Resumen de Desarrollo embrionario y fetal de la vascularización del nervio óptico
A study of embryos and fetuses of increasing ages was made, from the embryo at 4mm. To the fetus al term. Serial sections of 15 microns were made, the specimens were stained in eosin-hematoxylin and studied by the triple method of microscopic inspection, Born's stereometric reconstruction, and photographic reproduction for the simultaneous comparison of successive sections. The following conclusions were reached from this study: blood vessels originating in the vascular system of the perineural pia mater and penetrating the optical peduncle (fig. 1) are found as early as the 19mm embryo. The existence of the ophthalmic vascular scheme described by Padget is proven in the 23mm. Embryo (fig. 2, 3, 4). The nutrition of the optical peduncle continues its dependence on the arterial plexus of the pia which in turn is reinforced by a carotid branch that we have termed the embryonic peduncular artery (figs. 5, 6, 7, 8). In the 30mm. Embryo the ophthalmic vascular system anastomoses with the orbital vessels of stapedic origen, forming the definitive, yet rudimentary, ophthalmic artery. The most important branch of this artery is the hyaloid or future central retinal artery. In its short intraneural course, this hyaloid artery gives origen to al least one colateral branch which irrigates the distal portion of the optic nerve. The hyaloid artery dilates (fig. 9) when passing from the papilla to the vitreous space, reference to which we have not found until the 100mm. Fetus. The hyaloid vein is very large in its intraneural axial trajectory, having the aspect of a venous sinus following the axis of the optic nerve head and persisting to a lesser extent until the end of gestation (fig. 10). The circle of Haller-Zinn is already formed. The vascularization of the optic nerve originates principally in the pia vascular system. During the third month of development, both the perineural vascular system of the pia and the connected vessels that penetrate the optic nerve become increasingly more abundant (figs. 13 y 14). These penetrating vessels interconnect and form an intrincate intraneural network. Penetrating vessels serving the optic nerve head also originate in the Haller-Zinn ring (figs. 15 y 16). During the fourth and fifth month of development in the intraneural network cited, nourishing itself at the expense of the perineural system of the pia, samall longitudinal vessels are seen following the course of the nerve fibers and serving various depths (figs. 17, 18, 19 y 20). The ascending intraneural portion of the central retinal artery forms an angle of 30º with the axis of the nerve; it shows a dilatation in the proximal end of its intraneural axial portion (fig. 21), as well as the dilatation of its distal end described since the 30mm. Embryo; this axial portion originates collateral branches supplying the optic nerve head, some of which anastomose with vessels coming from the vascular network of the pia mater. The axial venous sinus of the optic nerve head is not only drained by the vessels of the juxtabulbar portion of the nerve but also by its postcapital zones. The area of the optic nerve head in transverse section exhibits a 4/3 relationship with the transverse sectional area of this nerve's postcapital portion; this volume increase of the optic nerve head appears to stem from its vascular enrichment. During the last months of development, the vascular network of the pia and its intraneural penetrating branches become gradually less visible, but numerous radial penetrating vessels originating in the vascular network of the pial plexus and which anastomose among themselves or end in some of the longitudinal vessels proceding from the pia establish connection with collaterals of the central vessels of the retina al the level of the optic nerve head (fig. 22). The axial portion of the intraneural segment of the central retinal vein is found as a venous sinus until the end of gestation (fig. 23). The Haller-Zinn circle continues emitting vessels toward the optic nerve head (fig. 24).
