Intrasubject tear osmolarity changes with two different types of eyedrops

To analyze tear osmolarity over time after instillation of two commercially available eyedrops.

This prospective, nonrandomized, simultaneous, comparative, open-label, unmasked study included 40 eyes of 20 consecutive subjects (mean age, 34.8 ± 11.8 years) with a diagnosis of moderate dry eye. Subjects were instructed to administer contralaterally controlled lubricants to the right ([RE] Blink Intensive Tears, Abbott Medical Optics, Santa Ana, CA) and left ([LE] Optive Eye Drops, Allergan Inc., Irvine, CA) eyes three times daily for 21 days. The impact of hypoosmotic (RE) and osmoprotective (LE) drops on tear osmolarity (TearLab Osmolarity System, TearLab Corporation, San Diego, CA) was measured before and 30, 60, 90, 120, and 180 minutes after instillation of the first set of drops. Follow-up measurements were performed 22 days later, 1 day after the subjects stopped using the drops.

In RE, compared with baseline, tear osmolarity values were significantly reduced at all time points after instillation, including at 180 minutes (p < 0.01). In LE, osmolarity was significantly reduced from baseline at all time points through 120 minutes (p < 0.01) but returned toward baseline at 180 minutes (p < 0.11). The minimal value reached at 90 minutes after instillation or the average reduction from baseline osmolarity was 27.6 ± 9.5 mOsm/L for RE as compared with 22.1 ± 12.3 mOsm/L for LE. Both groups showed significantly lower tear osmolarity at 21 days compared with that at baseline (hypoosmotic, 307.8 ± 11.9 mOsm/L vs. 329.4 ± 8.4 mOsm/L, p < 0.001; osmoprotective, 316.1 ± 12.5 mOsm/L vs. 327.6 ± 8.4 mOsm/L, p < 0.002).

Our results showed that both eyedrops reduced tear osmolarity within a short time frame after drop instillation (i.e., up to 120 minutes) and after a longer time frame (i.e., 21 days of application). However, hypoosmotic drops with sodium hyaluronate reduce tear osmolarity at a greater and more sustained rate than glycerin and carboxymethylcellulose-based osmoprotectants.