Abstract
Abstract: :
Purpose: Wavefront correction in the eye can be achieved by corneal surgery, contact lenses, spectacles and/or crystalline lens replacement. Despite the continuous improvement in all these techniques in recent years, there are several limiting factors in what can be achieved with static wavefront correction: eye movement, micro–fluctuations of accommodation and tear film evaporation. In this work we measured the effect of the dynamics of tear film topography on the optical quality of the eye. Methods: We designed and built a shear interferometer to measure the topography of the tear film over a 3mm pupil. Sequences of interferograms were taken from 20 subjects at 5Hz over 20 seconds intervals. The instrument also allowed to study the tear film topography on the front surface of contact lenses, and two type of contact lenses (soft and hard) were tested. Results: We recorded a number of different tear topography features, being some of the most interesting the after–blink undulation, bubbles, ridges , and the roughness of pre–contact lens tear surface. In general, it was found that the surface of the normal tear does not affect the optical quality of the eye significantly, in terms of wavefront RMS, in comparison with other sources of variability of wavefront sensing measurements, like micro–fluctiations of accommodation. Conclusions: The tear film dynamics seems not to be the main source of variability of wavefront sensing measurements. The instrument developed for this study is a promising tool for tear topography study (e.g. dry eye diagnosis), and in particular for testing of contact lenses and tear substitutes.
Keywords: refractive surgery • cornea: tears/tear film/dry eye • refraction