Temperaturabhängige Vermessung weicher Kontaktlinsen

Abstract

Purpose. The study objective was to measure the tempera- ture-dependent change in the refractive index, base curve, and back vertex power of soft contact lenses. Material and Methods. For each material group according to ISO 18369-1 a representative soft contact lens brand was selected according to ISO 18369-1 (polymacon, nelfilcon A, ocufilcon D, balafilcon A, somofilcon A, lotrafilcon B). The parameters were measured in vitro at 20 °C and 35 °C. First, the refractive index was determined using the automatic refractometer (VariRef C, Schmidt + Haensch), followed by the base curve measurement using the OCT (is830, Opti- mec) in conjunction with the temperature controller (TC20i, Opitmec). The back vertex power difference was determined using the precision lens meter (NIMO TR1504, Lambda-X SA). Results. The following values (refractive index 20 °C // re- fractive index 35 °C; base curve 20 °C // base curve 35 °C; Li back vertex power from 20 °C to 35 °C) were obtained for the hydrogels polymacon (1.4464 // 1.4430; 8.4706 // 8.4240; −0.077 D), nelfilcon A (1.3875 // 1.3870; 8.7854 // 8.5817; −0.022 D), ocufilcon D (1.4198 // 1.4171; 8.5622 // 8.4647; −0.076 D) and the silicone hydrogels balafilcon A (1.4197 // 1.4196; 8.7205 // 8.8287; −0.016 D), somofilcon A (1.4024 // 1.4004; 8.9100 // 8.6800; −0.076 D), lotrafilcon B (1.4246 // 1.4212; 8.6791 // 8.5801; −0.091 D). All materials except balafil- con A showed a statistically significant change (p < 0.05 paired samples), related to at least two of the measured parameters. Conclusion. The materials showed a reduction in refractive index and base curve with temperature increase. The back vertex power became more negative. The changes are within the tolerances specified in ISO 18369-2. Since no clinically relevant parameter changes were observed between the dif- ferent temperatures, it is acceptable to continue the current practice and measure lens parameters at room temperatures. Keywords Contact lenses, contact lens properties, measuring temperature