Evan H. Black (editor) - Smith and nesis Ophthalmic Plastic and Reconstructive Surgery

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Part 1
Anatomy

Evan H. Black , Frank A. Nesi , Christopher J. Calvano , Geoffrey J. Gladstone and Mark R. Levine (eds.) Smith and Nesis Ophthalmic Plastic and Reconstructive Surgery 10.1007/978-1-4614-0971-7_1

Springer Science+Business Media, LLC 2012

1. Anatomy of the Ocular Adnexa, Orbit, and Related Facial Structures

Bradley N. Lemke 1 and Mark J. Lucarelli 2

(1)

University of Wisconsin School of Medicine and Public Health, Madison, WI 53717, USA

(2)

Department of Oculoplastics Service, Ophthalmology & Visual Sciences, University of Wisconsin Hospital and Clinics, 600 Highland Avenue, F4/348 CSC, Madison, WI 53792, USA

Mark J. Lucarelli

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Abstract

Understanding the structural abnormalities and the corrective surgical procedures described in this volume is predicated on a familiarity with normal anatomy. This chapter is designed to discuss this anatomy in sufficient detail and to provide key past and current references so as to be useful to the physician and surgeon working in this area.

Understanding the structural abnormalities and the corrective surgical procedures described in this volume is predicated on a familiarity with normal anatomy. This chapter is designed to discuss this anatomy in sufficient detail and to provide key past and current references so as to be useful to the physician and surgeon working in this area.

Osteology

Orbital Shape and Development

The confines and the relationships of the orbits are best understood by examining a skull (Fig. ].

Fig. 1.1

Anteroposterior view of adult skull

The adult lateral orbital walls are approximately 90 from each other, or 45 from anteroposterior. The medial orbital walls are nearly straight anteroposterior, angling slightly medial anteriorly. The divergent axis of each orbit thus becomes half of 45, or about 23 (Fig. ). The eyes tend to diverge in accordance with their bony surroundings, as is seen in individuals with acquired visual loss, under general anesthesia, or in death. It is not surprising to find the medial rectus, the thickest of the rectus muscles, because of the constant demand on it for torsion of the globe away from the orbital axis.

Fig. 1.2

Horizontal section through orbits. Medial walls are nearly parallel and lateral walls diverge 45 from midline

Facial development occurs from processes evident in the third week of development. The mandibular swellings are the most caudal and initially are separated by a midline depression. The frontonasal process is rostral with symmetric halves and is separated from the former by the median stomodeum, or primitive mouth, and laterally by the paired maxillary processes (Fig. ). The frontonasal and mandibular processes form the central face and mandible, respectively, while the maxillary processes later approach the midline to form the malar eminences.

Fig. 1.3

Facial development. ( a ) Frontonasal and mandibular processes separated by maxillary processes and mouth. ( b ) Lacrimal groove develops between lateral nasal and maxillary processes. ( c ) Medial expansion of maxillary processes forming lateral wall and floor of orbit. Medial wall is formed by lateral nasal process and roof by frontal process. ( d ) Medial nasal processes fuse, forming upper lip and hard palate

The lateral nasal process lies medial to the eye and fuses with the maxillary process situated beneath and lateral to the eye, thus forming the medial, inferior, and lateral orbital walls. The orbital roof is formed by the capsule of the developing forebrain. The enlarging globe stretches the surrounding connective tissue making it fairly dense and a relative restraint to further embryologic modeling in this area []. Within these condensed fibrous plates, numerous ossification centers first appear around the seventh week. Ossification of the orbital walls is completed by birth except at the orbital apex. The lesser wing of the sphenoid is initially cartilaginous, unlike the greater sphenoid wing and the other membranous orbital bones. The orbital walls are derived from cranial neural crest cells, which expand to form the frontonasal and maxillary processes.

The orbit most closely resembles a four-sided pyramid that becomes three-sided near the apex. The side lost is the floor, which is cut off by the inferior orbital fissure at two-thirds the orbital depth. The widest portion is 1 cm behind the orbital rim corresponding to the equator of the globe. The relative narrowing of the orbital rim is minimal at birth but proceeds with facial growth, especially with expansion of the frontal and maxillary sinuses. The depth of the orbit measured from the apex to the center of the orbital margin is approximately 45 mm, with substantial variation between individuals and slight differences between sides of an individual.

Orbital Margin

The adult orbital rim is a discontinuous spiral. It is roughly rectangular with a horizontal dimension of 40 mm and a vertical dimension of 32 mm. The zygomatic bone forms most of the lateral margin and the lateral half of the inferior rim (see Figs. ). This orbital protector or facial buttress can withstand severe trauma before fracture which usually occurs along the suture lines. Steps may then be felt inferiorly at the zygomaticomaxillary suture and superolaterally at the zygomaticofrontal suture. The frontal bone encompasses the superior orbital margin and extends laterally and medially to form portions of these borders. The newborn superior orbital rim is sharp. It remains so in the female but becomes rounded with development in the male. Medially between the superior orbits is the smooth glabellar area below which the nasal bones arise. In most skulls, the medial superior rim is indented by a supraorbital notch formed by the supraorbital nerve and artery rising to the forehead. In some skulls, the bone covers these structures, forming a foramen.

Fig. 1.4

Bones of orbit

The medial orbital margin is formed anteriorly by the maxillary bone rising to meet the maxillary process of the frontal bone. The lacrimal excretory sac complicates the medial rim by indenting the bone and forming anterior (maxillary bone) and posterior (lacrimal bone) crests (see the Sect. ].

The infraorbital nerve and attendant artery exit 4 mm or more below the inferior rim medially. In two thirds of skulls, a supraorbital notch can be found along the superomedial rim []. A foramen is seen instead of a notch in other skulls. The possibility of this variation should be considered during coronal or endoscopic brow lifting. The supraorbital ridge lies above the medial one half of the orbit.

Orbital Walls

The triangular orbital roof is formed primarily by the orbital plate of the frontal bone (Figs. ].

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