8. Anatomy Of Eye Flashcards
What are the openings into and out of the orbit?
Superior orbital fissure
Optic canal
Inferior orbital fissure
Which bones contribute to the orbit?
Frontal bone Ethmoid bone Lacrimal bone Maxilla Palatine bone Zygomatic bone Sphenoid bone
What are the blood vessels that enter the orbit?
Ophthalmic artery and its subsequent branches - including central retinal artery
What are the blood vessels that exit the orbit?
Ophthalmic veins (superior and inferior) drain into cavernous sinus, pterygoid plexus and facial vein
Which nerve supplies special sensory vision from retina?
Optic nerve
Which nerve supplies general sensory from eye?
Ophthalmic division of trigeminal
Which motor nerves supply the muscles of the eye?
Oculomotor
Trochlear
Abducens
What are some of the important anatomical relations of the orbit?
Paranasal air sinuses (maxillary and ethmoid)
Nasal cavity (nasolacrimal duct)
Anterior cranial fossa
What are the weakest parts of the orbital cavity?
Medial wall and floor of the orbit
What his the history of orbital blow out fractures?
Sudden increase in intra-orbital pressure (from retro pulse on of eye ball by fist or ball) fractures floor of orbit (maxilla)
What happens to the orbital contents in an orbital blow out fracture?
Can prolapse and bleed into maxillary sinus
Fracture site can trap structures such as extra ocular muscle located near orbital floor, and prevents upward gaze on affected side
What are the signs and symptoms of orbital blow out fractures?
History of trauma to eye/orbit
Periorbital swelling, painful
Double vision
Numbness over cheek, lower eyelid and upper lip on affected side - branch of maxillary division of CNV
What do the eyelids consist of?
Skin Subcutaneous tissue Orbicularis oculi (palpebral part) Levator palperae superioris Tarsal plate
What is the orbicularis oculi innervated by?
Facial nerve
What is the role of the orbicularis oculi in the eyelid?
Closing of eyelids
What is the levator palpebrae superioris innervated by?
Oculomotor nerve
What is the role of levator palpebrae in the eyelid?
Retract and elevate eyelid
Which glands contribute to tear film?
Meibomian glands
Sebaceous glands associated with lash follicle
What is a stye?
Blockage of sebaceous gland on eyelid
Usually caused by staphylococcal infection
Painful, red bump, white head
What is a chalazian?
Meibomian gland cyst - blockage
Painless
What is blepharitis?
Inflammation of lids (including skin, lashes and meibomian glands)
What is the orbital septum?
Thin sheet of fibrous tissue originating from orbital rim periosteum blends with tarsal plates
What do the orbital septum and tarsal players separate?
Subcutaneous tissue of eyelid and orbicularis oculi muscle from intra-orbital contents
What is the role of orbital septum?
Acts as a barrier against superficial infection spreading from the pre-septal to post-septal space
What is periorbital (pre-septal) cellulitis?
Infection occurring within eyelid tissue, superficial to orbital septum
Usually secondary to superficial infections e.g. from bites, wounds
Ocular function remains unaffected (eye movements/vision)
What is orbital (post-septal) cellulitis?
Infection within the orbit posterior or deep to the orbital septum
What are the features fo orbital cellulitis?
Proptosis/exopthalmous
Reduced/painful eye movements
Reduced visual acuity
Why can orbital cellulitis cause serious complications?
Orbital veins drain to cavernous sinus, pterygoid venous plexus and facial veins
Potential route for infection to spread intracranial
- cavernous sinus thrombosis
- meningitis
What are the contents of the orbital cavity?
Nerves and blood vessels Fat Lacrimal apparatus Eyeball Extra-ocular muscles
What are the 3 layers of the tear film and what are they produced by?
Oily, water, mucus
Meibomian glands, lacrimal glands, goblet cells in conjunctiva
What does blinking do?
Distributes tear film, rinsing an lubricating conjunctivae and cornea
What drains the tear film?
Lacrimal canaliculus into the lacrimal sac
What is epiphora?
Overflow of tears over lower eyelid due to obstruction in lacrimal sac
What maintains the position of the eyeball?
Suspension ligament - like a sling
Extra-ocular muscles
Orbital fat
What are the 3 layers of the eye?
Outer - sclera
Middle - choroid
Inner - retina
What is iritis?
Anterior uveitis
Painful, red eye, photosensitive
What produces the aqueous humour?
Ciliary body
What is the vitreous humour?
Firm, clear gel-like fluid
Fills large portion of globe of eye
Pushes up against retina but not stuck to it
What is the anterior surface of the eyeball covered with?
Conjunctival membrane - reflects onto inner safe of eye lids
Which blood vessel is the retina supplied by?
Central retinal artery (branch of ophthalmic artery) but also draws supply from underlying choroid layer
Where does the choroid layer get its blood supply from?
Ciliary arteries feed extensive capillary bed within choroid layer
What are the branches of the ophthalmic artery?
Central retinal artery Posterior ciliary Anterior ciliary Supra-orbital Supratrochlear
What happens in central artery occlusion?
Ischaemia of retina - pale
What refracts light to bring it into focus?
Tear film, cornea, lens (and aq. and vitrous humour)
What happens in the accommodation reflex?
Pupil constricts
Eyes converge
Lens becomes more biconvex by contraction of ciliary muscles
Why do eyes converge in accommodation reflex?
To ensure image remains focused on same point of retina in both eyes
What happens to the lens with age?
Becomes stiffer and less able to change shape - presbyopia
What is the ciliary muscle?
A ring of muscle surrounding the lens, can pull it tight or let it relax
What is a flat, thin lens good for?
Looking at distant objects
What are rods?
Active at low light levels, do not mediate colour vision
Abundant in peripheral parts of retina
What are cones?
High definition, colour vision - active at high light levels
Concentrated within macula of the retina
Fovea = only cones
What converts light signals into action potentials?
Photoreceptors
How are action potentials propagated?
Via retinal ganglion cells
RGC axons oldest in area of optic disc forming optic nerve
Action potentials propagated along visual pathway to occipital lobe for interpretation
What is the optic disc?
No photo receptors (blind spot)
What can decrease visual acuity?
Pathology affecting:
- transparency of structures anterior to retina e.g. cataract
- refractive ability of structures anterior to retina e.g. astigmatism, presbyopia
- retina or optic nerve e.g. retinal detachment, age-related macular degeneration, optic neuritis
What is astigmatism?
Irregularity of corneal surface
What is presbyopia?
Reduced ability of lens to change shape
If someone’s visual acuity is corrected with pin-hole testing, what is the diagnosis?
Errors of refraction
If someone’s visual acuity is not corrected with pin-hole testing, what is the diagnosis?
Indicates pathology involving retina or optic nerve
Why does pin-hole testing work in errors of refraction?
Light entering directly perpendicular to the cornea/lens does not require refraction to be focused onto macula
What is the most common cause of blindness in the UK?
Age-related macular degeneration
Describe the production and drainage of aqueous humour
Secreted by ciliary processes within ciliary body
Flows from posterior chamber, through pupil into anterior chamber
Nourishes lens and cornea
Drains through iridocorneal angle (between iris and cornea)
Via trabecular mesh work into canal of Schlemm
What is the canal of Schlemm?
Circumferential venous channel draining into venous circulation
What is glaucoma?
Optic nerve damage secondary to raised intraocular pressure
What causes rise in intraocular pressure?
Drainage of aqueous humour from anterior chamber blocked
What is chronic/open-angle glaucoma?
Trabecular mesh work deteriorates as age
Many asymptomatic
Increased IOP leading to increased optic disc cupping
Gradual loss of peripheral vision
What is acute/closed-angle glaucoma?
Narrowing of iridocorneal angle
Ophthalmological emergency
What are the signs and symptoms of acute closed angle glaucoma?
Acutely painful red eye Irregular oval-shaped pupil Blurring of vision Halos around lights Nausea and vomiting Medical then surgical treatment
