Arterial Supply: Ophthalmic Artery System
All structures of the eyeball receive arterial blood from branches of the ophthalmic artery (a. ophthalmica). One of its most critical branches is the central retinal artery (a. centralis retinae).
It penetrates directly into the substance of the optic nerve and is responsible for supplying the inner layers of the retina. Upon reaching the optic disc (discus nervi optici), this artery divides into superior and inferior branches. These subsequently give rise to smaller vessels supplying individual quadrants:
- superior and inferior macular arterioles (arteriolae maculares superiores et inferiores);
- superior and inferior retinal nasal arterioles (arteriola nasalis retinae superior et inferior);
- superior and inferior retinal temporal arterioles (arteriola temporalis retinae superior et inferior).
Ciliary Arteries and Uveal Blood Supply
In addition to the retina, the choroid, iris, and ciliary body require an intensive blood supply. This is accomplished by several groups of ciliary arteries:
- Long posterior ciliary arteries (aa. ciliares posteriores longae). They run along the lateral surfaces of the optic nerve. These vessels supply the choroid, ciliary body, and iris, and participate in forming the major arterial circle of the iris (circulus arteriosus iridis major).
- Short posterior ciliary arteries (aa. ciliares posteriores breves). They pierce the sclera around the circumference of the optic nerve and form a dense vascular-capillary network of the choroid proper.
- Anterior ciliary arteries (aa. ciliares anteriores). These vessels branch off from the arteries supplying the extraocular rectus muscles and also contribute to the formation of the arterial circles of the iris.
Venous Drainage of the Eyeball
The venous drainage system of the eye parallels the arterial system, ensuring the removal of deoxygenated blood from the tunics. The main drainage pathways include:
- Anterior and posterior ciliary veins (vv. ciliares anteriores et posteriores);
- Vorticose veins (vv. vorticosae). Typically numbering 4 to 6, they play a key role in collecting venous blood from the structures of the vascular tunic (uvea).
Blood from the inner layers of the retina is collected by retinal venules (venulae retinae), which run parallel to the arterioles. They merge into the central retinal vein (v. centralis retinae). This large vein exits the eyeball and drains into either the superior ophthalmic vein or directly into the cavernous sinus.
Innervation of the Eyeball
Neural regulation of eye structures is mediated by the long and short ciliary nerves (nn. ciliares longi et breves). These nerve trunks are mixed and carry three types of fibers simultaneously:
- Sensory fibers — originate from the ophthalmic nerve (n. ophthalmicus), providing pain and tactile sensation.
- Sympathetic fibers — perform vasomotor functions (regulate blood vessel tone).
- Parasympathetic fibers — synapse in the ciliary ganglion (ganglion ciliare).
Upon penetrating the interior of the eye, the nerve fibers form a dense ciliary plexus located within the substance of the ciliary muscle. From this plexus, terminal branches travel to the ciliary body and iris, ensuring appropriate responses to external stimuli.