Eliminating the influence of head and eye movements on the estimation of tear film surface parameters in lateral shearing interferometry.

Lateral sharing interferometry (LSI) can be used to assess tear film surface quality (TFSQ). Current estimates of TFSQ parameters are based on spectral measures of interferograms and are therefore dependent on the head and eye movements (HEM), especially those of longitudinal character. We propose an approach to address this in which the cross-ambiguity function is used to estimate the apparent change in the spatial scale robustly. Further, this estimate is used to scale the spectral representation of the interferogram, from which the TFSQ parameters are estimated. As a result, improved quality of spectral-based estimates of TFSQ has been achieved, where the effect of HEM is minimized. The adequacy of this approach has been confirmed with interferometry images of a moving glass sphere resembling a cornea surface. The results of the analysis for real eyes acquisitions are discussed in the context of the proposed spectral scaling, which provides new and important insight into the LSI-based assessment of TFSQ. The proposed method is more general and can be readily adapted to other types of interferometry or profilometry measurements of moving objects.