Atomic force microscopy analysis of the effect of plasma treatment on gas permeable contact lens surface topography

TitleAtomic force microscopy analysis of the effect of plasma treatment on gas permeable contact lens surface topography
Publication TypeJournal Article
Year of Publication2019
AuthorsGill, F., C. Purslow, and P. Murphy
JournalContact Lens and Anterior Eye
KeywordsArticle, atomic force microscopy, Comfort, controlled study, distilled water, drying method, Gas permeable contact lenses, in vivo study, intermethod comparison, methodology, nitrogen, Plasma-treatment, priority journal, rank sum test, Surface roughness, topography, visual analog scale

Purpose: Using atomic force microscopy (AFM) to investigate anterior surface topography (AST) in worn and unworn, plasma surface-treated (PST) and untreated (UT) gas permeable (GP) lenses, and influence of surface topography on in vivo comfort. Methods: GP lens AST evaluated with AFM in tapping mode, using an uncoated, 40 nm symmetric tip (sampling frequency: 300 kHz), at five randomised locations, over a 100μm 2 area, to produce mean average roughness (Ra) and root mean square (RMS) values for each sample. Four unworn lenses (two PST, two UT) were examined (Quasar/Boston EO material). Twenty worn lenses (ten PST, ten UT) of same design and material as unworn lenses collected after 3 months lens wear. General wearing comfort reported by visual analogue scale (VAS) at 3 months visit. For sample preparation, two worn UT GP lenses were divided into four segments; each segment underwent a different lens rinse and drying method. Results: Unworn: UT lenses had significantly higher mean RMS and Ra values compared to PST (Mann-Whitney, p < 0.05). Worn: UT Median RMS values were significantly higher than PST (Mann-Whitney, p < 0.05). Comfort: no correlation found between general comfort and RMS or Ra scores. Sample preparation: Method 4 (purified, distilled water rinse/nitrogen gas dry) produced optimum median RMS and Ra values. Conclusions: Unworn PST GP lenses had lower Ra and RMS values compared with unworn UT GP lenses. After 3 months wear, PST lenses had smoother surface topographies than UT lenses. No relationship was found between surface topography and lens wear comfort. Sample preparation protocol directly impacts AFM results. © 2019 British Contact Lens Association