8 ● Neuro-Ophthalmology

bone inferonasally (meeting at the zygomaticomaxillary suture). Medially, the orbital rim consists of the maxillary and lacrimal bones, which join the frontal bone superiorly. An additional 3 bones contribute to the orbit: (1) the ethmoidal bone medially, (2) the palatine bone inferiorly in the posterior orbit, and (3) the sphenoid bone laterally and superiorly in the orbital apex.

The orbit is surrounded by several important structures. The 4 paranasal sinuses sur-round the floor (maxillary sinus) and the medial wall (ethmoidal and sphenoid sinuses) of the orbit (Fig 1-4). The frontal sinus has a variable relationship to the anterior orbital roof. The other major structures around the orbit are the anterior cranial fossa superiorly (containing the frontal lobe) and the temporal fossa laterally (containing the temporalis muscle). The roof of the ethmoidal complex, delineated by the frontal ethmoidal suture (top of the ethmoidal bone, or lamina papyracea), marks the inferior boundary of the anterior cranial fossa. It is important to realize that surgical intervention above this anatomical

Frontal bone

Superior orbitalfissure

Greater wing ofsphenoid boneZygomatic bone

Inferior orbitalfissure

Lesser wing ofsphenoid bone

Optic canal

Maxillary bone

Lacrimal bone

Lacrimal fossa

A

B

Sphenoid body

Lesser wing ofsphenoid bone

Anterior clinoidOptic strut

Optic canal

Superior orbitalfissure

D

Frontal nerve

Superiorrectus muscleSuperior CN IIISuperior ophthalmic veinOphthalmic arteryCN VI

Lateral rectusmuscleInferiorophthalmic vein

Levator muscle

CN IV

Optic nervesheath

Nasociliarynerve

Inferior CN III

Inferior rectusmuscle

Optic nerve

Superioroblique muscle

Optic nerveAnnulus of Zinn

Medial rectusmuscleOphthalmicarteryInferior rectusmuscleInferiorophthalmic vein

Trochlear nerveFrontal nerveLacrimal nerveSuperiorophthalmic veinOculomotor nerve (superior division)

Lateral rectusmuscle

Abducens nerveNasociliary nerve

Oculomotor nerve(inferior division)

Zygomatic nerve

Levator muscle

Superior rectusmuscle

C

Ethmoidal bone

Figure 1-2 (continued) C, Anatomy of the orbital apex. The 4 rectus muscles arise from the annulus of Zinn. CNs II, III (superior and inferior branches), and VI and the nasociliary nerve all course through the annulus of Zinn. CN IV, the frontal and lacrimal nerves, and the ophthalmic veins are located outside the annulus. D, Anatomical dissection just anterior to the superior orbital fissure. (Parts A and C illustrations by Dave Peace; parts B and D courtesy of Albert L. Rhoton Jr, MD.)

Chapter 1: Neuro-Ophthalmic anatomy ● 9

landmark—as occurs, for example, during endoscopic sinus surgery—can result in entry into the anterior cranial fossa or a cerebrospinal fluid (CSF) leak.

The sphenoid sinus forms the medial wall of the optic canal (Fig 1-5). Surgery within the sphenoid sinus has the potential to damage the optic nerve; alternatively, the sphenoid sinus is a surgical route facilitating decompression of the optic chiasm. In approximately

Supraorbital notch

A (Roof) B (Lateral)

C (Floor)

Frontal boneFrontozygomaticsutureZygomatic bone

Maxillary sinus

Lacrimalbone

Ethmoidalbone

Ethmoidal boneFrontoethmoidal suture

Frontal bone

Zygomatic boneInferior orbital fissureMaxillary bone

Greater wing,sphenoid bone

Lesser wing,sphenoid bone

Palatine bone

Superiororbital fissure

Anterior clinoidprocess

Frontosphenoidsuture

Greater wing,sphenoid bone

Inferior orbital fissureGreater wing,sphenoid bonePalatine bone

Inferior orbital groove

Zygomatic boneMaxillary bone(orbital plate)

Infraorbital foramen

D (Medial)

Lacrimal bone

Frontal bone

Maxillary sinusMaxillary bone

Post. lacrimal crestAnt. lacrimal crest

Lacrimal fossaMaxilloethmoidal

sutureSphenoidbone

Frontozygomaticsuture

Nasolacrimal duct

Palatine bone

Figure 1-3 Bony anatomy of the right orbit. A, The orbital roof is composed of 2 bones: (1) the frontal bone and (2) the lesser wing of the sphenoid bone. The frontal sinus lies within the an-terior orbital roof. The supraorbital notch, located within the medial one-third of the superior orbital rim, transmits the supraorbital nerve, a terminal branch of the frontal nerve of the oph-thalmic division of CN V. Medially, the frontal bone forms the roof of the ethmoidal sinus and extends to the cribriform plate. B, The lateral orbital wall is formed by the zygomatic bone and the greater wing of the sphenoid bone. The junction between the lateral orbital wall and the roof is represented by the frontosphenoid and frontozygomatic sutures. Posteriorly, the wall is bordered by the inferior and superior orbital fissures. The sphenoid wing makes up the poste-rior portion of the lateral wall and separates the orbit from the middle cranial fossa. Medially, the lateral orbital wall ends at the inferior and superior orbital fissures. C, The orbital floor is composed of 3 bones: (1) the orbital plate of the maxillary bone, (2) the maxillary process of the zygomatic bone, and (3) the palatine bone. The nasolacrimal duct sits in the anterior me-dial area of the orbital floor, medial to the origin of the inferior oblique muscle. D, The medial orbital wall is formed by 4 bones: (1) maxillary (frontal process), (2) lacrimal, (3) sphenoid, and (4) ethmoidal. The largest component of the medial wall is the lamina papyracea of the eth-moidal bone. Superiorly, the anterior and posterior foramina at the level of the frontoethmoidal suture transmit the anterior and posterior ethmoidal arteries, respectively. The anterior medial orbital wall includes the lacrimal sac fossa, formed by the maxillary and lacrimal bones. The lacrimal bone is divided by the posterior lacrimal crest. The anterior part of the lacrimal sac fossa is formed by the anterior lacrimal crest of the maxillary bone. (Illustrations by Dave Peace.)