No abstract

The clinical picture of retinal venous occlusion is well known to ophthalmologists, but no corresponding description of vortex vein (VV) occlusion in man is so far available. After completing our present experimental study, we carried out an exhaustive search of the literature which revealed some old accounts of experimental occlusion of the different VVs. These were mostly designed to produce experimental glaucoma ( We have produced experimental occlusion of one, two, three, and all of the VVs in rhesus monkeys and have studied their short-term and long-term effects on the eye by a detailed clinical examination, intravenous fluorescein angiography, histopathological studies, and perfusion of the ocular vascular bed with silicone rubber. Since the uveal vasculature in man and rhesus monkeys is identical, it can be assumed that the findings in rhesus monkeys will hold good in man. A clinical picture of VV occlusion, derived from these studies, is presented in this paper. MaterialThis study was carried out in forty eyes of rhesus monkeys. MethodsAfter lateral orbitotomy the VVs were occluded by cauterizing them a short distance from their site of exit from the globe without any other interference with the ocular vessels. The details of the occlusions are shown in Table I.These eyes were followed up for variable periods (Table II).In all these eyes the following investigations were carried out soon after the occlusion, later on during the follow-up period, and at the termination of the experiment.

The literature contains no reference to the effects in vivo of occlusion of the posterior ciliary artery (PCA) on the choroidal circulation. It has simply been assumed that occlusion of one or more PCAs is not likely to produce any filling defect in the choroid because the choroidal vascular bed has been described as being one continuous bed, with no segmental distribution (Nicholls, I938; Vilstrup, 1952; Wybar, I954a, b; Correia, I957; Scullica, 1957; Ruskell, 196I; Ring and Fujino, I967). Our experimental studies involving occlusion of the PCAs in rhesus monkeys have, on the contrary, revealed that such an assumption is entirely incorrect and that the distribution of the PCAs is, in fact, segmental. These studies have also led to many interesting observations which are reported below. There is a good deal of confusion as to the nomenclature, number, origin, and distribution of the PCAs. One of us has helped to clarify these subjects (Hayreh, I962, I964, I970, 1971). Briefly, the ophthalmic artery in humans gives out one (in 3 per cent.), two (in 48 per cent.), or three (in 39 per cent.) PCAs. Each artery divides into multiple branches before piercing the sclera, medial (by the medial PCA) or lateral (by the lateral PCA) to the optic nerve. Of these branches, two small ones (one on the medial and the other on the lateral side) are called the long PCAs, while the rest are the short PCAs. Material The study was carried out in 85 rhesus monkey eyes. Methods By lateral orbitotomy, the PCAs were cauterized near their site of entry into the eyeball, leaving a small arterial stump close to the globe as follows: Lateral PCAs (LPCAs) in 3I eyes Medial PCAs (MPCAs) in 17 eyes All POAs (APCAs) in 37 eyes The Table (overleaf) shows the follow-up period after PCA occlusion in 85 eyes of rhesus monkeys. The choroidal circulation in these eyes was assessed by repeated intravenous fluorescence angiography (IVFA).

The clinical picture of central retinal artery occlusion is well-known. Little is known, however, about the clinical picture of occlusion of the posterior ciliary arteries (PCAs). We have, therefore, carried out experimental occlusion of the various PCAs individually or together in rhesus monkeys. The effects of such occlusions have been investigated in the choroid, pigment epithelium (PE), and retina of these monkeys over a period of time, ophthalmoscopically, by intravenous fluorescence fundus angiography (IVFA), and (after death) by histology. The study has revealed fundus lesions the nature of which has hitherto been obscure.There are usually two to three PCAs, arising from the ophthalmic artery, which supply the posterior half of the choroid up to the equator of the eye. These are designated medial (MPCA) and lateral (LPCA), depending upon their relationship to the optic nerve near their site of entry into the sclera. A detailed account of the anatomy of the PCAs is given elsewhere (Hayreh, i962, 1970).The effects of occlusion of the various PCAs on the choroidal circulation have already been described in detail (Hayreh and Baines, 1972). Briefly, the distribution of the PCAs in the choroid was seen to be segmental, so that occlusion of one PCA resulted in nonperfusion of the choroid in that region during the transit of the dye in IVFA. However, a very late and sluggish patchy filling of the choroid via the various collaterals took place; this improved with time, so that in 2 to 4 weeks the choroidal circulation was restored. MaterialThe study was carried out in 85 rhesus monkey eyes. MethodsBy lateral orbitotomy, the PCAs were cauterized near their site of entry into the eyeball, leaving a small arterial stump close to the globe as follows:Lateral PCAs (LPCAs) in 3' eyes.Medial PCAs (MPCAs) in I 7 eyes. All PCAs (APCAs) in 37 eyes.

The two or three posterior ciliary arteries (medial and lateral posterior ciliary arteries), which are the source of blood supply to the posterior choroid, are also the major souice of blood supply to the optic nerve head (Hayreh, i969, I970) and have a segmental distribution (Hayreh, I970, I97ib). The ciliary circulation is the only source of blood supply to the lamina cribrosa and prelaminar regions, and it is an important if not the only source of supply to the retrolaminar part of the optic nerve. Hayreh (i 969, I 97 I a) put forward the view based on these studies that ischaemic optic neuropathy is produced by acute occlusion of the posterior ciliary arteries (PCAs).The effects of acute occlusion of the PCAs on the optic nerve head have been investigated experimentally in rhesus monkeys. These produced a clinical and histopathological picture of ischaemic optic neuropathy. Intravenous fluorescence fundus angiography (IVFA) studies of patients with ischaemic optic neuropathy have further confirmed the presence of occlusion of the PCAs. MaterialThe study was carried out in 85 rhesus monkey eyes. MethodsBy lateral orbitotomy, the PCAs were cauterized near their site of entry into the eyeball, leaving a small arterial stump close to the globe, as follows:Lateral PCAs (LPCAs) in 3I eyes Medial PCAs (MPCAs) in I7 eyes All PCAs (APCAs) in 37 eyesThe following investigations were performed repeatedly during follow-up (see Table: Hayreh and Baines, I972a). At the end of the experiment, the carotid vascular tree was irrigated with 2 per cent. gluteraldehyde via the left ventricle. All except nine of the eyes followed up for 24 hrs or longer were excised and submitted to histological examination. In thirty of the experiments (2i eyes followed for up to 2 hrs; 9 for up to 3 mths), in which the eyes were not removed for histology, gluteraldehyde irrigation was followed by irrigation of the vascular tree with normal saline. Silicone rubber was then injected via the common carotid artery to perfuse the ocular vascular bed. The animal was stored in the deep freeze for 24 hrs or longer to "set" the silicone rubber, after which the eye and the optic nerve were removed and cleared, using the alcohol-methyl-salicylate clearing technique. The optic disc (OD) and optic nerve (ON) vasculature filling pattern was studied under the dissection microscope.