Surface softness comparison of select contact lenses by nanoindentation

Abstract

Purpose : The objective of the study was to determine surface softness differences between a new contact lens material with biologically inspired water gradient surface and five other contact lens types using nanoindentation and to assess any in-vitro to ex-vivo softness differences among the lenses.

Methods : In-vitro: Contact lenses made from a new contact lens material (NCLM) (5 lenses) and 5 other comparator lenses (samfilcon A, comfilcon A, senofilcon C, senofilcon A, and fanfilcon A; n=6 each) were removed from their packaging and placed in PBS/0.1% Pluronic F-127 testing solution for 30 minutes. All tested lenses were then mounted on a steel ball for nanoindentation using an Optics 11 Piuma nanoindentation system. In order to determine the surface softness the depth required for the probe to apply 5 kPa of pressure to the lenses was calculated.
Ex-vivo: NCLM lenses (n=6) were worn by patients daily and disinfected in OPTI-FREE® RepleniSH® nightly during the 30-day clinical trial. These lenses were tested using the same method as above and compared to the in-vitro NCLM from the same manufacturing lot as well as the 5 comparator lens types (Figure 1).

Results : In-Vitro: NCLM lenses were found to have a significantly greater (p<.05) depth to reach 5 kPa (490±72 nm) than the other 5 lens types tested (68±35 nm, 83±39 nm, 79±36 nm, 82±58 and 64±31 for samfilcon A, comfilcon A, senofilcon C, senofilcon A, and fanfilcon A, respectively).
Ex-vivo: Clinically worn NCLM lenses had comparable depth (518±89 nm) to in-vitro controls.

Conclusions : The in-vitro surface softness characterized by nanoindentation of the NCLM lenses showed they were significantly softer than samfilcon A, comfilcon A, senofilcon C, senofilcon A, or fanfilcon A lenses. The surface softness of the ex-vivo NCLM did not decrease after being worn on-eye, which indicates the integrity of the water gradient surface was maintained throughout daily wear for 30 days. Surface softness may provide good correlation with lubricity, which could indicate greater comfort during lens wear.

This is a 2021 ARVO Annual Meeting abstract.

 

Figure 1. Comparison of NCLM softness to other lens materials tested. Post-30 day trial worn NCLM lenses demonstrated similar softness to unworn lenses.