Soft Contact Lens Wear Prevents Localized Corneal Hyperosmolarity Spikes

Soft contact lens (SCL) wear can protect the cornea from pain caused by localized pre-lens tear film (PrLTF) hyperosmolarity spikes during regular blinking, according to a study published in Contact Lens & Anterior Eye. Soft contact lenses with low lens-salt diffusivities (D_s) can protect against hyperosmotic spikes and discomfort even during infrequent blinking (>10 s). 

Investigators incorporated 2-dimensional transient salt diffusion into a computationally designed SCL, post- lens tear film (PoLTF), and ocular surface. At the anterior surface of the SCL, the team introduced time-dependent localized hyperosmolarity spikes equivalent to those generated in the PrLTF. They followed salt spikes over time until they penetrated through the lens into the PoLTF. 

The team adjusted D_s to assess their importance on salt migration from the PrLTF to the ocular surface and correspondingly changed SCL and PoLTF conditions depending on D_s and on dry eye symptoms. They translated corneal surface osmolarities into pain scores. 

Investigators report that for D_s  above 10^{− 7}cm²/s, it takes around 5–10 s for the PrLTF hyperosmotic break-up spikes to diffuse across the SCL and reach the corneal surface. They note that salt concentrations are much lower than those in the progenitor PrLTF spikes, even if localized spikes penetrate to the ocular surface.

For D_s  less than 10^{− 7}cm²/s, the SCL protects the cornea from hyperosmotic spikes in both normal and dry eyes. After converting corneal hyperosmolarity into transient pain scores, the team determined that pain thresholds were lower in individuals with SCLs compared with those without SCLs. 

“Wear of a SCL protects the cornea from localized osmolarity spikes as long as lens wearers blink frequently,” according to the researchers. “However, if lens wearers blink infrequently, which is typically the case when the lens wearers are reading, watching TV, or working on a computer, corneas are more likely exposed to localized hyperosmotic spikes on the ocular surface.” The investigators add that D_s can be lowered to protect the cornea from localized osmolarity spikes. 

Study limitations include the use of computationally designed SCLs.

Disclosure: This research was supported by CooperVision, Inc. One study author declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

Reference

Kim YH, Lin MC, Peng C-C, Radke CJ. Prevention of localized corneal hyperosmolarity spikes by soft-contact-lens wear. Cont Lens Anterior Eye. Published online June 16, 2022. doi:10.1016/j.clae.2022.101722