Multimodal characterization of contact lenses

Abstract

A table top instrument has been designed, constructed and tested to characterize all of the primary optical and physical properties of contact lenses. Measured optical properties include base power, cylinder power, cylindrical axis, prism, refractive index and wavefront aberrations. Measured physical properties include center thickness, lens diameter and lens sagittal depth. The instrument combines a Shack-Hartmann wavefront sensor (SHWS), a machine vision sensor, and a low coherence light interferometer (LCI) all coaxially aligned into a single tabletop unit. The unit includes a cuvette, mounted in a translatable sample chamber for holding the contact lens under test, and it can be configured to measure wet or dry contact lenses. During operation, the vision sensor measures the diameter of the lens, and locates the center of the lens. The lens is then aligned for other measurements. The vision sensor can also measure various alignment marks on the lens, as well as identify any alpha numerical features, which can be used to associate the lens orientation with the measured aberrations. The LCI measures the center thickness, sagittal depth and index of refraction of the contact lens. The base radius of curvature is then calculated using these measured parameters. The SHWS measures the lenses prescription power, including spherical, cylinder, prism, and higher order wavefront aberrations. NIST traceable calibration artifacts are used to calibrate the SHWS, machine vision and LCI modalities. Repeatability measurements on a contact lens in a saline solution are presented.