Functional Antomy Of The Orbit And Eye Flashcards
Describe the orbital cavity, which bones make it up, what fissures are present?
Pyramidal shaped with apex pointing posteriorly
Superior to inferior: Frontal Sphenoid Ethmoid Lacrimal Zygomatic Nasal Maxillary
Superior orbital fissure and inferior orbital fissure below optic canal
Describe the blood
supply to the orbit
Main arterial supply (ICA->) ophthalmic A & it’s branches (-> orbital canal-> central retinal A)
Ophthalmic veins (superior and inferior) drain venous blood into cavernous sinus, pterygoid plexus and facial vein
Describe the nervous innervation to the eye
General sensory - trigeminal ophthalmic N (Va)
Special sensory vision from retina - optic N (2CN)
Motor nerves to muscles - oculomotor (3), abducens, trochlear (4), abducens (6)
CN 2,3,4,5,6
What are the weakest parts of the orbital cavity and why?
Medial wall and floor of orbit bc these are where the ethmoid paranasal sinus and maxillary paranasal sinus sit retrospectively
What is an orbital blow out fracture? Symptoms and signs
Sudden increase in intra-orbital pressure e.g. from retropulsion of eye ball by fist - fractures floor of orbit
Orbital contents can prolapse and bleed into maxillary sinus, Fracture site can trap structures e.g. soft tissue, extra ocular muscle located near orbit floor
- prevents upward gaze on the affect side (get pt to follow finger)
- history of trauma to orbit
- periorbital swelling, sinful
- double vision (worse on vertical gaze)
- numbness over cheek,lower eyelid and upper lip (and upper teeth and gums) on affected side due to injury to intra-orbital N (branch maxillary)
What are the eyelids made of
Consist of skin, subcutaneous tissue, tarsal plate,
muscles e.g. orbicularis oculi (palpebral part) - closes eyelids and levator palpebrae superioris - retracts eyelids
& glands e.g. meibomian (oily fluid come out end tarsal plate), sebaceous glands associated with lash follicle
How do you get a meibomian cyst? Treatment, location
Meibomian glands secrete oily (lipid- rich) substance onto eye lids, prevents evaporation of tear film and tear spillage - if blocked -> cyst
Deeper at the back of the lid -> can have excused or just goes with blood eye hygiene (clean lids with warm soapy water)
How do you get a stye?location, treatment
Eyelash follicle or its associated sebaceous gland can also block (infection- staphylococcus) causing styes
Edge of lid near eyelashes
Normally self- limited
What’s inflammation of the eyelids called, symptoms, treatment?
Blepharitis including skin, lashes, meibomian glands
Foreign body sensation and crusty
Goes with good hygiene, clean lids with warm soapy water
What is the orbital septum ?
Thin sheet of fibrous tissue originating from orbital rim periosteum blends with tarsal plates
Separates components/ contents orbital fossa and superficial structures (along with tarsal plates)
Just posterior to orbicularis occuli
Acts as a barrier against superficial infection spreading from pre-septal to post- septal space
What is periorbital cellulitis? Cause
Periorbital/pre-septal
Infection occurring within eyelid tissue superficial to orbital septum
Secondary to superficial infections e.g. bites, wounds, bacterial sinusitis in children
Confined to tissues superficial to orbital septum and tarsal plates
Ocular function unaffected
Difficult to differentiate between peri-orbital and more severe orbital cellulitis, of in any doubt refer urgently (high dose IV antibiotics+ surgical drainage)
What is orbital cellulitis? Signs, spread of infection.
More severe
Orbital/ post-septal
Infection within the orbit (orbital tissue/ fat/ extraocular muscles)
Signs:
Proptosis/ exophthalmos (pushes eyeball forwards)
Reduced +/- painful eye movements
Reduced visual acuity
Orbital veins (superior/ inferior ophthalmic veins) drain to cavernous sinus, pterygoid venous Plexus and facial veins - potential route for infection to spread intracranial e.g. cavernous sinus thrombosis, meningitis
Contents of the orbital cavity
Eyeball
Fat
Associated extra-ocular muscles (LPS, S oblique, IO, S rectus, MR, LR, IR)
Nerves and blood vessels (optic/ ophthalmic N, ophthalmic V/A
Lacrimal apparatus (production and drainage of tears)
What is the lacrimal apparatus?
Structures involved in tear film production and drainage
- lacrimal gland (tear production), lacrimal sac and ducts (tear drainage)
Ducts= canaloculi and nasolacrimal duct - blinking (orbicularis oculi palpebrae)distributes tear film across front of eye, rinsing and lubricating conjunctivae and cornea
- tears ultimately drained into nasal cavity
What is epiphora?
Obstruction to the drainage system leads to epiphora (overflow of tears over lower eyelid)
What are the three layers of the eyeball?
Outer: sclera (whit elf eye) continuous anteriorly as transparent cornea ‘fibrous tunic’
Middle: choroid, ciliary body and iris (vascular) ‘vascular tunic’
Inner: retina (inner photosensitive layer lying on an outer pigmented layer)
How is the eyeball maintained in position?
Suspension ligament (sits underneath)
Extra-ocular muscles
Orbital fat
What is the conjunctiva, where is it located?
Anterior surface of eyeball is covered with a conjunctival membrane (except for cornea)
Transparent mucous membrane -> mucous component of tear film
Covers white of eye (sclera) and lines inside of eyelids (forming a conjunctival sac)
Highly vascular small BVs within membrane
What is the limbus?
Junction of conjunctivae with cornea (cornea has its own epithelial covering)
What is a subconjunctival haemorrhage?
Haemorrhage from Bvs readily visible
|»_space; dense than conjunctivitis
Which structures refract light? Where do they refract light to?
All transparent:
Cornea and associated tear film (main)
Lens (behind pupil)
Aqueous humour and vitreous humour
Refract to macula on the retina
What is myopia and what causes it?
Short-sighted
Eyeball length too long so focal point anterior to retina
What is hypermetropia? What causes it?
Long- sighted
Eyeball too short so focal point posterior to retina
Explain the accommodation reflex. What’s the term for age-related inability to do this and what causes it?
Focusing near objects required greater refraction of light bc rays are more divergent so ….
- Pupils constrict (limit amount of light coming through
- eyes converge (image remains focused on same point of retina on both eyes)
- lens more biconvex/ fatter contraction by ciliary muscle
As we age lens becomes stiffer and less able to change shape - presbyopia (age related inability to focus near objects)
Describe the route of light signals within the eye to reach the sclera
Nerve fibres to optic nerve Ganglion cell Amacrine cell Bipolar cell Horizontal cell Cone Rod Pigment epithelium Choroid Sclera
Where are rods and cones found?
Outermost layer of retina
Compare rods and cones
Cones - more anterior, high definition, colour vision, active at high light levels, concentrated within the macula of the retina and fovea = only cones
Rods - more posterior, active at low light levels, don’t mediate colour vision, abundant in peripheral parts of retina (open eyes wide in dark)
How do we see?
Light hits photoreceptors and action potentials generated -> retinal ganglion cells -> collect in area of optic disc forming the optic nerve -> visual pathway -> occipital lobe interprets
What are some pathological causes of blurry vision?
- transparency of structures anterior to retina e.g. opacity in lens cataracts
- Ability of structures to refract light e.g. irregular corneal surface (astigmatism), ability of lens to change shape (presbyopia) or shape of eyeball
- retina/ optic nerve pathologies e.g. retinal detachment, age-related macular degeneration (most common cause adult blindness Uk) , optic neuritis
Decreased acuity
How can you test to see if blurry vision is due to errors of refraction?
Errors of refraction will have no effect on light travelling perpendicular to cornea/ lens
So acuity will improve with pin-hole testing
(If doesn’t improve problem with retina/ optic N/ transparency)
How is the shape of the eyeball maintained (not the position)?
Several chambers filled with fluid
Aqueous humour fills anterior and posterior chambers* (provides O2, glucose)
Vitreous humour within vitreous Chamber (more firm, transparent, helps keep the retina pushed back)
*anterior and posterior to iris
Where’s the blind spot?
The optic disc as there are no photoreceptors (where retinal ganglion cells axons meet forming the optic nerve)
Explain the production and drainage of aqueous humour
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 through trabecular meshwork into canal of schlemm (circumferential venous channel) -> venous circulation
Explain the pathology of chronic open- angle glaucoma (most common type) and the less common acute closed-angle
Drainage of aqueous humour from anterior chamber is blocked causing a rise in intra-ocular pressure
Chronic open- angle: trabecular meshwork deteriorates with age (many asymptomatic) -> increases IOP -> optic disc cupping (optic cup: disc ratio decreased slide 29) -> gradual loss of peripheral vision
Acute closed-angle: narrowing of iridocorneal angle -> iris listed forwards and closes-> , ophthalmic emergency. Intra-ocular pressure rises much more rapidly -> sight-threatening
How can you test for glaucoma?
Tonometry measure intra-ocular pressure when warm air is blown on the eyes
Signs and symptoms of acute angle- closure glaucoma. Treatment
> 55yrs
Acutely painful red eye
Fixed Irregular oval shaped pupil
Blurry vision
Halo’s around lights (corneal oedema)
Nausea and vomiting
✅Medical (drugs to reduce IOP) -> surgical treatment
