Three-dimensional measurement for spherical and nonspherical shapes of contact lenses

In recent years, with the development of precise lathe-cutting equipment, special shaped contact lenses (CL) have been crafted. However, while it is possible to manufacture such a lens, its shape evaluation has not been well-established. We conducted a basic optical experiment using special lenses to measure a spherical lens and nonspherical mold. As the measurement sample, a metal ball, special CL, and a toric-shaped mold were adopted. In order to accurately measure those real shapes, we proposed an algorithm in which the probe light is vertically incident to the sample surface within a numerical aperture of the optical probe. For this algorithm, we developed the specialized time-domain optical coherence tomography (TD-OCT), which was designed to conduct circular scanning while maintaining vertical incidence by driving a two-axis (vertical and horizontal) micro-electromechanical system mirror with a phase difference of 90°. The shape, thickness distribution, and curvature radii of both front and back surfaces of a CL were estimated with this OCT signal analysis and sphere fitting. The shape and curvature radius were evaluated by using the simulated data under the same experimental conditions. They were sufficiently accurate based on the resolution of this OCT. Also, a toric-shaped mold was evaluated by comparing the relationship between each coordinate and intensity of the interference signal. As a result, it is confirmed that the experimental result and the simulated matched well.