Fig. 10. Physiologic cup of approximately one third the disc diameter, resulting from a chorioscleral canal slightly larger than required to accommodate the exiting axons along with the astroglia and capillaries. The scleral lip is again present around the entire circumference, even though not conspicuous where the pink nerve fiber layer is thick enough to obscure it. There is no peripapillary zone of thin retinal pigment epithelium or choroid to form a crescent or halo.