(5.1) The Eyes Flashcards
What structure runs in the Optic Canal?
Optic nerve
Arteries & Veins to the Retina
What are the main bones make up the orbit?
- Roof: Frontal
- Floor: Maxilla
- Medial: Ethmoid
- Lateral: Zygomatic
- Sphenoid (roof & lateral)
What structures run the Superior Orbital Fissure?
- Lacrimal N
- Frontal N
- Trochlear N (CN XI)
- Superior br. Of Oculomotor N (CN III)
- Nasociliary N
- Inferior br. Of Oculomotor N (CN III)
- Abducens N (CN XI)
- Opthalmic V
- Sympathetic Nerves
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What is the happens in the Optic Chiasma? Hence what function does it achieve?
Optic nerve fibres PARTIALLY cross within it, to allow the visual cortex to receive the same hemispheric visual field from both eyes
What is a blow out fracture?
A fracture that displaces the orbital walls (usually medial and inferior, the weakest bones) and its contents
Which two ways may an infection from the orbit spread to cause meningitis?
- The Optic nerve is covered by the maters of the meninges e.g. continuous with the brain
- The Opthalmic V that drains the eyes continues into Cavernous Sinus, which in connected to the cranial cavity
How may a raised intracranial pressure affect the eyes?
- The Optic nerve is surrounded by the meninges with CSF
- Compression to the Optic Nerve -> compression to arteries supplying retina -> necrosis -> blind
- Occluded vein -> Papilloedema (Oedema of optic disc) + Venous engorgement
The medial and inferior are the weakest Orbital walls, what structures are likely to be involved by each if they are fractured?
- Medial -> Ethmoidal & Sphenoidal paranasal sinuses
- Inferior -> Maxillary paranasal sinuses
What are the 7 extraocular muscles? What are their innervations and actions?
- Superior Rectus - Oculomotor (CN III) - Look up
- Inferior Rectus - Oculomotor (CN III) - Look down
- Lateral Rectus - Abducens (CN XI) - Abduct
- Medial Rectus - Oculomotor (CN III) - Adduct
- Inferior Oblique - Oculomotor (CN III) - Extorsion (Look up + out)
- Superior Oblique - Trochlear (CN IV) - Intorsion (Look down + out)
- Levator Palpebrae Superioris - Oculomotor (CN III) - Lifts upper eyelids
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What are the blood supplies and venous drainages of the retina?
- Opthalmic A -> Central A of retina (an end artery)
- Central V of retina -> directly to Cavernous Sinus or via Opthalmic V (through Superior Orbital Fissure)
What is the Optic disc?
Optic disc = opening of Optic Canal at the cranial end eg
- Exit for axons of the Optic Nerve
- Exit of the major veins draining the retina
- Entrance of the major blood vessels of the retina
What is Ptosis? What are the possible causes?
Ptosis = dropping of the upper eyelids
- Damage of Oculomotor N -> Paralysis of Levator Palpebrae Superioris
- Horner’s Syndrome -> Lost of Sympathetic fibres -> Paralysis of Superior Tarsus -> partial ptosis
Where are the Tarsal glands located? What is their function?
- Within the Superior Tarsal
- Secrete oil, which helps to keep water in the eyes
What are the 4 structures in the Lacrimal Apparatus? Describe their roles individually.
- Lacrimal gland: secretes Lacrimal fluid (tears)
- Lacrimal ducts: drains into Conjunctival Sacs
- Lacrimal Canaliculi: drains into Lacrimal Sac (at the medial angle of the eyes)
- Nasolacrimal duct: drains into the Inferior Nasal Meatus (inferior to the inferior nasal concha)
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What extrocular muscles are used when you look to the left?
- Left eye: Lateral rectus
- Right eye: Medial rectus
Which Sensory neurone and which Motor neurone are involved in corneal blinking reflex?
- Sensory: CN Vi, Opthalmic N sensing irratation to the Cornea
- Motor: CN VII, Facial N supplying Orbicularis Oculi
What innervates for tear production? What are its functions?
- Parasympathetic fibres of Facial Nerve CN VII
- Provide nutrients & oxygen to Cornea
- Contains bactericidal lysozymes
Why may a patient with a damaged Oculomotor Nerve presents with a dilated pupil?
Paralysis of Sphincter Pupillae, unopposed action from Dilator Pupillae
What is Stye?
Infection of the Sebaceous gland at the base of eyelash (針眼)
What is Exopthalmos? What are the possible causes bilaterally and unilaterally?
- Bilateral: Grave’s Disease (Hyperthyroidism)
- Unilateral: Aneurysm/Haematoma
What is Horner’s Syndrome? What are the signs and symptoms?
Horner’s Syndrome = interruption of a cervical sympathetic trunk, hence lost of functions on the IPSILATERAL (same) side of the head
- Miosis: constricted pupil due to unopposed action of Sphincter Papillae
- Partial Ptosis: partial dropped upper eyelid due to paralysed Superior Tarsal (not a complete ptosis, levator palpebrae superioris unaffected)
- Temperature & redness: due to vasodilation
- Anhydrosis: absence of sweating
What is Exposure Keratitis? What is Ectropion?
Exposure Keratitis = dried out cornea
Ectropion = ulcerated corneal surface
Why may a disruption to the central artery of the retina cause immediate blindness?
It’s an end artery
What are the structures that form the protective layer of the eyes? What are their roles?
- Posteriorly: Sclera, provide attachment for extraocular muscles
- Anteriorly: Cornea, a transparent refractive medium
What structures form the middle vascular layer of the eyes? What is each of their functions?
- Iris: consist Sphincter & Dilator Pupillae that determines the amount of light enters the eyes
- Choroid: the largest vascular layer
- Ciliary Body (anterior endings of Choroid): contract to control the shape of the lens, hence to focus the light onto retina
What causes an Open Angle Glaucoma?
- The drainage of Aqueous Humour is blocked at the Trabecular Meshwork/Scleral Venous Sinus, hence increasing intra-ocular pressure
What produces Aqueous Humour and how is it drained?
- Produced by Ciliary Processes -> Posterior Chamber -> through Lens -> Anterior Chamber
- Drains into Trabecular Meshwork -> Scleral Venous Sinus
What happens in the lens when someone is reading? Through which nerve it is achieved?
- Parasympathetic input -> Oculomotor nerve -> Ciliary Body contract -> Lens become fat -> light is refracted more -> focus on Retina
What are the cells that are found in Retina that are responsible in providing vision? Where is vision the most acute?
- Photoreceptors
- Rods: sensitive to low light, sees black and white
- Cons: sensitive to bright lights, sees colours
What are the two main spots that are seen in a fundoscopy? Where are they seen from a fundoscope? What are their roles?
- Optic Disc (Blind Spot), found on nasal side: entrance/exits for neurovasculatures of the Retina
- Macula found laterally to Optic disc: high density of Cones, serve for acuity of vision
How do you test Superior Oblique muscle?
- Ask the patient to look medially (adduct) first
- Then ask the patient to look down
e.g. The downward action isn’t by Inferior Rectus
