Visual Problems, Nystagmus & Vertigo

 

• Field defects

  Definition

  • A field defect is loss of vision in part of an individual's vision, and dose not include unilateral or bilateral blindness.
  • Can occur anywhere on the optic pathway: retina → optic nerve → optic chiasm → optic tract (continuation of the optic nerve) → lateral geniculate nucleus → optic radiation → optic cortex.
  • Lesions are described according to their effect on the visual field, not the part of the retina affected e.g. chiasm compression affects information from the nasal retina, but leads to bitemporal hemianopia, as the temporal visual field falls on the nasal retina.

  Types and their causes

  • Central scotoma: optic neuritis (including MS), methanol, glaucoma, alcohol or tobacco amblyopia.
  • Bitemporal hemianopia: pituitary tumour compressing the optic chiasm.
  • Binasal hemianopia (very rare): ischaemic optic neuropathy, glaucoma.
  • Homonymous hemianopia: stroke or tumour anywhere between the optic chiasm and occipital cortex. Occipital cortex lesions may be macula sparing.
  • Altitudinal hemianopia: ischaemic optic neuropathy, anaemia, fusiform aneurysm, stroke.
  • Quadrantanopia: the location of the lesion is opposite to the defect. So superior lesions (superior occipital cortex or parietal lobe) cause an inferior homonymous quadrantanopia, and inferior lesions (inferior occipital cortex or temporal lobe) cause a superior homonymous quadrantanopia.

• Diplopia

  Binocular diplopia:

  • A problem aligning the 2 images, which is absent with 1 eye closed.
  • Can be caused by CN 3, 4, or 6 palsies i.e. paralytic strabismus (squint). CN4 lesions will cause diplopia when looking down and in. CN6 lesions will cause diplopia when looking laterally.
  • Other causes: myasthenia gravis, thyroid eye disease.

  Monocular diplopia:

  • Continues even when (unaffected) eye closed. Rare.
  • Causes include cataracts and astigmatism.

• Nystagmus

  Overview

  Eye movements:

  • Normal eye movements comprise saccades ('fast phase') – a jump between two points – and smooth pursuit ('slow phase') – following an object e.g. finger in neuro exam.
  • Most of our eye movements are saccades. Voluntary saccades can be tested by asking someone "look left, look right", and targeted saccades can be tested by asking someone to look at one object then another e.g. "look at my finger, look at my hand".

  Nystagmus:

  • Nystagmus is a back and forth movement of the eye, and can include both saccades and smooth pursuit. Can be in any direction (horizontal, vertical, torsional) with various waveforms (pendular, jerk, square wave jerk, complex); they can be uni or bilateral (commoner), and symmetrical or asymmetrical.
  • Pathological nystagmus can be congenital or acquired, the latter usually due to a vestibular lesion.
  • Congenital nystagmus is often non-pathological. However, nystagmus acquired in very early life may reflect serious pathology, such as sensory deprivation nystagmus (aniridia, blindness) or a space-occupying lesion.
  • When examining, check if the nystagmus is present in the primary position (looking ahead), and/or on directional gaze.

  Jerk nystagmus

  Smooth pursuit interspersed with corrective saccades; the direction of the saccades is the direction of the nystagmus.

  Gaze-evoked nystagmus (aka gaze paretic nystagmus):

  • Jerk is towards the direction of gaze e.g. left jerk on left gaze.
  • Also towards the side of the lesion, which may be brainstem, cerebellar, or vestibular.

  Central vestibular nystagmus:

  • No specific pattern. Jerk varies with gaze direction.
  • Caused by brainstem lesions: MS, stroke, tumour.

  Peripheral vestibular nystagmus:

  • Unidirectional, fast phase away from the lesion.
  • Associated with tinnitus and deafness.
  • Causes: labyrinthitis, Meniere's, BPPV

  Vertical nystagmus:

  • Antiepileptics and Wernicke's can cause down or upbeat nystagmus.
  • BPPV can cause upbeat nystagmus.
  • Arnold-Chiari malformation and cerebellar lesions cause downbeat nystagmus.

  Pendular nystagmus

  • Equal oscillations.
  • Causes: demyelination, toxicity.

  Non-pathological nystagmus

  • End-point nystagmus: jerk at extreme of gaze in the same direction. Fewer beats than gaze-evoked nystagmus.
  • Optokinetic nystagmus: jerk following moving object e.g. on a train.

• Gaze palsies

  • Weakness of conjugate eye movement i.e. when moving both eyes in the same direction.
  • Typically result from cortical lesions, and can be horizontal or vertical. The latter are less common, and are seen in progressive supranuclear palsy or Parkinson's disease.

  Frontal eye field lesions

  • The frontal eye fields control the contralateral gaze direction e.g. the left frontal eye field controls rightward gaze.
  • Cortical damage can cause a horizontal gaze palsy in which the patient looks towards the lesion side, as unaffected side is unopposed.
  • However, stimulation (as in a seizure) would cause the patient to look away from the affected side.

  Intranuclear ophthalmoplegia (INO)

  A horizontal conjugate gaze palsy.

  Pathophysiology and presentation:

  • When affected eye gazes contralaterally it cannot adduct, while the other eye abducts but with nystagmus.
  • Due to a lesion of the medial longitudinal fasciculus, which connects the CN3 nucleus (controlling medial rectus) of the affected side to CN6 nucleus (controlling lateral rectus) of the other side.
  • Diplopia may occur, but is often absent.

  Causes:

  • Bilateral INO: MS.
  • Unilateral INO: vascular, tumour.

• Pupillary defects

  Miosis

  Reduced pupillary diameter.

  Causes

  Horner's syndrome:

  • Unilateral miosis, ptosis, anhidrosis, and enophthalmos.
  • CNS causes: stroke, space occupying lesion, MS. Anhidrosis on face and upper chest.
  • Peripheral lesions between T1 and the ciliary ganglion: Pancoast tumour, TB, abscess, trauma. Anhidrosis on face only.
  • Peripheral lesions after the ciliary ganglion: carotid artery dissection or aneurysm, cluster headache. No anhidrosis.

  Bilateral pinpoint pupils:

  • Pontine haemorrhagic stroke.
  • Opioid toxicity.
  • Organophosphate toxicity.

  Mydriasis

  Increased pupillary diameter.

  Causes

  Holmes-Adie syndrome (aka tonic pupil):

  • Dilated pupil which reacts minimally to light.
  • May have associated sweating abnormality and hyporeflexia.
  • Due to parasympathetic denervation resulting from ciliary ganglion damage; may have infectious cause.

  Fixed dilated pupil:

  • CN3 compression: intracranial haemorrhage, posterior communicating artery aneurysm, tumour. See cranial nerve 3, 4, and 6 lesions.
  • Bilateral causes: coning, causing brainstem compression.

  Bilateral mydriasis:

  • Sympathomimetic drugs: TCA, cocaine, ephedrine.
  • Anticholinergics

  Relative-afferent pupillary defect (RAPD)

  • Aka Marcus Gunn pupil/syndrome.
  • Both pupils dilate as light shines onto affected side in swinging light test.
  • Usually CN2 lesion, though not a 'total' lesion in which there is also visual loss. Often due to optic neuritis, perhaps as part of MS.

• Vertigo

  Definition

  Vestibular impairment which makes it feel like the room is spinning or they are spinning.

  Peripheral vs. central vertigo

  Peripheral vertigo:

  • Common and less serious.
  • Due to pathology of the semicircular canals or utricles, or the vestibular nerve.
  • Causes: benign paroxysmal positional vertigo (BPPV), vestibular neuritis/labyrinthitis, Meniere's disease, vestibular migraine, herpes zoster oticus.

  Central vertigo:

  • Rare but serious.
  • Due to lesions of the vestibular nuclei (in the pons and medulla) or the cerebellum.
  • Causes: posterior stroke (typically cerebellar), tumour (acoustic neuroma, cerebellopontine angle), MS, drugs (alcohol, gentamicin [though some say this is peripheral]).

  Simplified clinical approach

  While peripheral vs. central is a useful way to think about the pathophysiology of vertigo, it is less useful clinically as the presentations don't neatly match this distinction. Most vertigo is due to BPPV or vestibular neuritis, but acutely a posterior circulation stroke must be ruled out. Learning to distinguish these three syndromes clinically is thus key.

  Episodic vertigo = BPPV:

  • Characterised by brief paroxysms (usually 20-30 seconds) of vertigo and vertical nystagmus triggered by head movements, often when rolling over in bed.
  • No ongoing dizziness or nystagmus when examined at rest.
  • Diagnose with the Dix-Hallpike maneuver.

  Ongoing vertigo ('acute vestibular syndrome') i.e. dizzy when you see them = vestibular neuritis (>95%) or posterior circulation stroke (rare but can't miss):

  • Vertigo is continuous, often present for hours-days after sudden or gradual onset, and worsened by head position.
  • Nystagmus present on lateral gaze and sometimes primary position.
  • Associated symptoms: nausea and vomiting, unsteady gait.
  • Vestibular neuritis is due to viral infection of the vestibular nerve, and there may be a recent history of viral URTI. The term labyrinthitis is used if hearing is affected (hearing loss or tinnitus).
  • Stroke is suggested by the presence of additional neurological symptoms (e.g. focal weakness, facial droop, dysphasia, diplopia, dysmetria), inability to walk, severe headache (suggesting haemorrhage), or significant neck pain or stiffness (vertebral artery dissection).
  • To further distinguishing, use the HINTS exam.

  If none of these three causes seem probable, then consider other causes.

  Management

  • Viral neuritis/labyrinthitis: prochlorperazine or an antihistamine.
  • BPPV: Epley maneuver.
  • Chronic vertigo: many causes of peripheral vertigo can lead to chronic symptoms, for which vestibular rehabilitation is effective and preferable to the often-prescribed betahistine.
  • Stroke and other central causes are managed as per the condition.