Flashcards in The Eye Deck (29)
Contents of the superior orbital fissure
Contents of inferior orbital fissure
Zygomatic branch of facial nerve
Contents of optic canal
Optic nerve, optic artery and vein
Describe the structure and function of the lacrimal apparatus
Lacrimal gland lies in fossa on superolateral part of orbit and secretes lacrimal fluid,
Drains through lacrimal ducts to lacrimal sac at medial angle of eye,
When the cornea gets dry, the eye blinks and the eyelids carry a film of fluid over the eye and sweeps dust and foreign material back to the medial angle.
Describe the gross structure and function of the eyeball
Spherical to permit a variety of movements within the orbit
Light sensitive cells transduce light energy into electrical impulses, and have a direct connection to the brain via the optic nerve
Electrical impulses are processed by the brain, resulting in sight and reflex functions
What is a blowout fracture?
Fracture of the orbital floor (maxillary bone) leading to herniation of the orbital contents into the maxillary sinus
Caused by trauma or injury leading to a sudden increase in intraorbital pressure
Causes vertical diplopia (as the inferior rectus muscle is trapped), enopthalmos, infra orbital anaesthesia
Symptoms of an orbital fracture
Restricted eye movements
Reduced visual field
Enopthalmos (or exopthalmos due to increased pressure)
Describe the nerve supply to the eye
Special sensory = optic nerve
Sensory supply to cornea = ophthalmic nerve
Motor innervation = oculomotor, trochlear, abducens (SO4 LR6 R3)
Parasympathetic = fibres from ciliary ganglion travel with inferior oculomotor nerve to sphincter papillae and ciliary muscles
Sympathetic = fibres from superior cervical ganglion travel with superior oculomotor to dilator papillae and tarsal muscles
Describe the structure of the optic nerve
It is an extension of the brain, so is surrounded by cranial meninges: Pia mata, arachnoid mata, dura mata
Has central artery and vein
What are the three layers of tissue around the eyeball
Sclera = protective outer fibrous layer, forms white of the eye, provides attachment for extraocular muscles, has transparent part at front to let light through (cornea).
Choroid = middle vascular layer, gives red light reflex, terminates anteriorly as the ciliary bodies.
Retina = inner layer with photoreceptors
What are the macula lutea, fovea centralis and optic disc?
All parts of the retina
Macula lutea is a specialised area for visual acuity, containing the most photoreceptors
Fovea centralis is the centre of the macula lutea
Optic disc is the circular depressed area where the optic nerve enters, has no photoreceptors (blind spot)
Describe the structure and function of the lens and iris
Lens = a transparent biconcave disc enclosed in a capsule, attached to the ciliary bodies by suspensory ligaments. Contraction of ciliary bodies changes the shape of the lens to focus light to the back of the retina
Iris = thin contractile diaphragm with a central aperture (pupil) for the transmission of light. Sphincter and dilator papillae muscles control the pupil size
Describe the different segments and chambers within the eye
Anterior segment = anterior to the lens, contains aqueous humor.
Split into anterior chamber (between the cornea and iris) and the posterior chamber (between the iris and the lens)
Posterior segment = posterior to the lens, contains vitreous humor
What is the function of aqueous humor and where is it made/found?
Provides 02 and nutrients to the lens
Produced by the ciliary bodies and flows out via the trabecular meshwork
Found in the anterior segment
What is the function of vitreous humor and where is it found?
Jelly like substance, supports lens and holds retina in place
Found in the posterior segment
Describe the structure and attachments of the eyelids
Palpebral conjunctiva over inner surface of eyelid
Bulbar conjunctiva covers the cornea (not over the iris)
Tarsal plates (connective tissue bands) strengthen the eyelids, contain the tarsal glands to lubricate the edge of the eyelids and prevent them sticking together
Difference between a style and a meibomian cyst
Meibomian cyst is inflammation of the tarsal glands
A style is inflammation of the ciliary glands
Both lead to obstruction of the ducts and a painful swelling in the eyelid
Describe the muscles and neural innervation involved in opening the eyelids
Levator Palpebrae Superioris - attached to the lesser wing of the sphenoid bone above the optic foramen, raises the superior eyelid, innervated by the Oculomotor nerve
Superior Tarsal Muscle - smooth muscle within the LPS, assists the LPS, sympathetic innervation
Explain the difference between partial and complete ptosis
Partial ptosis- occurs in damage to the sympathetic trunk in the neck (Horners syndrome) leading to denervation of the superior tarsal muscle
Complete ptosis- occurs in damage to the oculomotor nerve due to aneurysm, raised intracranial pressure or cavernous sinus thrombosis
What is glaucoma and what are the different types?
Glaucoma is raised intraocular pressure due to increased aqueous humor leading to compression of the retinal arteries and subsequent retinal damage and loss of vision.
Open angle: reduced outflow of aqueous humor through the trabecular meshwork, increases angle between cornea and iris.
Causes painless, gradual loss of vision
Closed angle: iris is forced against the trabecular meshwork, preventing drainage.
Emergency, can rapidly cause blindness
Describe cataracts and their clinical presentation
Flattening and hardening of the lens leading to gradual loss of vision and inability to focus light (glares)
Causes = diabetes, steroids, idiopathic
Describe orbital cellulitis and its clinical presentation
Inflammation of the eyelids due to infection
leading to pain, sticky discharge, fever, restricted eye movements, loss of vision, loss of colour vision
Describe thyroid eye disease and its clinical presentation
Ocular irritation leading to redness, diplopia, exopthalmos, lid retraction, lid lag, proptosis
Can lead to restrictive myopathy (due to enlarged extraocular muscles), optic neuropathy (muscles compress optic nerve), corneal ulceration
Describe the presentation of possible nerve palsies affecting the extraocular muscles
Oculomotor nerve palsy: down and out eye, pupil dilation, ptosis
Trochlear nerve palsy: paralysis of SO, patient can't depress abducted eye, diplopia walking down stairs, head tilt away from side of lesion
Abducens nerve palsy: paralysis of LR, patient can't abduct eye
What is papilloedema?
Swelling of the optic disc due to increased intracranial pressure (eg. Haemorrhage, tumour)
Pressure reduces venous return from the eye so fluid collects in retina and is visible in ophthalmoscopy
What is retinal detachment and how does it present?
Neural layer of retina separates from pigmented layer of retina, following a blow to the eye
Leads to flashes of light, 'floaters', darkening of peripheral vision
Describe occlusion of the retinal artery/vein and how they present
Central retinal artery occlusion: occurs in elderly due to embolism, leads to immediate and total blindness
Central retinal vein occlusion: occurs due to thrombosis, dehydration, leads to slow, painless loss of vision.
Gives stormy sunset appearance of retina due to numerous haemorrhages
Describe the blood supply to the eye
Opthalmic artery (branch of ICA)
Central artery of retina = specific branch to the retina