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A Dubra, JC Dainty, C Paterson; Measuring the Effect of the Tear Film on the Optical Quality of the Eye . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2045.
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Purpose:The reasons for inter-subject variability in wavefront sensing measurements in the eye are thought to be: eye movement, micro-fluctuations of accommodation and tear film evaporation. In this work we estimate the order of magnitude of the effects of the tear film on the optical quality of the eye by studying the topography of the precorneal tear film. Methods:The dynamics of the front surface of the tear film are studied using a shear interferometer. A series of interferograms containing the information of the topography of the surface of the tear is recorded from the subject. Then, computational post-processing of the interferograms is used to extract information about the topography of the tear surface: in particular its complexity and temporal variability. The tear film surface topography can be used to calculate the changes in the aberrations that the tear film introduces into the imaging of the eye and hence, an estimate of the effect of these aberrations in terms of placing a limit on the Strehl ratio that can be obtained. The important considerations in the design of the optical setup are discussed. Results:Results of measuring the evolution of the tear film topography are presented. The magnitudes of the micro-fluctuations in accommodation, diffraction and the effects of the tear film need to be known, so that a limit on the resolution that can be achieved with static aberration correction for retinal imaging and refractive surgery can be obtained. Conclusion:The implications of the dynamics of the topography of the tear are considered in the context of retinal imaging with adaptive optics systems and the resultant bandwidth necessary for such systems.
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