Polarization-sensitive swept-source OCT imaging of retinal pigment epithelium and subretinal fibrous tissues

Abstract

Purpose : Polarization-sensitive optical coherence tomography (PS-OCT) can measure polarization scrambling of melanin and birefringence of fibrous tissues. Improved image quality of PS-OCT may provide more insights for understanding retinal diseases. The purpose of this study is to demonstrate our prototype system of PS-OCT with the latest technology for retinal imaging.

Methods : The PS-OCT prototype was constructed using a 100 kHz swept laser at 1 μm wavelength for Jones matrix measurement. Polarization scrambling of melanin and birefringence of fibrous tissues were visualized by entropy of the Jones matrix with a spatial kernel size of 21×64 μm² (axial × lateral) and local phase retardation with an axial separation of 8 μm in tissue, respectively. Both images were calculated using an efficient algorithm of estimation called Cloude-Pottier decomposition. As an exploratory study, 6×6 mm² volumetric B-scan images were examined to find qualitative characteristics in normal subjects (14 eyes of 14 subjects), retinitis pigmentosa (RP, 16 eyes of 9 subjects) and age-related macular degeneration (AMD, 47 eyes of 33 subjects).

Results : All normal eyes showed high entropy in retinal pigment epithelium (RPE) and choroid, indicating polarization scrambling by melanin (Fig. 1b). En face entropy image of normal eyes at RPE showed relatively higher entropy in fovea than peripheral area (Fig. 1d). In the RP subjects, 11 eyes showed abrupt decrease of the entropy at parafoveal RPE (Fig. 1f,h). In the AMD subjects, 35 eyes showed focally or diffusely decreased entropy at RPE (white arrow and blue region in Fig. 2b), 14 eyes showed subretinal deposits with high entropy (red arrows in Fig. 2b), which might indicate migrated RPE, and 4 eyes showed high local retardation that indicates highly organized fibrous tissues (Fig. 2e).

Conclusions : PS-OCT provided additional contrasts that were not available in standard OCT for normal, RP and AMD subjects, and might be useful for identifying the RPE and fibrous tissues in the retina.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.

 

Fig. 1: Images of a normal eye (a-d) and an eye with RP (e-h). B-scan (a,e), en face (c,g) intensity, and B-scan (b,f), en face (d,h) entropy images are shown.

 

Fig. 2: Intensity (a) and entropy (b) images of AMD with decreased entropy at RPE and RPE migration, and intensity (c), entropy (d) and local retardation (e) images of AMD with fibrosis.