Abstract
Purpose :
Recent work highlights that lower salt diffusivity (Ds) of a soft contact lens (SCL) can prevent post-lens tear-film (PoLTF) hyperosmolarity and that the PoLTF osmolarity is significantly different from that of the tear meniscus and the pre-lens tear film (PrLTF) [Kim et al. 2021]. That effort focused on the spatially averaged PoLTF osmolarity and did not address localized tear break-up areas, which cause localized PrLTF osmolarity spikes that can be greater than 1000 miliosmolar (mOsM) [Peng et al. 2014]. Here, we assess the effect of localized PrLTF hyperosmotic spikes on PoLTF osmolarity and whether SCL wear can protect the cornea from hyperosmotic spikes.
Methods :
SCL and PoLTF were designed with Comsol Multiphysics 5.5 platform and incorporated into a 2D continuum diffusion model to determine the PoLTF osmolarity transiently. Lens-salt partition coefficient (ks), Ds, and lens thickness (hlens) were varied to assess their effect on PoLTF osmolarity. Localized hyperosmolarity spike follows the time-dependent results of Peng et al. [2014] and were used as the anterior lens-surface boundary-layer condition (Figure 1a). A no-flux boundary was incorporated at the PoLTF/cornea interface. Initial conditions for SCL and tear compartments were obtained from steady-state solutions of Kim et al. [2021] for normal and dry eyes with various Ds, ks, and hlens.
Results :
Figure 1b provides PoLTF osmolarity for normal eye with a given Ds, ks, and hlens (specified in Figure 1b) during various time points within an interblink while experiencing the PrLTF osmolarity spike of Figure 1a. Localized PoLTF osmotic spike did not occur until ~10 s into the interblink and the spike osmolarity was significantly lower than that of the PrLTF spike. For dry eye, osmolarities in break-up and non-break-up areas were elevated for a given Ds, ks, and hlens. Change in Ds significantly alters the peak magnitude.
Conclusions :
SCL wear can protect the cornea against localized hyperosmolarity caused by tear break-up spots on the PrLTF. The magnitude of protection increases as the value of Ds lowers. Infrequent blinking results in higher hyperosmolarity spikes for the cornea; however, high osmolarity spikes can be prevented by lowering the Ds.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.