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The primary organ responsible for vision is the eye. The eyeball is located within a bony orbital encasement, which protects it. The lacrimal apparatus keeps the eye moist and free of dust and other irritating particles through the production and drainage of tears. Eyelids protect the eye from external stimuli such as dust, wind, and excessive light.
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The bony orbit is the region of the skull that surrounds the eye and is composed of the following structures and openings (Figure 18-1A):
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Bones. Formed by parts of the parietal, frontal, lacrimal, ethmoid, maxilla, zygomatic, and sphenoid bones.
Supraorbital foramen. Transmits the supraorbital nerve [cranial nerve (CN) V-1] and vessels to the scalp.
Infraorbital foramen. Transmit the infraorbital nerve (CN V-2) and vessels to the maxillary region of the teeth and face.
Anterior and posterior ethmoidal foramina. Transmits the anterior and posterior ethmoidal nerves and vessels to the nasal cavity and the sphenoid and ethmoid sinuses.
Nasolacrimal canal. Drains tears from the eye to the inferior meatus in the nasal cavity.
Optic canal. Transmits the optic nerve (CN II) and the ophthalmic artery.
Superior orbital fissure. Transmits CNN III, IV, V-1, and VI and superior ophthalmic veins.
Inferior orbital fissure. Communicates with the infratemporal and pterygopalatine fossae and maxillary sinus; transmits CN V-2 and the infraorbital artery and vein.
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The lacrimal gland lies in the superolateral corner of the orbit (Figure 18-1B).
Tears. The lacrimal gland secretes tears that spread evenly over the eyeball through blinking and cleanse the eye of dust and foreign particles.
Drainage. Tears drain from the eyeball, via the nasolacrimal duct, into the inferior nasal meatus of the nasal cavity.
Innervation. The lacrimal gland is innervated by the greater petrosal nerve (a branch from CN VII) (Figure 18-4C).
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Watery eyes. The mucosa of the nasal cavity is continuous with the mucosa of the nasolacrimal duct system and as such a cold or “stuffy” nose often causes the lacrimal mucosa to become inflamed and swollen. Swelling constricts the ducts and prevents tears from draining from the eye surface, causing “watery” eyes.▼
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Eyelids protect the eye from foreign particles and from bright light (Figure 18-1C). The ...