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

To 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.

A 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.

The 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.

Since 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.