An optical coherence tomography optic nerve head image for measurement of the anterior lamina depth and prelaminar thickness.

At the center of the optic nerve head, the reference line (white horizontal line) connects the Bruch’s membrane opening (indicated as red dots). From a perpendicular line drawn from the reference line, the distance to the level of the anterior surface of the prelaminar tissue and lamina cribrosa were measured at three points: the maximally depressed point and two additional points (100 μm and 200 μm from the maximally depressed point in the temporal direction). For each patient, the mean of three values was used. The anterior lamina cribrosa depth was defined as the distance from the Bruch’s membrane opening plane to the level of anterior surface of the lamina cribrosa (yellow line) (B). The anterior prelaminar depth was determined by measuring the distance from the Bruch’s membrane opening plane to the level of the anterior surface of the prelaminar tissue, and the prelaminar tissue thickness was obtained by subtracting the anterior prelaminar depth from the lamina cribrosa depth (green line) (C).