FIGURE 11-4

Fundus photograph of the right eye. A cilioretinal artery can be seen looping up into retina at temporal edge of optic disc. (Courtesy Family Vision Center, Pacific University, Forest Grove, Ore.)

cc of the dye is injected into a vein in the arm. Serial black and white photos are taken of the fundus through filters that enhance the image. This documents the movement of the blood through the choroidal and retinal vasculature. The dye enters the skull through the internal carotid artery, passes into the ophthalmic artery, and then to the posterior ciliary arteries, which fill before

the central retinal artery. Within 10 seconds of injection the choroidal flush can be seen; the dye can leak out

of the fenestrated choriocapillaris easily but should not seep into the retina because of the blood-retinal barrier of zonula occludens in the RPE. Ten to 12 seconds after injection, the retinal arterioles fill and the capillaries are filled in the next second; another 1 to 2 seconds and the veins fill, and the dye starts to exit the ocular tissue. Defects in the RPE can be seen if the dye leaks into the retina before the retinal vessels fill. Abnormal retinal vasculature such as neovascularization and capillary leakage will be evident.

ETHMOID ARTERIES

As the ophthalmic artery courses near the medial wall, two branches arise and enter the ethmoid bone (see Figure­ 11-1). The posterior ethmoid artery passes through the posterior ethmoid canal to supply the posterior ethmoid sinus and the sphenoid sinus; it sends branches into the nasal cavity to supply the upper part of the nasal mucosa. The anterior ethmoid artery generally is larger and passes through the anterior ethmoid canal and supplies the anterior and middle ethmoid sinuses, the sphenoid sinus, the frontal sinus, the nasal cavity, and the skin of the nose.

SUPRAORBITAL ARTERY

The supraorbital artery arises from the ophthalmic artery as it lies medial to the optic nerve (see Figure 11-1). The supraorbital artery runs upward to a position above the superior extraocular muscles, turns anteriorly, and runs with the supraorbital nerve between the periorbita of the orbital roof and the levator muscle. It passes through the supraorbital notch or foramen, often dividing into two branches to supply the skin and the muscles of the forehead and scalp (see Figure 11-8). Terminal branches anastomose with the artery from the opposite side, with the supratrochlear artery, and with the anterior temporal artery from the external carotid. While the supraorbital artery is in the orbit, it sends branches to the superior rectus, superior oblique, and levator muscles and to the periorbita.

MUSCULAR ARTERIES

Much variation occurs in the vessels supplying the muscles, and in an individual, any combination of the vessels named here might be present. In one common presentation, the muscular arteries come from the ophthalmic artery as two branches, the lateral (or superior) and the medial (or inferior). The lateral (superior) branch supplies the lateral rectus, superior rectus, superior oblique, and levator muscles.7-9

The medial (inferior) branch supplies the medial rectus, inferior rectus, and inferior oblique muscles.7-9 Additional branches supplying the muscles may come from other sources. The lacrimal artery supplies the lateral and superior rectus muscles. The supraorbital artery supplies the superior rectus, superior oblique, and levator muscles. The infraorbital artery supplies the inferior rectus and inferior oblique muscles (Table 11-2).

ANTERIOR CILIARY ARTERIES

The anterior ciliary arteries branch from the vessels supplying the rectus muscles. These arteries exit the muscles near the muscle insertions, run forward along the tendons a short distance, then loop inward to pierce the sclera just outer to the limbus (see Figure 11-3). An accumulation of pigment may be evident at the point at which the artery enters the sclera. Before entering the sclera, the anterior ciliary arteries send branches into the conjunctiva, forming a network of vessels in the limbal conjunctiva (see Figure 11-6). Other branches enter the episclera to form a network of vessels before entering the uvea. The anterior ciliary arteries then enter the ciliary body and anastomose with the branches of the long posterior ciliary arteries, forming the major circle of the iris (see Figure 11-3).

Choroidal blood vessels

Retinal blood vessels

Vortex vein

Long posterior ciliary artery

Short posterior ciliary arteries

Central retinal artery

Central retinal vein

Anterior ciliary artery

Long posterior ciliary artery

Muscular artery to lateral rectus muscle

Muscular vein

Conjunctival capillary loops

Cornea

Canal of Schlemm

Iris

Ciliary body

Major circle of the iris

Generally, two anterior ciliary arteries emanate from each of the rectus muscles, with the exception of the lateral rectus, which provides only one such artery.

Clinical Comment: “Red Eye”

Inflammations generate an increase of the blood flow to the affected area, causing hyperemia. In cases of a “red eye,” an understanding of the organization of the blood supply in the limbal area can help in differentiating a less serious presentation, such as conjunctivitis, from a more serious situation, such as uveitis. In conjunctivitis and mild corneal involvement, the superficial blood vessels are injected, giving

the conjunctiva a bright-red color that often increases toward the fornix. The vessels move with conjunctival movement and can be blanched with a topical vasoconstrictor. In uveitis the deeper scleral and episcleral vessels are injected, giving the circumlimbal area a purplish or rose-pink color.22 These vessels do not move with the conjunctiva and are not blanched with a topical vasoconstrictor.

MEDIAL PALPEBRAL ARTERIES

Two medial palpebral arteries branch either directly from the ophthalmic artery or from the dorsonasal artery near the trochlea of the superior oblique muscle. The medial palpebral arteries pierce the orbital septum on either side of the medial palpebral ligament and enter the superior and inferior eyelids (see Figure 11-8). These branches run through the eyelid and form arches between the orbicularis muscle and the tarsal plate. They anastomose with branches from the lacrimal artery and form the vessels known as the palpebral arcades. Usually, two arcades occur in each lid: the marginal arcade, which runs near the marginal edge of the tarsal plate, and the peripheral

A

B

FIGURE 11-7

Fluorescein angiography in a 68-year old white male with internal carotid artery stenosis. (Note the delay in dye passage into the vessels.) A, Photo taken 20 seconds after injection; chorodial vessels fill first and then CRA (thin arrow) indicates choroidal vessel, (thick arrow) shows choroidal flush as dye seeps out of choriocapillaris but is prevented from entering retina by the tight junction of RPE. B, Photo taken 30 seconds after injection, dye has filled retinal capillaries and can now be seen along the walls of the retinal veins (arrow) as it exits the eye. (Courtesy Densie Good win, O.D., Pacific University Family Vision Center, Forest Grove, Ore.)

vasoactive substances such as nitric oxide, which causes vasodilation and endothelin-1, a vasoconstrictor.23,24 The choroidal blood flow is largely dependent on vasoactive autonomic innervation, and sympathetic stimulation causes vasoconstriction but the effect of parasympathetic stimulation is less clear.23 Retinal vessels lack autonomic innervation and are autoregulated,

and blood flow remains stable with transient increases in blood pressure.23 Retinal vessel walls have “pacemaker” mechanisms that regulate vessel wall tension, constriction and dilation, are influenced by changes in the environment in the surrounding tissue, responding to levels of O2 and CO2, as well as pH changes. Some investigators believe that choroidal vessels exhibit some autoregulation.25

Although blood flow through the choroidal vessels is extremely high compared with flow through retinal vessels (2000 ml/min/100 g tissue versus 60 ml/ min/100 g tissue), oxygen extraction from the choriocapillaris is low.24 The high choroidal flow rate provides high oxygen tension enhancing oxygen diffusion through Bruch’s membrane and the RPE to mitochondria in the photoreceptor inner segment. The high choroidal blood flow can also act to stabilize temperature, protecting the retina from thermal damage.24,25

E X T E R N A L C A R O T I D A R T E R Y

The other branch of the common carotid, the external carotid artery, passes upward through the tissue of the neck. Only those few branches of this artery that supply the globe and orbit are discussed.

FACIAL ARTERY

The facial artery arises from the external carotid near the angle of the mandible, runs along the posterior edge of the lower jaw, and curves upward over the outside of the jaw and across the cheek to the angle of the mouth. It ascends along the side of the nose and sends a terminal branch, the angular artery, to the medial canthus (Figure 11-9). The angular artery supplies the lacrimal sac, the medial part of the lower lid, and the skin of the cheek. Some branches pass beneath the medial canthal ligament to anastomose with the infraorbital artery, and some anastomose with the dorsonasal artery.

SUPERFICIAL TEMPORAL ARTERY

The superficial temporal artery is a terminal branch of the external carotid artery (see Figure 11-9). Branches of the superficial temporal artery that supply areas near the orbit are the anterior temporal, zygomatic, and transverse facial arteries.26 The anterior temporal artery supplies the skin and muscles of the forehead and anastomoses with the supraorbital and supratrochlear arteries. The zygomatic artery extends above the zygomatic arch and supplies the orbicularis muscle. The transverse facial artery supplies the