Figure 1.

Measurement of optic nerve parameters in a spectral domain optical coherence tomography (SDOCT) scan of an infant optic nerve. Using cross-sectional SDOCT B-scans, vertical disc diameter (vDiscDiam, dashed white line) and vertical cup diameter (vCupDiam, solid white line) were measured parallel to the anterior and posterior surface of the scan (not on the diagonal); vertical cup-to-disc ratio (vC:D) was calculated; cup depth (dotted white line) was measured parallel to the A-scans within the B-scan from the plane of the cup to the top of the lamina cribrosa (white triangles). To accommodate for image tilt in the B-scans, the plane of the disc (dashed white line) was defined as the plane halfway between the two points (white rectangles) defining Bruch’s membrane opening (BMO), which can be visualized as the outer edge of the retinal pigmented epithelium. The plane of the cup (solid white line) was defined as the plane halfway between the 2 points (gray circles) marking the cup border, set at a plane 200 μm superior to the BMO markings; the same 200 μm offset was used in the Cirrus Optic Disc Cube protocol for SDOCT.¹³ To assess the effect a change in offset between cup and disc planes would have on our measurements, we conducted secondary analyses of the same scans using 150 instead of 200 μm as the offset.