AT Nystagmus Slides.pdf

Nystagmus Advanced Techniques Dr Sheila Rae 1 Nystagmus Rhythmic oscillation of one or both eyes Physiological or pathological Horizontal, vertical, torsional or a combination Congenital or acquired Manifest or latent Prevalence ~ 1:1000 Common cause...

Nystagmus Advanced Techniques Dr Sheila Rae 1 Nystagmus Rhythmic oscillation of one or both eyes Physiological or pathological Horizontal, vertical, torsional or a combination Congenital or acquired Manifest or latent Prevalence ~ 1:1000 Common cause of visual impairment in children 2 Terminology Manifest Present when both eyes are open but may increase when one eye is covered Latent Only present when one eye is covered, steady fixation is achieved with both eyes open The result of an early insult to binocular vision, such as unilateral cataract, early onset strabismus 3 Physiological nystagmus Opto-kinetic nystagmus (OKN) Response to a moving scene (train) Vestibular nystagmus (VOR) Response to rotation of the head even in a completely dark room End point nystagmus In extreme lateral gaze > 400 Voluntary nystagmus 5% of the normal population 4 Pathological nystagmus Congenital / early onset Congenital idiopathic nystagmus Secondary to a visual deficit Albinism Retinal dystrophies Acquired Secondary to neurological deficit Intra-cranial lesions Drug toxicity 5 Terminology Waveform often only revealed by recording eye movements Jerk A fast phase (saccadic eye movement) followed by a slow eye movement phase Pendular No fast phase - sinusoidal May be complex and combinations of jerk/pendular May vary with gaze direction 6 Examples of waveform 7 Jerk nystagmus Magnitude of movement (degrees) Time (ms) A slow drift off the target, followed by a rapid corrective movement 8  Pendular nystagmus Magnitude of movement (degrees) Time (ms) Smooth oscillations, same velocity in either direction in a sinusoidal pattern 9 Terminology Amplitude The ‘excursion’ of the nystagmus Measure in degrees or arc minutes Frequency Number of oscillations per minute ‘coarse, medium or fine’ Intensity Frequency x amplitude 10 Terminology The foveation period The proportion of time that the image of the object under regard falls on or close to the fovea and is moving slowly enough for useful visual information to be attained 11 Waveform: effect of foveation period 12 Terminology Null zone Position of gaze of least movement (damping) If not coincident with primary position may lead to compensatory head posture (CHP) for best visual acuity Management implications and one reason for referral to ophthalmologist 13 Congenital or earlyonset nystagmus Usually onset from age two to three months but before the age of six months Two primary forms Sensory deficit nystagmus (SDN) – associated with an ocular anomaly resulting in poor vision i.e. cataract, albinism, cone dystrophy Needs careful examination of fundus and electrodiagnostic techniques therefore under-diagnosed Congenital idiopathic nystagmus (CIN) – associated with an anomaly in the motor pathway controlling fine eye movements Not possible to differentiate SDN/CIN from clinical observation of nystagmus 14 Waveform in congenital nystagmus Waveform may change during infancy and may initially present as large roving eye movements, developing into pendular/jerk Waveform may vary with position of gaze (e.g. pendular in primary position, jerk in lateral gaze) Almost invariably horizontal (may have a rotatory component) Uniplanar i.e. horizontal in all directions of gaze including vertical 15 Other features ofcongenital nystagmus Nystagmus usually similar in both eyes May increase on occlusion May have associated strabismus Nystagmus increases with fixation, stress and fatigue Implications for driving CIN may be x-linked, autosomal dominant or sporadic 16 Head nodding Seen in some patients with congenital nystagmus Spasmus Nutans Rare condition Presenting at 1-2/12; Triad of nystagmus, head nodding and CHP Self-limiting, resolves by 3 years but may be associated with pathology Refer to Ophthalmologist 17 Manifest latent nystagmus (MLN) Separate diagnosis from congenital nystagmus Associated with early onset strabismus & dissociated vertical deviation (DVD) Nystagmus continually present but worsens when one eye is covered Detected around 2 years of age, more pronounced if 1 eye occluded and in aBducted positon of gaze 18 Acquired nystagmus Different clinical characteristics from congenital nystagmus Usually represents intracranial pathology Multiple sclerosis Cerebral vascular accident Meniere’s disease Tumours Head trauma Side-effects of medication Presents with known onset and oscillopsia Oscillopsia is an awareness of the eye movements 19 Oscillopsia Oscillopsia is an awareness (by the patient) that their eyes are wobbling Congenital usually not aware until someone tells them Not usually a presenting sign in congenital nystagmus but may be recognised when tired as nystagmus increases or in the dark Complaint of oscillopsia strongly suggestive of acquired nystagmus (or voluntary) 20 Voluntary nystagmus (psychogenic) Presents as acquired nystagmus with oscillopsia and possible head nodding Rapid and poorly sustained back-to-back saccades (usually horizontal) Confirm by eye movement recordings 21 Management of congenital nystagmus in childhood Refraction and correction even small errors Fog other eye do not occlude Accurate assessment of near and distance VA Binocular most useful Allow patient to adopt CHP Check fundus carefully Volk Referral to ophthalmologist at initial presentation 22  Management of congenital nystagmus in childhood Ophthalmologist may arrange paediatric assessment (educational implications) and genetic counselling Assessment of consistence and significance of any CHP Advise teachers of correct positioning of child in class room Closer to the front if visual acuity reduced (likely) If null position present on right gaze, sit child to the left of board (as they look at it) Monitoring through childhood 23 Treatment to reduceCHP Surgery to extraocular muscles to move null zone to primary position Prisms to move visual environment to null point Prisms to reduce nystagmus through forced convergence Probably little value if CHP