Comparison of Ocular Lubricant Osmolalities

The aim of this study was to evaluate the osmolality of commercially available ocular tear lubricants.

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.

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).

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.