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Spatially Resolved Mueller Matrix Analysis of Properties of the Optic Nerve Head

^A Department of Physics & School of Optometry, ^B Department of Physics, ¹ University of Waterloo, Waterloo, ON, Canada
² Laboratorio de Optica, Universidad de Murcia, Murcia, Spain

Commercial Relationships: M.C.W. Campbell, None P; J.J. Hunter, None; C.J. Cookson, None; J.M. Bueno, None P; M.L. Kisilak, None.

Support: NSERC(Canada), PRO(Canada)

Abstract

Purpose: Light coming from different structures in fundus images is differentially polarized. These differing polarization states have been used in clinical applications such as the diagnosis of glaucoma and the assessment of foveal fixation. We and others have demonstrated image improvement in normal and diseased retinal structures. However, much of the work has been performed with partial polarimetry which can limit the interpretation of the data. We have previously shown that imaging polarimetry results in improved resolution and contrast of the lamina cribrosa and blood vessels. The reason for this is unclear. Therefore, we wish to fully characterise the polarization properties of the optic nerve head (ONH) using Mueller matrix polarimetry.

Methods: A high resolution CSLO was modified to include a polarization generator in the input path and an analyser in front of the detector. Series of 16 images of the ONH (10 degree field) were recorded for independent combinations of polarization states (4 for the generator and 4 for the analyser) in two eyes of two normal young adult subjects. For each combination of generator and analyzer, an individual frame and the average of different individual frames (up to 16) were processed. The Mueller matrix and various polarization properties were calculated (using Matlab) for each pixel in the images. This gave a spatially resolved Mueller matrix.

Results: Care was taken to keep pixel values in the brightest images below saturation levels to avoid incorrect calculations of the Mueller matrix. Moreover, the dynamic range in the analysis of the polarization properties is limited by the number of bits in the images. Preliminary results indicate that values of the matrix are dependant on both the imaged area and the eye. In particular, diattenuation results indicate that the lamina cribrosa and the vessels show some differential absorption of polarized light, while the retinal nerve fibre layer does not. The degree of polarization varies across the ONH and within the lamina cribrosa.

Conclusions: Mueller matrix polarimetry has been used to extract polarization properties of the ONH. However, new methods need to be developed to overcome the dynamic range limitations. Polarization properties in the ONH differ for the blood vessels, the lamina cribrosa and the retinal nerve fibre layer. These differences may underlie our previous improvement in images of fundus structures using polarization methods.

Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • lamina cribrosa • optical properties

© 2005, The Association for Research in Vision and Ophthalmology, Inc., all rights reserved. For permission to reproduce any part of this abstract, contact the ARVO Office at arvo{at}arvo.org.