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Joy Willemse, Maximilian Graefe, Aleid van de Kreeke, Frank D Verbraak, Johannes de Boer; Polarization-sensitive optical coherence tomography as a tool to visualize the birefringence and direction of retinal nerves.. Invest. Ophthalmol. Vis. Sci. 2020;61(7):3942.
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© ARVO (1962-2015); The Authors (2016-present)
It is hypothesized that changes in birefringence of the retinal nerve fiber layer (RNFL) may precede the thinning of the RNFL in the early symptoms of glaucoma. In this experimental proof-of-concept study polarization-sensitive optical coherence tomography (PS-OCT) was used in healthy volunteers to evaluate the birefringence and direction of the fibers of the RNFL.
Nine eyes of healthy volunteers were scanned with our in-house built PS-OCT system. PS-OCT imaging included intensity, local phase retardation, degree of polarization uniformity (DOPU), and relative optic axis images. The relative orientation of the RNFL was mapped by segmenting the RNFL and averaging its measured local optic axis in depth.
Figure 1a shows an en face intensity map of the retina of a healthy volunteer The RNFL was segmented automatically, and an en face RNFL thickness map was made (figure 1b). Local birefringence of the RNFL is shown in figure 1c. The relative orientation of the RNFL was found by averaging the measured local optic axis of the RNFL in depth. Figure 1d shows the en face intensity map with an overlay of red lines which delineate the orientation of the RNFL. It can be seen that the nerve fibers are leaving the optic nerve head (ONH) in all radial directions. Minimum RNFL thickness to extract the relative optic axis reliably was about 60 μm.
PS-OCT has been used to successfully extract the birefringence and orientation of the retinal nerves. The relative direction of the nerve fibers around the ONH can be visualized, demonstrating a radial pattern. This direction and its changes could possibly be correlated with areas of visual field loss, and might be used to identify areas of (expected) RNFL loss in glaucoma. In future research, we will scan glaucoma patients with the PS-OCT system to test this hypothesis.
This is a 2020 ARVO Annual Meeting abstract.
Fig 1. (a) Intensity en face image, (b) RNFL thickness image, (c) local birefringence image and (d) Intensity en face image overlaid with RNFL orientation as red lines. Color range in (b) indicates 0 – 300 μm. Color range in (c) indicates 0.5-0.15 °/μm. Images sizes: 5.7 x 6.2 mm (depth x height).
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