Session 8 Flashcards
Clinical application of anatomy of orbit
Orbital blow out fractures
Clinical application of anatomy of eyelids
Styles, meibomian cysts, blepharitis
Clinical application of anatomy of orbital septum
Pre-septal, post-septal, cellulitis
Clinical application of anatomy of lacrimal apparatus
Blockage
Clinical application of anatomy of eye ball
Acute red eye, CRAO, glaucoma
Clinical application of anatomy of how we see
Reduced visual acuity
Refractive vs non refractive
Description of shape of orbital cavity
Pyramidal shaped with apex pointing posteriorly
Describe walls of orbital cavity
4 bony walls
Base of pyramid faces anteriorly- tough orbital rim
Ethmoid bone = medial wall contribution
Maxillary bone = floor contribution
What are the weakest parts of the orbital cavity
Floor of orbit (maxillary bone) and medial wall (ethmoid bone)
Anatomical relations of the orbit
Anatomical relations of the orbit has implications for
Orbital surgery
Spread of infection (e.g. acute sinusitis involving ethmoid sinus)
Orbital trauma
What causes orbital blowout fracture
Sudden increase in intra-orbital pressure from trauma to the eye/orbit (e.g. from retropulsion of eye ball by fist or ball)
Fractures floor of orbit (maxilla)
What can happen in orbital blowout fracture
Management of orbital blowout fracture
Part of the ethmoid forming the medial wall of the orbit is known as the
Lamina papyracea- paper thin
What can cause orbital cellulitis
Air cells become infected (acute sinusitis), infection can break through thin lamina papyracea and track into orbit
Holes at apex of orbit
Optic canal- optic nerve and ophthalmic artery
Superior orbital fissure- CNs III, IV, VI and Va, superior ophthalmic vein
Inferior orbital fissure- infraorbital nerve (branch of Vb), inferior ophthalmic vein
What is more likely to fracture in orbital fracture, floor or medial wall
Floor
Superior ophthalmic vein communicates with
Cavernous sinus
Inferior ophthalmic vein communicate with
Pterygoid venous plexus
Opthalmic artery has several branches including the
Central retinal artery
Main artery supplying eye and structures
Opthalmic artery
Main arterial supply to orbit and eye
Opthalmic artery (branch of ICA), and its branches including central retinal artery
Main venous drainage of orbit and eye
Opthalmic veins (superior and inferior), connections with cavernous sinus, pterygoid plexus and facial vein
Retina is blood supplied by
Central retinal artery and underlying choroid layer
Ciliary arteries do what
Feed extensive capillary bed within choroid layer
Retina requires what
Both circulations to function properly:
Central retinal artery and Ciliary arteries from underlying choroid layer
Outer protective layer of eyeball comprises of
Tough fibrous sclera, continuous anteriorly as the transparent cornea
Provides attachment for extra-ocular muscles, gives shape to eyeball, continuous with dural sheath covering optic nerve at back of eye
What covers over the sclera
A thin transparent layer of cells called the conjuctaivae
Extends up to edge of cornea (limbus) anteriorly and reflects onto inner surface of eyelids posteriorly
Central retinal artery runs
In middle of optic nerve
What runs though the conjunctivae
Blood vessels
Layer of eyeball
Retina, choroid, sclera
Outer, middle, inner
What happens in conjunctivitis
Conjunctivae become inflamed
Blood vessels dilate and eye appears red
Usually viral aetiology
Highly contagious
Patients report uncomfortable and gritty eye with accompanying tearing
Treatment of conjunctivitis
Reassurance, hygiene advice, short course of topical chloramphenicol eye drops (reduces risk of secondary bacterial infection)
What can cause conjunctions in neonatal period
Infective organism such as chlamydia picked up from mothers vaginal mucous
Need systematic antibiotics- erythromycin
Eyelids consist of
Skin, subcutaneous tissue, muscles, tarsal plate
Key muscles running within eyelid
Orbicularis oculi (closes eyelid, facial nerve)
Levator palpebrae superioris (retracts eyelid, occulomotor and some sympathetic)
Glands within eye lids
Meibomian glands within tarsal plate- modified sebaceous, lipid layer of tear film, prevent tear evaporation and spillage over lid
Glands associated with lash follicle- sebaceous oily substance
Blockage of a gland can cause a lump within the eyelid
What is a Meibomian cyst
What is a style
What is blepharitis
Features of the middle layer of the eyeball
Richer vascular area
Includes choroid
Continues anteriorly as the ciliary body and Iris
ciliary body = vascular and muscular (ciliary process and muscle) connects choroid with iris
What is a subconjunctival haemorrhage
Can cause a red eye
One of the small conjunctival vessels ruptures often spontaneously, blood visible under transparent conjunctival layer, not painful, slowly resolve
What is the orbital septum
Thin fibrous sheet originating from orbital rim
Separates intra-orbital contents from muscle and subcutaneous tissue of eyelid
Barrier against infection spreading from superficial eyelid region (pre septal) into orbital cavity (post septal)
Infection involving superficial tissues is called
Pre-septal (periorbital) cellulitis
Anterior to septum
Infection involving tissues within orbit is called
Post-septal cellulitis
Posterior to septum
Features of periorbital (pre-septal) cellulitis
Secondary to superficial infections (bites, wounds)
Confined to tissues superficial to orbital septum (and tarsal plates)
Painful
Eye movements and vision remains unaffected
Features of orbital post septal cellulitis
Spread of infection from paranasal air sinus
Proptosis/exopthalmous
Reduced and or painful eye movements, reduced visual acuity
Why is post septal orbital cellulitis so dangerous
Orbital veins drain to cavernous sinus and pterygoid venous plexus
Potential route for infection to spread intracranially- cavernous sinus thrombosis, meningitis
What suggests serious underlying cause of red eye
Presence of acute pain e.g. uveitis (inflammation of choroid layer)
What is Uveitis
Inflammation of choroid layer
Red, painful eye, worse when trying to focus or look at bright lights
Associated with autoimmune conditions such as ankylosing spondylitis, IBS
Need urgent referral to ophthalmology for treatment (corticosteroids)
Features of the inner layer of the eye
Retina
Photosensitive and non-photosensitive parts
Cells either part of neurosensory layer or pigmented epithelial layer
Features of pigmented layer of retina
Lies between choroid and neurosensory layer, cells contain melanin
Melanin helps absorb scattered light that has passed into eye, reducing reflection and allowing us to focus images
Contents of orbital Cavity
Nerves, blood vessels, Fat, lacrimal apparatus, eyeball, extra-ocular muscles
Tear film consists of
3 layer- oily, water, mucus
Oily: Meibomian glands
Water: lacrimal gland
Mucus: goblet cells in conjunctiva
What does blinking do
Distribute tear film across surface of eye- rinsing and lubricating conjunctivae and cornea
What are lacrimal apparatus
Series of structures that collect and drain tear fluid
Obstruction to drainage causes epiphyseal (overflow of tears over lower eyelid)
Obstruction caused by infection,injury or stenosis
What makes up lacrimal apparatus
Eyeball is maintained in position by
Suspensory ligament, extra-ocular muscles, orbital fat
Features of neurosensory layer of retina
Senses light and is where photoreceptors (rods and cones) are found
Cones are responsible for high visual acuity and colour vision and many are concentrated in macula
Features of macula
Macula visible on fundoscopy as slightly darker, lateral to optic disc. Centre of macula called fovea, only contains cones
What causes colour blindness
Red green and blue sensitive cones respond to different wavelengths
Absence or dysfunction of one of these leads to colour blindness, inherited condition that affects males more frequently than females
What are rods responsible for
Vision in low intensity light, do not discern colours
Some towards central retina but more abundant in peripheral parts
What do photoreceptors do
Convert light energy into electrical impulses which reach optic disc
Optic disc represents the accumulation of retinal axons that leave the eye as the optic nerve- devoid of photoreceptors
Optic disc is blind spot
Overview of 3 layers of eye
What is responsible for central vision
Macula (and fovea): point of highest acuity vision
Thinnest part of retinal layer, lots of cones
Chamber of the eye
3- anterior, posterior and vitreous
Vitreous = transparent, jelly-like vitreous humour
Anterior and posterior = transparent liquid called aqueous humour
What is anterior chamber
Space between the cornea and iris, communicated with posterior chamber through pupil
What is posterior chamber
Space between iris and lens. Ciliary body and processes are found, which secrete aqueous humour filling both anterior and posterior chamber
Aqueous humour is important for
Supporting shape of eyeball by pressure it exerts, nourishment of lens and cornea as they are avascular
The aqueous humour drains through the
Irido-corneal angle into canal of Schlemm via trabecular meshwork and subsequently back in venous system
Sudden painless loss of sight in one eye developing over seconds can be caused by
Central retinal artery occlusion
Pale retina (ischeamia), cherry red spot = macula
Why do you get cherry red spot
Underlying choroidal layer blood supply un affected so remains perfused
Macular is thinnest part so underlying choroid accentuated due to surrounding pallor of ischemic retina
Production and drainage of aqueous humour
What is a glaucoma
Optic nerve damage secondary to raised intraocular pressure
2 types of glaucoma
Features of open angle glaucoma
Develops painlessly and insidiously over time
IOP can be determined using tonometry. Signs such as cupping of disc and visual field loss (especially peripheral) may be present
Treatment of open angle glaucoma
Topical medications (eye drops) That reduce production and increase drainage of aqueous humour e.g. Beta blockers such as Timolol
This reduces IOP, surgery may be required (trabeculectomy)
Presentation in closed angle glaucoma
Sudden onset of a painful red eye, blurred vision or halos around objects (due to corneal oedema)
Fixed or sluggish, semi-dilated often irregular, oval shaped pupil
Nausea and vomiting
Clinical examination on closed angle glaucoma
Eye is hard and tender to palpate though upper eyelid
Emergency requiring rapid recognition and management, irreversible sight loss can occur within a few hours
Management of closed angle glaucoma
Diuretics (acetazolamide), muscarinic eye drops (pilocarpine) and strong analgesia
Pupillary constriction helps open irido-corneal angle to improve route of drainage and reduce IOP
Surgery may be needed to make a hole in iris (iridotomy) with a laser or surgically, aqueous humour can flow from posterior to anterior chamber
Who is most at risk of closed angle glaucoma
Long sighted Middle Aged or elderly people with shallow anterior chambres
Features of the iris
Lies just anteriorly to lens
Thin contractile diaphragm, with a central aperture (pupil) for transmitting of light
Iris gives colour to eye, sphincter and dilator pupillae form the iris and control size of pupil
Autonomic nervous system
Features of lens
Posterior to iris
Transparent biconvex structure enclosed in a capsule
Without nerve innervation or blood supply, receives nutrients entirely from aqueous humour
Edges of the lens capsule attached to ciliary body by Suspensory ligament
What are cataracts
As we age, degradation of the proteins in the lens cause it to become clouded and less transparent
Cause visual impairment but treated with surgery
Contraction of the ciliary muscle (within ciliary body) are under the influence of the
Parasympathetic nervous system, alters tension in Suspensory ligaments
Allows for changes in shape of lens and its refractive power
At rest, ciliary muscle is relaxed and Suspensory ligaments are pulled taut, keeping lens flat
Important things to be able to see
What is refraction
The change in direction of light on passing through boundary of 2 different mediums
What is the accommodation reflex
Over view of rods and cones
Action potentials are propagated via
Retinal ganglion cells (RGCs)
Causes of decreased visual acuity
Most common cause of adult blindness in UK
Age related macular degeneration
How to check for decreased visual acuity due to reduced transparency of structures
Check for red reflex using ophthalmoscope- absent suggests light prevented from reaching retina and reflecting back e.g. cataracts
Most concerning cause of decreased visual acuity
Non refractive- retinal or optic nerve problem
Features of refractive cause of decreased visual acuity
Abnormal corneal surface
Inability of lens to change shape
Size of eyeball
How to tell if decreased visual acuity is from refractive error or not
What does pin hole testing do
Lacrimal fluid from the lacrimal gland enters the
Conjunctival sac through lacrimal ducts and passes into lacrimal lake at medial angle of eye
Fluid drains into lacrimal sac (S) before passing into nasal cavity via nasolacrimal duct (N)
What can occur if dirt or particles damage the cornea
Corneal abrasions and ulceration
Fortunately the outer epithelial layer of the cornea is constantly undergoing mitosis, so easily regenerates if damaged
Pathology interrupting the sympathetic innervation the eye leads to a
Partial ptosis
Which muscles control movements of the eyeball
Four Recti and 2 oblique
Most innervated by occulomotor
Lateral rectus and superior oblique innervated by Abducens and trochlear nerve respectively
4 recti muscles all arise from a
Common tendinous ring- fibrous cuff that surrounds the optic canal
How do the oblique muscles work with recti
Arise from bony walls of orbit and work synergistically with recti
What does LR6SO4 mean
LR supplied by Abducens, SO supplied by Trochlear nerve
What does asking the patient to follow a moving finger do
Text extra-ocular muscles
Allows the function of CN III, IV, and VI to be determined
Testing extra-ocular muscles
Why binocular vision
Allows for wider field of vision and depth perception, visual axis of both yes need to be aligned and conjugate eye movement is required
Two images that reach cortex are fused so perceived as one
Misalignment of visual axes causes
Diplopia
Muscles that move eye ball origin and attachment
Origin - apex of orbit
Attach- sclera
Extraocular muscles run in line with
Axis of orbit
Therefore some muscles attach at oblique angle
Confers several actions of movement on glove
Action of superior rectus muscle
Action of inferior rectus muscle
Action of superior oblique muscle
Action of inferior oblique muscle
Midline elevation and depression combine actions of
What is Ocular misalignment- Strabismus
