Atlas of Anatomy

33 Orbit & Eye

Bones of the Orbit

Fig. 33.1 Bones of the Orbit

Muscles of the Orbit

Fig. 33.2 Extraocular muscles
Right eye, superior view (except A). The eyeball is moved by six extrinsic muscles: four rectus (superior, inferior, medial, and lateral) and two oblique (superior and inferior).

Fig. 33.3 Cardinal directions of gaze
There are six cardinal directions of gaze, all of which are tested during clinical evaluation of ocular motility. Note: Each gaze requires activation of two different muscles (not a muscle pair) and therefore two cranial nerves.

Fig. 33.4 Innervation of the extraocular muscles
Right eye, lateral view with the temporal wall of the orbit removed.

Clinical

Oculomotor palsies

Oculomotor palsies may result from a lesion involving an eye muscle or its associated cranial nerve (at the nucleus or along the course of the nerve). If one extraocular muscle is weak or paralyzed, deviation of the eye will be noted. Impairment of the coordinated actions of the extraocular muscles may cause the visual axis of one eye to deviate from its normal position. The patient will therefore perceive a double image (diplopia).

Neurovasculature of the Orbit

Fig. 33.5 Veins of the orbit
Lateral view of the right orbit. Removed: Lateral orbital wall. Opened: Maxillary sinus.

Fig. 33.6 Arteries of the orbit
Superior view of the right orbit. Opened: Optic canal and orbital roof.

Fig. 33.7 Innervation of the orbit
Lateral view of the right orbit. Removed: Temporal bony wall.

Fig. 33.8 Cranial nerves in the orbit
Superior view of the anterior and middle cranial fossae. Removed: Cavernous sinus (lateral and superior walls), orbital roof, and periorbita (portions). The trigeminal ganglion has been retracted laterally.

Topography of the Orbit

Fig. 33.9 Neurovascular structures of the orbit
Anterior view. Right side: Orbicularis oculi removed. Left side: Orbital septum partially removed.

Fig. 33.10 Passage of neurovascular structures through the orbit
Anterior view. Removed: Orbital contents. Note: The optic nerve and ophthalmic artery travel in the optic canal. The remaining structures pass through the superior orbital fissure.

Fig. 33.11 Neurovascular contents of the orbit
Superior view. Removed: Bony roof of orbit, peritorbita, and retro-orbital fat.

Orbit & Eyelid

Fig. 33.12 Topography of the orbit
Sagittal section through the right orbit, medial view.

Fig. 33.13 Eyelids and conjuctiva
Sagittal section through the anterior orbital cavity.

Fig. 33.14 Lacrimal apparatus
Right eye, anterior view. Removed: Orbital septum (partial). Divided: Levator palpebrae superioris (tendon of insertion).

Clinical

Lacrimal drainage

Perimenopausal women are frequently subject to chronically dry eyes (keratoconjunctivitis sicca), due to insufficient tear production by the lacrimal gland. Acute inflammation of the lacrimal gland (due to bacteria) is less common and characterized by intense inflammation and extreme tenderness to palpation. The upper eyelid shows a characteristic S-curve.

Eyeball

Fig. 33.15 Structure of the eyeball
Transverse section through right eyeball, superior view. Note: The orbital axis (running along the optic nerve through the optic disk) deviates from the optical axis (running down the center of the eye to the fovea centralis) by 23 degrees.

Fig. 33.16 Blood vessels of the eyeball
Transverse section at the level of the optic nerve, superior view. The arteries of the eye arise from the ophthalmic artery, a terminal branch of the internal carotid artery. Blood is drained by four to eight vorticose veins that open into the superior and inferior ophthalmic veins.

Clinical

Optic fundus

The optic fundus is the only place in the body where capillaries can be examined directly. Examination of the optic fundus permits observation of vascular changes that may be caused by high blood pressure or diabetes. Examination of the optic disk is important in determining intracranial pressure and diagnosing multiple sclerosis.

Cornea, Iris & Lens

Fig. 33.17 Cornea, iris, and lens
Transverse section through the anterior segment of the eye. Anterosuperior view.

Fig. 33.18 Iris
Transverse section through the anterior segment of the eye. Anterosuperior view.

Clinical

Glaucoma

Aqueous humor produced in the posterior chamber passes through the pupil into the anterior chamber. It seeps through the spaces of the trabecular meshwork into the canal of Schlemm and enters the venous sinus of the sclera before passing into the episcleral veins. Obstruction of aqueous humor drainage causes an increase in intraocular pressure (glaucoma), which constricts the optic nerve in the lamina cribrosa. This constriction eventually leads to blindness. The most common glaucoma (approximately 90% of cases) is chronic (open-angle) glaucoma. The more rare acute glaucoma is characterized by red eye, strong headache and/or eye pain, nausea, dilated episcleral veins, and edema of the cornea.

Fig. 33.19 Pupil
Pupil size is regulated by two intraocular muscles of the iris: the pupillary sphincter, which narrows the pupil (parasympathetic innervation), and the pupillary dilator, which enlarges it (sympathetic innervation).

Fig. 33.20 Lens and ciliary body
Posterior view. The curvature of the lens is regulated by the muscle fibers of the annular ciliary body.

Fig. 33.21 Light refraction by the lens
Transverse section, superior view. In the normal (emmetropic) eye, light rays are refracted by the lens (and cornea) to a focal point on the retinal surface (fovea centralis). Tensing of the zonular fibers, with ciliary muscle relaxation, flattens the lens in response to parallel rays arriving from a distant source (far vision). Contraction of the ciliary muscle, with zonular fiber relaxation, causes the lens to assume a more rounded shape (near vision).