Fluorescein angiography of the optic disk

Vascular supply of the optic nerve head: implications for optic disc ischaemia

The vascular supply of the optic nerve head is complex and remains incompletely delineated. Over the past 50 years, various investigators have attempted to clarify the relative contributions of the choroid, the short posterior ciliary arteries and the central retinal artery to the vascular beds of the inner retinal, prelaminar, laminar and retrolaminar segments of the nerve head. Conflicting theories have evolved, in no small part due to differing techniques of study, involving both flow parameters and anatomical constructs. These have included studies, both in normal subjects and in those with optic nerve ischaemia, of histopathology, electron microscopic corrosion casting, orbital colour Doppler flow studies, fluorescein angiography, indocyanine green angiography, laser Doppler flow studies, laser speckle flowgraphy, microperfusion and labelling studies and optical coherence tomography angiography. The nature of the optic disc, peripapillary retina and choroid microvasculature has implications for the pathophysiology of ischaemic optic neuropathy.

Fluorescein angiography in acute nonarteritic anterior ischemic optic neuropathy

Fundus fluorescein angiograms from 41 patients with nonarteritic anterior ischemic optic neuropathy of less than three weeks' duration were compared with those from 43 age-matched control subjects. Patients with disease showed statistically significant delay in both the onset and the time to completion of prelaminar optic disk filling. Neither onset nor completion of peripapillary choroidal filling were markedly delayed when compared with control subjects. Frequency of occurrence of delayed filling within peripapillary choroidal watershed zones was not increased in patients with disease. There was no consistent correlation by quadrant between optic disk filling delay, choroidal filling delay, optic disk swelling or hyperfluorescence, and visual field deficit. No trend for change in characteristics was found with increasing time interval from onset of symptoms to performance of angiography. Fluorescein angiography in nonarteritic anterior ischemic optic neuropathy demonstrates delayed optic disk filling without consistent relation to adjacent peripapillary choroidal filling delay or other disease findings.

Inter-individual variation in blood supply of the optic nerve head. Its importance in various ischemic disorders of the optic nerve head, and glaucoma, low-tension glaucoma and allied disorders

There is no one standard pattern of the blood supply of the optic nerve head in all human eyes. There is a marked inter-individual variation in the blood supply of the optic nerve head, and the various factors which produce this include variations in (I) the anatomical pattern of blood supply, (II) the pattern of posterior ciliary artery (PCA) circulation (the main source of blood supply to the optic nerve head), and (III) the blood flow. The variations in the pattern of PCA circulation include the variations in (a) number of PCAs supplying an eye, (b) area of supply to the optic nerve head by each PCA, (c) location of the watershed zones between the various PCAs in relation to the optic nerve head, and (d) blood pressure in various PCAs as well as short PCAs. The variations in the blood flow in the optic nerve head can be produced by changes in (i) the intraocular pressure, (ii) mean blood pressure in the capillaries of the optic nerve head and (iii) peripheral vascular resistance. These variations are discussed in detail. A lack of appreciation of these complexities of the blood supply of the optic nerve head in health and disease is responsible for many of the current problems in the understanding of the role of vascular disturbances in anterior ischemic optic neuropathy, glaucoma, low-tension glaucoma and various ischemic disorders of the optic nerve head.

Increased vascular permeability in disc swelling produced by ocular hypotony

Chronic hypotony and swelling of the optic disc was produced in monkey eyes by ciliary body freezing. Associated changes in vascular permeability were detected with horseradish peroxidase (HRP) used as a marker of vascular integrity. Extravascular infiltration of HRP was seen in eyes with disc swelling in the lamina retinalis, lamina choroidalis, lamina scleralis and retrolaminar myelinated portion of the nerve head. In the anterior lamina retinalis, HRP was found in perivascular connective tissue and in interaxonal spaces around some vessels. Our findings suggest that the major source of extravascular HRP in the optic nerve head in disc swelling is leakage from the choriocapillaris through the perineural connective tissues, although focal leakage from vessels in the anterior portions of the swollen disc probably also occurs.

Embolic ischemic optic neuropathy

On examining the postmortem enucleated eyes of a 68-year-old man, we found the left eye had focal infarction 3 mm behind the lamina cribrosa caused by thromboembolic compromise of three discrete pial and pial-derived arterioles. The optic nerve had been destroyed focally, whereas the retinal and choroidal tissue supplied by a similarly occluded vessel had been preserved. We diagnosed nonarteritis ischemic optic neuropathy.

Reevaluation of the optic disk vasculature

The optic disk vessels of owl monkeys and humans were studied in whole mounts injected with silicone rubber and by serial sections of paraffin-embedded tissue. The capillary bed of the optic nerve head in continuous on one side with the retinal vessels and on the other side with the optic nerve behind the globe. The choriocapillaris is a separate capillary bed, even though it and the disk capillaries are both supplied by branches of the posterior ciliary artery. At the junction between choroid and optic disk is a cuff of vessels that seems equivalent to an anterior extension of the pial vessels. This cuff includes capillaries of the central nervous system, was well as arterial branches of the posterior ciliary artery that pass retrograde from the peripapillary choroid and sclera into the pial plexus. While not contradicting previous descriptions of the vascular anatomy in this region, we emphasized that the microvascular bed of the disk is anatomically an integral part of the retina-optic nerve vascular system and deemphasized its relationship to the choroidal vasculature.

Submacular choroidal circulation

A neoprene latex and pigment mixture was injected into the choroidal blood vessels of human cadaver eyes. When peripheral resistence was normal, a single arteriole filled a single lobule of the choriocapillaris drained by mulitple surrounding venules. The choridal veins interconnected and an increase in the peripheral resistance caused by elevation of the venous pressure resulted in filling of contiguous lobules in a retrograde manner through the venules that normally drain them.