Purpose: An experimental platform to replicate the human tear film on a contact lens is presented. The influence of interfacial viscoelasticity in stabilizing in vitro model tear films against breakup and dewetting is investigated using this instrument.
Methods: Model tear films consisting of bovine meibomian lipids (meibum) spread on either PBS or artificial tear solution (ATS) are created. The interfacial shear rheology of these films is measured as a function of temperature. The dewetting dynamics of these films is then investigated using the Interfacial Dewetting and Drainage Optical Platform (i-DDrOP) on top of silicone hydrogel (SiHy) contact lenses at 23 and 35°C. The film breakup times are evaluated using two parameters: onset of film breakup, Tonset for thick films (∼100 μm), and tear breakup times, TBU for thin films (∼1 μm). Thin film thinning rates as a result of evaporation are also calculated.
Results: The ATS/meibum films have the largest surface rheology and correspondingly show the largest Tonset times at both 23 and 35°C. The parameter TBU is also significantly larger for ATS/meibum (TBU ∼ 40 seconds) compared with that of ATS and PBS/meibum films (TBU ∼ 30 seconds) at room temperature. However, at 35°C, all three model tear films exhibit similar TBU ∼ 17 seconds and average rate of thinning of -4 μm/minute.
Conclusions: Tear film stability is influenced by both surface rheology and evaporation. The in vitro tear breakup times and thinning rates of model tear films at 35°C are in good agreement with in vivo measurements previously reported, highlighting the utility of the i-DDrOP for in vitro tear film breakup research.