Lectures 17 & 18 Eye & Orbit Flashcards
List bones of orbit?
- Frontal
- Zygomatic
- Maxillary
- Lacrimal
- Sphenoid - optic canal passes through sphenoid
- Ethmoid (orbital plate)
- Palatine bone (orbital process - a small contribution medial to inferior orbital fissure)
Superior orbital fissure is crossed by?
Oculomotor, branches of V1 (lacrimal, frontal, nasociliary), trochlear, abducens nerve
Openings of the orbit
- superior orbital fissure
- inferior orbital fissure
- infraorbital groove & foramen
- optic foramen
- lacrimal canal
- anterior & posterior ethmoid foramina
- zygomatico-orbital foramin
- supraorbital foramen
- trochleal fovea or spine
Infraorbital groove & foramen are crossed by?
Maxillary/infraorbital nerve (CNV/2)
Optic foramen is for which nerve?
Optic nerve (CN2)
Trochleal fovea or spine is located where and for what?
Halfway between supraorbital notch/foramen & frontolacrimal suture, for superior oblique muscle
Where does levator palpebrae superioris arise?
Arises lesser wing sphenoid, above superior rectus & optic canal
Function of levator palpebrae superioris
Raises upper eyelid
Frontal nerve is inferior to levator palpebrae superioris
False, it is superior
Rectus muscles insert where?
Recti insert into sclera about 6mm behind cornea & anterior to insertion of obliques
Superior, inferior, and medial recti arise?
Arises tendinous ring around optic nerve
______ has two heads - from lateral part of tendinous ring and from adjoining margin of ___________ ( _____ )
Lateral rectus, superior orbital fissure (sphenoid)
Oblique extrinsic muscles insert?
Obliques insert further back, behind equator of eyeball
__________ arises from body of sphenoid superomedial to optic canal.
Superior oblique muscle
___________ passes forwards along medial wall of orbit to tendinous band (called a trochlea) attached to trochleal fovea
Superior oblique muscle tendon
Where does superior oblique tendon insert?
Inserts into sclera between superior and lateral rectus
___________ arises orbital surface of maxilla lateral to nasolacrimal groove.
Inferior oblique
Where does inferior oblique muscle pass ?
Passes between inferior rectus and orbital floor and then between orbit and rectus lateralis
Inferior oblique muscle inserts?
Behind equator between rectos inferior and rectus lateralis
Medial and lateral recti rotate eye around horizontal axis
False, it rotates around vertical axis
Eye movement of superior and inferior rectus?
Elevation and depression
Eye movement of superior obliques
Down and out
Eye movement of inferior oblique
Turns eye up and out
List the structures of palpebral area
- tarsal plate
- tendon of levator palpebrae superioris
- lateral & medial palpebral ligaments
- orbital septum
- sebaceous tarsal glands
What is ‘orbital septum’?
Fascial sheet attached to periosteum of orbital rim & levator tendon
What are eyelids lined with?
Conjunctiva which is continuous with cornea
What does conjunctiva contain?
Goblet cells
Another name of sebaceous tarsal glands?
Meibom’s glands
Where do sebaceous tarsal glands empty into?
Free margin of the eyelid. The oily secretion spreads out over the tear film & contributes to its stability
Location of lacrimal glands
Mostly in superolateral orbit, some in eyelid lateral to tarsal plate between conjunctiva & palpebral fascia.
Composition of tears?
Mix of serous (from lacrimal glands), mucus (from conjunctiva goblet cells) and sebaceous (from sebaceous tarsal glands)
Where do tears drain?
Tears drain into medial corner of the eye & from there into the nasolarcimal duct via lacrimal canaliculi (one per eyelid, above & below plica semilunaris) & lacrimal sac
What is the canal of schlemm?
- Scleral venous sinus (trabecular meshwork)
- drainage of aqueous humour
What is the ora serrata?
- Junction of sensory and non-sensory retina
List the 3 layers of the wall of the eyeball?
- Sclera/cornea
- Uvea
- Retina
What is the cornea/sclera?
Fibrous outer coat
What is the uvea?
Vascular intermediate coat, includes choroid (underlies sensory retina) & anterior parts of ciliary body & iris
Retina has two which parts?
- Sensory retina
- non-sensory retina
Describe sensory retina
10 cell layers thick - photoreceptors (rods & cones) & other neurons
Describe non-sensory retina
2 cell layers thick - which forms the posterior parts of ciliary body & iris
Hollow centre of eyeball consists of anterior, posterior & vitreous chambers containing humours
True
Location of anterior chamber?
It’s between cornea & iris
Location of posterior chamber?
Behind iris and in front of lens
Location of vitreous chamber
Behind lens
Refractive media of eye includes?
- Conrea,
- Aqueous humour
- Lens
- Vitreous humour
What is the main refractive apparatus (focusing light onto retina)?
Cornea
Function of iris?
Variable aperture to control amount of light onto retina
Structure of iris?
Anterior part - uvea
Posterior part - non sensory retina (just 2 cells thick)
Which muscle contracts and expands iris?
Circular muscle around pupil contracts (sphincter) & expand (dilate)
Innervation of iris?
- Parasympathetic fibres of oculomotor origin - dilation via radial muscle extending outwards from pupil
- Sympathetic innervation
Two functions of ciliary body?
- Production of aqueous humour
- Accommodation for far and near vision
Structure of ciliary body?
- Anterior part: uvea
- Posterior part: non-sensory retina (2 cell layers thick)
Function of lens?
Accommodation for near & far vision
Describe structure of lens
- Flexible cellular structure
- Attached to ciliary body by zonule fibres
What is ‘accommodation’?
Adjusting focus to be able to see near or far objects. Lens, ciliary body and zonule fibres are involved.
How are lens attached to ciliary body?
Via zonule fibres (complex structure including collagen)
When ________ (circular muscle) of ciliary body contracts (parasympathetic control) the diameter of the ciliary body is reduced & there is less tension on zonule fibres
Sphincter, this in turn means less ‘pull’ on lens which rounds out/becomes less fat
A rounder lens accommodates for?
Near vision
How many layers of sensory retina?
10 layers
How to recognise sensory retina?
Thickened region on inner surface of posterior & lateral eyeball.
Junction of sensory retina and non-sensory retina of ciliary body?
Ora serrata
From outer to inner surface of sensory retina:
Pigment epithelium -> photoreceptors -> inner surface of retina
How thick is pigment epithelium? Location and function?
1 cell thick, and lies outside rods and cones and phagocytoses worn out components of rods and cones
What do photoreceptors consist of and location?
Rods and cones, and are in outer retina adjacent to posterior pigment epithelium
In sensory retina, the visual signal first goes inwards through a chain of neurons then over the inner surface of retina to the optic nerve.
True
What is the ‘blind spot’?
Special areas of the sensory retina include the optic disc at the site of the entry of the optic nerve (lacks photoreceptors)
What is the ‘macula/fovea’?
Region adjacent to the optic disc where the elements of the retina except the cones are reduced - region of greatest visual acuity.
There is an actual attachment between pigment epithelium & outer sensory retina which can become separated from the pigment epitheliulm (detached retina)
False, there is no actual attachment
Which type of humours fill which chambers in the eye?
- Aqueous humour fills anterior and posterior chambers.
- Vitreous humour fills vitreous chamber
Describe properties of aqueous humour
- Fluid similar to blood plasma, constantly renewed
- Aqueous humour is produced in folds of ciliary body
- Transported into posterior chamber
- Passes through pupil and into anterior chamber
Where does aqueous humour drain?
Drains from eye into scleral venous sinus (canal of Schlemm) & from there into OPTHALMIC VEINS
Describe vitreous humour
- Fluid connective tissue, not constantly renewed
- Stored in vitreous chamber, behind lens
The nerves oculomotor, ophthalmic, trochlear, abducent nerves pass through ______ along with internal carotid ______________.
Cavernous sinus, carrying carotid sympathetic plexus
Sympathetic fibres are transferred in the _______ from carotid plexus to other nerves crossing _______.
Cavernous sinus, cavernous sinus
List the nerves supplying extrinsic eye muscles
- Oculomotor
- Trochlea
- Abducent
What does oculomotor nerve supply?
Supplies all but two muscles of orbit
- superior division supplies superior rectus & levator palpebrae superioris
- inferior division supplies inferior & medial rectus, inferior oblique
What does trochlea nerve supply?
Superior oblique nerve
What does abducens nerve supply?
Lateral rectus
What does ophthalmic nerve supply?
Supplies structures within or near eyeball apart from intrinsic muscles & retina.
List branches of ophthalmic nerve
- Lacrimal
- Frontal
- Nasociliary
How do branches of ophthalmic nerve arise?
Arise as sensory nerves but lacrimal & nasociliary carry hitchikers
Lacrimal supplies lacrimal gland and skin
True
Parasympathetic fibres from the greater petrosal branch of facial nerve via pterygopalatine ganglion & maxillary nerve also supply lacrimal gland
True
Branches of frontal nerve?
Supratrochlear nerve, supraorbital nerve
Where does supraorbital nerve pass over?
Supraorbital nerve passes over superior surface of levator palpebrae superioris.
List branches of nasociliary branch of ophthalmic nerve
- sensory ganglion branches
- long ciliary nerves
- posterior ethmoidal
- infratrochlear nerve
- anterior ethmoid nerve
Sensory ganglion branches of nasociliary goes to parasympathetic ciliary ganglion
True
___________ (sympathetic & sensory) via sclera to dilator muscles of pupil & cornea
Long ciliary nerves
Posterior ethmoidal branches of nasociliary goes via posterior ethmoid foramina
True
What are the two terminal branches of nasociliary?
- Infratrochlear nerve
- Anterior ethmoid nerve
Describe infratrochlear nerve
A cutaneous nerve which emerges just medial to inner corner of eye
Describe anterior ethmoid nerve
Goes to anterior ethmoid sinuses, nasal cavity and has a cutaneous branch the external nasal nerve
_________ is about 1cm in front of the tendinous ring & between lateral rectus & optic nerve
Ciliary ganglion
Describe the roots of the ciliary ganglion
- Sensory fibres from nasociliary nerve via the short ganglion branches
- Preganglionic parasympathetic fibres from the (inferior division) of the oculomotor
- Sympathetic fibres from the ophthalmic artery plexus
What do ciliary ganglion branches supply and how many?
6-10 short ciliary nerves via sclera supply iris & ciliary body & to the cornea.
Parasympathetic innervation of iris and ciliary body are required to:
- contract sphincters of pupil & ciliary body
- contraction of ciliary muscle -> decrease tension on zonule fibres connecting ciliary body & lens result in a decrease in the diameter of the ciliary body. This results in lens becoming more round and gives accommodation for near vision - focusing light onto retina.
Sympathetic innervation is required to:
- dilate pupil
- vasomotor (constriction) to blood vessels
Describe the pupillary reflex
Light into one eye then both pupils should contract as retina sends fibres into optic tracts of both sides. If the parasympathetic supply to the sphincter of iris (oculomotor nerve) is compromised then sphincter is slow (“2 in, 3 out”)
Describe the corneal reflex
Afferent via ophthalmic nerve, efferent via facial to orbicularis oculi (“5 in, 7 out”)
________ is a branch of the internal carotid - enters optic canal with optic nerve.
Ophthalmic artery
Ophthalmic artery supplies?
Both orbit & eyeball.
Orbital branches of ophthalmic artery supply?
- Orbital structures - lacrimal gland, sclera, choroid, iris & ciliary body
- Supraorbital & supratrochlear branches to eyelids & skin of forehead
- Branches to ethmoid, frontal & sphenoid sinuses
- Some of the meninges
- Retinal branch
Define retinal branch and its supply
Central artery of retina (arises below optic nerve, enters retina at optic disc, divides into branches).
Central artery is the only supply to retina, no anastomosis between branches.
True
Describe the venous drainage of the retina
- Retinal veins - converge on optic disc & enter optic nerve as central vein of retina. These drain into superior ophthalmic vein -> cavernous sinus
- Inferior ophthalmic vein drains orbit -> cavernous sinus. Thus both ophthalmic veins have linkages with pterygoid venous plexus.
