboxymethylcellulose NPAT stored in closed zip‐lock plastic bags does not have a significant effect on the osmolality or pH of the solution. Storage of NPAT containing carboxymethylcellulose is an acceptable practice with regards to stability of pH and osmolality.