An Examination of the Frequency of Paravascular Defects and Epiretinal Membranes in Eyes With Early Glaucoma Using En-face Slab OCT Images

Abstract

Purpose: To examine the frequency of paravascular defects (PDs) and macular epiretinal membranes (ERMs) in eyes categorized as having mild glaucoma or glaucoma suspect using en-face slab analysis of optical coherence tomography (OCT) scans.

Materials and methods: Fifty-seven glaucomatous eyes, 44 low-risk suspect eyes, and 101 healthy control eyes were included in the study. The 101 glaucomatous and suspect eyes had a mean deviation better than -6 dB on the 24-2 visual field, and a spherical refractive error between±6 D or axial length <26.5 mm. Two OCT-graders masked to eye classification identified ERMs and PDs on en-face slab images of the macula and peripapillary retina using horizontal B-scans and derived vertical B-scans.

Results: Glaucomatous eyes had a significantly higher number of PDs and ERMs than healthy controls (PD, P<0.001; ERM, P=0.046) and low-risk glaucoma suspects (PD, P=0.004; ERM, P=0.043). PDs and/or ERMs were present in 16 of 57 (28.1%) glaucomatous eyes, 2 of 44 (4.5%) suspect eyes, and 3 of 101 (3.0%) control eyes. Further, PDs were present in 11 of the 57 (19.3%) glaucomatous eyes, 1 of the 44 (2.3%) suspect eyes and 0 of the 101 (0%) control eyes, ERMs were seen in 7 of the 57 (12.3%) glaucomatous eyes, 1 of the 44 (2.3%) suspects, and 3 of the 101 (3.0%) control eyes.

Conclusions: Eyes with early glaucoma have a higher frequency of PDs and ERMs than suspects or controls and exhibit PDs even in the absence of ERMs or high myopia.

Figure 1:

(A) B-scan (horizontal: vertical ratio of 1:6) through the optic disc of a left eye showing a slab (shaded green) with a fixed thickness of 52 μm (20 voxels) with the vitreous/ILM as the proximal border. (B) En-face image of the averaged voxel projection (AVP) of the 52 μm slab shown in (A) across all of the 256 B-scans. The dashed red line shows the location of the B-scan in panel A.

Figure 2:

(A) En-face image of the 52 μm-slab average voxel projection (AVP) of GL 2. Orange insets indicate the horizontal (upper) and derived vertical (left) B-scans at the location indicated by the solid orange line. The red line along the superior vessel indicates the presence and length of the paravascular defect (PD). (B) En-face image of the 52 μm-slab AVP of GL 12. Magenta insets indicate the horizontal (upper) and derived vertical (left) B-scans at the location indicated by the solid magenta line. The red arrow indicates the inferior border of the epiretinal membrane (ERM) on the en-face projection.

Figure 3:

En-face images of 4 eyes (GL 3, GL 6, GL 11, and GL 16) with PDs. The orange insets are the horizontal B-scans at the location indicated by the solid orange line in each image. The red lines indicate the location and length of the respective PDs, the white arrows demonstrate regions of arcuate RNFL damage, and the yellow arrow in en-face image of GL 16 indicates the presence of a small epiretinal membrane (ERM).