Figure 2. OCT neural canal and scleral flange anatomy, morphologic relationships, and scleral flange opening (SFO) segmentation.

(A1 – C1) Three OCT-radial B-scan from three representative eyes (FDA165 (A1) top, FDA261 (B1) middle, and Hi-Myo-GL-29, (C1) bottom). (A2 - C2) The scleral flange histologically refers to the peri-neural canal (pNC) sclera that is “central “or “internal” to the dural sheath insertion. The dural sheath adds substantial thickness to the outer layers of the posterior sclera. The potential thinness of the scleral flange relative to the adjacent posterior sclera may have important biomechanical implications on the flow of blood within the posterior ciliary arteries which pass through the scleral flange to achieve the juxta canalicular choroid as well as the lamina cribrosa. The anterior scleral canal opening (ASCO) is histologically defined to be the projection of the anterior scleral flange surface through the choroidal border tissues (CBT). The posterior scleral canal opening has been described histologically and using 3D histomorphometry (see Introduction) but is not consistently visualized in OCT imaging and is shown here for representation purposes only. For this study the scleral flange opening (SFO) was manually segmented either “geometrically” when identifiable (Panels B2 and C2, see Methods) or, when not geometrically identifiable, estimated visually by projecting the anterior laminar surface through the neural canal wall (Panel A2, see methods). (A3 – C3) Existing BMO and ASCO segmentations in combination with the segmented SFO points were used to define the externally oblique CBT (EOCBT) and Exposed Scleral Flange (ESF) which were parameterized within BMO reference plane as shown in Figure 5.