Abnormalities in the peripapillary retinal nerve fiber layer (RNFL) composition in earliest stages of diabetic retinopathy (DR) as assessed by polarization sensitive optical coherence tomography (PS OCT)

Abstract

Purpose : To study for the first time birefringence in the retinal nerve fiber layer of eyes with different DR stages using polarization sensitive OCT.

Methods : Thirty eyes of 18 diabetic (53±18 years) and 30 healthy controls (50±15 years) were included in this prospective cross-sectional study. Imaging was performed with a prototype PS OCT with a center wavelength of 860 nm, A-scan rate of 70 kHZ and an integrated retinal tracker. For each eye a raster scanning (250 B-scans, 1024 A-scans) centered on the optic nerve head (ONH) and an averaged circular scan (100 B-scans, 2048 A-scans) around the ONH was performed. After extraction of polarization parameters individual cornea compensated retardation tomograms are calculated and en face retardation maps are obtained from the retardation data at the IS/OS junction. The birefringence value at each A-scan position corresponds to the quotient of the retardation at the IS/OS junction and thickness of the retinal nerve fiber layer (RNFL) segmented from the averaged circular intensity images.

Results : Out of the 30 diabetic eyes 7 showed subclinical, 6 mild, 14 moderate and 3 severe NPDR with no previously reported or concurrent diabetic macular edema. All diabetic and healthy subjects had a RNFL thickness within the normal range as determined by Spectralis OCT and measured on PS OCT images (Fig.1b,e) with a mean of 104.89±9.12 µm for the diabetic and 104.95±12.18 for the healthy controls (p=0.99) on circular scans within a 1.5mm radius. The mean birefringence for the superior and inferior hemispheres (SH, IH) for RNFL>100µm is 0.128±0.018°/µm (0.132±0.019°/µm and 0.125±0.019°/µm respectively for SH and IH) for the diabetic (Fig.1d,f) and 0.154±0.016°/µm (0.156±0.015°/µm and 0.153±0.012°/µm respectively for SH and IH) for the healthy eyes (Fig.1a,c) (p<0.0001). Mean birefringence values (IH,SH,combined) correlate significantly with DR stages (p=0.018, 0.019, 0.026, respectively).

Conclusions : A significantly reduced birefringence of superior and inferior RNFL bundles as assessed by PS OCT is observed in diabetic compared to healthy eyes. Our results suggest changes in RNFL potentially related to abnormal axon composition already present in earliest DR stages.

This is a 2020 ARVO Annual Meeting abstract.