Automated contact lens measurement using optical coherence tomography

Optical Coherence Tomography (OCT) is a non-destructive imaging modality that has proven to be a useful tool for making quantitative measurements in a variety of applications. One area where non-destructive quantitative measurement is important is contact lens metrology, specifically prism. Prism is defined as the difference between the largest and smallest thickness measured at a fixed distance from the contact lens edge. We developed and tested an algorithm that automatically analyzes OCT images to accurately measure contact lens thickness. Images were obtained with the Thorlabs OCT930SR spectral radar OCT system. An automated rotation stage was used to precisely rotate the OCT probe 360° in small increments to acquire OCT images along the entire outer edge of the contact lens. The algorithm was able to successfully analyze hundreds of OCT images. For comparison, measurements were taken by physically slicing contact lenses and manually measuring their thickness using a microscope. The error between the two measurements had a mean of -1.268 μm and a range of 9.041 μm. Thickness measurements were repeatable with a maximum range of 1.8 μm. The success of the algorithm has demonstrated the possibility of using OCT images for performing non-destructive contact lens metrology.