title: Microscopic observation of unworn siloxane-hydrogel soft contact lenses by atomic force microscopy.
abstract: In the present study, samples of lotrafilcon A, balafilcon A, and galyfilcon A contact lenses were observed by atomic force microscopy (AFM) in tapping mode at areas ranging from 0.25 to 400 microm2. Mean roughness (Ra), root-mean-square roughness (Rms) and maximum roughness (Rmax) in nanometers were obtained for the three lens materials at different magnifications. The three contact lenses showed significantly different surface topography. However, roughness values were dependent of the surface area to be analyzed. For a 1 microm2 area, statistics revealed a significantly more irregular surface of balafilcon A (Ra = 6.44 nm; Rms = 8.30 nm; Rmax = 96.82 nm) compared with lotrafilcon A (Ra = 2.40 nm; Rms = 3.19 nm; Rmax = 40.89 nm) and galyfilcon A (Ra = 1.40 nm; Rms = 1.79 nm; Rmax = 15.33 nm). Ra and Rms were the most consistent parameters, with Rmax presenting more variability for larger surface areas. The higher roughness of balafilcon A is attributed to the plasma oxidation treatment used to improve wettability. Conversely, galyfilcon A displays a smoother surface. Present observations could have implications in clinical aspects of siloxane-hydrogel contact lens wear such as lens spoliation, resistance to bacterial adhesion, or mechanical interaction with the ocular surface.
authors.affiliation: Department of Physics (Optometry), School of Sciences, University of Minho, Braga, Portugal. jgmeijome@fisica.uminho.pt
authors.forename: José M
authors.initials: JM
authors.lastname: González-Méijome
authors.forename: Antonio
authors.initials: A
authors.lastname: López-Alemany
authors.forename: José B
authors.initials: JB
authors.lastname: Almeida
authors.forename: Manuel A
authors.initials: MA
authors.lastname: Parafita
authors.forename: Miguel F
authors.initials: MF
authors.lastname: Refojo
mesh_terms: D003263:Contact Lenses, Hydrophilic; D006801:Humans; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000737:chemistry* / Q000378:metabolism; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D012833:Siloxanes / Q000737:chemistry* / Q000378:metabolism; D013499:Surface Properties; D017155:Wettability
chemical_list: D012833:Siloxanes; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate