Technique for measuring forward light scatter in intraocular lenses

Purpose: To develop a technique for measuring the forward light scattering of intraocular lenses (IOLs). Setting: The Scatter Works, Tucson, Arizona, USA. Design: Evaluation of diagnostic technique. Methods: A scatterometer with laser sources of 488 nm and 633 nm was used to directly measure the forward-scattered light of IOLs. These sources illuminated balanced salt solution-immersed IOLs within a cylindrical wet cell. The wet cell was placed at the center of rotation of a goniometer arm. On the end of the arm was a detector that measured the amount of laser light scattered from the IOL as a function of incident-beam angle. The measurements provided a profile of the scatter distribution for regions outside the directly transmitted beam. Forward and back light scatter was measured in new and artificially aged IOLs. Results: Forward light scatter was increased in artificially aged IOLs compared with that in new unaged IOLs. The artificially aged IOLs developed sub-wavelength-diameter water nanoglistenings in the bulk material just below the surface. The measured scatter profiles were consistent with these subsurface droplets, suggesting Rayleigh-type scatter in the aged IOLs. The amount of light scatter from nanoglistenings does not appear to be sufficient to impair vision. Although the severely aged IOLs showed increased scatter, the level of increase was within 1 standard deviation of what is found in the normal population. Conclusion: A technique was developed enabling quantification of forward-scattered and back-scattered light from IOLs. Financial Disclosure: Drs. Das and Karakelle are employees of Alcon Laboratories, Inc. Dr. Stover has received consultant fees and Dr. Schwiegerling research funding from Alcon Laboratories, Inc.