skin of the cheek and anastomoses with the infraorbital artery.

Clinical Comment: Temporal

Arteritis

TEMPORAL ARTERITIS  (or giant cell arteritis) is an inflammatory condition that can affect large arteries but is found primarily in the arteries in the temporal or occipital region. The disease often is accompanied by swelling, redness, and tenderness in the temporal area. Ocular symptoms, including vision loss, may occur. Biopsy of the superficial temporal artery often is necessary to confirm the diagnosis before treatment begins.29 The biopsy is taken from the artery as it crosses the zygomatic process and travels superiorly anterior to the ear.28

MAXILLARY ARTERY

The other branch of the external carotid that supplies areas in proximity to the orbit is the maxillary artery. It passes through the infratemporal fossa and then upward, medial to the mandibular joint toward the maxillary bone (see Figure 11-9). Within the infratemporal fossa,

Table 11-2  Extraocular Muscle Blood Supply

the maxillary artery shows some variability in both its branching pattern and in its topographic relations with other structures.29-31 It runs along the pterygopalatine fossa and enters the orbit through the inferior orbital fissure as the infraorbital artery. The artery then runs forward along the infraorbital groove in the maxillary bone, passes through the infraorbital canal, and exits through

the infraorbital foramen (see Figure 11-8). It supplies the lower eyelid and lacrimal sac, and it anastomoses with the angular artery and the dorsonasal artery.26 While in the infraorbital canal, the infraorbital artery supplies the inferior rectus and inferior oblique muscles and sends some branches to the maxillary sinus and to the teeth of the upper jaw.

The branches from the internal and external carotid arteries that supply the ocular structures, as well as their most common anastomoses, are shown in the flow chart in Figure 11-10.

V E I N S O F T H E O R B I T

The veins of the orbit have no valves; thus the direction of blood flow may change and is determined by pressure gradients.5 Over a large part of their path, the veins are embedded within the connective tissue septa that compartmentalize the orbit.5 Unlike the parallel routes of veins and arteries in most of the body, many orbital veins follow a course that differs from the corresponding arteries.9,32 The orbit has a single ophthalmic artery but two ophthalmic veins. The superior and inferior

ophthalmic veins primarily drain into the cavernous sinus.

SUPERIOR OPHTHALMIC VEIN

The superior ophthalmic vein is formed by the joining of the angular and supraorbital veins within the orbit (Figure 11-11). The supraorbital vein enters the orbit through the supraorbital notch, and the angular vein passes through the orbital septum above the medial palpebral ligament.33

The superior ophthalmic vein, the larger of the two ophthalmic veins, runs with the ophthalmic artery and, as it passes posteriorly, receives blood from veins that drain the superior orbital structures. It passes below the superior rectus muscle and crosses the optic nerve to the upper part of the superior orbital fissure, where it leaves the orbit to empty into the cavernous sinus.

The veins that drain into the superior ophthalmic vein are the anterior and posterior ethmoid veins, the muscular veins draining the superior and medial ­muscles, the lacrimal vein, the central retinal vein, and the superior vortex veins.33

Internal Carotid Artery

Ophthalmic Artery

Middle meningeal artery

External carotid artery

FIGURE 11-10

Flow chart of branches of internal and external carotid arteries that supply orbital structures. Blue indicates branches of internal carotid artery; purple indicates branches of external carotid artery; green indicates target structures. Circles show anastomoses LR, Lateral rectus; SR, superior rectus; SO, superior oblique; MR, medial rectus; IR, inferior rectus; IO, inferior oblique.

213 Supply Blood Orbital  t  11 CHAPTER

FIGURE 11-11

View from lateral side of orbit showing veins draining globe and orbit.

Central retinal vein

Cavernous sinus

Inferior ophthalmic vein

Pterygoid venous plexus

CENTRAL RETINAL VEIN

The venous branches located in the retinal tissue come together and exit the eyeball as a single central retinal vein. This vessel leaves the optic nerve approximately 10 to 12 mm behind the lamina cribrosa alongside the central retinal artery. It emerges from the meningeal sheath of the optic nerve and either joins the superior ophthalmic vein or exits the orbit and drains directly into the cavernous sinus.

Clinical Comment: Spontaneous

Venous Pulsation

The pressure within the central retinal vein is approximately equal to the intraocular pressure (IOP) and at peak pulse pressure the vessel walls expand slightly. The increase

in blood volume can be seen during ophthalmoscopy of the healthy eye as the central retinal vein can be seen to pulsate at its exit through the optic disc. The IOP can vary slightly (1 to 2 mm Hg) with this change in blood volume.24

Clinical Comment: Papilledema

The sheaths that surround the optic nerve are continuous with the meningeal sheaths of the brain. The subarachnoid space, located within these layers, contains cerebrospinal fluid. Thus the fluid that surrounds the optic nerve is continuous with the fluid found throughout the cranial cavity. With increased

Frontal bone

Superior vortex

Superior vein ophthalmic vein

Supraorbital

vein

Angular vein

Infraorbital

vein

Inferior vortex vein

Maxillary bone

intracranial pressure, the central retinal vein can be compressed as it crosses the subarachnoid space on its exit from the optic nerve. The central retinal artery is not affected because it has a thicker sheath and is not compressed as easily as is the vein.34 The resultant blockage causes congestion of the retinal veins and edema of the retina. Edema of the optic nerve head (papilledema) will be evident as blurred disc margins, with hemorrhages sometimes evident as well.

VORTEX VEINS

The vortex veins drain the choroid, and usually one of the four or five vortex veins is located in each quadrant (see Figure 11-3). These veins exit the globe 6 mm posterior to the equator.8 The vortex veins can be seen with an indirect ophthalmoscope and a dilated pupil.

INFERIOR OPHTHALMIC VEIN

The inferior ophthalmic vein begins as a plexus near the anterior floor of the orbit. It drains blood from the lower and lateral muscles, the inferior conjunctiva, the lacrimal sac, and the inferior vortex veins.33 It may form two branches: one that empties into either the superior ophthalmic vein22,35 or the cavernous sinus and one that empties into the pterygoid venous plexus (see Figure 11-11). The latter branch exits the orbit through the inferior orbital fissure, and the other branch passes through the superior orbital fissure either to join the superior ophthalmic vein or to empty directly into the cavernous sinus.