title: Influence of spoliation in poly(2-hydroxy ethyl methacrylate) soft contact lens on its free volume and optical transparency.
abstract: The calcification in poly(2-hydroxy ethyl methacrylate) contact lens was investigated using positron annihilation spectroscopy (PLS). The two poly(2-hydroxy ethyl methacrylate) (PHEMA) lenses of different companies were calcified employing a simple mechanism of calcification in abiotic aqueous solutions. The calcium deposit was analyzed using energy dispersive X-ray spectroscopy (EDS). Calcified lenses showed decrease in ortho-positronium (o-Ps) lifetime and free volume hole size of the lens material suggesting diffusion of Ca2+ into these cavities. The change in optical property viz. refractive index of these calcified lenses were measured and correlated with positron results. To find a better correlation, a series of worn spoilt PHEMA lenses of the same power with mainly calcium deposits, were similarly characterized using PLS and refractive index. These results correlate well with the free volume of the material. For hydrophilic lenses this correlation is reported for the first time.
authors.affiliation: Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore 570006, India.
authors.forename: M V
authors.initials: MV
authors.lastname: Deepa Urs
authors.forename: C
authors.initials: C
authors.lastname: Ranganathaiah
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry; D011232:Chemical Precipitation; D018639:Contact Lens Solutions / Q000494:pharmacology; D003263:Contact Lenses, Hydrophilic; D004868:Equipment Failure; D007552:Isotonic Solutions / Q000494:pharmacology*; D055095:Optics and Photonics; D011102:Polyhydroxyethyl Methacrylate / Q000737:chemistry*; D012031:Refractometry; D013057:Spectrum Analysis; D017155:Wettability; D014961:X-Ray Diffraction
chemical_list: D002130:Calcium Phosphates; D018639:Contact Lens Solutions; C034229:ITS calcifying solution; D007552:Isotonic Solutions; D011102:Polyhydroxyethyl Methacrylate