Rods are sensitive to low/high levels of light and function for night vision and peripheral vision/colour vision
Cones function for night vision and peripheral vision/colour vision and acuity/seeing far off things
Rods - low levels of light, night vision/peripheral vision
Cones - colour vision and visual acuity
What are the 7 extra ocular muscles?
What is the mnemonic to remember which nerves supply which muscles?
Lateral rectus
Medial rectus
Superior rectus
Inferior rectus
Superior oblique
Inferior oblique
Levator palpebrae superioris
LR6 SO4 AO3
What are the different types of refractive error?
Myopia - short-sighted
Hyperopia - long-sighted
Astigmatism
Presbyopia
When taking a history from a patient, what symptoms would you ask about that are specific to vision? What other questions might you ask if taking an ophthalmic history?
Glare
Distortion
Photophobia
Flashing lights/floaters
Oscillopsia
Diplopia
Pain? Discomfort/dryness? Red/swollen? Itch? Discharge/watering?
What are some causative organisms of bacterial conjunctivitis in...
- neonates?
- other ages?
Neonates - Staph aureus, Neisseria gonorrhoea, Chlamydia trachomatis
Other ages - Staph aureus, Strep pneumoniae, Haemophilus influenzae
Bacterial conjunctivitis - treatment
Swab
Topical antibiotics - usually Chloramphenicol (drops or ointment) (Avoid Chloramphenicol if patient has a history of aplastic anaemia/allergy)
What cause of viral conjunctivitis is commonly associated with a preceding URTI?
Adenovirus
What are some of the features of chlamydial conjunctivitis?
Often chronic history
Unresponsive to treatments
May or may not have symptoms of urethritis, vaginitis
Suspect if bilateral conjunctivitis presents in young adults
What clinical signs will be present in someone with bacterial keratitis? How is it treated?
Big area clouding the cornea
Hypopyon - line of bacterial film along the bottom of the cornea, sight-threatening
Require admission for hourly drops of antibiotics and daily review
What are the causes of viral keratitis? Which is more common? What clinical features would be seen?
Herpes simplex (most common)
- Dendritic ulcer
- Very painful
- May be recurrent, becoming less painful as the sensation in the cornea lessens DONT TREAT WITH STEROIDS
Adenoviral
- Bilateral, usually following a URTI contagious
- May affect vision
- May give topical antibiotics prophylactically, and steroids CAN be used to speed up recovery
What fungi can cause keratitis? What are they associated with?
Acanthomoeba and Pseudomonas aeruginosa
Associated with contact lenses and a history of trauma associated with vegetation e.g. Farmers
Describe Orbital Cellulitis, what condition it's commonly associated with, and what precaution needs to be taken regarding investigation.
Cellulitis of septum (due to focal Orbital infection/post-operative) resulting in compartment syndrome and an increase in orbital pressure
Causes pain, especially on eye movements, proptosis (as a severe complication), pyrexia, is often associated with paranasal sinusitis and can be sight-threatening
CT scan needs to be performed to identify orbital abscess and determine if pre- or post-septal
What are the causative organisms of orbital cellulitis? What is the treatment?
Staphylococcus
Streptococcus
Coliforms
Haemophilus influenzae
Anaerobes
V broad spec antibiotics given and patient monitored closely. May require drainage. If there is any indication of restriction of muscles or optic nerve dysfunction then scan
What is endophthalmitis? What is the most common causative organism and how is it treated?
"Devastating" infection within the eye, very painful, very red eye, decreasing vision and sight threatening
Can be endogenous (often common commensals, Staph epidermidis being most frequent) or POST-OPERATIVE - major concern associated with surgery
Treatment - intravitreal amikacin/ceftazidime/vancomycin
What is chorioretinitis? What causes it?
Infection at the back of the eye
Causes
- CMV in HIV patients (pizza pie appearance)
- Toxoplasma gondii
- Toxocara canis
What antibiotics are commonly used in eye infections?
Chloramphenicol - inhibits peptidyl transferase, side effects include allergy, aplastic anaemia and "grey baby syndrome"
Penicillins and cephalosporins
Quinolones e.g. Ofloxacin inhibit DNA gyrase = cell death. Only used in bacterial keratitis
Fusidic acid - used to treat Staph aureus
Gentamicin - treats gram negatives including Pseudomonas
What substance can be used to better investigate ocular trauma?
Fluorescein drops
What is the name given to a fluid level of blood in the anterior chamber?
Hyphaema
What group is retinal detachment more common in?
Myopes (short-sighted people)
What is the term given to a bruised retina?
Commotion retinae
What is Seidel's test?
After applying fluorescein to an injured eye, it can be seen to dilute as fluid passes out of the sight of injury
What is sympathetic ophthalmia?
Exposure of one eye to antigens causes an immune reaction and subsequent Inflammation in both eyes
Can result in bilateral blindness from a unilateral injury, extremely rare
What should ALWAYS be done if an intra-ocular foreign body is suspected?
X ray orbits
What is of more concern when considering the eye - acid or alkali burns? Why?
Alkali burns - easy, rapid penetration into eye and continues to burn through structures. Concern is limbus ischaemia
Acid - less worrying, causes proteins to coagulate and there is little penetration
What should be done immediately following a chemical burn? What should give pause for thought and why?
Irrigation!
Unless cement/lime is suspected - this should be removed first prior to irrigation as if it dissolves it will form an alkali solution
Following irrigation, eye can then be assessed using a slit lamp
What compound, which helps disrupt the lipid layer of the tear film and aids in the penetration of some drugs, is used as a preservative?
Benzalkonium
With which nerve palsy might the patient present with tilting their head?
CN IV
What serious pathology must be suspected if someone presents with a painful CN III nerve palsy?
Aneurysm!
Name some causes of sudden visual loss
Vascular causes
Vitreous haemorrhage
Retinal detachment
Age-related macular degeneration (ARMD) - WET TYPE
Closed-angle glaucoma
Describe the blood supply to the eye
Branches of the ophthalmic artery - central retinal artery (inner 2/3rds of retina), choroid (supplies outer 1/3rd) and posterior ciliary arteries (supply the Optic head)
Central Retinal Artery Occlusion (CRAO) - presentation, cause and management
Presentation - sudden, painless loss of vision, relative afferent pupil defect (RAPD). On fundoscopy, appears as a pale retina with thin, thread-like vessels
Causes - carotid artery disease (most common), emboli from the heart (unusual)
Management - if within 24 hours, ocular massage to attempt to convert to BRAO. If later, establish source of embolus and assess/manage risk factors
What is amaurosis fugax?
Transient painless vision loss due to CRAO
Described as a "curtain coming down" over vision.
Lasts approx 5 mins with full recovery
Manage with urgent referral to stroke clinic and aspirin
Describe the general sensory nerve supply for the 3 branches of the trigeminal nerve
Opthalmic
- skin of the upper eyelid
- cornea
- all of the conjunctiva
- the skin of the route/bridge/tip of the nose
Maxillary
- skin of the lower eyelid
- skin over the maxilla
- skin of the ala of the nose
- skin/mucosa of the upper lip
Mandibular
- skin over the mandible and the TMJ joint (apart from the angle of the mandible, which is supplied by S2,S3)
Describe the sensory (afferent) and motor (efferent) pathways in the blink reflex
Sensory
- APs are conducted from the cornea via CN V1 branches to the trigeminal ganglion
- These are then transmitted to the pons
Motor
- APs are conducted via CN VII to the eyelid part of the orbicularis oculi
Through what nerves do ALL parasympathetic axons leave the spinal cord?
CN III, CN VII, CN IX, CN X and sacral spinal nerves
Describe CN III (Oculomotor)...
- where does it connect with the CNS?
- what cranial foramen does it pass through?
- which eye muscles does it supply?
- connects with CNS at junction between midline and pons
- passes through the superior orbital fissure
- supplies somatic motor to Superior, Medial and Inferior Rectus (SR, MR and IR), and Inferior Oblique (IO)
- also supplies somatic motor to Levator Palpebrae Superioris (LPS)
Describe the role of ciliary nerves in the eye
Supply autonomic axons to control the diameter of iris and the refractive shape of the lens
Long ciliary (form the first part of the blink reflex)
- sympathetic
- somatic sensory
Short ciliary
- sympathetic
- parasympathetic
What are the vestibulo-ocular and oculocardiac relfexes?
Vestibulo-ocular
- turns the eyes in the opposite direction to head movement, to allow the eyes to focus and stabilise gaze
- involves CNS connections between CN VIII and CNs III, IV and VI
Oculocardiac
- reflex bradycardia in response to tension on extraocular muscles/pressure on the eye
- involves CNS connections between CN V1 and CN X
How does sympathetic innervation affect the eye?
Opens eyes wider
Gets more light into the eyes
Allows focus on far away objects
??? emotional lacrimation?
How does parasympathetic innervation affect the eye?
Allows orbicularis oculi to work
Get less light into the eye (to protect the retina)
Allows focus on near objects
Relfex lacrimation (to wash away stimulant foreign body and clear the cornea)
What condition might present with a miotic pupil (excessively constricted)?
Horner's Syndrome
What might the following indicate...
- fixed pinpoint pupil
- fixed dilated pupil?
Both are serious pathological signs
Fixed pinpoint - opiate drugs
Fixed dilated - CN III pathology
Describe the pupillary light reflex
- Special sensory (afferent) limb of the reflex is ipsilateral - CN II
- Motor (efferent) limb of the relfex is bilateral - CN III
- Direct light relfex occurs in the stimulated eye, and a consensual reflex occurs in the non-stimulated eye
How does the ciliary body control the lens?
Connected to the circumference of the lens via the suspensory ligament
Ciliary muscle (within the ciliary body) relaxes in far vision - no involvement of parasympathetics, suspensory ligament tightens and the lens flattens
Ciliary muscle contracts in near vision - parasympathetic involvement, suspensory ligament relaxes and the lens becomes spherical to focus on closer objects
What are the 3 components of the accommodation reflex? What nerves are involved?
Bilateral pupillary constriction - CN III
Bilateral convergence of both eyes towards the midline - CN III
Bilateral relaxation of lens - CN III
Horner's Syndrome - symptoms and causes
Symptoms
- Miosis (small pupils)
- Ptosis (drooping eyelid)
- Anhydrosis (reduced sweating)
- Increased warmth and redness
Causes - due to impaired sympathetic innervation of head and neck
- Root of neck trauma
- Carotid dissection
- Internal jugular vein engorgement
- Deep cervical lymphadenopathy
- Pancoast tumours from the apices of the lung
In the case of a fractured zygoma, what direction does it tend to rotate in and what defect in vision may occur as a result?
What other local pathology may develop?
Fractured zygomas tend to rotate medially towards the floor of the orbit - Orbital blowout fracture
This may result in the lowering of the eye towards the orbital floor, which would cause vertical diplopia
The fractured zygoma may cause the infraorbital NVB within the infraorbital canal to become damaged, resulting in general sensory deficit of the facial skin
What is the purpose of the conjunctiva of the eye?
What is the name of the area where the lower eyelid meets the white sclera?
Purpose - defensive barrier to foreign bodies
Name of the area where the lower eyelid meets the sclera is the conjunctiva fornix
Describe the lacrimal apparatus: where is lacrimal fluid produced, which nerve innervates this, and where does the fluid drain to?
Lacrimal fluid is produced in the lacrimal gland - parasympathetic innervation (CN VII)
The fluid washes over the eye medially and drains through the lacrimal puncta to the canaliculi
Then it drains down the nasolacrimal duct, where it eventually drains to the inferior meatus
Describe the 3 layers of the eye, including the important features found in each...
1) Fibrous outer layer
2) Uvea (vascular middle layer)
3) Retina (photosensitive inner layer)
Fibrous outer layer
- sclera
- cornea
Uvea
- Iris - determines pupil diameter
- Ciliary body - controls the iris, shape of the lens and secretion of aqueous humour
- Choroid - responsible for nutrition and gas exchange
Retina
- macula (with the centre being the fovea)
- optic disc
Describe the anterior and posterior segments of the eye
Anterior segment
- In front of the lens
- Divided into 2 chambers
- anterior chamber - between the cornea and the iris, contains aqueous humour
- posterior chamber - between the iris and the suspensory ligaments, also contains aqueous humour
Posterior segment
- behind the lens
- 2/3rds of the eye
- Contains the vitreous body - this contains vitreous humour and is a common site for "floaters"
What is the name of the area around the iris, at the very edge of the sclera?
The Limbus (or corneascleral junction)
Describe the four steps of aqueous solution circulation
1) Aqueous solution is produced and secreted by the ciliary body (made up of smooth muscle and blood vessels)
2) Aqueous circulates within the posterior chamber and nourishes the lens
3) Aqueous passes through the pupil into the anterior chamber and nourishes the cornea
4) Aqueous is reabsorbed into the scleral venous sinus (Canal of Schlemm) at the iridocorneal angle
What artery passes through the cavernous sinus?
The internal carotid artery
Describe the blood supply to the eye
The central artery of the retina supplies the eye and comes off of the ophthalmic artery, which is a branch of the internal carotid
The eye is also supplied by the ciliary arteries, which also branch off of the ophthlamic artery
The central vein of the retina is the only vein draining the eye
What area of the eye is known as the "blind spot"? Why is this so?
The optic disc is also known as the blind spot. This is the case because there are no photoreceptors here - instead this is where the optic nerve and the central artery and vein of the retina emerge.
The macula is located medially/laterally to the optic disc.
The macula is the area of the eye with the greatest density of rods/cones
What is the centre of macula called, and what is its function?
The macula is located laterally to the optic disc
The macula is the area of the eye with the greatest density of cones
The fovea is the centre of the macula and is the area of most acute vision
Name the extraocular muscles. Where do they all insert and originate?
What nerve supplies each of them?
4 rectus muscles
- superior rectus (CN III)
- inferior rectus (CN III)
- medial rectus (CN III)
- lateral rectus (CN VI)
2 oblique muscles
- superior oblique (CN IV)
- inferior oblique (CN III)
levator palpebrae superioris (CN III)
All the rectus and oblique muscles insert onto the sclera and all of the rectus muscles originate from a common tendinous ring
What extraocular muscles are supplied by the following division of the oculomotor nerve?
- Superior division
- Inferior division
Superior - SR and LPS
Inferior - MR, IR, IO and ciliary ganglion
What nerve types are contained within the following ciliary nerves?
- Long ciliary nerves
- Short ciliary nerves
Which of the above form the first part of the blink reflex?
Long - sympathetic and somatic sensory
Short - sympathetic and parasympathetic
The long ciliary nerves form the first part of the blink reflex
What is Horner's Syndrome, generally? What can cause this?
What are the triad of symptoms?
Horner's syndrome is compression of the cervical parts of the sympathetic trunk
Causes
- root of neck trauma
- carotid dissection
- internal jugular vein engorgement
- deep cervical lymph node metastases
- pancoast tumours at the apex of the lung
Triad of symptoms
- Ptosis
- Miosis
- Anhydrosis (reduced sweating)
- (also increased warmth and redness)
What produces CSF?
How many times a day is it replaced?
secretory epithelium of the choiroid plexus
Replaced 3-4 times a day
How can CSF be used to aid in diagnosis?
What is normal CSF like?
CSF can be taken from the spinal cord via lumbar puncture and aids in the diagnosis of conditions affecting the brain, meninges and spinal cord
Normal CSF is clear and colourless, and contains very little protein
Where is choroid plexus found in the adult brain?
In the 3rd, 4th and lateral ventricles
How does CSF compare to normal blood plasma in terms of ion concentrations?
CSF has lower K+, glucose and much lower protein than blood plasma
CSF also has higher concentrations of Na+ and Cl-
The ventricular system is the name given to the continuum of ventricles in which CSF circulates. What are the names of the structures that connect each of these ventricles?
Lateral ventricles are connected to the 3rd ventricle by the Foramen of Monroe
The 3rd ventricle and 4th ventricle are connected by the Aqueduct of Sylvius
The 4th ventricle is connected to the subarachnoid space via two lateral apertures (Foramina of Luschka) and one median aperture (Foramen of Magendie)
After CSF has been produced by the choroid plexuses and transported through the ventricular continuum, where does it exit to and pass into?
Where does CSF return to venous blood?
After leaving the 4th ventricle through the lateral and median apertures, CSF passes into the sub-arachnoid space and then circulates in the central canal of the spinal cord
CSF then returns to venous blood through arachnoid granulations into the superior sagittal sinus (SSS)
What are some of the potential pathologies that could result from the ventricles, choroid plexus and CSF?
Tumours - colloid cysts, ependymomas, choroid plexus tumours
Ventricular haemorrhage - epidural hematoma, subdural hematoma, subarachnoid haemorrhage
Hydrocephalus (accumulation of CSF in the ventricular system or around the brain = increased pressure)
Idiopathic intracranial hypertension
What eye pathology may develop as a result of increased intracranial pressure?
How might this condition present - clinically and on fundoscopy?
Papilloedema (swelling of the optic disc, transmitted to the subarachnoid space surrounding the optic nerve)
Visual symptoms include enlarged blind spot, blurring of vision, visual obscurations and loss of vision
On fundoscopy, a bulging optic disc will be seen
What kind of squint are the following terms describing?
- Esotropia
- Exotropia
- Hypertropia
- Hypotropia
Esotropia - convergent squint
Exotropia - divergent squint
Hypertropia - high eye
Hypotropia - low eye
Is aqueous humour produced in an energy dependent or energy independent manner?
Energy dependent - it is an active process
What cells in the retina synthesise photoreceptors?
Pigmented epithelium
What are the two types of photoreceptor?
Which are more active in dim light, and which are more active in norma daylight?
Rods and cones (NB - there are also three types of cone!)
Rods enable us to see in dim light and are distributed across the entire retina
Cones enable us to see in normal daylight and the majority are found in the fovea
What colour do each of the three types of cone photoreceptor detect?
Short wave - blue
Middle wave - green
Long wave - red
What does "amblyopia" refer to? What can it be caused by and how can this be corrected?
Amblyopia = cortical blindness despite there being no problem with the eye, with one eye having better vision than the other
Can be caused by strabismus (squint) - intervening in infancy is required to prevent amblyopia developing, and is done by covering the infant's good eye with a patch for a few hours each day
Which is the only part of the eye with lymphatic drainage?
The conjunctiva
The eyes can be described as having immune privilege - what does this mean?
It means that they can tolerate introduction of antigens without necessarily eliciting an inflammatory immune response
What is Anterior Chamber-Associated Immune Deviation (ACAID)?
Introduction of a foreign antigen into the ocular microenvironment can induce a systemic form of tolerance (peripheral tolerance) to the antigen
This is an active mechanism that downregulates the immune response in the eye
What is sympathetic ophthalmia?
Rare, bilateral granulomatous uveitis due to trauma or surgery to one eye
The injured eye is known as the "exciting" eye, and the fellow eye is known as the "sympathetic eye". Clinically, both eyes will appear the same, and it is only by history that they can be differentiated.
This condition is a rare cause of blindness
Acute allergic conjunctivitis is an example of what type of hypersensitivity?
Type I - immediate hypersensitivity
Ocular cicatricial pemphigoid is an example of what type of hypersensitivity?
Type II - direct cell killing
Autoimmune corneal melting is an example of what type of hypersensitivity?
Type III - immune complex mediated
Corneal graft rejection is an example of what type of hypersensitivity?
Type IV - delayed-type
Name a couple of important ocular side effects associated with steroid use
Cataracts
Steroid-induced glaucoma
Name some conditions that may result in an increase in intracranial pressure
Brain tumour
Head injury
Hydrocephalus
Meningitis
Stroke
Benign intracranial hypertension
What is the Monroe-Kellie hypothesis?
Intracranial volume is a constant made up of brain, blood, CSF and any other additional components
The ICP cannot change without altering one of the above as the cranial cavity is an enclosed space
What are the three layers of the meninges called?
Where is CSF located?
Dura mater("hard mother")
Arachnoid mater ("spidery mother")
- CSF is located in the subarachnoid space -
Pia mater ("faithful mother")
At what spinal level is a lumbar puncture done?
L3/L4
or
L4/L5
If a patient had a bulging/swollen disc on fundoscopy, what could this indicate?
Could indicate raised ICP - this will compress the optic disc resulting in papilloedema
If a patient presented with a loss/slowness of the pupilary light reflex, a dilated pupil, ptosis and or the eye turned inferolaterally ("down and out"), what nerve might be affected?
Where does this nerve leave the brain?
CN III - Oculomotor
Leaves between the pons and the midbrain - only cranial nerve to do so
If a patient presented with an inability to move their eye inferomedially and had diplopia when looking down, which cranial nerve might be affected?
How might the patient be compensating?
CN IV - trochlear
Supplies superior oblique, and paralysis means that inferior oblique is unopposed
The patient may compensate by tilting their head
If a patient presented with medial deviation of their eye and an inability to move it laterally in a horizontal plain, what cranial nerve might be affected?
Where does this nerve come off of the brainstem?
CN VI - Abducens
Comes off at the junction between the midbrain and the pons
What gland in the eyelid are bacteria prone to colonising?
The Meibomian glands (housed in the tarsal plate)
What is the significance of the orbital septum in considering a patient presenting with cellulitis?
Pre-septal cellulitis tends to be self-limiting and not as serious as a condition
Orbital cellulitis can affect the eye and is potentially life-threatening.
This is why in all patients presenting with orbital cellulitis imaging of the orbit is required
What sensory and motor nerves are involved in tear film dynamics?
Sensation - CN V - tells the brain that the eye needs tears
Motor - CN VII parasympathetic fibres
What are the two types of conjunctiva? Where is each found?
Palpebral conjunctiva - covers the inner surface of the eyelids
Bulbar conjunctiva - lines the eyeball
The two meet at the fornix
The appearance of follicles on the palpebral conjunctiva is associated with _____ infection
The appearance of papillae on the palpebral conjunctiva is associated with ______
Follicles = viral conjunctivitis
Papillae = allergic conjunctivitis
From outside to inside, what are the names of the layers of the cornea? (5)
Epithelium
Bowman's membrane
Stroma
Descemet's membrane
Endothelium
What attaches the lens to the ciliary body?
What change in tension of these fibres allows for near-focusing?
Zonules attach the lens to the ciliary body
A decrease in the zonular fibre tension allows for focusing of the lens on near objects
What is the normal pressure of the eye?
12-22 mmHg
What artery does CN III lie in close proximity to? What pathology of this artery could result in a third nerve palsy?
CN III lies in close proximity to the posterior communicating artery
Anuerysm of this artery can result in CN III pathology
What is Hutchinson's sign?
The appearance of vesicles on the tip or the side of the nose, prior to the appearance of a dendritic ulcer as a result of herpes zoster
This occurs because the nasociliary branch of the trigeminal nerve innervates both the cornea and the tip of the nose
How might lesions at various points in the optic tract present clinically, in terms of visual defects?
NB - temporal lobe does superior vision, parietal lobe does inferior vision
