Changes in aberrations and retinal image quality due to tear film dynamics.

A reliable and objective method to measure aberration changes due to the tear film is essential in improving clinical assessment of the tear film and in vivo retinal imaging. The tear film of 11 subjects are studied by acquiring continuous wavefront measurements in real-time with a customized Shack-Hartmann wavefront sensor. The device has a high resolution lenslet array (190 mum) and a topographer unit with an infrared pupil illuminator (940 nm). A Fourier transform reconstructor algorithm [1] was used to estimate the eyes' wavefront aberrations from slope measurements. Increasing irregularities in the tear film produced observable wavefront variations. The temporal behavior of tear induced aberrations and retinal image quality was evaluated by the root mean squared (RMS) error of the residual wavefront and the volume modulation transfer function (MTF). Similar trends were observed from both metrics. Our analysis demonstrates the applicability of the SH wavefront sensor to assessing the dynamics of the human tear film.