ACCORDING TO THE Tear Film & Ocular Surface Society Dry Eye Workshop II (TFOS DEWS II) report, a loss of homeostasis of the tear film is a fundamental component of dry eye disease (Willcox et al, 2017). That report also notes that a stable tear film is essential to maintain ocular surface health and pristine vision, because it delivers nutrients, protects and moisturizes the ocular surface, and provides a smooth surface for the refraction of incoming light. The tear film contains lipids, proteins, and electrolytes, and in meibomian gland dysfunction there is an alteration of the outer lipid-containing layer that results in tear film instability (Willcox et al, 2017).

A contact lens divides the tear film into the pre- and post-lens tear film, alters tear film homeostasis, and modifies the tear film’s biophysical and biochemical properties (Craig et al, 2013). Contact lenses change the tear film lipid layer (TFLL), and tear film thickness is reduced (Craig et al, 2013). Tear film thinning is considerably faster on the surface of a contact lens than on the corneal surface (Craig et al, 2013). TFLL variations are more pronounced with rigid lens wear compared to soft contact lens wear (Craig et al, 2013).

Homeostasis of the ocular surface is complex, and the relationship between tear proteins and contact lenses may be multifaceted and can influence success with contact lenses (Scheuer et al, 2023). Ocular surface homeostasis may be altered by contact lens materials, lens designs, and solutions incorporated into the lens material (Scheuer et al, 2023).

Tear proteins function to maintain the balance of ocular surface homeostasis, as evidenced by the effects of their conformation relative to stabilizing the tear film and their potential impact on corneal epithelial cells.

In asymptomatic contact lens wearers, a change in tear lysozyme has been reported (Temel et al, 1991). Compared to the control group, the mean tear lysozyme levels of rigid and high-water-content contact lens wearers were increased. Tear lysozyme varied between high- and low-water-content contact lens wearers (Temel et al, 1991).

Contact lens solutions are essential to stabilize tear proteins. An in vitro study assessed the functionality of the components in daily replacement blister package solutions to help stabilize lysozyme, a tear protein, in denaturing conditions (Scheuer et al, 2023). Lysozyme was chosen due to its abundance in tears (with lipocalin and lactoferrin), its ability to deposit on soft contact lenses. Native versus denatured protein conformation was determined by an assay of the enzyme’s biological activity.

Contact lens solutions were sampled from nine daily replacement contact lens blister packages (two traditional hydrogel and seven silicone hydrogel). Phosphate buffered saline (PBS) served as a control. Lysozyme was incubated and then mixed with the protein denaturant sodium lauryl sulfate. Lysozyme activity was assessed by adding test solutions to a suspension of Micrococcus luteus. The Micrococcus luteus cell wall is lysed by native lysozyme, which decreases suspension turbidity. The stability of lysozyme activity was assessed by comparing suspension turbidity prior to and after exposure to test solutions.

For kalifilcon A solution, lysozyme stabilization was statistically significant at 90.7% compared to that of PBS, a negative control. No significant improvement was observed with any other contact lens solution (all lysozyme stabilization < 5.00%). No other contact lens solution demonstrated meaningful improvement.

In the unique kalifilcon A contact lens solution with dual moisturizers and dual osmoprotectants, lysozyme was appreciably more stable compared to PBS and other daily replacement contact lens solutions. This study validates the lysozyme activity assay and demonstrates mechanistic evidence that the contact lens solution containing kalifilcon A can stabilize proteins in environments that typically denature proteins, which may influence its ability to maintain ocular surface homeostasis. CLS

References

1. Willcox MDP, Argüeso P, Georgiev GA, et al. TFOS DEWS II Tear Film Report. Ocul Surf. 2017 Jul;15:366-403.
2. Craig JP, Willcox MD, Argüeso P, et al. The TFOS International Workshop on Contact Lens Discomfort: report of the contact lens interactions with the tear film subcommittee. Invest Ophthalmol Vis Sci. 2013 Oct 18;54:TFOS123-TFOS56.
3. Scheuer CA, Barniak VL, Phatak NR, Rah MJ, Reindel W. Effect of Contact Lens Solutions in Stabilizing the Activity of Tear Lysozyme. Clin Optom (Auckl). 2023 May 12;15:119-127.
4. Temel A, Kazokoglu H, Taga Y. Tear lysozyme levels in contact lens wearers. Ann Ophthalmol. 1991 May;23:191-194.