Fig. 1.

Landmarks of the retino-optic junction (A) and ultrastructural appearance of axons at representative levels of the optic nerve of mice at age 9 and 16 d (B–E). Distances along the optic nerve referred to in this study were determined relative to the retinal excavation point (50 and 700 μm) (A). The lamina cribrosa begins at 100 μm and ends at 150–200 μm, which marks the level along optic axons where myelin ensheathment occurs (bracketed).B, B′ and D, D′ denote a proximal axonal level (50 μm) at P9 and P16, respectively. A more distal level (700 μm) of a similar population of axons at P9 and P16 is shown in C, C′ and E,E′. Magnification of micrographs inB–E and B′–E′ is represented by scale bars in D (1 μm) and D′(0.2 μm), respectively.