Scatter measurement in the human eye based on a Shack‐Hartmann wavefront aberrometer with extended field of view

Abstract

PurposeForward scattered light from the anterior segment of the human eye can be measured by Shack‐Hartmann (SH) wavefront aberrometers with limited visual angle (approx.1°). We developed a novel system that allows a measurement of forward scattered light based on the reconstruction of the Point Spread Function (PSF) of an extended field of view up to 11.1°.MethodsFor proof of principle of our new optic design, we studied 12 young healthy subjects (20–40 year). 21 SH‐images with different stop diameters in a range of 0.7–11.1° were captured from the right eye. Therefore, we used a mechanical variable aperture as variable field stop which is conventionally used as a pinhole aperture for suppressing scatter and reflections. For each image, the average of the intensities of the subapertures images and the average intensity of the pupil area are calculated. The resulting 21 intensities represent integral values of the PSF which is consequently reconstructed by derivation with respect to the visual angle. Based on the reconstructed PSF, a stray light parameter Log(IS) is calculated. Scatter Filters (Tiffen BPM1, BPM2) were positioned in front of the subjects eyes, to evaluate our new optic design for increased stray light conditions. For statistical analysis, the stray light parameters Log(IS) were compared to Log(ISC) parameters measured by C‐Quant for normal and increased stray light conditions and the scatter density of the filters SDF using Spearman‐Rho‐correlation. Bonferroni corrected Wilcoxon tests were performed to compare Log(IS) for normal and increased stray light conditions.ResultsLog(IS) at 11.1° is significantly correlated with SDF (r = 0.809; p < 0.01) and Log(ISC) (r = 0.683; p < 0.01). The comparison of the filter groups showing significant differences of Log(IS).ConclusionsOur novel measurement technique allows for objective stray light analysis of visual angles up to 11.1 degrees and could be a useful extension to SH‐wavefront‐aberrometers.