Objective straylight assessment of the human eye with a novel device

Abstract

Forward scattered light from the anterior segment of the human eye can be measured by Shack-Hartmann (SH) wavefront aberrometers with limited visual angle. We propose a novel Point Spread Function (PSF) reconstruction algorithm based on SH measurements with a novel measurement devise to overcome these limitations. In our optical setup, we use a Digital Mirror Device as variable field stop, which is conventionally a pinhole suppressing scatter and reflections. Images with 21 different stop diameters were captured and from each image the average subaperture image intensity and the average intensity of the pupil were computed. The 21 intensities represent integral values of the PSF which is consequently reconstructed by derivation with respect to the visual angle. A generalized form of the Stiles-Holladay-approximation is fitted to the PSF resulting in a stray light parameter Log(IS). Additionaly the transmission loss of eye is computed. For the proof of principle, a study on 13 healthy young volunteers was carried out. Scatter filters were positioned in front of the volunteer’s eye during C-Quant and scatter measurements to generate straylight emulating scatter in the lens. The straylight parameter is compared to the C-Quant measurement parameter Log(ISC) and scatter density of the filters SDF with a partial correlation. Log(IS) shows significant correlation with the SDF and Log(ISC). The correlation is more prominent between Log(IS) combined with the transmission loss and the SDF and Log(ISC). Our novel measurement and reconstruction technique allow for objective stray light analysis of visual angles up to 4 degrees.