Letter to the Editor

Abstract

Embryology of the ophthalmic artery (OA) is complex, as elegantly depicted by Padget in detailed embryonic diagrams about 60 years ago1. However, Lasjaunias et Al explained its processes differently with angiographic images 2 (Figure ​(Figure1).1). According to their explanation, two primitive OAs supply the orbit first, i.e., the ventral OA (VOA) and dorsal OA (DOA) (Figure ​(Figure1A).1A). The VOA is the ocular artery, which originates from the anterior cerebral artery and passes through the optic canal while DOA originates from the internal carotid artery (ICA) at the carotid siphon runs through the superior orbital fissure (SOF). Then, two anastomoses are formed: one near the optic nerve in the orbit between the VOA and DOA (Figure ​(Figure1B),1B), and the other near the intradural optic canal between the VOA and the ICA (Figure ​(Figure1C).1C). The proximal parts of the VOA and DOA regress, resulting in the formation of the adult OA (Figure ​(Figure1D).1D). The remnant of the proximal DOA is the inferolateral trunk (inferior cavernous sinus artery). In the meanwhile, supraorbital artery (branch of the stapedial artery formed from the second aortic arch) also passes through the SOF and contributes to give off branches to the orbit, including ethmoidnasal and lacrimal arteries (Figure ​(Figure1E).1E). This concept has been well accepted in the neuroradiological field for more than 40 years3. Figure 1 Embryology of the ophthalmic artery proposed by P. Lasjaunias. Abbreviation in figures: ACho a, anterior choroidal artery, Br, branch of the primitive internal carotid artery, DOA, dorsal ophthalmic artery, OA, ophthalmic artery, SOF, superior orbital fissure, VOA, ventral ophthalmic artery. According to Padget1 (Figure ​(Figure2),2), however, the DOA first appears at the opposite side of the bifurcation of the primitive ICA, i.e., in front of the branch (future posterior communicating artery), giving off the hyaloid artery (future central retinal artery) and lateral posterior ciliary artery, which supply the dorsolateral aspect of the developing optic vesicle (Figure ​(Figure2A).2A). The VOA appears at the primitive ICA near the origin of the anterior choroidal artery, and gives off the medial posterior ciliary artery, supplying the ventro-medial aspect of the optic vesicle. Subsequently, the origin of the DOA moves proximally after complex anastomotic processes called caudal migrationto the point of the adult OA (Figure ​(Figure2B).2B). It never goes down to the cavernous sinus. The proximal portion of the VOA regresses and the adult OA is formed finally. At the same time, the stapedial artery gives off two branches: supraorbital and maxillo-mandibular artery (Figure ​(Figure2C).2C). The supraorbital artery enters the orbit through the SOF and anastomoses with the VOA-DOA complex, making a small arterial ring around the optic nerve, at the future second intraorbital portion of the adult OA (Figure ​(Figure2D).2D). After regression of the ventral aspect of the arterial ring, the final adult configuration of the OA is established (Figure ​(Figure2E2E). Figure 2 Embryology of the ophthalmic artery observed by DH Padget. Abbreviation in figures: ACho a, anterior choroidal artery, Br, branch of the primitive internal carotid artery, DOA, dorsal ophthalmic artery, OA, ophthalmic artery, SOF, superior orbital fissure, VOA, ventral ophthalmic artery. As the arteries run together with the corresponding nerves in principle, the supraorbital artery accompanies the ophthalmic nerve (V1) and the maxillo-mandibular artery (future infraorbital artery and inferior alveolar artery) accompanies the maxillary (V2) and mandibular nerves (V3), respectively. Thus, each artery accompanies the division of the trigeminal nerves and passes through the corresponding fissure or foramina (SOF, foramina rotundum and ovale). Embryologically, maxillary and mandibular nerves are related to the first aortic arch, but the ophthalmic nerve is different and not related to the first aortic arch. There is a possibility that the ophthalmic nerve is related to the premandibular arch. In consideration of the branching order from the ICA of mandibular artery (vidian artery after exiting the skull base), maxillary artery (inferior hypophyseal artery), and the inferolateral trunk, and accompanying trigeminal nerves, the inferolateral trunk could be related to the dorsal remnant of the premandibular arch (Figure ​(Figure2E2E). In this communication, I would like to revise the widely accepted concept that only the VOA passes through the optic canal and contributes to vision, and the remnant of the DOA is inferolateral trunk. As Padget observed, I believe that the optic canal is for the ocular artery for vision consisting of both the VOA and DOA, and the SOF is for the orbital artery for lacrimal secretion and orbital muscles consisting of the supraorbital artery of the stapedial artery. The DOA is more important for vision than the VOA since the DOA branches off the central artery of the retina.