Neuro-ophthalmology: Nystagmus

Question 1

Why do abnormal eye movements (nystagmus) occur?

Answer 1

• Inability to maintain fixation:
  o E.g. albinism – absence of a normal foveal contour – do not have really packed together cones & no point of really good VA – fixation is driven by this central point – no fixed point for eyes to concentrate on
• Loss of normal inhibitory influences on eye movement control system:
  o There is stimulation & inhibitory movements & balance between the 2 results in what muscles do at any point in time – so if have loss of inhibition then other signals to those muscles predominate – if have loss of inhibition then have less control over eye movement system – can result in nystagmus
• Loss of normally symmetrical input from one of vestibular pathways to ocular motor nuclei:
  o If asymmetrical, one overrides other so the eyes move in one direction more often than the other

Question 2

Describe nystagmus?

Answer 2

• Rhythmic, to-and-fro eye movements
• Slow phase & rapid recovery phase
  o Slow phase – abnormal movement, drifting away from object of interest – slow away
  o Rapid phase – recovery saccadic motion back to what px is trying to fixate on – fast back
• Amplitude (how far eyes move): coarse (big) or fine
• Frequency (how fast eyes move): low, moderate, high
• Jerk: slow drift away, fast saccadic correction
• Pendular: most common type – non-saccadic in both directions, slow
• Mixed: pendular in primary position – jerk on lateral gaze
  o IMPORTANT to characterise the movement when you see it so that next time you see them you can see if it has changed – so know if cause if progressive or if something has changed

Question 3

Is nystagmus more likely to be congenital or acquired? Describe most common cause of congenital nystagmus?

Answer 3

Albinism: rare but is most common cause of nystagmus – congenital nystagmus
Most nystagmus conditions are congenital – some problem with developing macula/developing fixation – produces congenital nystagmus

Question 4

Describe the types of nystagmus with their acquired causes?

Answer 4

• See-Saw:
  o Vertical nystagmus – one eye goes up & other goes down
   Midbrain lesions
   Pituitary tumours
   Severe visual loss
• Downbeat:
  o Eye drifts up & then there’s a quick down motion back to centre
   Cerebellum lesions
   Medulla lesions
   Idiopathic
• Upbeat:
  o Slow downwards movement then there’s a quick up motion back to centre/fixation
   Medullary lesions
   Cerebellum lesions
   Benign positional paroxysmal vertigo
• Abducting nystagmus of INO:
  o Demyelination
  o Brainstem stroke
• Periodic Alternating:
  o Predictable alternating eye movement
   Arnold-Chiari
   Demyelination
   Trauma
   Encephalitis
   Syphilis – systemic
   Posterior fossa tumours
   Visual deprivation
• Pendular nystagmus:
  o Non-saccadic in both directions – slow
   Demyelination
   INO
   Brain stem dysfunction
• Spasmus Nutans:
  o Generally, affects children – affects head movements
   Idiopathic in children
   Glioma
• Gaze-evoked:
  o Most common seen in practice – px does not have nystagmus in primary position but when px moves eyes they get nystagmus in other positions of gaze
   Drugs
   Alcohol

Question 5

Which questions are important to ask in a px with nystagmus?

Answer 5

• Onset:
  o Age of onset
  o Constant or intermittent
  o Aggravating or alleviating factors (e.g. head position, eye position – is it worse at any particular time of day/year)
   Think of the causes then think of Q’s you want to ask in relation to those
• Associated Symptoms:
  o Symptoms of demyelinating disease – loss of vision, eye pain, numbness, weakness, paraesthesia (burning/prickling sensation in hands, arms, legs, or feet)
  o Vertigo or oscillopsia (feeling that world around you is moving) – suggests vestibular system abnormality
  o Deafness or tinnitus present in vestibular lesions
  o Blurred vision
  o Double vision in particular position of gaze – internuclear ophthalmoplegia (INO)

Question 6

Describe assessing motility in nystagmus?

Answer 6

• Assess ocular stability in primary gaze
  o Do they have nystagmus? What type if do? – where is the slow/fast phase? – horizontal/vertical?
• Then examine in 9 cardinal positions to determine if:
  o Monocular or binocular – cover eye to check if still there when cover
  o Conjugation – do eyes behave similarly in each position?
  o Are abnormal movements are horizontal, vertical, torsional or mixed?
  o Are abnormal movements continuous or intermittent (are induced by particular eye positions)?
  o Only, slow, fast, both phases are seen
  o There is a null point – if there is, px will naturally move their head so they are looking in that position
   Often the null point is downwards – can be good as it helps people w/ reading tasks
• Could advise px to move their visual tasks into that position
• Advise them that they may get a sore neck/shoulders because holding head in abnormal position
• Explain to px why they have this head position – “it is helping eyes get into this null point”
• Head position, movements
• Visual fields – some causes of nystagmus could affect VFs
• Romberg test – helps w/ diagnosis – sees if vestibular system is affected
  o Get them to stand with arms out in front of them & shut their eyes – see if they can still keep standing still or whether they fall to a particular side
   If they cannot keep standing with their eyes shut it suggests a problem w/ vestibular system

Question 7

Describe management of nystagmus?

Answer 7

• Acquired – investigate for cause:
  o They may be scanned to investigate for lesions, demyelination etc
  o Urgency of referral will depend on what you think the cause is based on history & examination
• Advice:
  o If been there since birth & cause is obvious like albinism or they’ve previously been at hospital & had their diagnosis & now coming back to you for help w/ vision
  o Advise on null position, how to hold head, how to position their various visual material to get best out of their eyesight
• Refractive management; spectacle choices:
  o When they become presbyopic – where they have the add may be slightly unusual – e.g. if null point at top then reading section may need to be at top
• Low vision aids