Polarimetric analysis of the human cornea measured by polarization-sensitive optical coherence tomography

Félix Fanjul-Vélez,Bernhard Baumann,Christoph K. Hitzenberger,Erich Götzinger,José Luis Arce-Diego,Michael Pircher

doi:10.1117/1.3486540

Abstract

Corneal polarimetry measurement has been the object of several papers. The results of techniques like polarization-sensitive optical coherence tomography (PS-OCT), scanning laser polarimetry, or polarization microscopy are contradictory. Some studies propose a biaxial-like birefringence pattern, while others postulate that birefringence grows at corneal periphery. Several theoretical approaches were proposed for the interpretation of these measurements, but they usually lack accuracy and an adequate consideration of the nonnormal incidence on the tissue. We analyze corneal polarization effects measured by PS-OCT. In vivo and in vitro PS-OCT images of the human cornea are acquired. PS-OCT measurements are apparently not in agreement with the biaxial-like birefringence pattern. We present a polarimetric model of the human cornea based on the extended Jones matrix formalism applied to multilayered systems. We also apply the Poincaré equivalence theorem to extract optic axis orientation and birefringence. The results show that for a fibrils orientation pattern composed by alternating circular and radial fibrils, the birefringence is biaxial-like at the corneal center, and there is an almost circularly symmetric high-birefringence area at corneal periphery. The model could be useful for diagnosis of corneal diseases or corneal compensation in retinal polarimetric imaging.

Highlights

The optical properties of the eye are especially suitable for the application of optical techniques
We chose two patterns for simulation that are in agreement with the microscopic observation of localapproximatelyperpendicular fibril orientation in successive layers and that are reasonable from a biomechanical point of view
Several papers reported corneal birefringence measured by means of different optical techniques, such as scanning laser polarimetrySLP, PS-OCT, or polarization microscopy

Summary

Introduction

The optical properties of the eye are especially suitable for the application of optical techniques. Laser polarimetry.[12] From the results obtained, the authors assume a biaxial or biaxial-like optical behavior This was first proposed by Van Blokland and Verhelst,[13] who used Mueller matrix ellipsometry. A layered model based on on-axis Jones retarders with varying optic axis orientation was previously proposed.[17] We presented a study with a similar model and different fibrils arrangements.[18] In both approaches, light must be perpendicular to the corneal surface and fibrils must be contained in a plane perpendicular to the incident radiation. The model proposed here is based on the extended Jones matrix formalism This enables the consideration of nonnormal incidence and arbitrary fibril orientation.[19] The Poincaré equivalence theorem is applied to extract optic axis orientation and retardation at each point.

Polarization Model

PS-OCT Measurements

Results and Discussion

Conclusions