8) Anatomy of Orbit and Eyeball Flashcards
What is contained in the orbit?
Eyeball, its muscles, nerves, vessels and lacrimal apparatus
What bones form the superior orbit?
Frontal and sphenoid
What bones form the lateral orbit?
Zygomatic and sphenoid
What bones form the medial orbit?
Ethmoid, maxillary, lacrimal and sphenoid
What bones form the inferior orbit?
Maxillary and zygomatic
What are the entrances to the orbit and through which bone?
Optic canal, superior orbital fissure and inferior orbital fissure
Sphenoid bone
What are the vulnerable points of the orbit?
Inferior and medial walls are thin
What are the 3 layers of the eyeball?
Outer fibrous
Middle vascular
Inner
What does the outer fibrous layer consist of?
Sclera and cornea
What does the middle vascular layer consist of?
Choroid, ciliary body and iris
What forms the inner layer of the eyeball?
Retina
What features can be seen in fundoscopy?
Optic disc - where optic nerve enters eye
Vessels, macula with fovea at centre
How can you tell which eye is being examined by the fundus?
Optic disc is on nasal side
What are the consequences of retinal detachment?
If left too long, cells of retina will die leading to partial blindness
How can meningitis affect the eye and why?
Optic nerve is surrounded by meninges so inflammation can cause photophobia - discomfort or pain of light exposure
What are the three chambers of the eye?
Anterior: cornea to iris
Posterior: iris to lens
Vitreous: filled with vitreous humour
How does the aqueous humour drain?
Irido-corneal angle into canal of Schlemm via trabecular meshwork then into venous circulation
What is glaucoma?
Obstruction in drainage of aqueous humour so intra-ocular pressure increases
What are the consequences of untreated glaucoma?
Damage to optic nerve = vision impairment and blindness
What is the cause of open angle glaucoma?
Blockage in trabecular meshwork, causing rise in intra-ocular pressure, cupping of optic disc and/or visual field loss
What is the treatment for open angle glaucoma?
Reduction in production of aq. humour or surgery
What is the cause of closed angle glaucoma?
Irido-corneal angle narrowed as access to trabecular meshwork is blocked off. Rapid rise in intra-ocular pressure
How does closed angle glaucoma present?
Painful red eye, blurred vision, oval shaped pupil, hard eye
What is the treatment for closed angle glaucoma?
Muscarinic eye drops, analgesia and drugs to reduce intra-ocular pressure
Describe the iris:
Coloured and have sphincter and dilator pupillae muscles
What structure are involved in changing lens shape?
Ciliary muscle fibres, suspensory ligaments and autonomic nerves
What causes cataracts?
Degradation of proteins in lens
What is the accommodation reflex?
Automatic contraction of pupil and convergence of eyes when suddenly focusing on a near object after a distant object
What is presbyopia?
Impaired ability to accommodate
What is the mechanism of the accommodation reflex?
Contraction of ciliary muscles causes loosening of suspensory ligament and lens becomes rounder
What are the functions of the eyelids and lacrimal glands?
Preventing injury, foreign bodies, excessive light and dryness
What gives eyelids their shape?
Tarsal plates (dense bands of CT)
What is the difference between a Meibomian cyst and a stye?
Cyst - tarsal gland inflamm
Stye - pus in ciliary glands
What muscles cause opening of eyelid?
Levator palpabrae superioris (CN III) Superior tarsal (sympathetic) (minor)
How would an oculomotor lesion and Horner’s syndrome differ in presentation (eyelid)?
Complete ptosis in CN III lesion
Partial in Horner’s
Describe the drainage of tears:
Lacrimal lake at medial angle of eye, then in lacrimal sac via lacrimal canal. Into nasal cavity by nasolacrimal duct
What is the conjunctiva and its clinical relevance?
Film on top of cornea
Inflamed in conjunctivitis causing redness
Describe the arterial supply to the eye:
ICA -> ophthalmic artery -> central retina artery
Describe the venous drainage of the eye:
Central retinal vein -> superior ophthalmic vein -> cavernous sinus
What is the innervation of the extra-ocular muscles?
LR6 SO4 R3
Where do the recti muscles originate?
Common tendinous ring around optic canal
Where do the oblique muscles arise?
Bony walls of orbit
What does superior oblique travel through?
Trochlea (ligament sling)
What is the movement of superior oblique?
Down and in
What is the movement of inferior oblique?
Up and in
What is the movement of superior rectus?
Up and out
How would you test the eye muscles in isolation?
Line up gaze with line of attachment of muscle e.g. SR - look out then ask to move eye up
How does a blow out fracture of the orbit present?
Blood in maxillary sinus
Inferior rectus moves down so eye can’t move upwards (tethered)
Loss of sensation under eye, damage to infra-orbital nerve
