Optical power mapping using paraxial laser scanning

Abstract

A new instrument has been developed and built to measure the spatially resolved optical power of intra-ocular and contact lenses. Currently available instruments are based on either Hartmann Shack or Moiré Fringe techniques, which both have inherent limitations in terms of measurement range, sensitivity and achievable lateral resolution. Our new method uses a narrow laser beam which is scanned paraxially across the surface of the lens. The angle of the deflected beam is determined by capturing the lateral laser spot position at two different axial locations by means of a beam-splitter and two position sensitive, optical detectors. From the matrix of deflection angles, the spherical and cylindrical power components as well as higher order aberrations can be extracted and displayed as spatially resolved power maps. While measurement speed is compromised due to the scanning operation, the achievable lateral resolution can be as high as 20μm and the power accuracy in the order of milli-diopters. Soft contact lenses and foldable IOLs can be placed in wet cells to maintain hydration and form stability. Sample measurements of contact and intra ocular lenses are presented.