Objective quantification and spatial mapping of cataract with a Shack-Hartmann wavefront sensor.

ABSTRACT

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 [Formula see text] 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 [Formula see text] category on the LOCS III N scale, which approximates the [Formula see text] precision of classic cataract measurements carried out with the greatest care.