Head And Neck Week 6

Question 1

What is the orbit?

Answer 1

A pyramidal shaped bony cavity within the facial skeleton which contains (and protects) the eyeball, its muscles, nerves, vessels and most of the lacrimal apparatus

Question 2

What is the orbital region?

Answer 2

The area of the face overlying the orbit and eyeball. Includes the upper and lower eyelids and lacrimal apparatus

Question 3

Describe the orbits

Answer 3

Bilateral bony cavities in the facial skeleton that resemble hollow, quadrangular pyramids with their bases directed anterolaterally and their apices posteromedially medial walls separated by the ethmoidal sinuses and upper parts of nasal cavity - nearly parallel lateral walls are approximately at a right angle Orbital axes - 45 degrees optical axes - parallel - run directly anteriorly in primary position

Question 4

What are the accessory visual structures contained and protected within the orbital region?

Answer 4

eyelids - bound the orbits anteriorly - controlling exposure of anterior eyeball extra-ocular muscles - position the eyeballs and raise the superior eyelids nerves and vessels - in transit to eyeballs and muscles orbital fascia - surrounding eyeballs and muscles mucous membrane (conjunctiva) - lining the eyelids and anterior aspect of the eyeballs and most of the lacrimal apparatus which lubricates it

Question 5

What is in the space not occupied by the eyeballs or accessory visual structures?

Answer 5

Orbital fat - forms a matrix in which the structures of the orbit are embedded

Question 6

Describe the walls of the orbit

Answer 6

Base - outlined by orbital margin - surrounds the orbital opening - bone reinforced to afford protection to the orbital contents and provides attachment for the orbital septum - fibrous membrane that extends into the eyelids Superior wall - approximately horizontal - formed mainly by the orbital part of the frontal bone, near the apex formed by lesser wing of sphenoid - anterolaterally - fossa for lacrimal gland in orbital frontal bone accommodates lacrimal gland Medial walls - parallel to contralateral - formed primarily by orbital plate of ethmoid bone - contributions from frontal process of maxilla, lacrimal and sphenoid bones - anteriorly indented by lacrimal groove and foosa for lacrimal sac - trochlea located superiorly - thin Inferior wall - mainly maxilla and partly zygomatic and palatine - shared by orbit and maxillary sinus - slants inferiorly from apex to inferior orbital margin - demarcated from lateral wall by inferior orbital fissure - gap between orbital maxilla and sphenoid Lateral walls - frontal process of zygomatic bone and greater wing of sphenoid - strongest and thickest wall - most exposed and vulnerable to direct trauma - posterior part separates robit from temporal and middle cranial fossae - nearly perpendicular to contralateral Apex -optic canal - lesser wing of sphenoid just medial to superior orbital fissure

Question 7

What does the widest part of the orbit correspond to ?

Answer 7

Equator of the eyeball - imaginary line encircling eyeball - equidistant from its anterior and posterior poles

Question 8

What are the bones forming the orbit lined with and where is it continuous?

Answer 8

Periorbita (periosteum of orbit) Continuous at: Optic canal and superior orbital fissure with periosteal layer of dura mater Over the orbital margin and through the inferior orbital fissure with periosteum covering external cranium Orbital septa at the orbital margins Fascial sheaths of extraocular muscles Orbital fascia that forms the fascial sheath of the eyeball

Question 9

What is the function of the eyelids and lacrimal fluid?

Answer 9

Protection of the cornea and eyeballs from injury and irritation (dust and small particles)

Question 10

Describe the eyelids

Answer 10

Moveable folds that cover the eyeball anteriorly when closed - protecting it from injury and excessive light keep cornea moist by spreading lacrimal fluid covered externally by thin skin and internally by transparent mucous membrane (palpebral conjunctiva)

Question 11

What is the palpebral conjunctiva continuous as?

Answer 11

Reflected onto the eyeball where it is continuous with bulbar conjunctiva

Question 12

Describe the bulbar conjunctiva

Answer 12

thin, transparent and attached loosely to anterior surface of eyeball loose and wrinkled over the sclera contains small, visible blood vessels adherent to the periphery of the cornea

Question 13

What are the names of the deep recesses formed by the reflection of the palpebral conjunctiva onto the eyeball?

Answer 13

Superior and inferior conjunctival fornices

Question 14

What is the conjunctival sac?

Answer 14

Space bound by the palpebral and bulbar conjunctivae closed space when the eyelids are closed but opens via an anterior aperture - palpebral fissure (gap between eyelids) when eyes open Specialised form of mucosal bursa Enables eyelids to move freely over surface of the eyeball as they open and close

Question 15

What is the palpebral fissure?

Answer 15

Gap between the eyelids when they are open

Question 16

What strengthens the eyelids?

Answer 16

Dense bands of connective tissue - superior and inferior tarsi - form the skeleton of the eyelids

Question 17

What is contained in the tarsi?

Answer 17

Fibres of the palpebral portion of the Orbicularis oculi superficial to the tarsi and deep to the skin Tarsal glands Eyelashes Ciliary glands - sebasceous glands of the eyelashes

Question 18

What is the function of the tarsal glands?

Answer 18

produce a lipid secretion that lubricates the edges of the eyelids - prevents them sticking together when they close - forms barrier that lacrimal fluid does not cross when produced in normal amounts - when production excessive, spills over the barrier onto cheeks as tears

Question 19

What are the junctions of the superior and inferior eyelids known as?

Answer 19

medial and ateral palpebral commissures defining the medial and lateral angles of the eye/canthi

Question 20

What structure connects the tarsi to the medial margin of the orbit?

Answer 20

medial palpebral ligament

Question 21

What is significant about the medial palpebral ligament?

Answer 21

The orbicularis oculi originates and inserts onto this ligament

Question 22

Where does the lateral palpebral ligament attach?

Answer 22

Tarsi to the lateral margin of the orbit

Question 23

What is the orbital septum?

Answer 23

Fibrous membrane that spans from the tarsi to the margins of the orbit - becomes continuous with the periosteum Keeps orbital fat contained and - due to continuity with periorbita - limits spread of infection to and from the orbit Constitutes the posterior fascia of the orbicularis oculi muscle

Question 24

What does the lacrimal apparatus consist of?

Answer 24

Lacrimal gland - secretes lacrimal fluid Excretory ducts of lacrimal gland - convey fluid from glands to conjunctival sac Lacrimal canaliculi - commence at lacrimal punctum (opening on papilla near medial angle of eye) - drain lacrimal fluid from lacrimal lake (triagnular space at medial angle of eye where tears collect) to lacrimal sac (dilated superior part of nasolacrimal duct) Nasolacrimal duct - conveys lacrimal fluid to inferior nasal meatus (inferior to inferior nasal concha)

Question 25

What is the function of lacrimal fluid?

Answer 25

watery physiological saline containing the bacteriocidal enzyme lysozyme cleanses particles and irritants from conjunctival sac moistens and lubricates surfaces of conjunctiva and cornea provides some nutrients and dissolved oxygen to the cornea when produced in excess constitutes tears

Question 26

Describe the lacrimal gland

Answer 26

Almond shaped Approx 2cm long Lies in fossa for lacrimal gland in superolateral part of each orbit Divided into superior orbital and inferior palpebral parts by lateral expansion of the tendon of the levator palpebrae superioris Accessory glands may also be present - sometimes in middle eyelid - or along superior and inferior fornices of conjunctival sac - more numerous in superior than inferior eyelid

Question 27

Describe the production of lacrimal fluid

Answer 27

Stimulated by parasympathetic impulses from CN VII (facial nerve) Secreted through 8-12 excretory ducts which open into lateral part of superior conjunctival fornix of conjunctival sac Fluid flows inferiorly under influence of gravity When cornea becomes dry eye blinks - eyelids come together in lateral to medial sequence pushing film of fluid medially over the cornea

Question 28

Describe the drainage of lacrimal fluid

Answer 28

Lacrimal fluid pushed towards medial angle of the eye by blinking - eyelids come together in lateral to medial sequence - accumulates in lacrimal lake from which it drains by capillary action through lacrimal puncta and lacrimal canaliculi to lacrimal sac Fluid then passes to inferior nasal meatus of nasal cavity through nasolacrimal duct drains posteriorly across floor of nasal cavity to nasopharynx eventually swallowed

Question 29

Describe the innervation of the lacrimal gland

Answer 29

Both sympathetic and parasympathetic Presynaptic parasympathetic secretomotor fibres - from facial nerve –> greater petrosal nerve –> nerve of pterygoid canal –> pterygopalatine ganglion - synapse –> zygomatic nerve of maxillary nerve –> lacrimal branch of opthalmic nerve Sympathetic fibres (vasoconstrictive) postsynaptic –> superior cervical ganglion –> internal carotid plexus –> deep petrosal nerve –> join parasympathetic course as nerve of pterygoid canal

Question 30

Describe (briefly) the eyeball

Answer 30

Contains optical apparatus of visual system Occupies most of anterior portion of orbit suspended by 6 extrinsic muscles that control its movement and a fascial suspensory apparatus Approx 25mm diameter All anatomical structures within have circular or spherical shape Eyeball proper - 3 layers additional connective tissue layer supports it in orbit - composed posteriorly of fascial sheath of eyeball (bulbar fascia) - forms actual socket for the eyeball - anteriorly of bulbar conjunctiva - fascial sheath most substantial portion of suspensory apparatus Loose connective tissue layer - episcleral space - potential space - lies between fascial sheath and outer layer of eyeball - facilitates movement of eyeball within fascial sheath

Question 31

What is the episcleral space?

Answer 31

potential space - lies between fascial sheath and outer layer of eyeball - facilitates movement of eyeball within fascial sheath

Question 32

Describe the layers that make up the eyeball proper

Answer 32

Fibrous layer - sclera and sornea Vascular layer - choroid, ciliary body and iris Inner layer - retina (optic and non-visual parts)

Question 33

Describe the fibrous layer of the eyeball

Answer 33

External fibrous skeleton of the eyeball provides shape and resistance Sclera - tough opaque part - covers posterior 5/6ths - provides attachment for extraocular and intrinsic muscles of eye - anterior part visible through transparent bulbar conjunctiva as the “white of the eye” Relatively avascular Cornea - transparent part - covers anterior 1/6th - convexity greater than the sclera - appears to protrude from eyeball when viewed laterally completely avascular - nourishment from capillary beds around periphery and fluids on external and internal surfaces (lacrimal fluid and aqueous humour) - lacrimal fluid provides oxygen absorbed from air Drying may cause ulceration Highly sensitive to touch (CNV1) - small foreign bodies (dust) elicits blinking, flow of tears and sometimes severe pain Corneal limbus - angle formed by the intersecting curvatures of sclera and cornea at the corneoscleral junction (a 1mm wide, gray, translucent circle - includes numerous capillary loops - nourishing avascular cornea)

Question 34

Describe the vascular layer of the eyeball

Answer 34

Also called uvea Consists of choroid, ciliary body and irris choroid - dark reddish brown layer between sclera and retina - largest part of vascular layer - lines most of sclera - larger vessels located externally, capillary lamina of choroid (extensive capillary bed) are innermost - adjacent to retina (avascular) which it supplies with oxygen and nutrients - engorged with blood - highest perfusion rate per gram of tissue of all vascular beds in body - responsible for “red eye” reflection that occurs in flash photography - attached firmly to retina but can easily be stripped from the sclera - continuous anteriorly ith ciliary body ciliary body - ring-like thickening of the layer posterior to the corneosceral junction - muscular as well as vascular - connects choroid with iris - provides attachment for lens - contraction and relaxation of circularly arranged smooth muscle controls thickness and therefore focus of the lens - folds on internal surface - ciliary processes - secrete aqueous humour - fills anterior segment of eyeball (interior of the eyeball anterior to the lense, suspensory ligament, and ciliary body) Iris - lies on anterior surface of lens - thin,contractile diaphragm - central aperture (pupil) for transmitting light - size of pupil varies continually to regulate amount of light entering eye

Question 35

What is the anterior segment of the eyeball?

Answer 35

interior of the eyeball anterior to the lense, suspensory ligament, and ciliary body

Question 36

Which muscles control the size of the pupil and what is their innervation?

Answer 36

Two involuntary muscles Sphincter pupillae - circularly arranged - decreases diameter - contracts pupil - miosis - parasympathetic dilator pupillae - radially arranged - dilates pupil - sympathetic

Question 37

How quickly does dilation and contraction of the pupil occur?

Answer 37

Paradoxical May take up to 20 min for the pupil to dilate in response to low lighting - sympathetic (normally faster than parasympathetic) Constriction is normally instantaneous - parasympathetic abnormal sustained pupillary dilation (mydriasis) may occur in certain diseases or as a result of trauma or the use of certain drugs

Question 38

Describe the inner layer of the eyeball

Answer 38

Retina Sensory neural layer Two functional parts with distinct locations - optic part and a non-visual retina optic part - sensitive to visual light rays and has two layers - neural layer and pigmented layer - neural layer is light receptive - pigmented layer - single layer of cells that reinforces the light absorbing property of the choroid in reducing the scattering of light in the eyeball - terminates anteriorly along the ora serrata (irregular posterior border of ciliary body) non visual retina - anterior continuation of the pigmented layer and a layer of supporting cells - extends over the ciliary body (ciliary part of retina) and the posterior surface of the iris (iridial part of retina) to the pupillary margin Internal aspect of the posterior part of the eyeball where light is focused - referred to as the fundus of the eyeball - retina of the fundus includes optic disc(papilla) where sensory fibres and vessels converyed by the optic nerve enter the eyeball - contains no photoreceptors - insensitive to light - blind spot Lateral to optic disc - macula of retina - yellow colour when examined with red-free light - small oval area with special photoreceptor cones - specialised for acuity of vision - not normally observed with an ophthalmoscope - centre of the macula - depression called fovea centralis - area of most acute vision - 1.5mm diameter - foveola in centre does not have the capillary network visible elsewhere deep to the retina Except for cones and rods of neural layer - retina supplied by central artery of the retina - branch of opthalmic artery - cones and rods of outer neural layer receive nutrients from capillary lamina of the choroid Corresponding system of retinal veins unites to form the central vein of the retina

Question 39

Explain the blind spot

Answer 39

optic disc(papilla) where sensory fibres and vessels converyed by the optic nerve enter the eyeball - contains no photoreceptors - insensitive to light - produces blind spot

Question 40

What is the fovea centralis?

Answer 40

depression at centre of the macula - area of most acute vision - 1.5mm diameter - foveola in centre does not have the capillary network visible elsewhere deep to the retina

Question 41

What is the macula and where can it be seen on the fundus?

Answer 41

macula of retina - yellow colour when examined with red-free light - small oval area with special photoreceptor cones - specialised for acuity of vision - not normally observed with an ophthalmoscope - seen lateral to the optic disc

Question 42

What is the optic disc and where can it be seen?

Answer 42

optic disc(papilla) where sensory fibres and vessels converyed by the optic nerve enter the eyeball - contains no photoreceptors - insensitive to light - blind spot - medial to macula

Question 43

What is the refractive media of the eyeball through which lightwaves pass?

Answer 43

cornea (primary refractory medium), aqueous humor, lens and vitreous humor - cornea bends light to greatest degree, focusin an inverted image on the light-sensitive retina of the fundus of the eyeball

Question 44

Where is the aqueous humor produced and where does it lie?

Answer 44

Produced in posterior chamber by ciliary processes - lies in anterior segment of eyeball

Question 45

How can the anterior segment of the eyeball be subdivided?

Answer 45

By the iris and pupil anterior chamber - space between cornea anteriorly and iris/pupil posteriorly posterior chamber - between iris/pupil anteriorly and lens and ciliary body posteriorly

Question 46

What is the function of the aqueous humor?

Answer 46

Provides nutrients for avascular cornea and lens

Question 47

Describe the drainage of aqueous humor

Answer 47

Passes through pupil into anterior chamber Drains through a trabecular meshwork at the iridocorneal angle into the sceral venous sinus humor removed by limbal plexus - network of scleral veins close to the limbus drain into both tributaries of the vorticose and anterior ciliary veins

Question 48

What determines intra-ocular pressure?

Answer 48

the balance between production and outflow of aqueous humor

Question 49

Describe the lens

Answer 49

Posterior to the iris Anterior to vitreous humor of vitreous body Transparent, biconvex structure enclosed in a highly elastic capsule that is anchored by zonular fibres (collectively suspensory ligament of the lens) to the encircling ciliary processes convexity of the lens - particularly anterior surface - constantly varies to fine-tune the focus of near or distant objects on the retina - in the absence of external attachment and stretching would be nearly round ciliary muscle of ciliary body changes shape of lens in absence of nerve stimulation - diameter of relaxed muscular ring is larger - lens is under tension as periphery is stretched - causes it to be thinner (less convex) - brings more distant objects into focus (far vision) Parasympathetic stimulation via oculomotor nerve causes sphincter-like contraction of ciliary muscle - ring becomes smaller - tension on lens reduced - thickens - more convex - near vision - accomodation

Question 50

Describe how the thickness of the lens is altered

Answer 50

ciliary muscle of ciliary body changes shape of lens - in absence of nerve stimulation - diameter of relaxed muscular ring is larger - lens is under tension as periphery is stretched - causes it to be thinner (less convex) - brings more distant objects into focus (far vision) Parasympathetic stimulation via oculomotor nerve causes sphincter-like contraction of ciliary muscle - ring becomes smaller - tension on lens reduced - thickens - more convex - near vision - accomodation Thickness of lens increases with aging so that the ability to accommodate typically becomes restricted after age 40

Question 51

What is the term for the active process of changing the shape of the lens for near vision?

Answer 51

accommodation

Question 52

What is the function of the vitreous humor and where does it lie?

Answer 52

Watery fluid enclosed in the meshes of the vitreous body (transparent jelly-like substance in posterior 4/5ths of eyeball posterior to lens - posterior segment) Transmits light, holds retina in place, supports lens

Question 53

Where is the posterior segment of the eyeball?

Answer 53

Posterior 4/5ths of eyeball - posterior to lens

Question 54

Describe the extraocular muscles of the orbit

Answer 54

Levator palpebrae superioris : origin - lesser wing of sphenoid bone - superior and anterior to optic canal insertion - superior tarsus and skin of superior eyelid innervatrion - oculomotor nerve (superior tarsal muscle supplied by sympathetic fibres) action - elevates superior eyelid Deep lamina of the distal part of the muscle includes smooth muscle fibres - superior tarsal muscle - additional widening of the palpebral fissure - especially during sympathetic response (fright) - seem to function continuously because absence of sympathetic supply produces partial ptosis (horner’s) Recti: all originate at common tendinous ring that surrounds optic canal and from part of superior orbital fissure at apexand insert into sclera just posterior to corneoscleral junction all but lateral rectus innervated by oculomotor nerve superior - action - elevates, adducts and rotates eyeball medially inferior - action - depresses, adducts and rotates eyeball laterally medial - action - adducts eyeball lateral- innervation - abducent nerve - action - abduct eyeball Obliques: inferior - origin - anterior part of floor of orbit insertion - sclera deep to lateral rectus muscle innervation - oculomotor nerve action - abduct, elevate and laterally rotate eyeball - main action is elevation in adducted position (convergence for reading) superior - origin - body of sphenoid bone insertion - tendon passes through fibrous ring/trochlea, changes direction and inserts in sclera deep to superior rectus muscle innervation - trochlear nerve action - abducts, depresses and medially rotates eyeball - main action is depression of pupil in adducted position (convergence for reading) All motions require action of several muscles in same eye, assisting each other as synergists or opposing eahc other as antagnonists - may be synergistic for one action and antagonistic for another

Question 55

What are yoke muscles?

Answer 55

To direct the gaze, coordination of both eyes must be accomplished by the paired action of contralateral yoke muscles (functionally-paired contralateral extra-ocular muscles) e.g. in directing the gaze to the right - right LR and left MR act as yoke muscles

Question 56

In practice how would you test the muscles responsible for eyeball movements?

Answer 56

LR - physician directs patient to follow finger laterally (tests abducent nerve) SR and IR - once in lateral position physician directs patient to follow finger superiorly and inferiorly - isolate and test function of SR and IR - integrity of oculomotor nerve MR - physician directs patient to follow his or her finger medially (oculomotor nerve) SO and IO - once in medial position physician directs patient to follow finger superiorly and inferiorly - isolates SO (trochlear nerve) and IO (inferior division of CN III)

Question 57

What forms the actual socket for the eyeball?

Answer 57

fascial sheath of the eyeball - extends psoteriorly from conjunctival fornices to optic nerve

Question 58

Describe the muscular sheaths of the extraocular muscles

Answer 58

The cup-like fascial sheath is pierced by tendons of the extra-ocular muscles and is reflected onto each of them as a tubular muscle sheath The sheaths of levator and superior rectus are fused - when gaze directed superiorly - superior eyelid is further elevated out of line of vision triangular expansions from medial and lateral rectus sheaths - medial and lateral check ligaments - attached to the lacrimal and zygomatic bones - respectively - limit abduction and adduction Bledning of check ligaments with fascia of inferior rectus and inferior oblique - forms hammock-like sling - suspensory ligament of eyeball inferior check ligament - fascial sheath of inferior rectus - retracts inferior eyelid when gaze directed downwards collectively check ligaments act with oblique muscles and retrobulbar fat to resist posterior pull on eyeball produced by rectus muscles - disease of starvation reduce retrobulbar fat - eyeball retracted into orbit (inophthalmos)

Question 59

Which structures travel through the optic canal?

Answer 59

Optic nerve Opthalmic artery

Question 60

Which structures pass through the superior orbital fissure?

Answer 60

Abducent nerve, inferior and superior branch of oculomotor nerve, nasociliary, frontal and lacrimal branches of ophthalmic nerve, trochlear nerve, superior ophthalmic vein

Question 61

Which structure passes through the inferior orbital fissure?

Answer 61

Inferior ophthalmic vein

Question 62

What instrument can be used to look into the eyeball?

Answer 62

Ophthalmascope/fundoscope

Question 63

What does a raised optic disc indicate?

Answer 63

papilloedema - raised intracranial pressure - due to slowed venous return from retina and increased CSF pressure in the extension of the subarachnoid space around the optic nerve

Question 64

Why can retinal detachment occur?

Answer 64

Layers of developing retina are separated in embryo by intraretinal space - in early foetal period the layers fuse - obliterating the space pigment cell layer becomes firmly fixed to the choroid its attachment to neural layer is not firm Blow to eye may cause neural layer to separate from pigment cell layer - follows seepage of fluid between neural and pigment cell layer perhaps days or even weeks after the initial trauma May complain of flashes of light or specks floating in front of the eye

Question 65

What is the clinical significance of the optic nerve being a continuation of the brain itself?

Answer 65

Meningitis - photophobia

Question 66

Describe glaucoma and its consequences

Answer 66

.Outflow of aqueous humor not occuring at same rate as production - e.g. blockage - pressure builds up in anterior and posterior chambers

can result in blindness from compression of inner layer of eyeball and retinal arteries if aqueous humor production not reduced to maintain normal intraocular pressure

Open angle - drainage angle is open - blocked outflow at trabeculae or scleral venous sinus - non emergency

Closed angle - iris closes drainage angle and onstructs outflow of aqueous - emergency

Question 67

Describe an orbital blow out fracture

Answer 67

Inferior and medial walls thinnest - can fracture while margin of orbit remains intact - orbital floor/maxillary sinus roof (air filled space) - medial wall / wall of ethmoidal and sphenoidal sinuses (air filled) With floor fracture - Inferior rectus can get stuck in break - tethered - cant look up in midline Bruising - superficial vein damage Blood can collect in maxillary sinus, ethmoidal sinus or sphenoidal sinus depending on position of fracture- fluid line on xray Tear drop sign - contents of orbit leaking out

Question 68

Describe superior oblique palsy

Answer 68

Cant look down in the medial position

Question 69

Describe inferior oblique palsy

Answer 69

Cant look up in medial position

More common for oculomotor nerve palsy to occur which would produce down and out appearance of eye with ptosis

Question 70

Describe the arterial supply of the orbit

Answer 70

Mainly from ophthalmic artery - branch of ICA - gives rise to central artery of retina - inferior to optic nerve - pierces sheath of optic nerve and runs within nerve to the eyeball - emerges at optic disc - branches spread over internal surface of retina - terminal branches are end arteries - only blood supply to internal aspect of retina posterior ciliary arteries (branches of ophthalmic) - short (6) posterior ciliary arteries - directly supply choroid - nourishes outer non-vascular retina - long (2) posterior ciliary arteries - one on each side of eyeball - pass between sclera and choroid - anastamose with anterior ciliary arteries (continuations of muscular branches of ophthalmic artery to rectus muscles) to supply ciliary plexus infraorbital artery - from ECA - contributes blood to structures related to orbital floor External retina - supplied by the capillary lamina of the choroid

Question 71

Describe the venous drainage of the orbit

Answer 71

Superior and inferior ophthalmic veins - pass through superior orbital fissure and enter cavernous sinus Central vein of retina usually enters cavernous sinus directly but may join an ophthalmic vein The vortex/vorticose veins - vascular layer of eyeball - drain into inferior ophthalmic vein Scleral venous sinus - vascular structure encircling anterior chamber of eyeball - through which aqeuous humor returns to blood circulation

Question 72

Describe the innervation of the orbit

Answer 72

Optic nerves (CN II) - purely sensory - transmit impulses generated by optical stimuli - develop as paired anterior extensions of forebrain - actually CNS fibre tracts formed of second order neurons - begin at lamina cribrosa of sclera - unmyelinated nerve fibres pierce sclera and become myelinated posterior to optic disc - exit orbits via optic canals - throughout course in orbit surrounded by extensions of cranial meninges and subarachnoid space, occupied by thin layer of CSF intraorbital extensions of the cranial dura and arachnoid constitute optic nerve sheath - continuous anteriorly with fascial sheath of eyeball and sclera layer of pia mater covers surface of optic nerve within the sheath In addition nerves that enter through superior orbital fissure and supply ocular muscles - oculomotor, trochlear and abducent nerves oculomotor nerve divides into superior and inferior division - superior supplies SR and LPS - inferior division supplies MR and IR and IO and also carries presynaptic parasympathetic fibres to the ciliary ganglion Ophthalmic nerve - passes through superior orbital fissure to supply structures related to anterior orbit (lacrimal glands and eyelids), face and scalp ciliary ganglion - small group of postsynaptic parasympathetic nerve cell bodies associated with ophthalmic nerve - located between optic nerve and LR - posterior limit of orbit - receives : - sensory fibres from ophthalmic nerve - via snesory or nasociliary root of ciliary ganglion -presynpatic parasympathetic fibres from CN III via parasympathetic or oculomotor root of ciliary ganglion Postsynaptic sympathetic fibres from internal carotid plexus via sympathetic root of ciliary ganglion short ciliary nerves - bracnhes of ophthalmic nerve - arise from ciliary ganglion - carry parasympathetic and sympathetic fibres to ciliary body and iris - also afferent fibres from nasociliary nerve Long ciliary nerves - branches of nasociliary nerve (ophthalmic) - pass to eyeball, bypassing ciliary ganglion - convey sympathetic fibres to dilator pupillae and afferent fibres from iris and cornea Posterior and anterior ethmoidal nerves - branches of nasociliary - arise in orbit - exit via openings in medial wall of orbit to supply mucous membrane of sphenoidal and ethmoidal sinuses and nasal cavities - as well as dura of anterior cranial fossa

Question 73

Describe the surface anatomy of the eye and lacrimal apparatus

Answer 73

Anterior part of sclera covered by transparent bulbar conjunctiva - contains minute but apparent conjunctival blood vessels - irritated –> vessels enlarge noticeably - pink appearance sclera often appears slightly blue in infants and children and slightly yellow in elderly Anterior transparent part of eye - cornea - continuous with sclera at margins Most of visible part of eye protrudes slightly through palpebral fissure Cornea has greater convexity than rest of eyeball - corneal limbus occurs at the corneoscleral junction - this makes movements of eyeball apparent when eyelids are closed pupil - surrounded by iris (coloured) - relative size of pupil and iris varies with brightness of entering light but contralateral pupils and irides should be the same superior part of cornea and iris covered by edge of superior eyelid and inferior part of cornea and iris fully exposed above inferior eyelid - usually exposing narrow rim of sclera bulbar conjunctiva reflected from sclera onto deep surface of eyelid - palpebral conjunctive - normally red and vascular - assessment of anaemia tarsal glands can be distinguished thr

Question 74

Describe the surface anatomy of the eye and lacrimal apparatus

Answer 74

Anterior part of sclera covered by transparent bulbar conjunctiva - contains minute but apparent conjunctival blood vessels - irritated –> vessels enlarge noticeably - pink appearance sclera often appears slightly blue in infants and children and slightly yellow in elderly Anterior transparent part of eye - cornea - continuous with sclera at margins Most of visible part of eye protrudes slightly through palpebral fissure Cornea has greater convexity than rest of eyeball - corneal limbus occurs at the corneoscleral junction - this makes movements of eyeball apparent when eyelids are closed pupil - surrounded by iris (coloured) - relative size of pupil and iris varies with brightness of entering light but contralateral pupils and irides should be the same superior part of cornea and iris covered by edge of superior eyelid and inferior part of cornea and iris fully exposed above inferior eyelid - usually exposing narrow rim of sclera bulbar conjunctiva reflected from sclera onto deep surface of eyelid - palpebral conjunctive - normally red and vascular - assessment of anaemia tarsal glands can be distinguished through palpebral conjunctive of everted superior eyelid as yellow vertical stripes - openings of these glands can be seen on margins of the eyelids - posterior to the eyelashes palpebral fissure is mouth of the conjunctival sac medial angle of eye - reddish shallow reservoir of tears - lacrimal lake - within the lake is the lacrimal caruncle - small mound of moist modified skin - lateral to this is a semilunar conjunctival fold - sightly overlaps the eyeball when edges of eyelids everted - small pit - lacrimal punctum - visible at medial end on summit of a small elevation - lacrimal papilla

Question 75

Describe orbital fractures

Answer 75

strong blow to bony rim of margin - fracture usually occurs at the three sutures between the bones forming the margin blow out fracture - fracture of orbital wall while margin remains intact superior wall - stronger - thin enough to be penetrated by sharp object - enter frontal lobe of brain fractures often result in intra-orbital bleeding - pressure on eyeball - exophthalmos trauma to eye may effect adjacent structures - displacement of maxillary teeth, bleeding into sinuses, fracture of nasal bones - haemorrhage, airway obstruction and infection which can spread to cavernous sinus through ophthalmic vein

Question 76

Describe the clinical consequences of orbital tumours and their managment

Answer 76

Closeness of optic nerve to sphenoidal and posterior ethmoidal sinuses - malignant tumour in these sinuses may erode the thin bony walls of the orbit and compress the optic nerve and orbital contents –> exophthalmos EAsiest entrance into orbital cavity for tumour in middle cranial fossa is through superior orbital fissure - tumours in temporal or infratemporal fossa go through inferior orbital fissure lateral wall doesnt reach as far anteriorly as medial wall - nearly 2.5cm of eyeball exposed when pupil is turned medially as far as possible - good approach for operations on eyeball

Question 77

What is the consequence to the eyelids of an oculomotor nerve lesion

Answer 77

partial ptosis

Question 78

What is the consequence to the eyelids of a lesion to the facial nerve?

Answer 78

paralysis of the orbicularis oculi - prevents eyes closing properly - normal rapid blinking also lost excessive lacrimal fluid production

Question 79

How does a sty form?

Answer 79

Ducts of ciliary glands are obstructed - painful red suppurative swelling develops on eyelid

Question 80

What is a chalazion/meibomian cyst?

Answer 80

Obstruction of a tarsal gland –> produces inflammation - protrudes toward the eyeball and rubs against it as eyelids blink

Question 81

What causes hyperaemia of the conjunctiva?

Answer 81

Vessels become dilated and congested due to local irritation or a contagious infection called conjunctivitis (pink eye)

Question 82

What causes subconjunctival haemorrhages and how do they present?

Answer 82

common birth or dark red patches deep to and within the bulbar conjunctiva injury or inflammation may cause - blow to eye, excessively hard blowing of nose, paroxysms of coughing or violent sneesing Rupture of small subconjunctival capillaries

Question 83

Describe the nerve control of the pupillary light reflex

Answer 83

Tested using pen light Involves CN II (Afferent) CN III (efferent) rapid constriction of the pupil in response to light - direct

When light enters one eye - both pupils constrict because each retina sends fibres into the optic tracts of both sides - consensual

Question 84

What is uveitis?

Answer 84

inflammation of vascular layer of eyeball (uvea) - may progress to severe visual impairment and blindness if not treated by specialist

Question 85

What can be seen during ophthalmoscopy?

Answer 85

Fundus

Retinal arteries and veins

Optic disc (medial)

Pulsation of vessels visible

Macula - lateral to optic disc - appears darker due to black melanin pigment in choroid and pigment in cell layer not being screened by capillary blood

Question 86

What is presbyopia?

Answer 86

As people ago lenses become harder and more flattened - gradually reduces the focusing power of the lenses - presbyopia

Question 87

Describe cataracts and how they are managed

Answer 87

Loss of transparency of the lens from areas of opaqueness

Cataract extraction combined with intra ocular lens implant - common operation

extracapsular cataract extraction involves removing the lens but leaving the capsule of the lens intact to receive a synthetic intraocular lens

Intracapsular lens extraction involves removing the lens and lens capsule and implanting a synthetic intraocular lens in the anterior chamber

Question 88

What is coloboma of the iris?

Answer 88

Absence of a section of the iris may result from birth defect - choroid fissure fails to close properly, penetrating or non-penetrating injuries to eyeball or surgical iridectomy

Iridial fissure does not heal after injury

Question 89

What is hyphema and what is the management process?

Answer 89

Haemorrhage in anterior chamber of eyeball

blunt traume to eyeball - squash ball or hockey stick

Initially anterior chamber tinged red but blood soon accumulated

Initial haemorrhage usually stops in a few days

Recovery usually good

Question 90

Describe how to test a corneal reflex

Answer 90

Touch cornea with wisp of cotton

Positive response is a blink (normal)

Absence of blink suggests lesion of ophthalmic nerve - a lesion of the facial nerve supply to orbicularis oculi may also impair this reflex

presence of contact lens may hamper or abolish ability to evoke this reflex

Question 91

What is the consequence of an ophthalmic nerve lesion?

Answer 91

Damage to sensory innervation of cornea –> vulnerable to injuy by foregin matter - can have a corneal transplant from donors or implants of non-reactive plastic material

Question 92

Describe features of extraocular muscle paralysis

Answer 92

may be paralysed by disease in brainstem or head injury

limitation of movement of eyeball in field of action of muscle - diplopia when attempting to use said muscle

oculomotor nerve palsy - affects most of ocular muscles - ptosis due to levator palpebrae superioris paralysis - pupils fully dilated due to unopposed sympathetic action on dilator pupillae - pupil down and out due to unopposed activity of lateral rectus and superior oblique

adbucent nerve palsy - only lateral rectus paralysed - cannot abduct pupil on affected side - pupil fully adducted by unopposed action of medial rectus

Question 93

What sign during fundoscopy suggests central artery occlusion and what are the consequences of this?

Answer 93

Cherry red spot on pale background

end arteries –> ischaemia

results in instant, total blindness

will lead to necrosis

usually unilateral and occurs in older people

Question 94

How can the central vein of the retina become occluded and what is the consequence of this?

Answer 94

Thrombophlebitis of cavernous sinus that spreads thromubs to central retinal vein - blocks small retinal veins

Dehydration

see oedema with fundoscopy

usually results in slow, painless loss of vision