Real-time structured polarized light imaging (rtSPLI) for thick ocular tissue dynamics

Abstract

Purpose : Structured polarized light imaging (SPLI) has been proven useful to characterize collagen microstructure of static ocular tissues. However, slow speed precludes time sensitive applications, such as tissue dynamics. Herein, we present real-time SPLI (rtSPLI).

Methods : Similar to SPLI, rtSPLI integrates structured light illumination (SLI) and polarized light imaging (Fig. 1), allowing measurement of surface collagen orientation and retardance. The real-time imaging capability was achieved by polarization-state multiplexing, and synchronized pattern project and image acquisition. Fresh porcine scleral slabs (2mm thick, 10mm long) were stretched uniaxially while imaged transversely using rtSPLI. Tissue displacement and deformation were quantified using tracking techniques, and the angle between crossing fiber bundles measured manually.

Results : An imaging speed of 55 frames per second with centimeter field-of-view covering the whole sample was achieved using rtSPLI. Compared to imaging without SLI (Fig. 2B), the visibility of the collagen fibers was improved with SLI (Fig. 2A). This revealed that the wider regions of the sclera slab had sparser fiber bundles. Displacements (Fig. 2F) and deformations (Fig. 2E) varied substantially and were larger where the sclera was wider. Angles between bundles decreased by 19.8% and 34.1% for red and green regions in Fig. 2D, respectively, indicating also substantial local shear.

Conclusions : The patterns of deformations were contrary to what would be expected in simple materials, where the largest deformations occur where the sample is narrow. The additional microstructural information provided by rtSPLI suggests that this may be due to sparser in-plane collagen bundles in the wider sclera. These results demonstrate that rtSPLI can provide crucial information to understand ocular tissue dynamics.

This is a 2020 Imaging in the Eye Conference abstract.

 

The rtSPLI system for tissue mechanical testing.

 

Reflectance images of the sclera imaged with (A) and without (B) SLI before stretching. Yellow arrows indicate the directions of the uniaxial stretching. (C) collagen fiber orientation map. (D) Close-ups of the center region of the tissue before and after stretching. (E) First principal strain map. (D) Displacement map.