Abstract
Feeling comfortable is an important issue for contact lens wearers as contact lenses are worn for an extensive period of time. It has been shown that the in vitro friction coefficient of contact lenses is correlated to the degree of in vivo comfort, thus many studies focus on establishing friction testing methods for investigating the friction coefficient of contact lenses or contact lens care solution. We have previously demonstrated the lubricating property of poly-gamma-glutamic acid (γ-PGA)-containing care solution, and it could reduce the high friction coefficient caused by lysozyme. However, the mechanism of how γ-PGA-containing care solution reduces the lysozyme-induced friction coefficient of contact lenses is unclear. We investigated the bio-tribological effect of γ-PGA on ionic contact lenses in the presence of lysozyme by testing load and velocity variations. The ability to remove lysozyme deposition by γ-PGA and viscosity analysis of γ-PGA-containing care solutions were also investigated to understand the potential mechanism. Our results showed that the friction coefficient of γ-PGA-containing care solution with lysozyme was the lowest in both load and velocity variations, and γ-PGA functions distinctly in the lysozyme-ionic contact lens system. We proposed a model of how γ-PGA could reduce the friction coefficient in these two conditions.
Highlights
Many myopia patients choose to wear contact lenses for convenience and appearance in addition to correct vision
The raw data of the friction coefficient curve was shown in Figure 1 as an example, the lens was sliding in phosphate-buffered saline (PBS) at 0.2 cm/s when the normal load was 0.4 mN
When the normal load was larger than 4 mN, the friction coefficient was lower if the solution contained γ-PGA (Figure 2)
Summary
Many myopia patients choose to wear contact lenses for convenience and appearance in addition to correct vision. Feeling comfortable becomes a critical factor for contact lens wearers due to an extensive wearing period. Once contact lenses are worn, some tear film components such as proteins are immediately deposited on the surface of the lens. When tear proteins accumulate on the contact lens, immune reactions can be triggered resulting in discomfort, red eyes, or even eye conditions such as conjunctivitis [1,2]. It has been shown that the in vitro friction coefficient of contact lenses is corresponded to an in vivo comfort degree [3,4], modifying the materials or the surface of contact lenses has been investigated for reducing friction coefficient of contact lenses [5]. Non-functionalized polyvinyl alcohol (PVA) is added to Nelfilcon-A lenses during the manufacturing process to provide comfort.
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