Imaging retinal nerve fiber bundles using optical coherence tomography with adaptive optics

Early detection of axonal tissue loss in retinal nerve fiber layer (RNFL) is critical for effective treatment and management of diseases such as glaucoma. This study aims to evaluate the capability of ultrahigh-resolution optical coherence tomography with adaptive optics (UHR-AO-OCT) for imaging the RNFL axonal bundles (RNFBs) with 3 × 3 × 3 μm3 resolution in the eye. We used a research-grade UHR-AO-OCT system to acquire 3° × 3° volumes in four normal subjects and one subject with an arcuate retinal nerve fiber layer defect (n = 5; 29–62 years). Cross section (B-scans) and en face (C-scan) slices extracted from the volumes were used to assess visibility and size distribution of individual RNFBs. In one subject, we reimaged the same RNFBs twice over a 7 month interval and compared bundle width and thickness between the two imaging sessions. Lastly we compared images of an arcuate RNFL defect acquired with UHR-AO-OCT and commercial OCT (Heidelberg Spectralis). Individual RNFBs were distinguishable in all subjects at 3° retinal eccentricity in both cross-sectional and en face views (width: 30–50 μm, thickness: 10–15 μm). At 6° retinal eccentricity, RNFBs were distinguishable in three of the five subjects in both views (width: 30–45 μm, thickness: 20–40 μm). Width and thickness RNFB measurements taken 7 months apart were strongly correlated (p < 0.0005). Mean difference and standard deviation of the differences between the two measurement sessions were −0.1 ± 4.0 μm (width) and 0.3 ± 1.5 μm (thickness). UHR-AO-OCT outperformed commercial OCT in terms of clarity of the microscopic retina. To our knowledge, these are the first measurements of RNFB cross section reported in the living human eye.

► Effective treatment of glaucoma requires early detection of retinal nerve fiber loss. ► Our instrument measured the cross sectional profile of single RNFL bundles. ► These are the first such measurements taken in a living human eye. ► Measurements were collected on 4 normal subjects and one with a RNFL defect. ► The instrument successfully remeasured the same bundles 7 months later.