Fig 1.
Measurement of the lamina cribrosa (LC) curvature index using swept-source optical coherence tomography (SS-OCT) scans.
The optic disc scan performed by SS-OCT without (A) and with (B) guidelines. The line connecting the two Bruch’s membrane openings (BMOs) is selected as the reference plane. The anterior LC surface has been manually depicted as a yellow dotted line (B). The two vertical lines are drawn from the anterior laminar insertion (ALI) to the BMO reference plane. The distance between the two cross-points is measured as D. The two black solid lines are drawn parallel to the BMO reference plane at each ALI, and the black dotted line indicates the mean level of the ALI. This corresponds to the mean anterior laminar insertion depth (ALID). The area surrounded by the anterior LC surface, BMO reference plane, and the two vertical lines is measured as S. The mean LC depth (mLCD) is computed by dividing S by D. The LC curvature index is the difference between the mLCD and mean ALID. The schematic diagram is demonstrated in Fig 1C.
Table 1.
Subject demographics.
Fig 2.
Measurement of the lamina cribrosa (LC) curvature index in healthy eye.
Horizontal and vertical optic disc scans of a 53-year-old healthy woman. The image delineated with yellow guidelines is the same as that depicted on the left side. The horizontal and vertical mean anterior laminar insertion depth (ALID) was 238.8 μm and 311.9 μm, respectively. The horizontal and vertical mean LC depth was 278.5 μm and 325.7 μm, respectively. The horizontal LC curvature index was 39.8 μm and the vertical LC curvature index was 13.8 μm. The yellow-shaded area exhibits the degree of the posteriorly located anterior LC surface according to the mean level of the anterior laminar insertion (ALI).
Fig 3.
Measurement of lamina cribrosa (LC) curvature index in primary open-angle glaucoma eye.
The horizontal and vertical optic disc scans of a 70-year-old patient with primary open-angle glaucoma (POAG). The image delineated with yellow guidelines is the same as that depicted on the left side. The horizontal and vertical mean anterior laminar insertion depth (ALID) was 304.6 μm and 274.1 μm, respectively. The horizontal and vertical mean LC depth was 404.9 μm and 366.4 μm, respectively. The horizontal LC curvature index was 100.3 μm and the vertical LC curvature index was 92.3 μm. The yellow-shaded area exhibits the degree of the posteriorly located anterior LC surface according to the mean level of the anterior laminar insertion (ALI).
Table 2.
Comparison of anterior laminar insertion depth (ALID), mean lamina cribrosa depth (mLCD), and lamina cribrosa (LC) curvature index between the eyes with primary open-angle glaucoma and healthy control.
Table 3.
Factors associated with increased lamina cribrosa curvature index (univariate analysis).
Table 4.
Factors associated with increased lamina cribrosa curvature index (multivariate analysis).
Fig 4.
Differences of LC curvature index according to glaucoma stage.
Eyes with mild (n = 92, MD > -6 dB) and moderate-to-advanced glaucoma (n = 31, MD < –6 dB) showed an increased LC curvature index relative to the healthy eyes (n = 92, 50.2 ± 26.6 μm, all P < 0.05). However, there was no significant difference between mild and moderate-to-advanced glaucoma eyes (67.3 ± 27.3 vs. 69.2 ± 29.0 μm, P = 0.95).
Table 5.
Patient demographics according to the severity of glaucoma.
Fig 5.
The schematic diagram showing the structural difference of lamina cribrosa (LC) between the eyes with primary open-angle glaucoma (POAG) and healthy individuals.
Structural differences of the LC between POAG and healthy eyes are demonstrated. The orange dotted line corresponds to the reference plane of Bruch’s membrane openings. The thicker green and red dotted line indicates the anterior LC surface of healthy and POAG eyes, respectively. The thinner green and red dotted line presents the level of mean anterior laminar insertion depth (ALID). The green and red shaded area represents the relative posterior location of the anterior LC according to the mean ALID level of healthy and POAG eyes, respectively. Each shaded area reflects the degree of LC posterior bowing (LC curvature index). The ALID and LC posterior bowing (LC curvature index) are higher in POAG eyes than in healthy eyes. Note that vertical insertions are deeper than horizontal insertions. Additionally, the horizontal LC curvature index is larger than the vertical LC curvature index in both healthy and POAG eyes, due to the central hump-like structure in the vertical scan.