Spatially resolved polarization properties of in vitro mammalian corneas have been studied by using a Mueller-matrix imaging polarimeter in transmission mode. Sixteen images corresponding to independent combinations of polarization states in the illumination and analyzing pathways are recorded. Spatially resolved Mueller matrices of the samples are calculated from them. Results show that the birefringence of the cornea is almost linear. Although the magnitude of retardation depends on the sample, it is approximately constant at the center and increases towards the periphery. Dichroism and polarizing power are negligible. Maps of the degree of polarization indicate that the cornea basically does not depolarize the totally polarized incident light.
Tear film stability plays an important role in the quality of vision. We present an interferometric method for assessing the stability of precorneal tear film in real time. A lateral shearing technique is applied as a noninvasive and sensitive method for investigating tear film stability and the smoothness of the tear film surface by quantitative evaluation of the interference fringe pattern. The evaporation of tears and the appearance of tear film break-up between blinks cause changes in the fringe geometry. For quantitative assessment of the fringe smoothness and consequently of the tear film structure, the fast Fourier transform (FFT) is applied. Four parameters are used to quantitatively estimate dynamic changes in the tear film stability of the cornea 20 s after the eye blink. Examples of examined interferograms recorded in patients with healthy eyes, patients suffering from dry-eye syndrome, and patients wearing contact lenses are given. Significant differences between the stability of the tear film in the healthy eye and that in the dry eye and the eye with a contact lens are observed. The favorable influence of artificial tears applied in patients with dry-eye syndrome or contact lenses is also discussed.
A general method for measuring the birefringence of nondichroic, linear retarder media has been presented. The method is based on phase-stepping imaging polarimetry and permits the azimuth angle, phase retardation, and transmission coefficient of a sample to be calculated. The method uses a simple setup, a sample at rest, and permits fast acquisition of data. With the mathematical description applied, various algorithms for different optical configurations can be used and any number of intensity patterns can be generated. Experimental results for photoelastic samples and the results of measurements of the birefringence of optical components and biological samples are also presented.
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