The cilioretinal arteries belong to the posterior ciliary artery system. They usually arise from the peripapillary choroid or directly from one of the short posterior ciliary arteries. The existence of the cilioretinal arteries is a congenital anomaly rather than one acquired due to some disease, inflammatory, or other morbid process. It was first described by Müller [1] in 1856 (Fig. 3.1) and first demonstrated histologically in 1876 by Nettleship [2], who stated that in sectioning of a human eye, he found “a small artery from the choroid turning round the edge of the disc, and running uninterruptedly for some distance in the retina, where it breaks up into capillaries.” Since then, there have been many reports of the presence of a cilioretinal artery (Table 3.1) [3–26]. Nettleship [27] in 1876 reported 7 cases of cilioretinal arteries. In 1879, he [3] published many important observations, still relevant, about the cilioretinal arteries. He stated the following:

He stated that this cilioretinal vessel may be either an artery or a vein. We now know that it is almost always an artery and only rarely a vein.

Like Nettleship [3], Lang and Barrett [6] in 1888 defined a cilioretinal vessel as “one which dips into the nerve near the margin of the optic disc and which can be seen to arch outwards,” and did not regard a vessel without this curve as cilioretinal. Jackson [9] stated that the artery curved as it emerged. This characteristic sharp hook-like appearance at its site of entry into the retina at the optic disc margin was described as a diagnostic feature of this artery by Salzmann [10] and Duke-Elder [28].

Salzmann [10] stated that a nasal cilioretinal artery was associated with anomalies of the optic disc. Collier [15] demonstrated an association of cilioretinal arteries with congenital anomalies of the optic disc and fundus and with refractive errors (he found ametropia in 195 eyes, of which 47 % were astigmatic; 40.2 % had hypermetropia, with or without astigmatism, and 32.5 % had myopia). Glees [29] suggested some genetic association between cilioretinal vessels and various abnormalities of the retinal vessels, cerebral angiomata, and aneurysms of the cranial vessels and stressed their value as diagnostic signs. Loring [4] stated that cilioretinal arteries were seen where the nutrition of the retina had suffered from morbid processes, but Nettleship [3] found no association with any disease. In my clinic, I have seen a cilioretinal artery as a common finding in normal eyes, with no evident association with any ocular disease.

Birnbacher [30] in 1887 rightly stated that every artery which appeared at or near the disc margin was not necessarily a cilioretinal artery. Duke-Elder and Wybar [31] described the division of the central retinal artery within the substance of the optic nerve into two, four, or even eight arteries, which emerged separately at the disc, no parent trunk being visible ophthalmoscopically. Blunt [17] found the central retinal artery bifurcating 0–4 mm behind the disc in one case, and one of the branches passed to the margin of the lamina cribrosa to emerge from the disc at the periphery. The condition described resembles somewhat the left side of my reported cases in a rhesus monkey [32]. Bloch [33] and Salzmann [10] saw patients with arteries at the periphery of the disc and no central artery. According to Parsons [34], this possibility cannot always be eliminated. Thus, rarely the artery that looks like the cilioretinal artery ophthalmoscopically may in reality be an early branch of the central retinal artery, arising within the optic nerve, and in such cases a normal central retinal artery would also be seen. In such cases, fluorescein fundus angiography is helpful, because normally the cilioretinal artery fills at the same time as the choroid and usually before the onset of filling of the central retinal artery or its branch (Fig. 3.2). On the other hand, if it is an early branch of the central retinal artery, the branch and the main central retinal artery fill simultaneously.