Clinical anatomy of the eye Flashcards
What is the eyelid formed from?
Eyelid is formed from:
Thin skin
Obicularis Oculi muscle
Tarsal glands,
thin fat pads surrounding structures
What are two important ligaments within the eyelid?
Lateral palpebral ligament and medial palpebral ligaments
Help support the eye, and keep it within the socket during increased pressure, blends in with a number of dense tissue structures.
What is the bulge of tissue seen at the corner of the eye?
where are tears produced and how do they sweep across the eye?
towards what anatomical landmark?
How do tears drain from the eye? What do these structures sit on?
where do tears drain to (via what) and into what structure?
Bulge of tissue at the corner of the eye is called the lacrimal caruncle, part of lacrimal apparatus.
Tears are produced superiorly and laterally in the lacrimal glands, when you close your eyes tears are swept downwards and medially towards the lacrimal lake where tears will pool.
Tears need to drain from the eye and drain via Punctums. These punctums are sat on the lacrimal papilla.
Tears drain from lacrimal punctum to the nasal cavity via the lacrimal duct. (Drains into the inferior nasal meatus underneath inferior concha.
What structure is shown?
What is the conjunctiva?
The conjuncativa is a covering that covers the sclera.
It extends from the border of the cornea to the sclera and then reflects in both at superior and inferior conjunctival fornix.
It is continueous on the inner sides of the eyelids both upper and lower, it is a continual lining.
Describe the layers of the eyelid shown?
What glands are immediately before the eye within the eyelid?
Skin, subcut fat, obicularis oculi, superior tarsal plate, Tarsal glands.
They run from medial to lateral palpebral ligaments on the upper and lower eyelids.
They have an opening on both the upper and lower eyelids
What other glands (not tarsal glands) are also contained within the eyelid?
Sebaceous glands (Zeis) located around the eyelash hair follicles.
What conditions may affect the eyelids and conjunctiva?
Infection of the conjunctiva and inflammation = Conjunctivitis
Painful burning sensation, usually treated with steroid eyedrops.
Infection of the sebaceous (Zeis) Glands = Stye (external hordeolum)
Infection of the Tarsal (Palpebral/ Meibomian) glands (inside the eyelid) –> inflammation due to duct blockage = Chalazion (internal hordeolum)
What may patients have within their conjunctiva (think purposefully put there)
Conjunctival implants –> metal inserted under the conjunctiva, must be careful when doing MRI
Label the image shown
What are the conjunctival fornices?
Conjunctival fornices are regions where the conjunctiva reflects from the sclera onto the inner eyelid
Foreign bodies/ contact lenses can get stuck here.
Presentation: Woman with gradual swelling of her upper eyelid over a period of 4 yrs. Contact lense user for astigmatism therefore hard contact lenses, it got stuck within the superior conjunctival fornix and herniated through the skin after becoming stuck in superior orbital fat
What muscle is found immediately under skin of the eyelid?
How does it contract?
Which CN innervates this muscle?
What are the two parts of the muscle?
Deep to eyelid skin and a bit of fat is the Obicularis Oculi muscle, which squeezes more laterally and superiorly first and then towards the midline.
Innervated by CNVII and closes the eye in a sphincter like fashion.
Helps squeeze the lacrimal glands to drain them and helps sweep tears across the eye towards drainage area.
Two parts: 1) Palpebral part 2) Orbital part
What reflex can be tested that includes action of obicularis oculi?
Corneal reflex:
Afferent –> touching of the cornea, sensory impulse via CN VC
Efferent –> CN 7 motor to obicularis oculi
Damage to what cranial nerve can lead to dry eyes?
- Cranial nerves 3/7/9/10 carry parasympathetics to the head and neck.
- Cranial nerve 7 has the autonomics that innervates the lacrimal gland, it hitchhikes on CN Va
What structures exist deep to the obicularis oculi muscle?
Deep to muscle you find the Tarsal plates of the eyelid (superior and inferior).
These plates blend in with the ring of dense connective tissue around the orbit called the Orbital septum.
This septum is important as it connects the superior and inferior tarsal plates with the medial and lateral palpebral (or canthal) ligaments.
What is the role of the Orbital septum?
Orbital septum is a tough fascia, helps prevent the eye from moving anteriorly and holds orbital fat inside the orbit, and limits the spread of infection to and from the orbit.
(Also remember is connects the tarsal plates to the margins of the orbit by the medial and lateral canthal ligaments.
What tendon is shown?
Why is this tendon special?
Tendon of levator palpebrae superioris (helps to lift the eyelid)
The tendon of levator palpebrae superiors blends into the superior tarsal plate, obicularis oculi m and even into the eyelid skin.
Remember LPS is innervated by CN 3.
Where does the superior tarsal muscle insert?
What type of muscle fibres is the superior tarsal muscle composed of?
What innervates this muscle?
How could there be damage to this muscle?
Superior tarsal muscle stretches between the LPS and the superior tarsal plate.
Superior tarsal muscle is composed of smooth muscle, therefore autonomically innervated.
Superior tarsal muscle if innervates by postganglionic sympathetic fibres from the superior cervical ganglion. (Remember these autonmics wrap around the internal carotid).
Patient may present with partial ptosis and damage to the superior tarsal muscle due to damage to superior cervical ganglion, or as autonmics pass the apex of the lungs (apical lung tumour). (plus horners syndrome).
Eyelids contain multiple arteries and sensory nerves:
Describe the arterial supply
what does the main supply come from?
Describe the nerve supply
where does this come from?
How do branches get to the eyelid?
- Majority of arterial supply to the orbit/ eyeball is by the opthalmic artery which branches off the ICA, given off immediately after the cavernous sinus
- There are also some tributaries from facial artery
- Innervation of the eyelid is from CN V1 and V2
- Note the key branches of these nerves are located around 2.5 cm from the midline of the face
- V1 and V2 branches travel via the supra and infraorbital foramen.
The Orbit: What bones form it?
What is special about the periosteal lining of the orbit?
what does this mean for blood accumulation?
- The periosteal lining of the bony orbit BINDS to sutures and foramen, and is loose in between
- When there is orbital trauma, blood accumulates compartmentalised, on scans it may look like pockets of blood.
What are the three foramen shown?
What structures pass through here?
- Optic canal –> runs through lesser wing of sphenoid bone, transmits optic nerve and opthalmic artery
- Superior orbital fissure –> sits between the lesser and greater wings of sphenoid bone, transmits CN3, 4, 6, V1 (lacrimal, frontal and nasociliary branches), superior and inferior divisions of opthalmic vein, sympathetic fibres from cavernous plexus. (Damage during orbital blow out fracture)
- Inferior orbital fissure –> transmits zygomatic branch of maxillary nerve and ascending branches of pterygopalatine ganglion, infraorbital vessels (inferior opthalmic vein)
(Note pterygopalatine ganglion is a parasympathetic ganglion found in pterygopalatine fossa, innervated by greater petrosal nerve (branch of facial), axons project to lacrimal glands and nasal mucosa.)
What structure is shown?
How is this relevant to infection?
Ethmoid air cells, laterally see the thin lamina papyracea of the ethnoid bone.
Infection can track easily from ethmoid air cells into the orbit and vice versa due to the thin bone.
What is the structure shown and what is its function?
Structure shown = Orbital septum, attached to the periosteum around the orbital margin
Function= To separate the orbit into multiple spaces, prevents infection spreading from front of orbit to back.
What is the function of the multiple connective tissue septa and spaces within the orbit?
Function is to support the eyeball, guide/limit movement and surround the fat filled compartments
What is the patient suffering with?
CT scan shows a build up of fluid behind the patient’s right eye
Retrobulbar bleeding = bleeding behind the eye
Can lead to compartment syndrome and is often associated with facial trauma.
This is a medical emergency!
Why is Retrobulbar bleeding a medical emergency?
Bleeding post septally or behind the eye is a medical emergency as there is a risk of compartment syndrome, pressure may build up so high as the compress vascular and neural supply (we want to avoid visual loss).
Label the image shown
- Superiorly –> transverse ligament of whitnall
- Inferiorly –> suspensory ligament of lockwood
- medially –> medial palpebral ligament
- laterally –> lateral palpebral ligament
- Around the eyelid –> Superior and inferior tarsal plates
- Coming up to meet the inferior tarsal plate –> fibrous extension to inferior tarsus
- Coming off the transverse ligament of whitnall – >levator aponeurosis
- medially and laterally off levator aponeurosis medial and lateral horn
How to you treat retrobulbar pressure?
- Complex series of ligaments span orbit and join the lateral and medial palpebral ligaments
- Two incisions:
- lateral canthotomy incision –> alleviates the pressure
- This incision can be extended inferiorly –> Inferior cantholysis
- Allows lower eyelid to fall down, pressure to be relieved and to preserve the optic nerve
- lateral canthotomy incision –> alleviates the pressure
Is this a retrobulbar bleed and how can you tell?
- No this is a subconjunctival bleed, bleeding stops where the conjunctiva stops at the corneal scleral junction
What are the check ligaments and what is their purpose?
Check ligaments are anterior thickenings of fascia covering the lateral and medial rectus muscles
They are slightly deeper than the medial and lateral palpebral ligaments
Check ligaments may limit eyeball abduction and adduction
What ligament comes off the inferior rectus and inferior oblique muscle?
What is its role?
The sheaths of the inferior oblique and the inferior rectus muscles blend and join into the check ligaments –> formthe suspensory ligament of the eye (acts like a hammock under the eye).
(also called suspensory ligament of lockwoods
What are the 3 layers of the eyeball?
Describe each layer (its role) and what it becomes anteriorly?
What supplies the optic nerve and where does it enter the eye? What is clinically relevant here?
Eyeball has 3 layers: Sclera, Choroid (vascular) and retina
Sclera = white of the eye, anteriorly becomes the cornea
Choroid layer is the vascular layer, anterior it becomes the ciliary body/ ciliary muscle, which itself leads into and becomes the iris.
Retina stops at the ora serrata and is the neural layer of the eye that actually allows us to see the imagery.
Optic nerve is supplies by one Central retinal artery. This supplies all the neural components of the retina. It enters the eye at the papilla.
Clinical: Central retinal arterial occlusion can cause blindness.
What is the macula?
What sits in the middle of the macula?
The macula is the part of the retina at the back of the eye, within its centre sits the fovea (yellow spot) which is the region of highest visual acuity.
What forms the sclera?
Sclera is the white of the eye formed by collagen and glycosaminoglycans –> polar which attracts water, enables sclera to remain fluid
Vessels and nerves also pass through the sclera.
What is the sclera replaced with anteriorly?
Is this structure avascular? How does it get its blood supply?
Describe its shape and how it gets nourishment?
What is it made from (majority)?
What is it responsible for?
What would a change to the shape of this structure alter?
Anteriorly the sclera is replaced by the transparent cornea (allows light through)
Cornea is avascular -> gets its blood supply by densely packed choroid layer, via diffusion
Protrudes anteriorly and gets its nourishment from lacrimal glnds and vascular beds nearby
Cornea –> not aneural, supplied by V1 of CN V
Majority of cornea made from type 1 collagen
Responsible for the optic power of the eye
Changes to shape can alter refractive ability of the eye
What is the uvea/ uveal tract?
Uvea/ Uveal tract is the continous vascular lining of the eye consisting of the:
Choroid posteriorly, ciliary body and iris anteriorly
It forms a huge vascular net that embeds these structures and notice the vessels and nerves pass through the sclera
What is Uveitis?
Uveitis = inflammation of this vascular network associated with autoimmune disorders and different parts can be affected
What layers form the iris?
Describe the layers and their function
The iris is formed by many different pigments superficially.
This epithelial pigmentation aids in light absorption.
Deep to the pigmented layer is the muscular layer formed of two muscles:
Dilator pupillae (under sympathetic control from the superior cervical ganglion, hitchhikes along CNVa to target) -> dilates pupil
Sphincter pupillae (directly around pupil), under parasympathetic cntrol, CN III to ciliary ganglion -> constricts pupil.
Describe how the pupil can change in size
PNS stimulation via CN III to ciliary ganglion –> causes circular muscles to contract and pupillary constriction
SNS stimulation via superior cervical ganglion in the neck which travels along internal carotid artery through carotid canal to foramen lacerum–> hitchhikes along CNVa–> causes radial muscle to contract –> pupillary dilation
What is the lens?
What reflex is the lens involved in?
What type of vision does this allow?
The lens is a flexible, transparent biconvex structure that can change its shape to bring about accommodation.
Accomodation occurs via the ciliary body, parasympathetics cause contraction of the ciliary muscle (circular muscle around the whole lens) leads to increased laxity in suspensory ligaments, lens becomes fatter to increase refractive ability for near vision
What is invovled in the development of refractive ability of the eye?
What is normal vision?
What is short or nearsightedness?
What is farsightedness?
Behvaiour and environment play roles in refractive development, but heritable factors are also important.
In normal vision (Emmetropia) –> focal point occurs on the retina
Short/ nearsightedness –> distant objects are focused in front of the retina when lens is “relaxed”
Farsightedness –> distant objects are focuse behind the retina when the lens is “relaxed”
What region exists anterior to the lens but posterior to the cornea?
Anterior to the lens but posterior to the cornea is the anterior and posterior chambers of the eye, both separated by the iris.
The iris forms the boundary between the anterior and posterior chambers, with communication via the pupil.
What is produced in the posterior chamber and by what?
Aqueous humour is produced in the posterior chamber by the ciliary epithelium
This aqueous humour fills the anterior and posterior chambers and provides nutrients and removes metabolic waste from the avascular cornea
What happens to the aqueous humour?
What is the role of the trabecular meshwork?
Aqueos humour is constantly produced, recycled and fluid drains into the canal of Schlemm via the trabecular meshwork
Trabecular meshwork provides resistance to fluid absorbance resulting in a 15mmHg pressure in the eye (range 10-21 mmHg)
What is the iridocorneal angle?
Between the cornea and the anterior surface of the attached margin of the iris is an angular recess called the iridocorneal angle
What can glaucoma cause
What are the two types?
Glaucoma can cause damage to the retina/ optic nerve and visual loss –> can be caused by increase in intraocular pressure although not always
1) Chronic open angle glaucoma ( COAG) –> reduced flow through trabecular network, slow and painless
2) angle closure glaucoma –> iridocorneal angle differences, where iris contacts trabecular mesh, may be ethnic origin related, can be painful
What fills the main part of the eye posterior to the lens?
what can happen with ageing?
Vitreous humour fills the main part of the eye posterior to the lens
Mostly filled by water and glycosaminoglycans, centre is more liquid, periphery more gel like.
Contacts the retina, the lens and ciliary body
With ageing:
- vitreous liquefaction with posterior detachment resulting in visual floaters
- vitreous shrinkage with age can pull on retina resulting in retinal detachment and macular holes
What does the retina run up to?
Retina runs up to the ora serrata near to the ciliary body
