Abstract
Purpose :
In the Boramae Myopia Cohort Study, we observed the shift of lamina cribrosa compared to the Bruch’s membrane opening (BMO). Highly myopic eyes with glaucoma are known to have retinal nerve fiber layer (RNFL) defects wider and closer to the fovea, observed as vulnerable zones. In this study, we investigated the angular location of RNFL defects in myopic open-angle glaucoma compared by BMO and disc center.
Methods :
We retrospectively reviewed medical records and included 60 eyes from 60 open angle glaucoma patients with localized RNFL defects. Based on axial lengths (AXL), they were classified into 3 groups: emmetropia (AXL<24 mm), moderate myopia (24<AXL<26 mm), high myopia (AXL>26 mm). On red-free photographs, RNFL defect margins were marked: the angular location of the margin close to the fovea (angle α), and the furthermost margin (angle β). By OCT imaging, the BMO and disc center was determined. Two reference lines were drawn from the fovea: 1) foveo-BMO axis (a), 2) foveo-disc axis (b), and both angles were measured from the two reference lines: 1) α-BMO (c) or β-BMO (d), and 2) α-Disc (e) or β-Disc (f), respectively. The angular width of RNFL defect (angle γ): 1) γ-BMO (d-c), 2) γ-Disc (f-e) was calculated and the difference of α-BMO and α-Disc was compared along the degree of myopia.
Results :
Each group included twenty eyes and the AXL was 23.37±0.91 mm in the emmetropia group, 24.70±0.57 mm in the moderate myopia, and 27.48±1.10 mm in the high myopia group (P<0.005). There was no difference of mean deviation (emmetropia -4.52±3.64 dB, moderate myopia -4.79±2.18 dB, high myopia -3.54±1.99 dB, P=0.559) or width of RNFL defect between the groups (emmetropia 34.94±15.6°, moderate myopia 46.43±9.82°, high myopia 46.20±22.95°, P =0.243). The difference of α-BMO and α-Disc was largest in the high myopia group 12.57±4.71°, following by moderate myopia group 8.75±5.02°, and emmetropia group 5.52±3.95° (P=0.007). The difference of α-BMO and α-Disc had a significant correlation with AXL (r=0.584, P=0.001).
Conclusions :
Angular location of the RNFL defect was closer to the fovea when it was measured from the disc than when it was measured from the BMO center. It implies that the different pattern of RNFL defects in high myopia represents the shifting of lamina cribrosa including a vulnerable zone.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.