Glaucomatous Damage of the Retinal Nerve Fiber Layer Can Be Better Visualized with En-Face OCT Imaging than with Typical OCT Thickness Maps

Abstract

 

Purpose

 

The appearance of the retinal nerve fiber layer (RNFL) seen using summed voxel projections (SVP) of en-face images of optical coherence tomography (OCT) scans was compared to RNFL thickness maps derived from the same scans.

 

Methods

 

Swept-source OCT, 9x12 mm cube scans (DRI-OCT, Topcon Inc) were obtained from 9 patients with glaucomatous damage of the macula confirmed with 10-2 visual fields. The RNFL of the OCT scans was segmented using an automated algorithm and manually corrected where required. SVP of en-face images were obtained using the ATL 3D-Editor,[1] custom software with depth- and layer-specific en-face capabilities. SVP images were obtained for the RNFL (SVP_RNFL), and for layers (SVP_SLAB) with a fixed thickness and distance from the vitreous-retinal interface (VRI). The SVP images were compared to RNFL thickness maps derived from the same scans, and to peripapillary images obtained using an adaptive optics scanning light ophthalmoscope (AO-SLO).[2]

 

Results

 

Abnormal RNFL regions in all eyes were as easy, or easier, to identify in SVP images (Fig. 1A,2A) as in RNFL thickness maps (Fig. 1B). Details of glaucomatous damage, often missed on RNFL thickness maps, were easier to see in the SVP images. In 4 of the 9 eyes, preserved bundles (e.g. green arrows in figures) were detected with SVP within regions of deep OCT thickness defects and were confirmed with AO-SLO (Fig. 2B). In RNFL thickness maps, these bundles were easily confused with blood vessels (red arrows, Fig. 1A,1B). Further, in 7 of the 9 eyes, local missing or abnormal RNF bundles seen using AO-SLO were more readily identified with SVP (orange arrows). This may be due in part to the spatial filtering inherent in segmentation algorithms. In addition, the details of the damage seen with SVP_SLAB (Fig. 2A), for a 52u thick slab below the VRI, were comparable to those seen in corrected SVP_RNFL images (Fig. 1A).

 

Conclusions

 

For detecting glaucomatous RNFL damage, en-face reflectance imaging, especially the SVP_SLAB projection, can add important information to that available on OCT thickness maps. Further, they are less affected by segmentation errors, as they only require marking the VRI, an easy task for automated algorithms.  

 

Fig. 1: See text.

 

 

Fig. 2: See text.