Based on wavefront sensor images an objective and quantitative method is presented
for characterising cataract. By separating direct and scattered light in the focal
plane of the microlenses, the new procedure is able to make two-dimensional maps of
the spatial variation of scattering properties in the crystalline lens, and also provides
a single figure descriptive for the whole eye. The developed evaluation algorithm
successfully quantifies cataract, especially that of nuclear type. To demonstrate
its operation, a custom-built measurement setup was constructed using a Shack-Hartmann
wavefront sensor with 40 x 32 microlenses to capture 12-bit images of the pupil plane,
and a superluminescent diode of 830 nm wavelength as a light source. Slit-lamp clinical
measurements served as reference for calibration and to estimate the accuracy of the
new method. The tests were carried out on 78 eyes with cataract in different progression
state ranging from healthy to above 5 on the LOCS III scale. The residual error of
the calibration (i.e. the standard deviation of difference between clinical reference
and our algorithmic characterisation) turned out to be +/- 0.29 category on the LOCS
III N scale, which approximates the +/- 0.33 precision of classic cataract measurements
carried out with the greatest care.
