Factors Influencing Central Lamina Cribrosa Depth: A Multicenter Study

Abstract

Purpose: To quantify the influence of ocular and demographic factors on central laminar depth (LD) in healthy participants.

Methods: A total of 362 normal subjects underwent optical coherence tomography (OCT) enhanced depth imaging of the optic nerve head (ONH) with a 24 radial B-scan pattern aligned to the fovea-to-Bruch's membrane opening (BMO) axis. BMO, anterior lamina, anterior scleral canal opening (ASCO), Bruch's membrane (BM), and the peripapillary scleral surface were manually segmented. The extent of laminar segmentation was quantified within 72 ASCO subsectors. Central LD was quantified relative to four reference planes: BMO, ASCO, BM, and scleral. The effects of age, sex, ethnicity, IOP, BMO area, ASCO area, and axial length on LD were assessed.

Results: Laminar visibility was most consistent within the central ASCO (median 89%, range, 69%-95%). LDBMO and LDBM were significantly shallower in eyes with greater age, BMO area, and axial length and in females. LDASCO was shallower in eyes with greater ASCO area and axial length and in European and Hispanic descent compared to African descent eyes. LDSclera behaved similarly, but was not associated with axial length. BMO and ASCO area were not different between African descent and European descent eyes.

Conclusions: Central LD was deeper in African descent eyes and influenced least by age, axial length, and sex, but more by ASCO area, when measured relative to the ASCO and sclera. However, the magnitude of these effects for all four reference planes was small, and their clinical importance in the detection of glaucoma and its progression remains to be determined.

Figure 1

Manual segmentation of each radial B-scan. (A) A representative 15° radial B-scan is shown, with its location depicted in the inlayed infrared image (bottom left). (B) Manually segmented B-scan shown in (A). Light blue lines/points indicate the ILM, white lines/points the posterior surface of the RNFL, orange lines/points are the posterior surface of the BM/RPE complex (BM), gold lines/points are anterior surface of sclera. Green lines/points are neural canal wall, purple lines/points are anterior lamina cribrosa surface. Red points are the BMO, and blue points are the ASCO. (C) Point cloud of segmented points from the complete set of 24 radial B-scans obtained for this ONH.

Figure 2

The extent of laminar segmentation and the central region of the lamina are both defined relative to the anterior sclera canal opening (ASCO). (A) Segmented anterior laminar surface points (purple) are projected onto an ASCO reference plane that is based upon a continuous B-spline (blue line) fit to the segmented ASCO points (blue). (B) Segmented points are resampled (now in purple with black border) to be equidistant along the segmented portion of the anterior lamina within each B-scan. (C) The ASCO B-spline is scaled into a unit circle and divided into twelve 30° sectors and 72 subsectors of equal area, which are positioned relative to the fovea-to-BMO axis (not shown). Each segmented point is scaled into the same unit circle. Subsectors containing ≥1 segmented point are defined as “visible.” (D) The unit circle and contained segmented points are transformed back into the original ASCO space. The parameter central laminar depth consistently samples the central 24 ASCO subsectors (green outline in D) regardless of the reference plane used for the depth measurement (see Fig. 3). (E) Laminar visibility was quantified by summing the number of visible subsectors within the central 24 subsectors (green outline in D) and within superior (S, blue shade), inferior (I, orange shade), nasal (N, pink shade), and temporal (T, green shade) quadrants.

Figure 3

The parameter central laminar depth (LD) measures laminar depth within the central anterior scleral canal opening (ASCO) relative to four reference planes (left) and is schematically depicted on the right. (A1, A2) Central LD_BMO is the mean depth of the segmented anterior surface points within the central 24 ASCO subsectors, measured relative to the BMO (two red points) reference plane, which is shown in cross section as a red line. (B1, B2) Central LD_BM is the mean depth of the same central ASCO segmented points measured relative to a BM reference plane, defined by the segmented BM points (orange dots) located 1700 μm away from the BMO centroid and seen in cross section as an orange line. (C1, C2) Central LD_ASCO is the mean depth of the same central ASCO segmented points (blue dots) measured relative to an ASCO reference plane seen in cross section as a blue line. (D1, D2) Central LD_Sclera is the mean depth of the same central ASCO segmented points measured relative to a scleral reference plane, defined by the segmented anterior scleral points (gold dots) located 1700 μm away from the ASCO centroid and seen in cross section as a gold line.

Figure 4

Frequency of anterior lamina cribrosa surface delineation by anterior scleral canal opening (ASCO) subsector in 362 healthy eyes. Yellow lines demarcate 30°, fovea-to-BMO ASCO sectors that are subdivided into 72 ASCO subsectors of equal area. Data are plotted in right eye orientation relative to a unit circle representation of the ASCO of each study eye (blue outline) (see Fig. 2). For a given eye, at least one segmented point per subsector was required for that subsector to achieve “visualization.” Frequency data (gray scale) represent the percent of 362 eyes in which an individual subsection was visualized. The anterior laminar surface was most frequently segmented within the central (green circle) and temporal subsectors of the ASCO.

Figure 5

Scatter plot and univariate linear regression for central laminar depth and age. The relationship between central laminar depth and age is shown with points shaded gray and their circumference colored according to their reference plane. Solid colored lines: fitted linear regression lines; dotted colored curves: the 95% CI of the regression lines; gray circles with colored border: individual values. The slope of the regression line achieved significance (P ≤ 0.05) for LD_BMO and LD_BM. The regression equations are LD_BMO = 440 − 0.76 × Age (P = 0.006; R² = 0.02) and LD_BM = 536 − 0.74 × Age (P = 0.049; R² = 0.01).

Figure 6

Scatter plot and univariate linear regression for central laminar depth and BMO or ASCO area. The relationship between laminar depth and BMO or ASCO area is shown with points shaded gray and their circumference colored according to their reference plane. Solid colored lines: fitted linear regression lines; dotted colored curves: the 95% CI of the regression lines; gray circles with colored border: individual values. The slope of the regression line achieved significance (P ≤ 0.05) for LD_BM, LD_ASCO, and LD_Sclera. The regression equations are LD_BM = 602 − 56.45 × BMO Area (P = 0.001, R² = 0.03), LD_ASCO = 395 − 38.42 × ASCO Area (P < 0.001, R² = 0.04), and LD_Sclera = 416 − 37.58 × ASCO Area (P = 0.002, R² = 0.03).

Figure 7

Scatter plot and univariate linear regression of central laminar depth with axial length. The relationship between central laminar depth and axial length is shown, with points shaded gray and their circumference colored according to their reference plane. Solid colored lines: fitted linear regression lines; dotted colored curves: the 95% CI of the regression lines; gray circles with colored border: individual values. The slope of the regression line achieved significance (P ≤ 0.05) for LD_BMO, LD_BM, and LD_ASCO. The regression equations are LD_BMO = 693 − 12.26 × Axial Length (P = 0.018, R² = 0.02) and LD_BM = 1075 − 24.29 × Axial Length (P < 0.001, R² = 0.03), LD_ASCO = 564 − 10.75 × Axial Length (P = 0.033, R² = 0.01).

Figure 8

Scatter plot and univariate linear regression of laminar depth and IOP. The relationship between laminar depth and IOP is shown, with points shaded gray and border line colored according to their reference plane.