Purpose: The aim of this study was to evaluate the osmolality of commercially available ocular tear lubricants.
Methods: Thirty-seven (n = 37) ocular lubricants, measured three times each, were evaluated for osmolality using a vapor pressure osmometer (Wescor VAPRO 5520). The osmometer was calibrated before each use, and the order of the lubricants was randomized. Ambient temperature and humidity were monitored for stability.
Results: Of the 37 ocular lubricants tested, 35 (94.6%) had an osmolality of less than 295 mmol/kg, one (2.7%) had between 295 and 308 mmol/kg, and one (2.7%) had more than 308 mmol/kg. The ambient room temperature was stable and ranged from 21.9°C to 22.0°C, and the relative humidity ranged from 21.2% to 25.6% during experimentation. When ocular lubricants were grouped by ingredient (carboxymethylcellulose and hydroxylpropyl methylcellulose, hyaluronic acid, and hydroxypropyl guar), no significant difference in osmolality was noted between groups (Mann-Whitney U test, P > .05).
Conclusions: The majority of the ocular lubricants tested had low osmolalities, mimicking the osmolarity of newly formed tears (295 to 300 mOsm/L). Several factors need to be considered when choosing a tear lubricant, which have more complex formulations than ever. Knowledge of their osmolality may be an added parameter to consider when choosing therapeutic options for dry eye.
*OD, MSc, FAAO
Ecole d’Optométrie, Université de Montréal, Montreal, Quebec, Canada (all authors).
Etty Bitton École d’Optométrie Université de Montréal PO Box 6128, Downtown Station Montreal, Quebec, Canada H3C 3J7 e-mail: firstname.lastname@example.org