nystagmus - MEH Flashcards
what is nystagmus?
rhythmic oscillation of 1 or both eyes
is nystagmus manifest or latent?
can be both
what are the 4 classifications of nystagmus?
physiological
pathological
infantile/congenital
acquired
what is physiological nystagmus
a form of involuntary eye movement part of the VOR characterised by alternating smooth pursuit in 1 direction and saccadic movements in the other
where does physiological nystagmus occur>
extreme lateral gaze
how much of the normal population can give themselves voluntary nystagmus?
5%
what is pathological nystagmus?
result of damage to 1 or more components of the vestibular system
which parts of the vestibular system can be damaged to cause pathological nystagmus?
- semi-circular canals
- otilith organs
- vestibular cerebellum
does pathological nystagmus cause vision impairment?
some degree of vision impairment but severity varies widely
what is benign idiopathic congenital nystagmus secondary to?
- visual defect (e.g albinism or retinal dystrophies)
- neurological deficit (intra-cranial lesion, drug toxicities, stroke, MS)
what are the 2 types of waveforms?
jerk and pendular
what is a jerk reflex?
a slow drift off the target, followed by a rapid corrective movement
how is the direction of beating of jerk nystagmus defined?
the direction of the fast phase of the movement
is the jerk reflex to do with vestibular or optokinetic?
vestibular
what is a pendular nystagmus?
sinusodial (smooth oscillations)
which direction does pendular nystagmus occur in>
can occur in any direction
how do you find out if the nystagmus is jerk or pendular?
electronystagmography
what is the amplitude of a waveform?
the ‘excursion’ of the nystagmus
what is the frequency of the waveform?
number of oscillations per minute
how can you rate the frequency of a waveform?
coarse medium or fine
what is the intensity of the waveform?
amplitude x frequency
what is a manifest nystagmus?
when both eyes are open, may increase when one eye is covered
what is a latent nystagmus
only occurs when one eye is covered and steady fixation with both eyes open
what is a latent nystagmus caused by?
an early disrupt to BV, e.g unilateral cataract, early onset squint
what age does congenital/early onset nystagmus occur?
2 to 6 months
what are the 2 primary forms of congenital nystagmus?
- sensory deficit nystagmus (SDN)
- congenital idiopathic nystagmus (CIN)
how do you differentiate between SDN and CIN?
not possible from clinical observation
aetiology of CIN
unknown
may be x linked, autosomal dominant or sporadic
aetiology of SDN
early macular deprivation e.g. dense bilateral congenital cataracts, retinal cone dysfunction, albinism)
how do you detect SDN
careful examination of fundus and media and electro diagnostic testing
what is manifest latent nystagmus associated with?
early onset strabismus & DVD
when is a manifest latent nystagmus detected?
around 2 years of age, more pronounced if 1 eye is occluded and in abducted position
does the waveform change with position of gaze in congenital nystagmus?
yes it can do (e.g. pendular in pp, jerk in lateral gaze)
what is the direction of nystagmus in congenital nystagmus?
horizotal (uniplanar - horizontal in all directions of gaze including up gaze and down gaze)
what is the null zone?
position of gaze of least head movement and VA is best
what might a px do for the best VA?
px may adopt abnormal head posture for best VA
what vision testing do you do in someone with nystagmus>
- with AND without AHP (monocular and both eyes)
what is the VA in CIN?
can be 6/9
what is the VA in SDN?
often 6/60 or less
what is an indicator for active management?
significant AHP
how do you test px’s near vision in nystagmus?
- test at px’s preferred distance
- write down AHP and distance
what increases nystagmus?
may increase on occlusion. Nystagmus is normally similar in both eyes
what is seen in some px’s with congenital nystagmus?
head nodding (HN)
what is spasmus nutans?
rare condition presenting at 1 or 2 months with nystagmus, HN, AHP
when does spasmus nutans resolve?
by 3 years
what is spasmus nutans caused by?
tumours ON, optic chiasm, 3rd ventricle
what is oscillopsia?
an illusion of an unstable vision, made up of the perception of to-and-fro movement of the environment
what is a strong sign of acquired nystagmus?
oscillopsia
what is voluntary nystagmus also known as?
psychogenic
what is voluntary nystagmus?
brief high frequency horizontal nystagmus that cannot be sustained for more than ~5 seconds
how does voluntary nystagmus present?
as acquired nystagmus with oscillopsia and possible head nodding
what is the management of nystagmus>?
no cure but many helpful treatments (only cure for underlying conditions)
why is onward referral to an ophthalmologist important?
diagnosis of initial condition
potentially consult a geneticist
how do you manage congenital nystagmus?
- refraction and correction of all refractive error
- accurate assessment of near (1/3m and preferred distance) and distance VA
- ophthalmologist may arrange paediatric assessment and genetic counselling
- assessment of consistence and significance of any AHP
- monitoring through children
what are some treatment options for congenital? (6)
- glasses/CLs
- low vision aids
- prisms
- drugs
- botox
- surgery
what would be better for correcting nystagmus - glasses or cls? AND WHY
contact lenses - they move with the eye therefore ensure best corrected vision in all planes
how do low vision aids help?
- magnifiers can help with reading
- tinted glasses can help with glare
- can help children struggling with school work
why are prisms not the best option for nystagmus?
limited success rate esp if null zone in extreme periphery
what prisms could you give to force convergence?
base IN prisms on both eyes
if the null zone is on the left, and therefore AHP is on the right , which prisms do you give?
BO RE and BI LE
how do you incorporate prism ?
first as a fresnel then applied to glasses if happy
what are the 2 most commonly used drugs in treatment?
gabapentin and memantine - BUT DOES NOT WORK FOR EVERYONE
how many listed drugs are there for the treatment of acquired nystagmus?
17 - inlcuding alcohol and cannabis
how does botox help with acquired nystagmus?
reduce symptoms of oscillopsia BUT effects are temporary
what is the treatment for reducing AHP?
prisms to move visual environment to null point
prisms to reduce nystagmus through forced convergence
surgery to EOMs to move null zone to primary position
why must you wait until child is 8 to suggest surgery to EOMs for AHP?
surgery is of little value if AHP is less than 15 degrees,, so wait until 8 to fully evaluate AHP and px is visually mature
what are the results of surgery for nystagmus?
-Usually improves but may not abolish AHP
- Effect may not last may need “re-do” Sx
- May improve vision
- Most patients will not reach driving standard
what is biofeedback?
treatment technique combining auditory, visual and tactile feedback and visual attention
gives voluntary control over nystagmus but no practical long term advantage in vision
which type of nystagmus represents intracranial pathology?
acquired nystagmus ( MS, CVA, tumours, head trauma)
how do you differentially diagnose between congenital and acquired?
HISTORY- onset, signs & symptoms
cause of abducting nystagmus?
lesion to medial longitudinal folliculus MLF
what are the 4 different treatment options for acquired nystagmus?
- drugs
- surgery to shift null zone
- retrobulbar botox (limited success)
- removal of cause may help
which of these options is not an example of physiological nystagmus?
1. optokinetic
2. vestibular
3. retinal dystrophies
4. voluntary
retinal dystrophies
Which of the following is the correct definition for nystagmus:
1. Rhythmic oscillation of one or both eyes
2. Asymmetrical oscillation of one or both eyes
3. Horizontal jerky movements with reduced vision
4. Circular motion of one or both eyes
- Rhythmic oscillation of one or both eyes
A 34 year old presents with acquired nystagmus and complaining of oscillopsia, which of the following would you not offer this patient?
1. Prisms if there is a null zone
2. Surgery to reduce AHP
3. Drugs to reduce nystagmus
4. Contact lens trial.
- Surgery to reduce AHP
Which of the following statements are incorrect with regards to waveforms?
1. Often only revealed by electronystagmography
2. May be a combination of jerk/pendular
3. May vary with gaze direction
4. Symmetrical in both eyes with electronystagmograph
- Symmetrical in both eyes with electronystagmograph
