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J. M. Bueno, C. J. Cookson, J. J. Hunter, M. L. Kisilak, M. C. W. Campbell; Imaging the Fundus of the Eye Through Polarization: Dependence With Age. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3209. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Apart from aberrations and scattering, the quality of retinal images may be affected by ocular polarization properties. These change with retinal position, pathologies and age. Our purpose is firstly to explore the amount of polarized light in confocal scanning laser ophthalmoscope images as a function of age. Secondly we have analyzed the improvement in images given by using a Stokes-Mueller formalism.
A polarimetric confocal scanning laser ophthalmoscope (CSLO) has been used to record 15-degree field of view optic nerve head (ONH) images of subjects with different ages. The polarimeter adds two combinations of linear polarizer plus rotating quarter-wave to the CSLO, one in the illumination pathway (generator) and another in the recording pathway (analyzer). With the former fixed, four video segments were recorded for appropriate orientations of the latter. The eight frames with the highest correlation were extracted from every video segment and after subtraction of a background frame, they were aligned and averaged. The four resulting averaged frames were used to compute the imaged Stokes vector (SV) for each image pixel and the map of degree of polarization (DOP) of the light emerging from the eye. Measurements were carried out in one eye of each of 10 subjects ranging in age from 19 to 64 years. Different global image metrics were used to compute the quality of the four original images, the image corresponding to the intensity of the computed SV and the DOP image.
The quality of the initial ONH images depended on both the subject and the polarization state of the analyzer. No correlation between the polarization state maximizing the image quality and age was found. For every metric both the image corresponding to the SV intensity and the DOP image were better than any of the original images. The improvement in the image quality of the SV intensity image and the DOP image significantly increased with age.
The visualisation of the ONH and surrounding retinal structures can be improved by computing the corresponding spatially resolved SV and/or the DOP image. Both often show small retinal features unseen in the original images. When comparing the constructed images with the original ones, the improvement was found to increase significantly with age. This polarimetic analysis procedure may be broadly useful in clinical diagnosis.
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