In vitro measurement of central thickness in hydrated soft contact lenses using different instruments, brands, and optical designs: a pilot study

Abstract

The central thickness of contact lenses is a parameter related to oxygen permeability and comfort. However, its value is not usually reported in the lens specifications of different laboratories. In this pilot study, the central thickness of several soft contact lenses of different spherical powers, additions, and materials was measured with two different devices, the Rehder electronic thickness gauge model ET-3 and the Nikon V-12B profile projector, to study whether different measurement conditions (with the lens in air or immersed in saline solution) affected the results. First, the lenses were measured with the ET-3 device, and then the thickness of a central section of each lens was measured with the Nikon V-12B projector. Bland-Altman and correlation analyses were performed. The results of the Bland-Altmann analysis suggest that both instruments and measurement methods are interchangeable. Statistical analysis of the results of multifocal lens measurements suggests that central thickness changes significantly only in high-power lenses, independent of other factors. This work presents the first validation study of a method for measuring the central thickness of contact lenses immersed in saline solution, which could prevent evaporation and the potential reduction of their properties.