Quantification of forward scattering based on the analysis of double-pass images in the frequency domain.

Joan A Martínez‐Roda,Antoni Salvador,Jaume Pujol,Carlos E García‐Guerra,Fernando Diaz‐Doutón,Meritxell Vilaseca

doi:10.1111/aos.14122

Joan A Martínez‐Roda, Antoni Salvador + Show 4 more

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https://doi.org/10.1111/aos.14122

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Abstract

PurposeTo assess forward intraocular scattering by means of a new parameter (Frequency Scatter Index, FSI3) based on the analysing double‐pass retinal images in the frequency domain, which minimizes the impact of aberrations on the results.MethodsA prospective observational study was carried out in the Department of Ophthalmology, Hospital Universitari Mútua de Terrassa (Spain) on a group of 19 patients diagnosed with nuclear cataracts of various LOCSIII grades and a control group (CG) with nine healthy eyes. We recorded double‐pass retinal images with a custom set‐up based on a high‐sensitivity digital camera. The FSI3 was then computed using spatial frequencies below three cycles per degree. A preliminary validation of the FSI3 was performed on an artificial eye and two eyes of volunteers with and without commercial diffusers, and under defocus.ResultsThe FSI3 was hardly affected by defocus values up to 2.50 D. The mean (and standard deviation) FSI3 values were as follows: for the CG, 1.19 (0.21); and for LOCSIII grades nuclear opacity 1, 2 and 3, 1.30 (0.12), 1.62 (0.21) and 1.85 (0.21), respectively. Eyes with cataracts showed FSI3 values significantly different than healthy eyes (p = 0.001). A good correlation (ρ = 0.861, p < 0.001) was found between the FSI3 and objective scatter index provided by a commercial instrument.ConclusionSince aberrations have little impact on the FSI3, the light scatter assessment becomes less dependent on the patient's refractive error compensation and the presence of higher‐order aberrations. The FSI3 can further the clinical and scientific understanding of forward intraocular scattering.

Highlights

Forward intraocular scattering is a phenomenon of human vision that can currently be quantified by psychophysical and objective methods (Franssen & Coppens 2006, Westheimer & Liang 1994)
A good correlation (ρ=0.861, p
We propose a new parameter to quantify intraocular scattering based on the analysis of the information contained in the DP image at eccentricities between 0.59° and 2.35°, in order to minimize the impact of aberrations on the results

Summary

Introduction

Forward intraocular scattering is a phenomenon of human vision that can currently be quantified by psychophysical and objective methods (Franssen & Coppens 2006, Westheimer & Liang 1994). Ginis et al recently presented an experimental system to reconstruct a wide-angle version of the point spread function (PSF) of the eye (Ginis et al 2012), where the reconstructed curve contains data up to 8° and may be used to quantify intraocular scattering. We propose a new parameter to quantify intraocular scattering based on the analysis of the information contained in the DP image at eccentricities between 0.59° and 2.35°, in order to minimize the impact of aberrations on the results. The region selected is hardly affected by aberrations while containing the effects of intraocular scattering (van den Berg, Franssen & Coppens 2009). The parameter is computed in the frequency domain applied to the lowest part of the spectrum of the DP image, the range comprised between 0 and 3 cycles per degree (cpd) of the ocular modulation transfer function (MTF)

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