Mechanism of Production of Papilloedema.

THE optic disc is an intriguingly small and intricate structure. Some of the pathological processes known or assumed in other conditions can be of help to us in elucidating the changes occurring in papilloedema. By papilloedema in this study I mean the non-inflammatory type found typically in cases of raised intracranial pressure, but also occurring, as we shall see, in some other conditions. The tissue of the disc derives its blood supply from the arterial circle of Haller (or Zinn) (Fig. 1). Each trabecula of the lamina cribrosa (nourishing the nerve fibre bundle within it) is essentially the result of the ingrowth of a vessel derived from the circle of Haller accompanied by glial and connective tissue (Wolff, 1954). The circle of Haller is formed by about three of the short ciliary arteries which also supply the anterior end of the optic nerve. There are connexions usually on a capillary level across the cribriform plate with the inconstant artery of the optic nerve (Fran9ois and Neetens, 1963), and with twigs from the central retinal artery arising just behind the cribriform plate. Although these are usually quite inadequate to maintain the vitality of the retina if there is a blockage of the central retinal artery, this may reflect