3.Orbit, Eyelid & Lacrimal apparatus, Eye (79 slides).pptx
Transcript of 3.Orbit, Eyelid & Lacrimal apparatus, Eye (79 slides).pptx
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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