Analysis of deep optic nerve head structures with spectral domain and swept-source optical coherence tomography

Histological evidence indicates that the earliest structural changes to the optic nerve head (ONH) in glaucoma occur in the lamina cribrosa (LC) and its interface with the sclera. However, clinical imaging of these structures remains challenging. We compared the visibility of deep ONH structures with newer iterations of spectral-domain (SD) and swept-source (SS) optical coherence tomography (OCT).

Twelve patients with open-angle glaucoma were imaged with SD-OCT with 24 radial B-scans centred on Bruch's membrane opening (BMO) and SS-OCT with a horizontal and vertical raster scan pattern containing five lines each, centred on the ONH. Single best-matched horizontal and vertical scans from the two modalities were selected and exported. Three independent observers masked to modality determined if BMO, posterior choroid surface, anterior scleral canal opening and anterior and posterior LC insertions into the sclera were detectable in the matched B-scan images. We determined the interobserver agreement and concordance in detecting each structure with the two OCT imaging modalities.

There was a high interobserver agreement with both SS-OCT and SD-OCT (inter-item correlations: 0.81-0.93 and 0.77-0.82, respectively). There was a consistent tendency for higher overall detection rates with SS-OCT, however, the differences failed to reach statistical significance. With respect to individual structures, only the posterior LC insertion in the nasal quadrant was statistically different, with a detection rate of 13 and 6 (pooled out of a total of 36 across the three observers) with SS-OCT and SD-OCT, respectively (p=0.04).

Overall, both SS-OCT and SD-OCT showed statistically equivalent visualisation of ONH structures, however, SS-OCT tended to have higher visualisation rates.