Fractal Features and Surface Micromorphology of Unworn Surfaces of Rigid Gas Permeable Contact Lenses

ABSTRACT

Purpose: The aim of this exploratory study was to investigate the micromorphology of surfaces of rigid gas permeable (RGP) contact lenses (CLs) using atomic force microscopy (AFM) followed by fractal analysis.

Materials and methods: In order to characterize in a quantitative manner the micromorphology of surfaces of new and unworn RGP CLs made of twelve different materials, AFM was taken and then analyzed using fractal methods. Surface topography was sampled in an intermittent-contact mode in air, on square areas of 5 × 5 µm² (MultiMode with Nanoscope V (Bruker). Spatial characteristics of 3-D surface texture were obtained using parameters defined in ISO 25178-2: 2012 norm.

Results: The surface texture turned out to have complex 3-D nanoscale geometry. For quantitative characterization of the properties of surface geometry at nanometer level of CL on the global scale, a series of fractal parameters was used.

Conclusions: Statistical and fractal parameters of 3-D surfaces can be used by manufacturers to assess the micromorphology of CLs in order to improve their 3-D surface texture characteristics. These parameters can also be used in an elastic–plastic finite element model with contact elements to simulate the friction, wear and micro-elastohydrodynamic lubrication at a nanometer scale between the CL with the corneal surface.

KEYWORDS:

• Atomic force microscopy
• contact lenses
• fractal analysis
• rigid gas permeable material
• surface roughness

Author disclosure statement

There are no commercial associations that might create a conflict of interest in connection with the submitted manuscript. No competing financial interests exist.

Proprietary interest

The authors have no proprietary or commercial interest in any of the materials discussed in this article.