Offset of openings in optic nerve head canal at level of Bruch’s membrane, anterior sclera, and lamina cribrosa

Abstract

We compared the central retinal vascular trunk (CRVT) position, as a surrogate of lamina cribrosa (LC) offset, with the anterior scleral opening (ASCO) offset from the Bruch’s membrane opening (BMO). Based on the BMO-centered radial scans, the BMO and ASCO margins were demarcated, and each center was determined as the center of the best-fitted ellipse for each margin. The ASCO/BMO offset was defined as the offset between each center. Angular deviations and the extent of ASCO and CRVT offsets from the BMO center were compared directly. Incomplete demarcation of ASCO was found in 20%, which was associated with a larger BMO area and a larger ASCO offset from the BMO. The angular deviation of ASCO offset was associated with that of CRVT offset and that of the longest externally oblique border. The ASCO offset was smaller than the CRVT offset, and, unlike the CRVT offset, it was rarely deviated to the inferior side. The complete ASCO margin might not be demarcatable when determined on BMO-centered radial scans in the presence of an offset. Also, the ASCO, which reflects only the superficial scleral layer, might not reflect the LC position, because the LC might be shifted further from the ASCO.

Hemisphere opposite to central retinal vascular trunk deviation is earlier affected by glaucomatous damage in primary angle‐closure glaucoma

“…In this study, EOB presence differed according to the offset direction (Table 4): the EOB rarely existed in cases of inferior LC/BMO offset (Figure 3). This finding was in line with our previous study which demonstrated the difference between the LC/BMO and ASCO/BMO offsets (Lee et al, 2021a). This implies that the ASCO/BMO offset, which is visualized as the presence of EOB, would be an imperfect surrogate for LC/BMO offset, especially when its direction is towards the inferior side.…”

“…Mismatch was associated with more negative CRVT angular deviation–inferotemporal CRVT (Table 3). We speculated that the LC/BMO offset would be smaller in that direction, as we have previously reported (Lee et al, 2021), which subsequently would lead to a higher probability of mismatch in PACG eyes.…”

“…In cases of invisible CRVT due to being located outside the BMO, the offset index was defined as 1.0 and the angular deviations were not determined. Using a customized MATLAB code that fits the best ellipse for a given set of dots, the BMO centre was calculated, and the CRVT position was determined for further analysis, as stated in our previous study (Lee et al, 2021a).…”

“…The EOB was determined by the obliquity of the ONH borders on radial B‐scan images (internally oblique vs. non‐oblique vs. externally oblique) (Reis et al, 2012), and the meridian of the longest EOB (in cases larger than 100 μm) was also marked on the infrared image and read by our customized software (Lee et al, 2021a).…”

Association between eyeball asymmetry and offset of openings in optic nerve head canal assessed by posterior polar eyeball topography

“…Visual signals are transferred to the brain via the retinal ganglion cells (RGCs), whose axons exit the eyeball through a gateway: the optic nerve head (ONH). The ONH being a three-dimensional (3D) structure with multiple layers, its morphology is determined by the offset of openings in different layers 1 – 7 . Offset is incurred as a result of expansion undergone by the eyeball during growth.…”