Orbit, Orbital Region, and Eyeball G.LUFUKUJA

The orbits The orbits are bony cavities in the facial skeleton that resemble hollow quadrangular pyramids with their bases directed anterolaterally and their apices, posteromedially

The orbits… The orbits contain and protect the eyeballs (globes of eyes) and accessory visual structures, which include the Eyelids, Extraocular muscles, Nerves and vessels in transit to the eyeballs and muscles. Mucous membrane (conjunctiva) lining the eyelids and anterior aspect of the eyeballs and most of the lacrimal apparatus, which lubricates it

The Eyeball The eyeball contains the optical apparatus of the visual system and occupies most of the anterior portion of the orbit. The eyeball proper has three layers: Fibrous layer (outer coat), consisting of the sclera and cornea. Vascular layer (middle coat), consisting of the choroid, ciliary body, and iris. Inner layer (inner coat), consisting of the retina that has both optic and non-visual parts.

Two involuntary muscles of the iris control the size of the pupil: the parasympathetically stimulated sphincter pupillae closes the pupil, and the sympathetically stimulated dilator pupillae opens it

Parasympathetic fibres from the oculomotor nerve supply sphincter pupillae and the ciliary muscle via the ciliary ganglion, and from the facial nerve innervate the lacrimal gland. Sympathetic fibres supply dilator pupillae NOTE: only the parasympathetic fibres synapse in the ganglion.

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Arteries of the Orbit The blood supply of the orbit is mainly from the ophthalmic artery, a branch of the internal carotid artery; the infraorbital artery, from the external carotid artery The central artery of the retina, a branch of the ophthalmic artery arising inferior to the optic nerve, runs within the dural sheath of the optic nerve until it approaches the eyeball The central artery pierces the optic nerve and runs within it, emerging at the optic disc

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Veins of the Orbit Venous drainage of the orbit is through the superior and inferior ophthalmic veins, which pass through the superior orbital fissure and enter the cavernous sinus The scleral venous sinus is a vascular structure encircling the anterior chamber of the eyeball through which the aqueous humor is returned to the blood circulation.

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Applied Anatomy: Glaucoma When drainage of aqueous humor through the scleral venous sinus into the blood circulation decreases significantly, pressure builds up in the anterior and posterior chambers of the eye, a condition called glaucoma. Blindness can result from compression of the inner layer of the eyeball (retina) and the retinal arteries if aqueous humor production is not reduced to maintain normal intraocular pressure G.LUFUKUJA

Extraocular Muscles of the Orbit The extraocular muscles of the orbit are the levator palpebrae superioris, four recti (superior, inferior, medial, and lateral), and two obliques (superior and inferior). G.LUFUKUJA

Extraocular Muscles of the Orbit… G.LUFUKUJA

Axes of movements: Depression Elevation Transverse axis G.LUFUKUJA

Axes of movements: Adduction Abduction Vertical axis G.LUFUKUJA

Axes of movements: Intorsion Extorsion Medial movement of the superior pole of the eyeball is intorsion; lateral movement of the superior pole is extorsion. L M Antero-posterior axis G.LUFUKUJA

Common tendinous ring G.LUFUKUJA

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Oblique muscles: Superior oblique: It arises from the undersurface of the lesser wing above and medial to the common tendinous ring The tendon of the muscle passes through a fibro-cartilaginous pulley and is inserted into the sclera behind the equator in postero-superior quadrant of the eyeball Abducts, depresses, and medially rotates eyeball Inervated by Trochlear nerve (CN IV) G.LUFUKUJA

Inferior oblique: It arises from the orbital surface of maxilla in the floor of the orbit Inserted into the sclera behind the equator in the postero-superior quadrant of the eyeball Abducts, elevates, and laterally rotates eyeball Inervated by Oculomotor nerve (CN III) G.LUFUKUJA

Superior rectus It arise from a common tendinous ring It attaches at the sclera just posterior to corneoscleral junction Its function is to elevates, adducts, and rotates eyeball medially Its inervetion is by Oculomotor nerve (CN III) G.LUFUKUJA

Inferior rectus It arise from a common tendinous ring and attaches at the sclera just posterior to corneoscleral junction Its function is to depresses, adducts, and rotates eyeball medially Its inervetion is by Oculomotor nerve (CN III) G.LUFUKUJA

Medial rectus It arise from a common tendinous ring and attaches at the sclera just posterior to corneoscleral junction Its function is to Adducts eyeball Its inervetion is by Oculomotor nerve (CN III) G.LUFUKUJA

Lateral rectus It arise from a common tendinous ring and attaches at the sclera just posterior to corneoscleral junction Its function is to Abducts eyeball Its inervetion is by Abducent nerve (CN VI) G.LUFUKUJA

Levator palpebrae superioris It arises from lesser wing of sphenoid bone, superior and anterior to optic canal and attaches to the Superior tarsus and skin of superior eyelid It is innervated by oculomotor nerve; deep layer (superior tarsal muscle) is supplied by sympathetic fibers Its function is to elevates superior eyelid G.LUFUKUJA

Summary of the Nerve supply: Lateral rectus - Abducent nerve (CN 6) Medial rectus - Oculomotor nerve (CN3) Superior rectus - Oculomotor nerve (CN3) Inferior rectus - Oculomoter nerve (CN3) Inferior oblique - Oculomotor nerve (CN3) Superior oblique - Trochlear nerve (CN4) S O4; L R6 G.LUFUKUJA

Action of individual muscles: MEDIAL LATERAL Elevation Superior rectus Inferior oblique A B D U C T I O N A D U C T I O N Extorsion Intorsion Lateral rectus Medial rectus Extorsion Intorsion superior oblique Inferior rectus Depression G.LUFUKUJA

Lateral and Medial Recti Lateral Rectus Basic function is to ABDUCT the eye Innervated by cranial nerve VI, the abducens nerve Medial Rectus Basic function is to ADDUCT the eye Innervated by cranial nerve III, the oculomotor nerve

Superior Rectus Inferior oblique Basic function is to ELEVATE the eye Tested by asking the patient to look up while the eye is abducted Innervated by cranial nerve III Inferior oblique Basic functions are EXTORSION and ELEVATION of the eye Tested by asking the patient to look up while the eye is adducted

Inferior Rectus Superior Oblique Basic function is to DEPRESS the eye Tested by asking the patient to look down while the eye is abducted Innervated by cranial nerve III Superior Oblique Basic functions are INTORSION and DEPRESSION of the eye Tested by asking the patient to look down while the eye is adducted Innervated by cranial nerve IV, the trochlear nerve

Eye movements produced by muscles: No movement is done by a single muscle, while some muscle acts as a prime movers and other acts as synergists MOVEMENT MUSCLE Adduction Medial rectus, assisted by superior and inferior recti Abduction Lateral rectus, assisted by the superior and inferior oblique muscles Elevation Superior rectus and inferior oblique muscles Depression Inferior rectus and superior oblique muscles Intorsion Superior rectus and inferior oblique Extorsion Inferior rectus and inferior oblique G.LUFUKUJA

Lacrimal Apparatus The lacrimal apparatus consists of the: Lacrimal glands: secrete lacrimal fluid, a watery physiological saline containing the bacteriocidal enzyme lysozyme. The fluid moistens and lubricates the surfaces of the conjunctiva and cornea and provides some nutrients and dissolved oxygen to the cornea; when produced in excess, it constitutes tears. Lacrimal ducts: convey lacrimal fluid from the lacrimal glands to the conjunctival sac.

Lacrimal Apparatus…

Lacrimal canaliculi Lacrimal canaliculi: commence at a lacrimal punctum (opening) on the lacrimal papilla near the medial angle of the eye and drain lacrimal fluid from the lacrimal lake (L. lacus lacrimalis; a triangular space at the medial angle of the eye where the tears collect) to the lacrimal sac (the dilated superior part of the nasolacrimal duct). Nasolacrimal duct: conveys the lacrimal fluid to the inferior nasal meatus.

Lacrimal fluid Production of lacrimal fluid is stimulated by parasympathetic impulses from CN VII. When the cornea becomes dry, the eye blinks. The eyelids come together in a lateral to medial sequence pushing a film of fluid medially over the cornea, somewhat like windshield wipers when washing the car windshield In addition to cleansing particles and irritants from the conjunctival sac, lacrimal fluid provides the cornea with nutrients and oxygen.

Applied Anatomy: Weakness or paralysis of a muscle causes squint/strabismus. In this condition the two eyes appear to look in different directions Nystagmus is characterised by involuntary oscillatory movements of the eyes. This in due to incordination of the ocular muscles G.LUFUKUJA

Ear The ear consists of external, middle, and internal parts. The external and middle parts are mainly concerned with the transference of sound to the internal ear, which contains the organ for equilibrium (the condition of being evenly balanced) as well as for hearing. G.LUFUKUJA

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Applied anatomy – Acute Otitis Externa Otitis externa is an inflammation of the external acoustic meatus. The infection often develops in swimmers who do not dry their meatus after swimming and/or use ear drops, but it may also be the result of a bacterial infection of the skin lining the meatus. The affected individual complains of itching and pain in the external ear. Pulling the auricle or applying pressure on the tragus increases the pain. G.LUFUKUJA

NASAL CAVITY

Nasal Cavity The nasal cavity is entered anteriorly through the nares. It opens posteriorly into the nasopharynx through the choanae. G.LUFUKUJA

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Vasculature and Innervation of the Nose G.LUFUKUJA

Innervation of nasal cavity G.LUFUKUJA

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Applied anaomy- Rhinitis The nasal mucosa becomes swollen and inflamed (rhinitis) during severe upper respiratory infections and allergic reactions (e.g., hayfever). Swelling of the mucosa occurs readily because of its vascularity. Infections of the nasal cavities may spread to the: Anterior cranial fossa through the cribriform plate. Nasopharynx and retropharyngeal soft tissues. Middle ear through the pharyngotympanic tube (auditory tube), which connects the tympanic cavity and nasopharynx. Paranasal sinuses. Lacrimal apparatus and conjunctiva G.LUFUKUJA

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Applied anaomy- Epistaxis Epistaxis (nosebleed) is relatively common because of the rich blood supply to the nasal mucosa. In most cases, the cause is trauma and the bleeding is from an area in the anterior third of the. Epistaxis is also associated with infections and hypertension. Spurting of blood from the nose results from rupture of arteries. G.LUFUKUJA

Paranasal Sinuses The paranasal sinuses are air-filled extensions of the respiratory part of the nasal cavity into the following cranial bones: frontal, ethmoid, sphenoid, and maxilla G.LUFUKUJA

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Applied anatomy -Sinusitis Because the paranasal sinuses are continuous with the nasal cavities through apertures that open into them, infection may spread from the nasal cavities, producing inflammation and swelling of the mucosa of the sinuses (sinusitis) and local pain. Sometimes several sinuses are inflamed (pansinusitis), and the swelling of the mucosa may block one or more openings of the sinuses into the nasal cavities. G.LUFUKUJA