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Suraj Borkar and Gerald G. Fuller* (Chemical Engineering, Stanford University)
Tear Film Stability and Electrolytic Composition : Implications for Dry Eye Treatment
Dry Eye Syndrome (DES) affects approximately 10% of the global population. DES is caused by inadequate tear production or poor tear quality, leading to increased friction between the cornea and the conjunctiva. Hyperosmolarity of the tear film is a common marker of DES, but the role of electrolytic composition in tear film stability remains unclear.
This study investigates the effects of sodium chloride (NaCl) and hydrogen phosphate-based salts on the dewetting of electrolytic aqueous films on a curved glass dome. The experiments were carried out by elevating the glass dome across an air-water interface and tracking film drainage using interferometry. The results show that an increased concentration of NaCl leads to the formation of crystals during evaporative thinning of tear films. These crystals act as points for heterogeneous nucleation-based dewetting of the thin films.
In contrast, the presence of hydrogen phosphate-based salts such as sodium phosphate dibasic and potassium phosphate monobasic significantly delays dewetting of the aqueous films. This delay is attributed to several factors, including increased viscosity due to hydrogen bonding, suppression of NaCl crystal growth, and solutal Marangoni-driven influx into the film. Furthermore, the increased film viscosity caused by hydrogen phosphate-based salts leads to a Taylor-Saffman instability (viscous fingering) during the observed fluid influx from the bulk reservoir into the film.
Overall, this study demonstrates the significant impact of electrolytic composition on tear film stability and highlights the potential of hydrogen phosphate-based salts as a treatment for DES.