System based on the contrast of Purkinje images to measure corneal and lens scattering

Abstract

Current methods to measure intraocular scattering provide information on the total scattered light, which consists of the combined contributions originating from different ocular structures. In this work, we propose a technique for the objective and independent assessment of scattering caused by the cornea and the lens based on the analysis of the contrast of the third and fourth Purkinje images. The technique is preliminarily validated first by using artificial eyes with different levels of corneal and lens scattering; second, it is validated in eyes wearing customized contact lenses to simulate corneal scattering and eyes with nuclear cataracts. Finally, it is tested on a larger population of eyes with cataracts and corneal disorders to prove its clinical usefulness.

A Purkinje image-based system for an assessment of the density and transmittance spectra of the human crystalline lens in vivo

“…In the future, we expect that our Purkinje image-based system will be improved so as to enable evaluation of not only spectral density and transmittance but also spectral scattering characteristics in the ocular media by applying Santos's approach 36 . Although the evaluated scattering consists of the combined contributions originating from the cornea, anterior chamber and lens, there is a possibility that the spectral scattering characteristics of the anterior segment can be measured by contrast of the IVth Purkinje image, which is detected easily even in the visible light wavelength region.…”

“…As another approach for assessment of the optical property of the lens using Purkinje images, Santos et al proposed a technique for objective and independent assessment of light scattering caused by the cornea and the lens 36 . This technique is based on analysis of the contrast of the IIIrd and IVth Purkinje images generated by incident near-infrared (> 760 nm) light.…”

Complexity of crystalline lens wobbling investigated by means of combined mechanical and optical simulations

“…Due to its high magnification, while changing the lens position (its tilt and/or lateral displacement), PIII rapidly goes beyond the area of interest (usually associated with the pupil) and is markedly truncated by the iris. All these features make the PIII images barely visible in normal, healthy eyes, if at all, and it is particularly difficult to register and to process for further investigations [ 6 ]. For all these reasons, the wobbling of the crystalline lens is commonly observed only in the form of PIV movement, and not the mutual movements of PIII and PIV.…”

“…Therefore, those reflections find widespread use in unambiguous determination of IOL position after cataract surgery, namely: estimation of its axial and lateral positions and tilt [ 7 – 11 ]. Some authors use them to measure intraocular scattering as well, to provide information on the total scattered light from different ocular structures [ 6 , 12 ].…”