Blood supply of the optic nerves and chiasma and its clinical significance.

The blood supply of the optic nerve has been a subject of controversy for at least 200 years, since the description of the arterial circle around the optic nerve head by Zinn (1755) and Haller (1754). Numerous papers have been written concerning the subject and in the past few years new techniques of injection, micro-angiography, and dissection and Neoprene casts have resulted in further papers on the subject. Older writers, using relatively crude techniques, differed widely in their interpretation of the blood supply of the nerve. What is, perhaps, more surprising is that modern workers using highly elaborate and skilled techniques have also differed considerably in their descriptions of the vascular supply. The differences are especially noteworthy when considering the central vessels of the optic nerve, the anastomoses around the optic nerve head, and the blood supply of the intracranial portion of the optic nerve. All observers are agreed that the optic nerve is surrounded by a pial plexus of vessels and also that it contains some system of central vessels. There is disagreement concerning the contribution made to these systems by individual vessels and the degree of anastomosis between them. Most workers seem to be agreed that the outer layers of the optic nerve in its orbital portion are nourished from a capillary pial plexus. This is contributed to mainly by twigs from the ophthalmic artery, and its branches the long and short posterior ciliary arteries. Fran9ois and Neetens (1954) postulate also twigs from the lacrimal artery. How much of the nerve is supplied by this pial plexus seems to be a matter of speculation. Steele and Blunt (1956) and many other writers have noted that branches from this plexus appear to penetrate the optic nerve for short distances only, so that it may be inferred that probably less than half the fibres are supplied from this source and that they are those situated peripherally in the nerve. There seems to be no convincing evidence from these studies that there is any horizontal or vertical division of blood supply in this peripheral portion. The only other point at issue over the pial plexus is the contribution from the central artery itself. All writers other than Fran9ois and Neetens agree that this vessel