Ophthalmology - Neurological Conditions Flashcards
What is mydriasis?
A dilated pupil
What is miosis?
A constricted pupil
Does raised intracranial pressure cause mydriasis or miosis?
Mydriasis (dilated)
Does Horner’s syndrome cause mydriasis or miosis?
Miosis
Do opiates cause mydriasis or miosis?
Miosis
Does trauma cause mydriasis or miosis?
Mydriasis
Do cluster headache cause miosis or mydriasis?
Miosis
Does CN III palsy cause miosis or mydriasis?
Mydriasis
What are the motor functions of CN III?
- Levator palpebrae superioris
- Extra-ocular muscles (except lateral rectus and superior oblique)
What is the parasympathetic function of CN III?
Sphincter pupillae muscles → causes constriction
What are the 2 types of CN III palsy?
- Surgical
- Medical
What is a surgical CN III palsy?
Refers to compressive lesions e.g. posterior communicating artery aneurysm
What is a medical CN III palsy?
Refer to non-compressive lesions e.g. multiple sclerosis, vascular causes such as diabetes or hypertension, vasculitis
Describe the presentation of the eye in CN III palsy
- ‘Down and out pupil’
- Ptosis
- Double vision
- Pupil dilation (in surgical CN III palsy)
Why does CN III palsy lead to a ‘down and out’ pupil?
Due to unopposed activation of lateral rectus and superior oblique
Why does CN III palsy lead to ptosis?
Due to impaired innervation to levator palpebrae superioris
Why does a ‘surgical’ CN III cause pupil dilation?
Due to parasympathetic (constrictive) fibres run on outside of nerve so external compression will impair function of these
Does a fixed pupil dilatation indicate a ‘surgical’ or ‘medial’ CN III palsy?
Surgical
What is the most common cause of a ‘surgical’ CN III palsy?
Posterior communicating artery aneurysm
What are some causes of a ‘medial’ CN III palsy?
- Multiple sclerosis
- Vascular causes e.g. diabetes, hypertension, vasculitis
What is the motor function of CN IV (trochlear)?
Superior oblique extra-ocular muscle → pulls eye down and inwards
What is the presentation of CN IV palsy?
- Double vision – worse in the vertical plane
-
Hypertropia (potentially) – this is a type of strabismus where either eye drifts/looks upwards
- Eye points upwards and inwards
- Patient may present with tilted head to compensate
What are the 2 major causes of CN IV palsy
- Ocular trauma
- Diabetes mellitus
What is the motor function of CN VI (abducens)?
Lateral rectus extra-ocular muscle → abducts eye horizontally away from midline
In which plane is the double vision in CN VI palsy worse?
Horizontal plane
In which plane is the double vision in CN IV palsy worse?
Vertical plane
Presentation of CN VI palsy?
Double vision worse in horizontal plane
CN VI palsy is known for being a ‘false localising sign’. What does this mean?
A false localising sign is a neurological sign that reflects dysfunction distant or remote from the expected anatomical locus of pathology.
CN VI palsy is known for being a ‘false localising sign’ due to path of the 6th nerve within the brain, making it easily compromised in a state of raised intracranial pressure.
What are the causes of CN VI palsy?
- Diabetic neuropathy
- Stroke
- Infection
- Trauma
What is Horner’s syndrome?
Damage to the sympathetic nervous system supplying the face
What are the 4 main causes of Horner’s syndrome?
- Pancoast tumour (apices of lungs)
- Stroke
- Carotid artery dissection (red flag = neck pain)
- Multiple sclerosis
Clinical features of Horner’s syndrome?
- Triad of:
- 1) Ptosis (drooping of upper eyelid)
- 2) Miosis (pupil constriction)
- 3) Anhidrosis (lack of sweating)
- May have enophthalmos (sunken eye)
Are light & accommodation reflexes affected in Horner’s syndrome?
No
What is papilloedema?
Swelling of optic disc 2ary to raised intracranial pressure.
Pathophysiology behind papilloedema?
The sheath around the optic nerve is connected with the subarachnoid space so CSF under high pressure can flow into the optic nerve sheath.
What visual field defect will pre-chiasmal lesions result in.
ipsilateral monocular visual field defect.
What visual field defect will post-chiasmal lesions result in.
homonymous visual field defects of the contralateral side.
Describe the visual field defect in an optic nerve lesion
Ipsilateral monocular visual field defect
Give some causes of an optic nerve lesion
- Optic neuritis
- Amaurosis fugax
- Optic atrophy
- Trauma
Describe the visual field defect in an optic chiasm lesion
Bitemporal hemianopia
What is the main cause of an optic chiasm lesion?
Pituitary adenoma e.g. prolactinoma
Describe the visual field defect in an optic tract lesion
Contralateral homonymous hemianopia
What are 2 main causes of an optic tract lesion?
- MCA stroke
- Tumour
Describe the visual field defect in an optic radiation lesion
Homonymous contralateral quadrantanopia
Describe the visual field defect in an optic radiation lesion affecting Meyer’s loop
Homonymous upper quadrantanopia (‘pie in the sky’)
Which lobe is Meyer’s loop?
Temporal
Describe the visual field defect in an optic radiation lesion affecting the parietal lobe?
Homonymous lower quadrantanopia (‘pie on the floor’)
Describe the visual field defect in a lesion of the calcarine sulcus of the occipital lobe
Homonymous hemianopia with sparing of macula
What are the 2 main cause of a calcarine sulcus of the occipital lobe lesion?
- PCA stroke
- Trauma
What type of visual field defect would an MCA stroke cause?
Contralateral homonymous hemianopia
