Short-Term Changes In Tear Osmolarity After Instillation Of Different Osmolarity Eye Drops In Patients With Dry Eye

Several hypotonic tear substitutes have been developed that focus on the central role of tear hyperosmolarity in the pathogenesis of dry eye syndrome and are expected to reduce tear osmolarity and restore osmotic balance. A few studies have investigated hypotonic tear substitutes and reported enhanced effects on the tear film stability and ocular surface integrity. However, those studies indirectly evaluated the effect of hypotonic tear substitutes using other clinical assessments instead of direct changes in tear osmolarity. The purpose of this study was to investigate short-term changes in tear osmolarity of dry eye patients after using artificial tears containing sodium hyaluronate (SH) at different osmolarities.

This study was a prospective and randomized study conducted from June 2017 to February 2018 that included participants who met the Korean guidelines for dry eye syndrome and whose tear osmolarity as assessed using TearLab was 300 mOsm/L or greater. Patients with other concomitant ocular pathology, a history of ocular surgery, or who reported any systemic disease that might affect tear film stability were excluded. Only one eye per patient with higher osmolarity was included in this study.

A total of 80 patients was recruited, and they were randomly divided into 4 groups of 20 patients: Group 1 (isotonic 0.1% SH), Group 2 (isotonic 0.15% SH), Group 3 (isotonic 0.3% SH), and Group 4 (hypotonic 0.18% SH). Clinical evaluation included slit-lamp examination, tear film break up time (TBUT), corneal staining score, and tear osmolarity. All measurements were taken in the same space in the afternoon by one ophthalmologist. Osmolarity was measured first, followed by TBUT and corneal staining score. The tear osmolarity was assessed using the TearLab system immediately after blinking. Tear osmolarity was evaluated 4 times for each participant: at baseline and at 1, 5, and 10 minutes after instillation of the eye drop.

As there have been no reports on the changes that take place in tear osmolarity after instillation of SH eye drops, we investigated how isotonic and hypotonic eye drops affect tear osmolarity and the duration of the effect. In this study, the 4 SH eye drops all produced a significant decrease in tear osmolarity at all time points up to 10 minutes after instillation. And the hypotonic SH drops produced an immediate improvement compared to the isotonic SH drops. But, tear osmolarity lowering effect of the hypotonic SH solution was lower at 10 minutes than at 5 minutes after instillation. Therefore, unless used frequently, any additional lowering effect of hypotonic SH eye drops on tear osmolarity may be limited.