Orbit, Orbital Region, and Eyeball

Learning Objectives Knowledge of the anatomy of the normal nasolacrimal system To describe the anatomy of the orbit and its contents To describe the extra ocular muscles and their nervesupply,

actions and applied importance Be able to describe the anatomy of the eyeball

Orbit: Quadrangular pyramids Bases directed

anterolaterally Apex directed

posteromedially. Medial wall separated by

the ethmoidal sinuses and the upper parts of the nasal cavity

Lateral walls are nearly at a right (90°) angle.

Orbit, Orbital Region, and Eyeball

Orbit contains: Eyelids, bound the orbit anteriorly. Orbital fascia surrounding the eyeballs and muscles. Extraocular muscles. Nerves and vessels in transit to the eyeballs and muscles Mucous membrane (conjunctiva) lining the eyelids and anterior aspect of

the eyeballs Lacrimal apparatus Orbital Fat

Orbit, eyeball, and eyelids. A. The contents of the orbit are shown. The subarachnoid space around the optic nerve is continuous with the space between the arachnoid and the pia covering the brain. The numbers refer to structures labeled in part C. B. This MRI study shows a sagittal section through the optic nerve (CN II) and eyeball. M, maxillary sinus; S, superior ophthalmic vein; arc, optic canal. C. This detail shows the superior eyelid. The tarsus forms the skeleton of the eyelid and contains tarsal glands.

Base: outlined by the orbital margin that surrounds the orbital opening.

Apex: at the optic canal in the lesser wing of the sphenoid just medial to the superior orbital fissure.

Orbit

Lateral wall: Formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid.

Medial walls: Formed primarily by the Ethmoid boneFrontalLacrimalSphenoids. Anteriorly, indented by the lacrimal

groove and fossa for the lacrimal sac.

Inferior wall (floor): Formed mainly by the

maxilla and partly by the zygomatic and palatine bones.

Demarcated from the lateral wall of the orbit by the inferior orbital fissure.

Superior wall (roof): Formed mainly by Orbital part of the frontal

bone Lesser wing of the

sphenoid.

Periorbita (periosteum of orbit): Continuous at the optic canal and superior orbital fissure with the

periosteal layer of the dura mater. Continuous over the orbital margins and through the inferior orbital

fissure with the periosteum covering the external surface of the cranium (pericranium), and with the orbital septa at the orbital margins, with the fascial sheaths of the extraocular muscles, and with orbital fascia that forms the fascial sheath of the eyeball .

Periorbital Ecchymosis Loose nature of the

subcutaneous tissue within the eyelids, even a relatively slight injury or inflammation may result in an accumulation of fluid, causing the eyelids to swell.

Significant swelling and hemorrhage into the eyelids and extravasation of blood into the periorbital skin (ecchymosis) occur. This type of injury is common in boxers.

Fractures of the Orbit Indirect traumatic injury that

displaces the orbital walls is called a blowout fracture.

Thinness of the medial and inferior walls of the orbit commonly involved

Fractures of the medial wall may involve the ethmoidal and sphenoidal sinuses

Fractures of the inferior wall may involve the maxillary sinus.

Fracture of the superior wall may involve the frontal lobe of the brain due to penetrating injury.

Looking Straight aheadA

B Looking upwards

Fractures of the Orbit Result in intraorbital bleeding, which

exerts pressure on the eyeball, causing exophthalmos (protrusion of the eyeball).

Trauma to the eye may affect adjacent structures for example Bleeding into the maxillary sinus, Displacement of maxillary teeth Fracture of nasal bones resulting in

hemorrhage, airway obstruction Infection may spread to the cavernous

sinus through the ophthalmic vein.

Exophthalmos

Orbital Tumors Closeness of the optic nerve

to the sphenoidal and posterior ethmoidal sinuses, a malignant tumor in these sinuses may erode the thin bony walls of the orbit and compress the optic nerve and orbital contents.

Tumors in the orbit produce exophthalmos.

Orbital Sarcoid -primarily involving the lacrimal gland

A child with orbital extension of retinoblastoma

Fascial Sheath of the Eyeball: (L. fascia bulbi, Tenon capsule): Envelops the eyeball from the optic

nerve nearly to the corneoscleral junction, forming the actual socket for the eyeball.

Triangular expansions from the sheaths of the medial and lateral rectus muscles, called the medial and lateral check ligaments, are attached to the lacrimal and zygomatic bones, respectively.

A blending of the check ligaments with the fascia of the inferior rectus and inferior oblique muscles forms a hammock-like sling, the suspensory ligament of the eyeball.

Pierced by the tendons of the extraocular muscles.

Eyelids Movable folds.

Cover the eyeball anteriorly and protect from injury and excessive light.

Keep the cornea moist by spreading the lacrimal fluid.

Covered externally by thin skin and internally by transparent mucous membrane, the palpebral conjunctiva.

Palpebral conjunctiva reflects onto the eyeball and continue with the bulbar conjunctiva.

Bulbar conjunctiva: thin and transparent and attaches loosely to the anterior surface of the eyeball. It is loose and wrinkled over the sclera and adherent to the periphery of the cornea.

Conjunctival fornices : the lines of reflection of the palpebral conjunctiva onto the eyeball form deep recesses, the superior and inferior conjunctival fornices.

Conjunctival sac: the space bound by the palpebral and bulbar conjunctivae.

Closed space when the eyelids are closed, but opens via an anterior aperture, the palpebral fissure.

Mucosal bursa that enables the eyelids to move freely over the surface of the eyeball as they open and close.

Eyelids

Superior and Inferior eyelids : strengthened by dense bands of connective tissue, the superior and inferior tarsi (sing. tarsus).

Tarsal glands: Embedded in the tarsi

Lipid secretion of which lubricates the edges of the eyelids

Prevents sticking together when eyelids are closed.

Lipid secretion also forms a barrier that lacrimal fluid does not cross when produced in normal amounts.

Eyelashes are in the margins of the lids.

Sebaceous glands associated with the eyelashes are ciliary glands.

Junctions of the superior and inferior eyelids make up the medial and lateral palpebral commissures

Each eye has medial and lateral angles, or canthi.

Medial palpebral ligament: present between the nose and the medial angle of the eye, which connects the tarsi to the medial margin of the orbit.

Lateral palpebral ligament: attaches the tarsi to the lateral margin of the orbit

Orbital septum: Weak membrane Spans from the tarsi to the

margins of the orbit Continuous with the periosteum. Limit the spread of infection to

and from the orbit.

Eyelids

Lacrimal ApparatusConsists of the: Lacrimal gland Excretory ducts of the gland Lacrimal canaliculi Lacrimal sac Nasolacrimal duct

Lacrimal gland: Almond shape Approximately 2 cm long Lies in the fossa for the lacrimal gland in the

superolateral part of each orbit.

Divided into superior (orbital) and inferior (palpebral) parts by the lateral expansion of the tendon of the levator palpebrae superioris.

Secrete lacrimal fluid, a watery physiological saline containing the bacteriocidal enzyme lysozyme.

Provides the cornea with nutrients and oxygen.

Moistens and lubricates the surfaces of the conjunctiva and cornea and provides some nutrients and dissolved oxygen to the cornea;

In excess, it constitutes tears.

Lacrimal ducts: convey lacrimal fluid from the lacrimal glands to the conjunctival sac.

Lacrimal canaliculi: Commence at a lacrimal punctum

(opening) on the lacrimal papilla near the medial angle of the eye.

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.

Nerve supply of the lacrimal gland: Presynaptic parasympathetic secretomotor fibers: conveyed from the facial

nerve by the greater petrosal nerve and then by the nerve of the pterygoid canal to the pterygopalatine ganglion, where they synapse with the cell body of the postsynaptic fiber.

Vasoconstrictive, postsynaptic sympathetic fibers, brought from the superior cervical ganglion by the internal carotid plexus and deep petrosal nerve, join the parasympathetic fibers to form the nerve of the pterygoid canal and traverse the pterygopalatine ganglion.

The zygomatic nerve (from the maxillary nerve) brings both types of fibers to the lacrimal branch of the ophthalmic nerve, by which they enter the gland.

Injury to the Nerves Supplying the Eyelids

Lesion of the oculomotor nerve: causes paralysis of the levator palpebrae superioris muscle, and the superior eyelid droops (ptosis).

Damage to the facial nerve: involves paralysis of the orbicularis oculi, preventing the eyelids from closing fully.

Normal rapid protective blinking of the eye is also lost.

Inferior eyelid causes the lid to fall away (evert) from the surface of the eyeball, leading to drying of the cornea.

Irritation of the unprotected eyeball

Eyelid droops (ptosis)

Damage to the facial nerve

Inflammation of the Palpebral Glands If the ducts of the ciliary glands

are obstructed, a painful red suppurative (pus-producing) swelling, a sty (hordeolum), develops on the eyelid.

Cysts of the sebaceous glands of the eyelid, called chalazia, may also form.

Obstruction of a tarsal gland produces inflammation, a tarsal chalazion, that protrudes toward the eyeball and rubs against it as the eyelids blink.

Sty (hordeolum)

Chalazia

Obstruction of a Tarsal gland

Hyperemia of the Conjunctiva Conjunctiva is colorless, except

when its vessels are dilated and congested (bloodshot eyes).

Hyperemia of the conjunctiva is caused by local irritation (e.g., from dust, chlorine, or smoke).

Inflamed conjunctiva, conjunctivitis (pinkeye), is a common contagious infection of the eye.

Grade -1

Grade -2

Grade -3

Grade -4

Subconjunctival Hemorrhages Manifested by bright or dark red

patches deep to and within the bulbar conjunctiva.

Hemorrhages may result from injury or inflammation.

A blow to the eye, excessively hard blowing of the nose, and paroxysms of coughing or violent sneezing can cause hemorrhages resulting from rupture of small subconjunctival capillaries.

Extraocular Muscles of the Orbit: Levator palpebrae superioris Four Recti : Superior, Inferior, Medial, and Lateral Two obliques : Superior and Inferior.

Levator Palpebrae Superioris Bilaminar aponeurosis

Superficial lamina: attaches to the skin of the superior eyelid

Deep lamina: Attaches to the superior tarsus. Smooth muscle fibers, the

superior tarsal muscle, that produce additional widening of the palpebral fissure during a sympathetic response (e.g., fright).

Recti Muscles (L. rectus, straight): Arise from a fibrous cuff, the

common tendinous ring, that surrounds the optic canal and part of the superior orbital fissure.

Extraocular Muscles of the OrbitMuscle Origin Insertion Innervation Main Action

Levator palpebrae superioris

Lesser wing of sphenoid bone

Superior and anterior to optic canal

Superior tarsus and skin of superior eyelid

Oculomotor nerve Deep layer

(superior tarsal muscle) by sympathetic fibers

Elevates superior

eyelid

Extraocular Muscles of the OrbitMuscle Origin Insertion Innervation Main Action

Superior oblique(SO)

Body of sphenoid bone

The tendon passes through a fibrous ring or trochlea, changes its direction, and inserts into sclera deep to superior rectus muscle

Trochlear nerve (CN IV)

Abducts Depresses Medially

rotates the eyeball

Muscle Origin Insertion Innervation ActionsInferior oblique

(IO) Anterior part

of floor of orbit

Sclera deep to lateral rectus muscle

Oculomotor nerve (CN III)

Abducts, elevates

Laterally rotates eyeball

Extraocular Muscles of the Orbit

Muscle Origin Insertion Innervation ActionsSuperior rectus

(SR) Common

tendinous ring

Sclera just posterior to corneoscleral junction

Oculomotor nerve (CN III)

Elevates, adducts Rotates eyeball medially

Muscle Origin Insertion Innervation ActionsInferior rectus

(IR) Common

tendinous ring Sclera just

posterior to corneoscleral junction

Oculomotor nerve (CN III)

Depresses, adducts, and rotates eyeball medially

Muscle Origin Insertion Innervation ActionsMedial rectus

(MR) Common

tendinous ring Sclera just

posterior to corneoscleral junction

Oculomotor nerve (CN III)

Adducts eyeball

Muscle Origin Insertion Innervation ActionsLateral rectus (LR) Common

tendinous ring

Sclera just posterior to corneoscleral junction

Abducent nerve (CN VI)

Abducts eyeball

Nerve supply of the extraocular musclesSO4 LR6 O3

Superior and Inferior Recti and Obliques cause rotation of the eyeball around an anteroposterior axis.

Medial movement of the superior pole of the eyeball is intorsion

Lateral movement of the superior pole is extorsion.

Absence of these movements resulting from nerve lesions contributes to double vision.

Muscle movementsA given extraocular muscle moves the pupil, at the front of the eye, in a specific direction or directions, as follows: Medial rectus (MR): Moves the eye inward, toward the nose: AdductionLateral rectus (LR): Moves the eye outward, away from the nose: AbductionSuperior rectus (SR):

Primarily moves the eye upward: Elevation Secondarily rotates the top of the eye toward the

nose: Intorsion Tertiarily moves the eye inward: Adduction

Inferior rectus (IR): Primarily moves the eye downward: Depression Secondarily rotates the top of the eye away from

the nose: Extorsion Tertiarily moves the eye inward: Adduction

Superior oblique (SO):Primarily rotates the top of the eye toward the nose: Intorsion Secondarily moves the eye downward: Depression Tertiarily moves the eye outward: Abduction

Inferior oblique (IO):Primarily rotates the top of the eye away from the nose: Extorsion Secondarily moves the eye upward: Elevation Tertiarily moves the eye outward: Abduction

In addition to the optic nerve (CN II), the nerves of the orbit include those that enter through the superior orbital fissure and supply the ocular muscles: Oculomotor (CN III) Trochlear (CN IV) Abducent (CN VI) Ophthalmic nerve (CN V1): Frontal, Nasociliary and Lacrimal nerves

Nerves of the Orbit

Ciliary ganglion: located between the optic nerve and the lateral rectus. The ganglion receives nerve fibers from three sources: Sensory fibers: from CN V1 via

the communicating branch of the nasociliary nerve (the sensory or nasociliary root of the ciliary ganglion).

Presynaptic parasympathetic fibers from CN III via the parasympathetic or oculomotor root of the ciliary ganglion.

Postsynaptic sympathetic fibers from the internal carotid plexus via the sympathetic root of the ciliary ganglion.

Corneal Reflex During a neurological examination, the examiner touches the cornea with a

wisp of cotton. A normal (positive) response is a blink. Absence of a blink response suggests a lesion of CN V1; a lesion of CN VII (the

motor nerve to the orbicularis oculi) may also impair this reflex. Examiner must be certain to touch the cornea (not just the sclera) to evoke

the reflex. Presence of a contact lens may hamper or abolish the ability to evoke this

reflex.

Oculomotor Nerve PalsyAffects most of the ocular muscles, the levator palpebrae superioris, and the sphincter pupillae. Superior eyelid droops and cannot

be raised voluntarily because of the unopposed activity of the orbicularis oculi (supplied by the facial nerve).

Pupil fully dilated and non-reactive because of the unopposed dilator pupillae.

Pupil fully abducted and depressed (down and out) because of the unopposed activity of the lateral rectus and superior oblique, respectively.

Horner Syndrome Results from interruption of a cervical

sympathetic trunk Manifest by the absence of sympathetically

stimulated functions on the ipsilateral side of the head.

Includes the following signs: Miosis: Constriction of the pupil because

the parasympathetically stimulated sphincter of the pupil is unopposed

Ptosis: Drooping of the superior eyelid due to paralysis of the smooth muscle fibers inter digitated with the aponeurosis of the levator palpebrae superioris that collectively constitute the superior tarsal muscle, supplied by sympathetic fibers.

Vasodilation: Redness and increased temperature of the skin

Anhydrosis: Absence of sweating .

Paralysis of lateral rectus due to injury to the abducent nerve (CN VI),individual cannot abduct the pupil on the affected side.

Pupil fully adducted by the unopposed pull of the medial rectus.

Paralysis of the Extraocular Muscles: One or more extraocular muscles may be paralyzed by disease in the

brainstem or by a head injury, resulting in diplopia (double vision).

Arteries of the Orbit From the ophthalmic

artery, a branch of the internal carotid artery

Infraorbital artery, from the external carotid artery, also contributes blood to structures related to the orbital floor.

Arteries of the OrbitArtery Origin Course and Distribution

Ophthalmic Internal carotid artery

Traverses optic foramen to reach orbital cavity

Central artery of retina

Ophthalmic artery

Runs in dural sheath of optic nerve Pierces nerve near eyeball Appears at center of optic disc Supplies optic retina (except cones and rods)

Arteries of the OrbitArtery Origin Course and Distribution

Supraorbital Ophthalmic artery

Passes superiorly and posteriorly from supraorbital foramen

Supply forehead and scalp

Supratrochlear Ophthalmic artery

Passes from supraorbital margin to forehead and scalp

Lacrimal Ophthalmic artery

Passes along superior border of lateral rectus muscle Supply lacrimal gland, conjunctiva, and eyelids

Artery Origin Course and Distribution Dorsal

nasalOphthalmic

arteryCourses along dorsal aspect of nose and supplies its surface

Artery Origin Course & distribution Anterior

ciliaryOphthalmic

artery Pierces sclera at

attachments of rectus muscles and forms network in iris and ciliary body

Infraorbital Third part of maxillary artery

Passes along infraorbital groove and foramen to face

Arteries of the OrbitArtery Origin Course and Distribution

Short posterior ciliaries

Ophthalmic artery

Pierce sclera at periphery of optic nerve to supply choroid Supplies cones and rods of optic retina

Long posterior ciliaries

Pierce sclera to supply ciliary body and iris

Arteries of the OrbitArtery Origin Course and Distribution

Posterior ethmoidal

Ophthalmic artery

Passes through posterior ethmoidal foramen to posterior ethmoidal cells

Anterior ethmoidal

Passes through anterior ethmoidal foramen to anterior cranial fossa

Supplies anterior and middle ethmoidal cells, frontal sinus, nasal cavity, and skin on dorsum of nose

Veins of the Orbit:Superior and inferior ophthalmic veins, which pass through the superior orbital fissure and enter the cavernous sinus.

Veins of the Orbit:

Central vein of the retina usually enters the cavernous sinus directly, but it may join one of the ophthalmic veins.

Vortex or vorticose veins from the vascular layer of the eyeball drain into the inferior ophthalmic vein.

Glaucoma: 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.

Blindness can result from compression of the inner layer of the eyeball (retina).

Blockage of the Central Artery of the Retina:

Central artery of the retina are end arteries

Obstruction by an embolus results in instant and total blindness.

Blockage of the artery usually unilateral.

Occurs in older people.

Blockage of the Central Vein of the Retina:

Central vein of the retina enters the cavernous sinus

Thrombophlebitis of the sinus may result in the passage of a thrombus to the central retinal vein

Produce a blockage in one of the small retinal veins.

Occlusion of a branch of the central vein of the retina usually results in slow, painless loss of vision.

Eyeball Contains the optical apparatus of

the visual system

Occupies most of the anterior portion of the orbit.

Has three layers: Fibrous layer Vascular layer Inner layer (Retina)

Eyeball

The three layers of the eyeball are the : 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.

Fibrous Layer: Sclera: Tough opaque part of the fibrous Posterior five sixths of the eyeball. Fibrous skeleton of the eyeball Provide attachment for both the

extrinsic (extraocular) and the intrinsic muscles of the eye.

Anterior part: visible through the transparent bulbar conjunctiva as the white of the eye. �

Cornea: transparent part of the fibrous coat covering the anterior one sixth of the eyeball.

Vascular Layer of the Eyeball: Choroid, Ciliary body and Iris: Vascular layer of the eyeball also called the uvea or uveal tract. Choroid: Dark reddish brown layer.

Between the sclera and the retina,

Continuous anteriorly with the ciliary body.

Firmly attached to the pigment layer of the retina, but it can easily be stripped from the sclera.

Uveitis: Inflammation of the vascular layer of the eyeball (uvea).May progress to severe visual impairment and blindness.

Ciliary body: Muscular as well as vascular

Connects the choroid with the circumference of the iris.

Provides attachment for the lens

Contraction and relaxation of the smooth muscle of the ciliary body controls thickness of the lens by contraction and relaxation of the smooth muscle .

Ciliary processes: secrete aqueous humor, which fills the anterior and posterior chambers of the eye.

Anterior chamber of the eye: the space between the cornea anteriorly and the iris/pupil posteriorly.

Posterior chamber of the eye: between the iris/pupil anteriorly and the lens and ciliary body posteriorly.

Iris: Lies on the anterior surface of the

lens Thin contractile diaphragm with a

central aperture, the pupil Regulates the amount of light

entering the eye. Two involuntary muscles control the

size of the pupil Parasympathetically stimulated

sphincter pupillae closes the pupil Sympathetically stimulated dilator

pupillae opens the pupil.

Pupillary Light Reflex:

Reflex, involving CN II (afferent limb) and CN III (efferent limb), is the rapid constriction of the pupil in response to light.

When light enters one eye, both pupils constrict because each retina sends fibers into the optic tracts of both sides.

Sphincter pupillae muscle: innervated by parasympathetic fibers; interruption of these fibers causes dilation of the pupil because of the unopposed action of the sympathetically innervated dilator pupillae muscle.

The first sign of compression of the oculomotor nerve: ipsilateral slowness of the pupillary response to light.

Direct and Consensual Light ReflexesIf a light is shone into one eye, the pupils of both eyes normally constrict. The constriction of the pupil on which the light is shone is called the direct light reflex; the constriction of the opposite pupil, even though no light fell on that eye, is called the consensual light reflex.

Inner Layer of the Eye: Retina: consists of two functional parts: optic part and a non-visual retina. Optic part of the retina

is sensitive to visual light rays and has two layers: Neural layer and Pigment cell layer.

Neural layer is light receptive.

Inner Layer of the Eye: Retina Pigment cell layer: Consists of a single layer of cells.

Reinforces the light-absorbing property

Non-visual retina: anterior continuation of the pigment cell layer and a layer of supporting cells over the ciliary body (ciliary part of the retina) and the posterior surface of the iris (iridial part of the retina), respectively.

Fundus: Posterior part of the eyeball.

Has a circular depressed area called the optic disc (optic papilla).

Sensory fibers and vessels conveyed by the optic nerve enter the eyeball.

Contains no photoreceptors, the optic disc is insensitive to light.

Commonly called the blind spot.

Optic disc

Macula Lutea (Yellow spot) Lateral to the optic disc Yellow color of the macula is apparent

only when the retina is examined with red-free light.

Small oval area of the retina with special photoreceptor cones.

Normally not observed with an ophthalmoscope.

At the center of the macula lutea: a depression, the fovea centralis (L. central pit), the area of most acute vision.

Fovea, approximately 1.5 mm in diameter

Retina: Retina terminates anteriorly along

the ora serrata (L. serrated edge), an irregular border slightly posterior to the ciliary body.

Ora serrata marks the anterior termination of the light-receptive part of the retina.

Retina is supplied by the central artery of the retina, a branch of the ophthalmic artery.

Cones and rods of the outer neural layer receive nutrients from the capillary lamina of the choroid, or choriocapillaris.

A corresponding system of retinal veins unites to form the central vein of the retina.

OphthalmoscopyPhysicians use an ophthalmoscope (funduscope) to view the fundus (posterior part) of the eye .

Retinal arteries and veins radiate over the fundus from the optic disc.

Pale, oval disc appears on the medial side with the retinal vessels radiating from its center in the ophthalmoscopic view.

Pulsation of the retinal arteries is usually visible.

Centrally, at the posterior pole of the eyeball, the macula appears darker than the reddish hue of surrounding areas of the retina.

Macula appears darker because the black

melanin pigment in the choroid and pigment cell layer is not screened by capillary blood.

Retinal Detachment Results from seepage of fluid

between the neural and pigment cell layers of the retina, perhaps days or even weeks after trauma to the eye.

Persons may complain of flashes of light or specks floating in front of the eye.

Papilledema: An increase in CSF pressure slows venous return from the retina, causing edema of the retina (fluid accumulation).

Viewed during ophthalmoscopy as swelling of the optic disc

Results from increased intracranial pressure and increased CSF pressure in the extension of the subarachnoid space around the optic nerve.

Normal optic nerve (central pinkish disk)

An optic nerve with mild swelling (papilledema).

A sudden reduction of pressure in the spinal subarachnoid space, as might occur with lumbar puncture, could result in a potentially fatal herniation of brain tissue into the vertebral canal if performed when intracranial pressure is elevated.

Refractive Media of the EyeballOn their way to the retina, light waves pass through the refractive media of the eyeball: Cornea Aqueous humor Lens Vitreous humor

Vitreous humor

Cornea: Circular area of the anterior part of the

outer fibrous layer of the eyeball Transparent, owing to the extremely

regular arrangement of its collagen fibers and its dehydrated state.

Sensitive to touch: innervated by the ophthalmic nerve (CN V1).

Avascular: nourishment is derived from the capillary beds at its periphery, the aqueous humor, and lacrimal fluid. The latter also provides oxygen absorbed from the air.

Aqueous humor: Produced in the posterior

chamber by the ciliary processes of the ciliary body.

Passes to the anterior chamber through the

Drains into the scleral venous sinus (L. sinus venosus sclerae, canal of Schlemm) at the iridocorneal angle.

Provides nutrients for the avascular cornea and lens.

Removed by the limbal plexus, a network of scleral veins close to the limbus, which drain in turn into both tributaries of the vorticose and the anterior ciliary veins.

Lens: Lies posterior to the iris and anterior

to the vitreous humor of the vitreous body.

Transparent, biconvex structure enclosed in a capsule.

Elastic capsule, anchored by the zonular fibers (suspensory ligament of the lens) to the ciliary body and encircled by the ciliary processes.

Convexity of the lens, particularly its anterior surface, constantly varies to fine-tune the focus of near or distant objects on the retina.

Vitreous humor

Ciliary muscle: Changes the shape of the lens

Stretched within the circle of the relaxed ciliary body, the attachments around its periphery pull the lens relatively flat so that its refraction enables far vision.

Parasympathetic stimulation causes muscle to contract and the tension on the lens is reduced. The increased convexity makes its refraction suitable for near vision.

In the absence of parasympathetic stimulation, the ciliary muscles relax again and the lens is pulled into its flatter, far-vision shape.

Vitreous humor:

Transparent jelly-like substance in the posterior four fifths of the eyeball posterior to the lens

Transmits light

Holds the retina in place and supports the lens.

Corneal Abrasions: Foreign objects such as sand or

metal filings (particles) produce corneal abrasions

Cause sudden, stabbing pain in the eyeball and tears.

Opening and closing the eyelids, painful.

Corneal lacerations: Caused by sharp objects such as

fingernails or the corner of a page of a book.

Corneal Abrasions

Corneal lacerations

Presbyopia and Cataracts As people age, their lenses

become harder and more flattened.

Gradually reduce the focusing power of the lenses, a condition known as presbyopia (G. presbyos, old).

Experience a loss of transparency (cloudiness) of the lens from areas of opaqueness (cataracts). Cataract extraction is a common operation.

Cataracts

Hemorrhage into the Anterior Chamber(Hyphema or Hyphemia): Results from blunt trauma

to the eyeball, such as from a squash or racquet ball or a hockey stick.

Anterior chamber: tinged red but blood soon accumulates in this chamber.

Artificial Eye The fascial sheath of the

eyeball forms a socket for an artificial eye when the eyeball has to be removed (enucleated).

Suspensory ligament preserved during surgical removal of the bony floor of the orbit because it supports the eyeball

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