CONTACT LENS WETTABILITY is intrinsically linked to comfortable contact lens wear and a contact lens material’s hydrophilic surface (Guillon et al, 2016). A dewetted surface leads to more friction during each blink. Thus, improved contact lens comfort and potentially better vision can be obtained with an enhanced lubricated surface (Vidal-Rohr et al, 2018). Additionally, the stability of a thin liquid film over time is clinically relevant since instability can negatively impact vision (Kolbe et al, 2020).

Various methods have been established for contact lens in vitro wettability including the sessile drop and captive bubble methods, or the Wilhelmy plate method (Maldonado-Codina and Efron, 2006; Tonge et al, 2001; Fagehi et al, 2013). These methods evaluate the propensity of a solution to extend over a surface revealed to a solid object.

Researchers have investigated how a wetted lens surface is sustained over time since a liquid film on a solid substrate does not have consistent performance (Oron et al, 1997). This is activated by the surface free energy minimization thermodynamics and is kinetically facilitated by the hydrodynamics of the liquid (Leroy et al, 2016). Surface dewetting considers the current kinetic effect over time, which the conventional methods do not consider.

The contact lens dewetting process is an effect of solution, material properties, and environmental factors. A recent publication depicts an investigational approach that describes dewetting characteristics of several daily replacement contact lens solutions and material combinations (Marx et al, 2022). Contact lenses were analyzed utilizing a noninvasive keratograph dewetting procedure (noninvasive keratograph dry-up time). Additional dewetting characteristics were determined by investigating in vitro dewetting data of identical contact lens materials soaked in artificial tear and saline solution.

Six unique soft contact lens materials and three dissimilar test conditions were measured by noninvasive keratograph dry-up time. Contact lens materials in blister pack solution were examined after being exposed to saline and artificial tears. Each material and solution combination were analyzed after an eight-hour soak, during a 180-second dewetting observation, and the findings were stated by the area under the curve (AUC) values.

Lenses were presoaked in blister solution and then collected. The dewetting curves demonstrated a broad variety of results based on the lens material. For all materials, dewetting commences within the first 10 seconds and is similar until 30 seconds, due to a sufficiently thin film and a comparable evaporation rate. After 30 seconds, the speed of dewetting differs. Nelfilcon A had the slowest dewetting and its original solution in the blister pack had the lowest mean AUC value. After 180 seconds, all lens materials exhibited complete dewetting, excluding the combination of nelfilcon A and its blister solution, which demonstrated a partially wetted surface (Marx et al, 2022).

Thus, contact lens wettability should be seen more as a kinetic dewetting process. The AUC data characterizes that thin film dewetting is a dynamic process (Maïssa and Guillon, 2010) and consequently could depict in vitro wettability better than an individual time frame to reach a certain dewetting. Adhesive forces among the solution molecules and the contact lens surface play a vital role since the dewetting process happens when adhesive forces are lesser than cohesive forces.

The healthy tear film layer is complex, and a thin film of pure saline is not a perfect representation of the tear film since it lacks lipid layer evaporative protection. Artificial tears are more likely to mimic the natural tear film.

In vitro dewetting information in association with the solution from the blister pack allows a theoretical inference about lens wear following initial lens application. Compared to saline solutions, blister solutions demonstrated benefits in delayed dewetting. Thus, an enhanced blister pack solution should not be rinsed off prior to contact lens application. CLS

References

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