Nystagmus

What is nystagmus?

Nystagmus can be defined as a repetitive, involuntary, to-and-fro oscillation of the eyes. It may be physiological or pathological and may be congenital or acquired. It is a symptom, not a diagnosis. It is usually involuntary.

• Physiological nystagmus occurs during rotation of the body in space (vestibular nystagmus) or during ocular following of moving scenes and acts to preserve clear vision (optokinetic nystagmus, respectively).¹

• Pathological nystagmus causes the eyes to drift away from the visual target, thus degrading vision.²

Classification of nystagmus²

Nystagmus is described according to:

• The direction of movement: this may be horizontal, vertical, torsional or nonspecific.

• Amplitude - how far the eyes move: this can be fine or coarse.

• Frequency - how often the eyes oscillate: this is said to be high, moderate or low.

Most nystagmus consists of an alternation of unidirectional drifts away from the target with its correction by fast movements (saccades) which temporarily bring the visual target back to the fovea; this is jerk nystagmus. A rarer form, pendular nystagmus, consists of to-and-fro quasi-sinusoidal oscillations. The three types of waveform are:

• Jerk nystagmus: this is characterised by a slow drifting movement followed by a fast corrective jerking movement. The direction of nystagmus is described according to the fast component.

• Pendular nystagmus: the drifting and corrective movements occur slowly.

• Mixed nystagmus: there is a pendular movement in the primary position of gaze (ie looking ahead) but a jerk nystagmus on lateral gaze.

Symmetry in nystagmus:

• Nystagmus may be symmetrical but is more commonly asymmetrical.

• It is usually bilateral.

• It may be conjugate (both eyes move together) or disconjugate (the eyes appear to move independently of each other).

Voluntary nystagmus resembles pendular nystagmus in waveform. In a 1978 survey of college-age subjects, 8% could produce voluntary nystagmus. Most had relatives who could also produce it. In these cases, neuro-ophthalmological examination was normal.³

How common is nystagmus? (Epidemiology)

The exact incidence and prevalence of nystagmus is not known but it is thought to occur in about 24 in 10,000 people.⁴

Pathophysiology²

The ocular motor system consists of the vestibular ocular nystagmus saccade system, the pursuit system, the fixation and gaze-holding system and the vergence system. All help stabilise images on the retina during eye and head movements. Any disturbance of one of the systems can cause instability of the eyes (eg, nystagmus).

Involuntary or abnormal eye movements cause excessive motion of images on the retina, without a corresponding efference copy (or corollary discharge), leading to blurred vision and to the illusion that the seen world is moving (oscillopsia). This leads to spatial disorientation, impaired postural balance and vertigo.²

The causes of nystagmus and the patterns of nystagmus produced are discussed at the end of this article.

Differential diagnosis

Nystagmus should be distinguished from inappropriate saccades that prevent steady fixation (eg, ocular flutter). Saccades are fast movements, so that the smeared retinal signal because of these movements is largely unperceived. However, patients in whom abnormal saccades repeatedly misdirect the fovea often complain of difficulty in reading.²

The differential diagnosis of downbeat nystagmus is wide-ranging and includes cerebrovascular disease, neurogenerative disease and intoxication.⁵

Nystagmus symptoms

In general, late-acquired nystagmus and saccadic oscillations cause oscillopsia, nausea and vertigo; in contrast, most nystagmus presenting congenitally or in early childhood is not accompanied by oscillopsia.²

The majority of patients with early-onset or congenital nystagmus also have reduced acuity.

Assessment of the patient with nystagmus⁶

The degree to which the condition can be assessed depends on the patient's age and ability to co-operate with instructions. Some history and examination are possible in most patients, as even very young babies should look with interest at brightly coloured objects or the light of a pen torch.

History

• Ask about age of onset: this will help determine which type of nystagmus it is and hence point to a possible diagnosis.

• Ask when it occurs and when/whether it ceases - accommodation and sleep are two occasions to enquire about specifically.

• Ask about related visual symptoms. Some patients describe oscillopsia (the perception of continual movement of the visual environment). Generally, if a patient is unaware of oscillopsia, the nystagmus is likely to be congenital.

• Ask about a history of headaches, tearing, avoidance of near tasks, and blurry vision.

• Ask about dizziness and loss of balance, nausea and vomiting.

• Related systemic symptoms - particularly with regard to the nervous system - are highly relevant.

• Use of prescribed or non-prescribed drugs is important, particularly anticonvulsants.

• Ask about family history.

Examination

• Nystagmus is described in terms of

  • Direction (of the faster, corrective phase).

  • Amplitude (fine or coarse).

  • Frequency (high, moderate or low).

  • Waveform (jerk, pendular or mixed).

  • Symmetry and conjugacy (if bilateral).

• Note in which position of gaze it occurs:
  

  • Primary position - looking straight ahead.

  • Secondary positions - looking straight up/down, straight right or left.

  • Tertiary positions - these are the four oblique positions: up and right, down and right, up and left, down and left.

  • Cardinal positions - these include all the secondary and tertiary positions.

• Examine the patient sitting facing you: observe the nystagmus in the primary position.

• Using a small fixation target, observe the nystagmus in all positions of gaze.

• Ask the patient to comment on visual symptoms as the eyes move (eg, blurring, double vision).

• Enquire about the 'null' point: this is an angle which some patients find minimises their visual impairment - it often results in abnormal head positioning.

• Check oculocephalic reflex (doll's head phenomenon):

  • This reflex is produced by moving the patient's head left to right or up and down. When the reflex is present, the eyes remain stationary while the head is moved, moving in relation to the head.

  • An alert patient normally does not have the doll's-eye reflex because it is suppressed. Inability to suppress the oculocephalic reflex suggests vestibular imbalance.

  • The test may be performed by having the patient extend the arm out in front of the body and fixate on the outstretched thumb:

    • Patients should be instructed to rotate their torso such that the thumb remains in front of the body at all times.

    • Patients with the ability to suppress the oculocephalic reflex should be able to maintain fixation on their thumb while rotating.

    • An abnormal test result would show the patient continuously losing fixation of the thumb.

• Other tests of the vestibular system include Romberg's test and caloric testing (see 'Vestibular nystagmus', below).

• Carry out a full neurological examination.

• Other examination depends on findings.

Associated problems

• The majority of those with nystagmus have vision which is significantly worse than average: in the UK many people with nystagmus are eligible to be registered as partially sighted and a small number meet the criteria to be registered as severely sight impaired.

• The combination of reduced acuity and oscillopsia may cause difficulties with facial recognition which are more severe than would be expected from low acuity alone.

• At school, difficulties arise when copying information both from books and from overhead devices. This is partly due to difficulties with manipulating the null point to maximise vision, and partly due to altered acuity.

• Nystagmus can have profound personal and social consequences for young people, affecting relationships, confidence, educational and work opportunities and their self-image.

• Patients with nystagmus can tire easily from the extra effort it takes to look at things.

• Patients may experience balance problems, as their depth of perception may be impaired: uneven surfaces or stairs may be difficult to negotiate. This may be perceived as clumsiness by others.

• Oscillopsia may mean that tasks such as riding a bicycle, if not impossible, are more precarious because of apparent movement of the roadside or parked cars.

• There may be associated stress and nervousness at being in unfamiliar surroundings, particularly as they often have poor vision.

• Patients often have difficulty in making and maintaining eye contact.

• School children and students may need extra time for reading and sitting exams. Small print can usually be read with aids but children will find it hard to share books.

• Patients need to inform the DVLA - many will not be authorised to drive.

Nystagmus treatment and management^{4 7}

This will vary with the underlying cause. It is often difficult and often disappointing. The outcome depends on the visual potential, the presence of visual symptoms such as oscillopsia and the location of a null position, if there is one.

• Patients with nystagmus should be referred for further investigation. Ophthalmologists may be helpful but abnormal neurological findings warrant a neurological referral.

• Subsequent management depends on the underlying condition. It may be conservative, medical (eg, gabapentin, baclofen) or surgical. The latter is unusual and involves altering the insertion of the relevant extraocular muscles.

• Neurosurgery may be performed where there is an underlying resectable lesion. There are several surgical techniques available,⁸ but there is currently a lack of high-quality supportive evidence for their efficacy.⁹

• Botulinum toxin injections can reduce some nystagmic movements, although there is little evidence of the efficacy of this therapy.¹⁰

• Some people with nystagmus benefit from biofeedback training.

• Gabapentin and memantine have also been shown to have some success at reducing the effects of acquired nystagmus and may be helpful for congenital nystagmus.¹¹

• There is often a 'null point' where the eye movement is reduced, meaning that vision is improved by holding the head at a particular angle. Sometimes surgery on the external eye muscles can reduce the awkwardness of the head posture (angle).

• Most patients will have some degree of decreased visual acuity requiring spectacles; some will be so severely affected as to need registration as sight impaired or severely sight impaired.

• Associated physical and psychosocial factors need to be explored and addressed where necessary (see 'Associated problems', above).

• Relaxation therapies may help indirectly by reducing stress, as stress may worsen congenital nystagmus. People with acquired nystagmus also find that anxiety, fatigue and illness can make the oscillopsia worse and there is experimental evidence that there is a link between the systems that process anxiety and vestibular signals.¹²

Advice to patients, parents and schools

Encouragement

• Parents should be encouraged to explain nystagmus to family, friends and others. The explanation should be short and positive, emphasising that most people with nystagmus can see, learn and interact well enough to lead normal lives.

• Parents should not lower expectations for their child.

• Children with nystagmus need help in understanding why their eyes are different. They also need to be able to explain their condition to other children, who will ask them about it. Counselling may be helpful to support young people through the social and personal challenges often associated with nystagmus.

• Fatigue and stress can make nystagmus worse.

Maximising functional vision⁴

• In most children with nystagmus, a spectacle or lens prescription improves vision significantly. Both spectacles and contact lenses can maximise acuity: the majority of patients with nystagmus will have some benefit from this.

• Patients often find contact lenses superior, as with glasses, the eyes sweep back and forth over the lens centres and vision is not as clear. With contacts, the lens centres move with the eyes. Some patients find that contact lenses reduce their nystagmus. A prism may be put in spectacles to help position the eye at its null point.

• Low vision devices such as telescopes and magnifiers may help people if their vision cannot be fully corrected with spectacles and contact lenses.

• Tinting glasses or using sunglasses may decrease nystagmus in patients with albinism.

• Acupuncture, biofeedback and vision therapy have been successful for some patients.

• In school the pupil should be allowed to sit near the front and be supplied, where possible, with hard copy of what they must copy from boards, so that they can place it appropriately to maximise their vision of it. On black chalkboards and on whiteboards, high-contrast colours are often easier to see.

• It may sometimes be necessary for the teacher to read out what they have written. Teachers should check frequently that pupils are able to access material as offered.

• Large-print books can help, particularly for children learning to read.

• Extra reading time should be allowed in school examinations, as reading may be slower.

• Children should not be expected to share textbooks in class, as this may impede their freedom to find the best reading position.

• Some patients have found it helpful to block out moving text on the edges of TV screens (eg, during news programmes), which subjectively improves their ability to fix on the screen.

• Home training with a perceptual learning app has been shown to be beneficial to vision.¹³

Causes of nystagmus⁶

Nystagmus may result from lesions or malfunctions in may parts of the optic (optokinetic nystagmus) and vestibular (vestibular nystagmus) systems.

Most congenital nystagmus is neurological in origin, although other important causes include albinism, congenital cataracts, eye movement disorders and very high myopia or astigmatism.

Acquired nystagmus is most commonly caused by vestibular disorders, stroke, multiple sclerosis (MS), trauma and drug toxicity.

Acute nystagmus, with or without oscillopsia, may be associated with ataxia, reduced visual acuity and falls. The most important differential diagnosis is ischaemia, bleeding or inflammation of the brain stem.

If the symptoms are chronic or chronically progressive, possible causes include metabolic, neurodegenerative, inherited or inflammatory disorders (multiple sclerosis or encephalitis) or tumours.

Physiological nystagmus

This is normal nystagmus, occurring after 6 months of age. It includes end-point and optokinetic nystagmus.

End-point nystagmus is the nystagmus associated with extreme positions of gaze. It is a fine jerk nystagmus with the fast phase being in the direction of the gaze.

Optokinetic nystagmus describes the nystagmus that occurs when following a moving object (such as looking out of a train window). It is a jerk nystagmus - the slow phase follows the target and the fast phase fixates on to the next target:

• An optokinetic drum is an instrument consisting of a handle on which is mounted a cylinder which can rotate. The cylinder is printed with thick, regularly spaced vertical black and white stripes and as it rotates, optokinetic nystagmus is induced. It is a helpful instrument in assessing the visual acuity of very young infants and also to assess patients who are feigning visual loss, as happens occasionally.

8% of the normal population can induce voluntary nystagmus - a predominantly horizontal, high-frequency, low-amplitude rhythmic oscillation of the eyes. It is sometimes associated with behavioural tics.

Early-onset nystagmus: 0-6 months of age

Congenital nystagmus has a prevalence of 1/1,000. It may be:

• Idiopathic.

• Neurological in origin.

• As a result of sensory deprivation.

Babies presenting with nystagmus need referral to a paediatric ophthalmologist for investigation.

Sensory deprivation nystagmus (SDN)

This occurs as a result of an abnormality somewhere in the visual pathway, leading to sensory deprivation. It accounts for 80-90% of childhood nystagmus.

• Children often present within the first two to three months of life with bilateral, conjugate nystagmus. Movements are horizontal and disappear during sleep. There is often a family history of sensory deprivation and examination reveals poor vision, photophobia, abnormal pupillary reactions and optic neuropathy. High refractive error and retinopathy are common findings.

• The aetiology is thought to be a congenital disturbance of the fixational system.

• Any abnormalities of the eyes causing abnormal vision may result in SDN, including corneal opacities, aniridia (absence of the iris), cataracts, albinism, retinopathy of prematurity and the rod/cone dystrophies, chorioretinal abnormalities, Leber's congenital amaurosis and optic nerve abnormalities.

• Management will depend on the underlying cause of the sensory deficit, as will the prognosis.

Neurological nystagmus

• Neurological disease can present with many forms of nystagmus. Babies tend to present before 2 months of age. A history of faltering growth, developmental abnormalities or other neurological features should raise suspicions.

• Neurological nystagmus is associated with space-occupying lesions, metabolic diseases, neurodegenerative disorders and trauma. Management and prognosis depend on the underlying cause.

Congenital idiopathic nystagmus (CIN)¹⁴

This diagnosis is made when neurological and ocular abnormalities have been excluded.

• Babies present before the age of 2 months and have nystagmus in all positions of gaze, with clinically normal eyes and normal developmental milestones. CIN may be X-linked, autosomal recessive or autosomal dominant.

• The nystagmus is horizontal and may be pendular or jerk. It dampens with convergence/accommodation and disappears during sleep. Visual acuity is usually fairly good (of the order of 6/9-6/12). The child may adopt an abnormal compensatory head position. The continual movement of the eye may reduce visual acuity (depending on the speed of movement, whether there are periods of rest from the movement and whether the nystagmus is reduced by accommodation) and visual correction with spectacles may be necessary. There is no progression of the severity after the first few months of life.

Late-onset nystagmus: presentation >6 months of age

This group of conditions is subdivided into symmetrical and asymmetrical nystagmus. The symmetrical conditions can be further classified according to the direction of movement of the eyes. The management and outcome depend on associated diseases and cause. Patients presenting with late-onset nystagmus need to be referred for investigation.

Symmetrical vertical nystagmus

• Upbeat nystagmus:
  

  • This is a jerk nystagmus with the fast phase going upwards. It is apparent on looking forwards but increases on looking up. It is most commonly seen as a side-effect of anticonvulsants but it may also occur in cerebellar and pontomedullary abnormalities and in Wernicke's encephalopathy. Occasionally, it is seen with benign paroxysmal positional vertigo or in atypical familial CIN.

• Downbeat nystagmus:
  

  • This jerk nystagmus has a fast downward phase present on looking forwards but worse on looking down. There is a variety of causes, including abnormality at the craniocervical junction (eg, Arnold-Chiari malformation), cerebellar degeneration and drug intoxication (particularly lithium, phenytoin, carbamazepine and barbiturates).¹⁵ It also occurs in Wernicke's encephalopathy, demyelination, brain stem encephalitis, tumours at the foramen magnum and hydrocephalus.

Symmetrical horizontal nystagmus

• Periodic alternation nystagmus (PAN):
  

  • This is a horizontal jerk nystagmus, whose direction usually reverses every 2-3 minutes. The nystagmus amplifies and then decreases in phases, with an interlude of 10-20 seconds before the reversal occurs. It is associated with cerebellar and brain stem abnormalities, demyelination, Louis-Bar syndrome, drug intoxication (especially phenytoin) and atypical CIN. It is also seen following head trauma, with encephalitis and with syphilis. Binocular visual deprivation may produce PAN.

Symmetrical mixed vertical/horizontal nystagmus

• Gaze paretic nystagmus:
  

  • This is a jerk nystagmus in the direction of eccentric gaze (eg, when the patient looks right, the nystagmus is to the right). When it is unilateral, its direction is towards the side of the causative lesion. It is associated with vestibular, cerebellar and brain stem disease and with drug intoxication.

• Rebound nystagmus:
  

  • This is a horizontal jerk nystagmus which changes direction after several seconds of eccentric gaze and then reverts back to its original pattern when the eyes are returned to their primary position. It occurs in posterior fossa lesions and in cerebellar disease.

• Acquired pendular nystagmus:
  

  • This is a high-frequency, low-amplitude pendular nystagmus in all directions of gaze. Causes include demyelinating disease, oculopalatal myoclonus and drug intoxication.

Asymmetrical nystagmus

• Spasmus mutans:
  

  • This rare self-limiting condition involves an acquired monocular or asymmetrical fine, rapid nystagmus usually occurring within the first year of life. It usually resolves by the fourth year of life. It is often accompanied by head nodding and torticollis. All signs disappear during sleep. It is a benign condition, although space-occupying lesions (especially gliomas of the anterior visual pathway) can present in a similar way.

• Latent nystagmus:
  

  • This bilateral jerk horizontal nystagmus only manifests if one eye is occluded or partially occluded. The fast phase is towards the uncovered eye. It is associated with infantile esotropia.

• See-saw nystagmus (of Maddox):
  

  • This pendular nystagmus is characterised by one eye rising and intorting as the other simultaneously lowers and extorts. It is classically seen with space-occupying lesions in the suprasellar region (there will also often be a bitemporal hemianopia). It is also associated with optic nerve hypoplasia, brain stem disease and retinitis pigmentosa.

• Ataxic nystagmus:
  

  • This is a rhythmic oscillation of the eye on abduction associated with internuclear ophthalmoplegia.

Other acquired nystagmus

Vestibular nystagmus²

The vestibulo-ocular reflex (VOR) normally generates compensatory eye rotations in the same plane but opposite direction to the head rotation that elicits them. Disorders of the vestibular periphery cause nystagmus in a direction determined by the pattern of the involved labyrinthine semicircular canals. Most vestibular nystagmus is peripheral in origin:

• The complete, unilateral loss of one labyrinth causes a mixed horizontal-torsional nystagmus that is suppressed by visual fixation.

• Loss of peripheral vestibular function causes impaired vision and oscillopsia during locomotion, because of the inability to compensate for the high-frequency head movements that occur with each footstep.

• Vestibular disease increases in the size of the overall VOR response, so patients complain of oscillopsia during rapid head movements.

• Peripheral nystagmus is unidirectional, uniplanar and with a torsional element. This is associated with vertigo, tinnitus and hearing loss. It may be found in acute labyrinthitis, Ménière's disease and benign paroxysmal positional vertigo. Vestibular nystagmus is often sporadic in these conditions. It is also sometimes seen when water is trapped in one ear.

• The treatment of oscillopsia because of bilateral vestibular failure (eg, idiopathic, post-meningitic, because of autoimmune diseases) is vestibular rehabilitation including head-eye co-ordination exercises.

• Central vestibular nystagmus varies with the direction of gaze. There are fewer symptoms of vertigo, tinnitus and deafness. Various brain stem diseases (eg, MS, CVA or tumours) can cause it. It is typically a straight horizontal beating nystagmus.

Paroxysmal vestibular episodes²

• Patients describe short, repeated, paroxysmal attacks of to-and-fro vertigo and unsteadiness of stance or gait lasting usually seconds (to minutes), which can sometimes be provoked by particular head positions.

• Other symptoms can be tinnitus, hyperacusis or facial contractions during the attacks. In some patients, such attacks can be triggered by head turning.

• Clinical examination between the attacks may reveal signs of permanent vestibular deficit, hyperacusis or facial paresis on the affected side.

• The cause is thought to be compression of the VIII nerve by an artery or vein in the region of the root entry zone of the vestibular nerve.

• The condition may respond to anticonvulsants. Sometimes a surgical approach is considered.

Convergence-retraction nystagmus

• This is caused by co-contraction of the extraocular muscles (especially the medial recti), resulting in a jerk nystagmus induced by optokinetic stimulation downwards. It is typically seen in Parinaud's syndrome (dorsal midbrain syndrome) and is caused by lesions of the pre-tectal area such as pinealomas and vascular accidents (particularly involving the basilar artery). Other causes include head trauma, MS and arteriovenous malformations.

Calorific response²

Vestibular nystagmus may be elicited by caloric stimulation in an attempt to discover the degree to which the vestibular system is responsive and symmetrical (this is a component of brain stem testing):

• When cold water is poured into the right ear, the patient develops a left jerk nystagmus (fast phase to the left).

• When warm water is poured into the right ear, the patient develops a right jerk nystagmus (fast phase to the right).

• When cold water is poured into both ears simultaneously, there is a fast upward phase: warm water produces a fast downward phase.

• Nystagmus that does not beat in the direction of the stimulated semicircular canal is because of a central vestibular lesion.

Dr Mary Lowth is an author or the original author of this leaflet.