Intensity Analysis of Hartmann-Shack Images in Cataractous, Keratoconic, and Normal Eyes to Investigate Light Scattering

Purpose

A clinical investigation of novel methods for evaluating light scattering using a Hartmann-Shack aberrometer.

Methods

Aberrometry was performed on normal eyes (n = 7; patient age, 26.7 ± 2.5 years, mean ± SD), eyes with keratoconus (n = 22; patient age, 26.1 ± 8.1 years), and eyes with cataract (n = 17; patient age, 56.5 ± 16.9 years) using a Hartmann-Shack wavefront aberrometer. We introduced two methods: (1) a contrast method, in which we calculated the inverse of contrast of the local images around 12 spots in a Hartmann-Shack image, and (2) a difference of point spread function (PSF) method, in which we analyzed the difference between the width of the PSF computed with aberration information and the width of the measured PSF, which contains both aberration and light scattering information.

Results

The inverse contrast in cataractous eyes (5.04 ± 3.06 inverse contrast units) was significantly larger than that in normal eyes (1.57 ± 0.56) or keratoconic eyes (1.83 ± 0.79). The difference of PSF in cataractous eyes (81.8 ± 65.2?μm) was also significantly larger than that in normal eyes (9.3 ± 4.3?μm) or keratoconic eyes (30.0 ± 20.1?μm). The inverse contrast and the difference in the PSF were highly correlated (r = 0.89, P < 0.0001).

Conclusions

The two methods introduced here successfully distinguished cataractous eyes from normal and keratoconic eyes. After the results were analyzed by a discriminant analysis, the separation of the three categories proved to be excellent.?Jpn J Ophthalmol 2006;50:323–333 © Japanese Ophthalmological Society 2006