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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.)