Fig. 41.1 Ossa orbitae
Table 41.2 Structures surrounding the orbita
Direction |
Bordering structure |
Superior |
Sinus frontalis |
Fossa cranii anterior |
|
Medial |
Cellulae ethmoidales |
Inferior |
Sinus maxillaris |
Certain deeper structures also have a clinically important relationship to the orbita: |
|
Sinus sphenoidalis |
Hypophysis (pituitary) |
Fossa cranii media |
Sinus cavernosus |
Chiasma opticum |
Fossa pterygopalatina |
Fig. 41.2 Musculi externi bulbi oculi
The bulbus oculi is moved by six mm. externi: four mm. recti (superior, inferior, medialis, and lateralis) and two mm. obliqui (superior and inferior).
Fig. 41.3 Actions of the musculi externi bulbi oculi
Superior view of opened orbita. Vertical axis, red circle; horizontal axis, black; anteroposterior (visual/optical) axis, blue.
Fig. 41.5 Innervation of the musculi externi bulbi oculi
Right eye, lateral view with the paries lateralis orbitae removed.
Oculomotor palsies
Oculomotor palsies may result from a lesion involving a m. externus bulbi oculi or its associated n. cranialis (at the nucleus or along the course of the nerve). If one m. externus bulbi oculi is weak or paralyzed, deviation of the eye will be noted. Impairment of the coordinated actions of the mm. externi bulbi oculi may cause the visual axis of one oculus to deviate from its normal position. The patient will therefore perceive a double image (diplopia).
Fig. 41.6 Veins of the orbita
Lateral view of the right orbita. Removed: Paries lateralis orbitae. Opened: Sinus maxillaris.
Fig. 41.7 Arteries of the orbita
Superior view of the right orbita. Opened: Canalis opticus and paries superior orbitae.
Cavernous sinus syndrome
Gravity allows venous blood from the danger triangle region of the face (see figure) to drain to the sinus cavernosus via the valveless vv. ophthalmicae. Squeezing a pimple or boil in this facial region can result in infectious thrombi being forced into the venous system and passing back into the sinus cavernosus. Cavernous sinus syndrome (CIS) is diagnosed by the loss of eyeball movement due to the various nn. craniales associated with the sinus cavernosus becoming infected.
The n. abducens (CN VI) is bathed in blood within the sinus, the first ocular movement to be affected is lateral deviation of the bulbus oculi. The nn. oculomotorius (CN III) and trochlearis (CN IV), embedded in the dural lateral wall of the sinus, are also eventually affected as the infection penetrates the dura. The bulbus oculi becomes frozen in the orbita as all nerves activating the mm. externi bulbi oculi become infected. CN V1 is also in the lateral dural wall, so a tingling/parasthesia is felt in the sensory region covered (sinciput). Occasionally CN V2 may also be involved and this parasthesia may also extend to the skin of the facies below the orbita. The sinus intercavernosi allow the infection to spread to the sinus cavernosus on the opposite side. If left untreated, death can result; however, cavernous sinus septic thrombophlebitis mortality has decreased from 100% to 20% with the of improvements in diagnosis and treatment.
Fig. 41.8 Innervation of the orbita
Lateral view of the right orbita. Removed: Paries lateralis orbitae.
Fig. 41.9 Nervi craniales in the orbita
Superior view of the fossae cranii anterior and media. Removed: Sinus cavernosus (lateral and superior walls), paries superior orbitae, and periorbita (portions). The ganglion trigeminale has been retracted laterally.
Fig. 41.10 Neurovascular structures of the orbita
Anterior view. Right side: M. orbicularis oculi removed. Left side: Septum orbitale partially removed.
Fig. 41.11 Passage of neurovascular structures through the orbita
Anterior view. Removed: Orbital contents. Note: The n. opticus and a. ophthalmica travel in the canalis opticus. The remaining structures pass through the fissura orbitalis superior.
Fig. 41.12 Neurovascular contents of the orbita
Superior view. Removed: Bony paries superior orbitae, peritorbita, and corpus adiposus orbitae.
Fig. 41.15 Apparatus lacrimalis
Right eye, anterior view. Removed: Septum orbitale (partial). Divided: M. levator palpebrae superioris (tendo of insertion).
Lacrimal drainage
Perimenopausal women are frequently subject to chronically dry eyes (keratoconjunctivitis sicca), due to insufficient tear production by the gl. lacrimalis. Acute inflammation of the gl. lacrimalis (due to bacteria) is less common and characterized by intense inflammation and extreme tenderness to palpation. The upper eyelid shows a characteristic S-curve.
Fig. 41.16 Structure of the bulbus oculi
Transverse section through right bulbus oculi, superior view. Note: The orbital axis (running along the n. opticus through the discus nervi optici) deviates from the axis opticus (running through the center of the eye to the fovea centralis) by 23 degrees.
Fig. 41.17 Blood vessels of the bulbus oculi
Transverse section through the right bulbus oculi at the level of the n. opticus, superior view. The arteries of the oculus arise from the a. ophthalmica, a terminal branch of the a. carotis interna. Blood is drained by four to eight vv. vorticosae that open into the vv. ophthalmicae superior and inferior.
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 discus nervi optici is important in determining intracranial pressure and diagnosing multiple sclerosis.
Fig. 41.18 Cornea, iris, and lens
Transverse section through the anterior segment of the eye. Anterosuperior view.
Glaucoma
Humor aquosus produced in the camera posterior passes through the pupilla into the camera anterior. It seeps through the spaces of the reticulum trabeculare into the sinus venosus sclerae (canal of Schlemm) before passing into the vv. episclerales. Obstruction of humor aquosus drainage causes an increase in intraocular pressure (glaucoma), which constricts the n. opticus in the lamina cribrosa sclerae. 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 vv. episclerales, and edema of the cornea.
Fig. 41.20 Pupilla
Pupilla size is regulated by two intraocular muscles of the iris: the m. sphincter pupillae, which narrows the pupilla (parasympathetic innervation), and the m. dilatator pupillae, which enlarges it (sympathetic innervation).
Fig. 41.21 Lens and corpus ciliare
Posterior view. The curvature of the lens is regulated by the muscle fibers of the annular corpus ciliare.
Fig. 41.22 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 fibrae zonulares, with relaxation of the m. ciliaris, flattens the lens in response to parallel rays arriving from a distant source (far vision). Contraction of the m. ciliaris, with relaxation of fibrae zonulares, causes the lens to assume a more rounded shape (near vision).
Clinical box 41.1
