Toggle section What is Nystagmus?
‘Nystagmus’ describes a rhythmic oscillation of the eyes. The word is derived from the Ancient Greek ‘nustagmos’, which describes the drowsy, rhythmic head nodding of a seated individual falling asleep. The ocular oscillations of nystagmus can be a normal physiological response to a stimulus or they can be due to a pathological disorder.
The information presented here is intended as an educational guide for clinicians, patients, parents and all those wishing to learn more about the subject. For a basic introduction to nystagmus, the RNIB provide an excellent description on their website. Support groups exist; click here to visit the UK Nystagmus Network’s website, or here for the American Nystagmus Network, for further links and resources please see Resources.
The content here covers all forms of nystagmus, to provide more of a complete picture and wider perspective of the condition. We are extremely grateful to Matt J Dunn BSc (Hons) postgraduate researcher and optometrist of Cardiff University, for authoring this section and the Research section of this website.Disclaimer: The content of this website is correct to the best of the author’s knowledge at time of writing. It is intended for use as an informational resource only. Do not use any of this information to perform any kind of self-diagnosis or examination. If you have any questions or queries of a medical nature, then please consult your optometrist, GP or ophthalmologist. We are not responsible for the content of external websites.
Toggle section Physiological Nystagmus
Under some circumstances, nystagmus is a normal behaviour of the oculomotor system.
Optokinetic nystagmus (OKN)
OKN is the normal response of the visual system to a moving visual scene (a common example is looking out of a moving train’s window). We can fixate an object outside the window as it drifts past. When the eyes reach the limit of their movement in the direction that the object is moving, a saccade is made in the opposite direction in order to refixate on a new object. This repeated pattern of drifting and refixation allows the visual scene to be partially stabilised so that more visual information can be gained than if we were to hold our eyes in a fixed position (which would cause the perception of a blurred image).
Vestibulo-ocular reflex (VOR) nystagmus
VOR is the visual reflex which allows stabilisation of the visual scene during rotational head movements (for example, when spinning on a chair or carousel). Rotation of the head causes movement of the fluid within the semi-circular canals of the inner ear. This results in a nystagmus with slow-phases (slow eye movements) in the same direction as the head rotation and quick-phases (fast eye movements) in the opposite direction. If rotation is stopped then the direction of the nystagmus will reverse with slow-phases opposing the previous direction of rotation and the quick-phases in the same direction as the preceding rotation. This after-effect occurs because the vestibular system is sensitive to changes in acceleration; ceasing rotation causes the perception of acceleration in the opposite direction.
End point nystagmus
End point nystagmus occurs when the eyes are forced to move to the extreme far point of their lateral (sideways) movement. This results in an oscillation of the eyes which will disappear if the extremity of the gaze is reduced. End-point nystagmus is chiefly caused by the shortcomings of the human 'neural integrator'.
Toggle section Classification
Nystagmus is classified according to the observed characteristics of the resulting oscillations.
The precise waveform (position-time relationship) of nystagmus can be recorded using eye tracking technology (a technique sometimes referred to as 'electronystagmography') which produces a graphical representation of the speed and direction of the oscillations. Nystagmus waveforms are typically visualised as shown below:
N.B. In horizontal eye movement recordings, an upwards deviation on the trace always indicates a rightward rotation of the eyes.
There are two major types of waveform:
The waveform has a long, slow movement of the eyes in one direction (slow-phase), followed by a short, fast movement of the eyes in the opposite direction (quick-phase).
The waveform has the same speed and amplitude in both directions.
There are in fact 12 recognised waveforms in infantile nystagmus syndrome:
|Pendular with foveating saccades|
|Pure pseudo pendular|
|Pseudo pendular with foveating saccades (one saccade is larger)|
Please note: Although we often refer to nystagmus oscillations as 'eye movements', it is important to clarify that these 'movements' refer to rotation, rather than translation.
(See Oscillation types)
The angle through which the eyes rotate during the oscillation. Amplitude is measured in degrees.
The number of full oscillation cycles that occur each second - measured in cycles per second (hertz).
The product of the amplitude and frequency of the oscillations (amplitude and frequency multiplied together).
Manifest / Latent
All infantile nystagmus will fall into one of three categories:
Manifest:Nystagmus is present with both eyes open and does not change intensity if an eye is covered
Latent latent:Nystagmus is only present when one eye is covered
Manifest latent:Nystagmus is present with both eyes open but becomes more intense if an eye is covered
Effect of Gaze
Gaze-evoked:Oscillations only appear if the eyes move from the primary position (straight-ahead)
Gaze-dependent:Nystagmus in which the oscillation waveform or intensity is altered by position of gaze
Conjugate:indicates that the oscillations are synchronous and the same in both eyes.
Asymmetric or dissociated:refers to the case in which the oscillations differ between the two eyes. Note that nystagmus can still be conjugate in the presence of strabismus.
Describes the (common) case in which two types of nystagmus present in one patient, e.g. jerk and pendular. Often the waveform can change spontaneously, or when the angle of gaze is changed.
NAF, NAFX, ANAF, NOFF, NAEF
In an attempt to provide a measure of visual function in nystagmus that takes into account visual acuity, intensity and foveation quality, a battery of quantitative measures have been devised. Sheth et al. (1995) developed the nystagmus acuity function (NAF), which seeks to estimate the maximum potential visual acuity that an individual with INS or FMNS could achieve in the absence of co-existing pathology, given an improvement in the characteristics of the nystagmus parameters. The function depends on the individual being capable of maintaining eye movement velocities ≤4°/s during their foveation periods, as well as a foveation accuracy of ±0.5°. To address these limitations, the function was improved upon by the so-called ‘expanded nystagmus acuity function’ (NAFX), which allows for expansion of the position and/or velocity limits of the NAF, which are dynamically altered depending on the nature of the data being analysed (Dell’Osso and Jacobs 2002).
Recently, a new measure was developed – the automated nystagmus acuity function (ANAF). ANAF was devised in order to perform NAFX measurement more quickly and easily (Tai et al. 2011).
Further measures also exist:
- Nystagmus optimum fixation function (NOFF) (Felius et al. 2011)
- Nystagmus acuity estimator function (NAEF) (Cesarelli et al. 2000)
Toggle section Pathological Nystagmus
There are many forms of pathological nystagmus; most are only subtly different from one another which can make accurate diagnosis of a specific form difficult. In general terms however, pathological nystagmus can be grouped into three categories:
- Nystagmus due to a visual defect
- Nystagmus due to an intracranial lesion or drug toxicity
- Nystagmus developing in infancy, but without a known cause
The actual defect of the visual system which causes nystagmus is not fully understood.
Pathological nystagmus is the fourth largest cause of registration for partial sight in the UK; its prevalence is estimated at 24 in 10,000 (Sarvananthan et al. 2009).
Nystagmus can also be described by its time of onset. Early Onset forms developing in infancy e.g Infantile Nystagmus, often have different symptoms to those developing due to an Acquired lesion. Some types of nystagmus can be Transient, such as those appearing during an epileptic seizure Epileptic nystagmus under Transient or drug intoxication. Some 'normal' individuals are able to spontaneously produce similar ocular oscillations at will (voluntary nystagmus).
Toggle section Early Onset
Early-onset nystagmus describes any form of nystagmus that presents within the first few months of life, unless precipitated by a condition causing acquired nystagmus within that time.
Early-onset nystagmus is usually primarily horizontal in direction, although vertical or torsional movement can also be exhibited, either as a major or secondary component to the movement. A recent study identified early-onset nystagmus in 0.35% of a sample of 2,546 pre-school children (Repka et al. 2012).
The three most common forms of early onset are:
- Infantile Nystagmus Syndrome
- Fusional maldevelopment nystagmus syndrome
- Spasmus nutans syndrome
1. Infantile nystagmus syndrome
Infantile nystagmus syndrome (INS) is a permanent, non-progressive condition causing involuntary oscillations of the eyes. It first appears within the first six months of life and is often associated with a congenital pathology of the visual system. In many cases however, no defect of the visual system can be found, in which case it is classified as 'idiopathic' INS. The oscillations in INS are usually conjugate (the same in both eyes) and horizontal in all directions of gaze. There is usually a particular direction of gaze in which the oscillations are at a minimum; this angle of gaze is known as the null zone. Over time, an abnormal head position may develop in order to use the better vision offered by this position.
Other factors are also known to affect the INS oscillations: relaxation, convergence and closing the eyes all tend to reduce the nystagmus intensity. Conversely, stress and tiredness will usually result in an increase in intensity. The inheritance of INS is governed by the type of inheritance shown by the sensory defect that has caused the nystagmus. In the case of idiopathic INS, inheritance can be autosomal dominant, but other forms of inheritance are known to occur.
INS is usually diagnosed within the first six months of life. INS rarely presents at birth. The average age of onset is estimated to be 1.9 months (Gottlob 1997). However, in cases of very low amplitude nystagmus, the condition may go unnoticed for many years.
Since INS often presents in conjunction with a pathology of the visual pathway, a full ophthalmological workup is required in any child presenting with nystagmoid eye movements for the first time. If no comorbid ocular pathology can be found, the INS is described as ‘idiopathic’.
The exact type of INS can be diagnosed through the use of eye tracking equipment. Such technology is rarely found in hospitals.
Prognosis / impact
INS is a permanent condition, which at present has no known cure. Unlike acquired nystagmus, INS does not usually cause oscillopsia (the illusory perception that the world is moving). The condition is also non-progressive; i.e. vision does not worsen, and the eye movements rarely increase, unless exacerbated by extraneous factors such as stress or ill health. A recent study identified the main aspects of daily life affected by nystagmus (McLean, Windridge and Gottlob 2012). The study identified issues including restricted mobility, difficulties forming relationships, and not wishing to stand out as being different.
Based on a large scale study of the population of Leicestershire, the incidence of INS is believed to be 14 in 10,000 (Sarvananthan et al. 2009).
Sensory defect infantile nystagmus syndrome
Around 70% of cases of INS are associated with some sort of ocular defect. There are a large range of seemingly unrelated conditions that are associated with INS. In all cases however, the ocular defect in some way impairs vision, usually bilaterally.
The most commonly associated conditions are albinism, cataract, aniridia, coloboma, cone dysfunction, achromatopsia and congenital stationary night-blindness.
The link between visual impairment at birth and the development of INS has led to the theory that nystagmus develops as a response to poor image quality (Harris and Berry 2006).
Idiopathic infantile nystagmus syndrome
When non-acquired nystagmus presents in the first six months of life with no other detectable abnormality of the eyes, it is referred to as ‘idiopathic infantile nystagmus syndrome’ (IINS). Idiopathic literally means ‘of unknown cause’, and at present it is not known in these cases whether nystagmus is the primary defect, or if an undetectable visual system abnormality exists. In some cases, there is a genetic link between individuals with IINS. Several mutations have been found in the ‘FERM domain containing 7’ (FRMD7) gene in X-linked IINS (Tarpey et al. 2006; Self and Lotery 2007; Xiao et al. 2011; Li et al. 2012; Radhakrishna et al. 2012).
Null zone and abnormal head positions
The intensity of nystagmus movement varies with direction of gaze. The position(s) of gaze in which nystagmus intensity is at a minimum is known as the ‘null zone’.
In a study of 224 people with INS, 73% were found to have a null zone within 10° of the primary position. Around 44% of nystagmats also exhibit a dampening of eye movements with convergence; therefore near vision may be better than distance in some situations (Abadi and Bjerre 2002).
Since the null zone position of gaze affords the individual better vision, often an abnormal head position (AHP) develops to put the eyes in the optimum position whilst looking straight ahead. In Abadi and Bjerre’s 2002 study, 69% of subjects with an eccentric null zone exhibited an AHP. When the null zone was ≥20° from the primary position, all nystagmats exhibited an AHP.
AHPs are one of the reasons that some individuals feel their nystagmus makes them stand out as being different (McLean, Windridge and Gottlob 2012). Often, the individual will have to choose between using a socially ‘normal’ head position, and adopting their AHP to maximise their ability to interpret social cues.
Effects on visual capability
Nystagmus can have many adverse effects on visual capability. The exact nature and extent of these effects is determined by the nature of the nystagmus, its waveform, intensity, fixation effort, viewing distance, stress and, if an eccentric null zone is present, head posture.
The presence of oscillating eye movements results in the motion of the visual image across the retina. Contrast sensitivity of the visual system is highly sensitive to even small image movements of a few degrees per second, especially at high spatial frequencies (fine detail). The oscillations in the slow-phase of nystagmus oscillations can reach speeds of 100 degrees per second which will obviously cause a large reduction in contrast sensitivity. Contrast sensitivity is what determines our ability to discriminate objects of different brightnesses apart and in the majority of situations contrast between objects is low. A reduced contrast sensitivity can therefore have a large impact on an individual's ability to navigate their way around their surroundings. Contrast sensitivity in nystagmus is determined by the speed of the slow-phases which are known as 'foveation periods'; the longer these foveation periods are, the better the vision will be. The reduction in sensitivity also causes nystagmats to be highly sensitive to visual 'crowding'. This causes increased difficulty in discriminating two objects that are close together.
Another factor which relates to the level of visual capability in nystagmus is the ability to align the fovea with the object of fixation during the foveation periods. This alignment of the fovea with the target is generally more accurate in adults with nystagmus than children, possibly due to adaptation of the visual system.
Nystagmats have a high incidence of with-the-rule astigmatism in which the eye has a higher power in the vertical meridian than the horizontal meridian. This may be due to a mechanical deformation of the eye or a response by the visual system to the blur caused by the oscillations. This will cause the eye to develop a higher power in one direction than the other in an effort to clarify the vision. Meridional amblyopia is also present, caused by the oscillations which occur along the meridian at 90 degrees to the direction of the oscillations which deprive the visual system of stimuli along that meridian.
Rarely, individuals with INS suffer from oscillopsia (the illusion that the world is moving), although this is much more common in acquired nystagmus.
No ‘cure’ for INS has yet been discovered; however there are a large number of interventions that have been shown to be effective in reducing the eye movements, moving the null zone, and/or improving visual function.
Contact lenses provide superior refractive correction over conventional spectacle lenses for nystagmats due to the reduction in aberrations, and induced prismatic effect experienced as the eye moves away from the primary position. Allen and Davies (1983) found an increase in visual acuity of at least one Snellen line in seven out of eight nystagmats using contact lenses compared to when wearing spectacles. This was confirmed by Biousse et al. (2004). Contact lenses also appear to dampen nystagmus eye movements in INS, but this effect is not present when the eye is anaesthetised (Dell’Osso et al. 1988). This finding suggests that the presence of the lens touching the eye – rather than the optical effects of the lens – serve to reduce the movement, which implies that nystagmus intensity is partially governed by signals from nerves in this region. Dell’Osso, Leigh and Daroff (1991) went on to show that cutaneous stimulation of the ophthalmic division of the trigeminal nerve can cause a reduction of nystagmus intensity, using gentle touches, vibrations, pressing and rubbing of the forehead and upper eyelids.
The fact that many nystagmats have a convergent null zone led to the suggestion that prescribing base out prism (to drive convergence) could improve visual function. A study by Dickinson (1986) found no improvement in the contrast sensitivity function with this method; nystagmus intensity was, however, reduced. Rarely, the null zone is in the divergent position, in which case base in prism has been shown to be useful. A study by Dell’Osso (2002) found an improvement in visual acuity of two Snellen lines when prisms were used both to drive convergence and to place the eyes into a null zone of gaze. As ever when prescribing prism, care must be taken to balance the refractive and prismatic prescriptions with respect to the accommodative convergence : accommodation ratio (Dell’Osso 2002).
Several surgical procedures have been advocated for INS. These include:
In 1953, Kestenbaum devised a surgery intended to move the null zone towards the primary position, thus reducing any AHP present. This procedure involves a recession of the rectus muscles with action in the direction of the face turn, and resection of the antagonists. A form of this procedure is still used today and is effective in reducing AHPs (Lee 2002).
Using a similar principle to base out prisms, performing resections in both lateral recti induces a latent exophoria which is overcome by employing fusional convergence (in patients with sufficient fusional reserves). This serves to reduce the intensity of nystagmus. In a surgical study by Zubcov et al. (1993), three out of six patients undergoing artificial divergence surgery experienced a measurable improvement in visual acuity. Five patients underwent combined Anderson-Kestenbaum and artificial divergence surgery, four of whom gained two or more lines of Snellen acuity.
Horizontal rectus recession
The recession of all four horizontal recti has been shown to increase visual acuity whilst reducing nystagmus intensity. It has been suggested as an easier-to-perform alternative to Anderson-Kestenbaum surgery. In a study on ten subjects with INS undergoing this procedure, eight exhibited a reduction in the amplitude of their nystagmus with a concordant average improvement in visual acuity of one line.
The ‘anterior tenotomy’ procedure was pioneered in 1999 (Dell’Osso et al.) on an achiasmatic mutant Belgian sheepdog with INS. The procedure was later performed on ten human subjects with no adverse events, leading to improved clinical visual acuity in five subjects, improved subjective visual function in nine subjects, and increased foveation periods in these same nine subjects. The procedure, which involves severing the horizontal recti, followed by reattachment at the original site, was first proposed in 1998 (Dell’Osso).
Given the number of surgical approaches available, surgeons have recently been implementing combinations and modifications of the above procedures, with generally positive outcomes in both the nystagmus intensity, and clinical visual acuity (Bishop 2011; Kumar et al. 2011).
Many medicines are known to reduce the intensity of nystagmus. In 2002, a list of fourteen treatments reported to improve the condition was published (Stahl, Plant, and Leigh). Of these, four have been shown to effectively dampen nystagmus intensity in INS (memantine, gabapentin, baclofen and cannabis). Memantine (20-24mg) and gabapentin (up to 2400mg) both reduce nystagmus intensity and improve visual acuity in INS, and have been validated in a controlled, double-masked randomised trial (Sarvananthan et al. 2006; Shery et al. 2006; McLean et al. 2007). One case report of a subject with IINS showed that smoking cannabis can cause a reduction in nystagmus intensity and an improvement in clinical visual acuity (Pradeep et al. 2008). Baclofen is often used in patients with periodic alternating nystagmus, as it is known to reduce nystagmus amplitude, improve visual acuity and alleviate AHP (Solomon et al. 2002; Comer et al. 2006).
Dexedrine, a stimulant used to treat attention deficit hyperactivity disorder, has been shown to increase foveation duration, improve stereopsis, reduce an exotropic deviation and improve visual acuity in a patient with INS associated with rod-cone dystrophy (Hertle et al. 2001).
A recent study demonstrated that brinzolamide, applied topically, can cause an improvement in NAFX in a patient with INS, providing hope for non-systemic approaches to nystagmus pharmaceuticals (Dell’Osso et al. 2011).
The mechanisms of the above medications are currently unknown, although their mode of action is suspected to be through sedation rather than specifically reducing the eye movements (Abel 2006). For a detailed account of the pharmacological treatments available for INS, the reader is directed to McLean and Gottlob (2009) and Strupp et al. (2011).
Biofeedback: Auditory biofeedback, derived from live eye movement recordings, provide nystagmats with direct feedback from their nystagmus, and with practice, patients are able to reduce the intensity of their nystagmus (Mezawa et al. 1990). This suggests that with practice, nystagmats can learn to consciously control their eye movements. After six half-hour sessions of auditory biofeedback, a study by Sharma et al. (2000) found nystagmus amplitude to be reduced by 51% and intensity reduced by 60%, with a subjective improvement in quality of vision. Abadi, Carden and Simpson (1980) found an objective improvement in visual acuity between 0.13 and 0.32 (logMAR). However, these improvements are generally not sustained following discontinuation of the therapy (Sharma et al. 2000), but in a study by Ciuffreda, Goldrich and Neary (1982), one subject was able to reduce their nystagmus eye movements to 50% of the pre-training level on demand, without biofeedback.
Acupuncture: In 1987 (Ishikawa, Ozawa, and Fujiyama), acupuncture was shown to reduce nystagmus intensity in nine out of 16 subjects tested. Blekher et al. (1998) showed that insertion of two acupuncture needles in the sternocleidomastoid muscles of the neck caused a significant increase in foveation durations in four out of six patients, which was observed five minutes following the end of treatment. In this experiment, one subject who was particularly responsive to the treatment later had a sham treatment administered, which caused exacerbation of his nystagmus. In this instance, foveation periods reduced at the times when the needle guide tubes were tapped, in contrast to an observed increase in foveation time during genuine acupuncture treatment.
2. Fusion maldevelopment nystagmus syndrome
Formerly known as ‘latent nystagmus’, fusion maldevelopment nystagmus syndrome (FMNS), is perhaps the most commonly seen form of pathological nystagmus, due to the fact that its onset often follows an infantile strabismus (squint). FMNS oscillations are conjugate (the same in both eyes) and display a jerk waveform with decelerating slow phases. The oscillations beat towards the fixing eye (more accurately, the eye that the subject believes they are fixing with). The oscillation intensity increases with abduction of the fixing eye (looking outwards) and decreases with adduction of the fixing eye (looking inwards). A head turn may be adopted in the direction of the fixing eye as the reduced nystagmus intensity in this position allows better vision. FMNS can be manifest or latent (See classification).
3. Spasmus nutans syndrome
Spasmus nutans syndrome is a rare disorder, which causes (in combination): a high frequency, low amplitude nystagmus of a disconjugate nature, irregular head nodding and an AHP. Its onset is usually within the first year of life and the condition ceases spontaneously, usually within two years of onset, although it has been known to persist for over eight years. A low-amplitude nystagmus (not detectable clinically) may persist until at least five to twelve years of age (Gottlob et al. 1995). The pathogenesis of spasmus nutans syndrome is unknown (Leigh and Zee 2006).
Toggle section Acquired
Acquired nystagmus describes any form of nystagmus not developing in early infancy (unless caused by a lesion). Nystagmus that develops later in life often leads to the illusion of visual motion (oscillopsia). The animation below illustrates oscillopsia:
Gaze evoked nystagmus
Gaze evoked nystagmus appears as jerk nystagmus induced upon deviation of the eyes away from the primary position (straight-ahead). In the primary position the usual presentation is of unsteady fixation but sometimes pendular nystagmus can also be observed. In lateral gaze positions a horizontal nystagmus will appear; in upgaze, upbeat nystagmus may appear, but with a smaller intensity than the horizontal nystagmus. A downbeat nystagmus in downgaze can also be present but is much less common. In the oblique gaze positions an oblique nystagmus can occur but if the vertical gaze-holding circuitry of the visual system is unaffected then the nystagmus will be purely horizontal. The variation in nystagmus with gaze position is shown in the animation here.
Gaze evoked nystagmus can be differentiated from FMNS by the absence of any change in the oscillations following the occlusion of one eye. It results from a mismatch between the gaze-holding systems and the movements of the extraocular muscles and can be linked to abnormal VOR, abnormal OKN and abnormal smooth pursuit. Gaze evoked nystagmus can be caused by cerebellar disorders or follow the use of sedatives, anticonvulsants, alcohol, cannabis, barbiturates, diazepam or chloral hydrate.
Rebound nystagmus is a characteristic of gaze evoked nystagmus that is seen when the subject is asked to maintain an extreme lateral gaze position. In this situation the horizontal nystagmus intensity gradually decreases and sometimes even reverses its direction. If this is followed by a rapid return to the primary position, then the brief rebound nystagmus occurs. The rebound nystagmus lasts for only a short time and beats away from the direction of the maintained lateral gaze. Rebound nystagmus can sometimes be observed in subjects who also show end-point nystagmus.
Downbeat nystagmus is most evident in the primary position. The nystagmus intensity increases in lateral gaze and the addition of a horizontal component results in oblique oscillations. The oscillations will often alter on upgaze but the changes are variable, they may reduce, intensify or change to an upbeat nystagmus. Downbeat nystagmus is affected by convergence which may result in an intensification of the oscillations, in fact downbeat nystagmus may only appear on covergence. Downbeat nystagmus can be accompanied by poor smooth pursuit, OKN and VOR.
Upbeat nystagmus is less common than downbeat nystagmus and does not intensify in lateral gaze. The oscillations intensify on upgaze and reduce on downgaze although occasionally upbeat nystagmus can change to downbeat nystagmus on downgaze. Convergence also has an effect on the oscillations which can result in a cessation of the upbeat nystagmus or even change it to downbeat nystagmus.
Acquired pendular nystagmus
Acquired pendular nystagmus presents as a high frequency, low amplitude pendular oscillation as shown in the animation here. The direction of the oscillations is variable and can be horizontal, vertical, eliptical, circular, monocular or asymmetric. The oscillations usually remain pendular in all positions with only small changes in their amplitude. OKN response is still present. Acquired pendular nystagmus can present in young children resulting from dysmyelinating and demyelinating conditions. If the nystagmus is late onset, it can often be monocular or asymmetric and can follow visual loss or amblyopia.
Vestibular nystagmus, as suggested by the name, is often associated with dizziness or vertigo. This can be brought about by various disorders that affect either the central nervous system or peripheral portions of the vestibular system. If a single semicircular canal in the inner ear is affected then the resulting nystagmus will occur in the same plane as the action of that canal.
The nystagmus itself is a jerk nystagmus and if caused by a peripheral vestibular disturbance it will quickly reduce due to the adaptation of the visual system. Differentiation between a central or peripheral vestibular abnormality can be determined due to the fact that peripheral vestibular nystagmus will intensify once visual stimuli are removed e.g. in the dark.
This is a specific type of vestibular nystagmus which is indicated by episodes of vertigo which result from particular head movements. Positional nystagmus is associated with benign paroxysmal positional vertigo (BPPV) which is caused by deposition of degenerated material onto the posterior semicircular canal which then produces increased responses due to its increased mass.
Positional nystagmus can be initiated by moving the subject rapidly from a seated position to a head down position towards the side of the vestibular abnormality. The nystagmus will reduce and stop over a period of about 40 seconds.
Retinal image stabilisation: This technique uses a high-plus spectacle lens to place an image at, or close to, the centre of the eye's rotation. The position of this focal point will therefore not be affected by the orientation of the eye. A high-minus contact lens is then used to bring this image into focus, as the contact lens moves with the eye it does not change the stability of the image. This technique can achieve a 90% stabilisation of the retinal image, unfortunately it also gives a small depth of focus and reduced visual field. As it also interferes with the VOR and prevents vergence movements (looking at objects at different distances) it can only be used monocularly.
Pharmacological: For a recent review of pharmacological treatments available for acquired nystagmus, the reader is directed to Mehta and Kennard (2012).
Toggle section Transient
Epileptic nystagmus is seen only during epileptic seizures and is brought on by flashing lights, image blurring, stress, fatigue, and changes in light intensity. Epileptic nystagmus can also occur spontaneously and can be accompanied by symptoms of oscillopsia, blurred vision, amaurosis and hallucinations. The most likely type of oscillations that will be seen in epileptic nystagmus are conjugate (the same in both eyes), horizontal, jerk waveform oscillations which beat in opposition to the direction of gaze.
There are two forms of epileptic nystagmus. In the first, the nystagmus oscillations cross the primary position with a large amplitude slow-phase. The second type of epileptic nystagmus has oscillations which do not cross the midline and always beat in opposition to the direction of gaze.
A small percentage of people (~8%) can induce a horizontal nystagmus oscillation of the eyes at will, often by forcing convergence (Zahn 1978). This movement is very small (~2-5° (Fisher, Davies and Wallis 1979)) and fast (15-30Hz (Ramat et al. 2008)), and is believed to be caused by inhibition of omnidirectional pause neurons, which are located in the raphe interpositus nucleus and serve to tonically inhibit excitatory burst neurons prior to saccade generation.
The release of tonic inhibition at the onset of a saccade is known as 'post-inhibitory rebound' and is what affords saccades their great speed. When the omnidirectional pause neurons are inhibited for long periods of time however, a feedback loop is created, causing oscillations to occur.
Voluntary nystagmus is not usually considered to be a pathological condition due to its voluntary nature, however cases of ‘involuntary’ voluntary nystagmus have been documented (Neppert and Rambold 2006).
Toggle section Examination of nystagmus patient
This section is intended for use by optometry students who wish to gain an insight into the types of examination techniques that can be applied to a patient who appears to have nystagmus.
History and symptoms
Make sure to ask if there is a family history of nystagmus or of the conditions that are commonly associated with nystagmus. The further back any problems can be traced the better as, due to the inheritance mechanisms, many conditions can skip several generations.
Ask about the observed time of onset of the symptoms and their characteristics such as their progression and changes in severity under different conditions e.g. lighting, stress etc. An intermittent problem may impede the examination process as it may or may not appear during the examination.
Also ask about any visual difficulties that the patient has experienced such as photophobia or poor night vision as these may indicate an underlying sensory defect that may be the cause of the problem. Make sure to enquire about any previous treatment that they could have received such as surgery or any medication that they may be taking.
A full examination should be carried out which should include ophthalmoscopy, slit-lamp, colour vision testing and refraction. Measure the patient's visual acuity binocularly and monocularly, at distance and near and with and without a head turn if applicable.
Axis: Determine the axis of the oscillations as horizontal, vertical, oblique, torsional or circumrotatory. Small or torsional oscillations can be observed by viewing fundus movements through an ophthalmoscope.
Asymmetry: Record any asymmetry in oscillations that occurs between the two eyes and in what position of gaze it appears.
Gaze-dependency: Record any changes in the oscillations that occur following a change of gaze position.
Monocular occlusion: Occluding one of the eyes will reveal any latent component of the nystagmus.
Electronystagmography: Eye movement recordings allow accurate classification of the nystagmus waveform.
These types of examination techniques are rarely available but can be useful, for instance, the determination of normal electroretinography and pattern visual evoked potentials is an indication of an IINS. Abnormal results in these electrophysiological tests can reveal less obvious sensory defects that may be present or identify a neurological abnormality.
Toggle section Oscillation types
Horizontal: The eyes oscillate horizontally
Vertical: The eyes oscillate vertically
Circumrotatory: The eyes oscillate horizontally and vertically at the same time. If these oscillations are in phase then the result is that the eyes move in an elliptical fashion
Oblique: The eyes oscillate horizontally and vertically at the same time but the oscillations are not in phase. This results in oscillations in an oblique direction
Torsional: The oscillations occur around the anteroposterior axes of the eyes resulting in torsional movements (i.e. the cornea will be seen to rotate clockwise and anti-clockwise)
The direction of nystagmus is defined as the direction of the quick-phases relative to the head. This can cause some confusion, as in the majority of waveforms this means that the nystagmus 'direction' is actually the direction the eyes spend less time travelling in. As pendular nystagmus has no quick-phase it also has no direction. Some individuals exhibit periodic alternating nystagmus, in which case the beat direction changes over a regular time period.
Horizontal / Vertical
Horizontal nystagmus is by far the most common type; especially in early-onset nystagmus. Often, a small vertical component is also present in early-onset nystagmus, although purely vertical nystagmus is not unheard of, especially if acquired (see downbeat nystagmus and upbeat nystagmus).
Torsional nystagmus describes oscillations about the anteroposterior pole of the eyes (as a result the iris is seen to rotate clockwise and anti-clockwise).
Tortional nystagmus as an isolated nystagmus is not common, however it is often seen in conjuction with other axes of oscillation in infantile nystagmus syndrome, fusion maldevelopment nystagmus syndrome, see-saw nystagmus and vestibular nystagmus.
Abduction nystagmus appears on abduction (looking away from the nose); the resulting oscillations are asymmetric with there being a much weaker nystagmus observed in the adducting eye. This is shown in the animation here.
The rare form of nystagmus known as see-saw nystagmus presents as oscillations in which one eye elevates and intorts (rotates towards the nose) whilst the other eye depresses and extorts (rotates away from the nose). These oscillations usually have a pendular waveform but can sometimes have a jerk waveform. See-saw nystagmus can be congenital or acquired. This animation shows see-saw nystagmus.
Periodic alternating nystagmus
Periodic alternating nystagmus (PAN) is a jerk nystagmus which will reverse direction every few minutes. PAN can be acquired condition or congenital and the oscillations themselves follow a repeating pattern of changes. The oscillations in the first direction gradually increase in intensity to reach a maximum level after about a minute. The intensity then begins to drop again and reaches a minimum intensity known as the neutral phase. The oscillations then begin again but in the opposite direction; each full PAN cycle taking approximately 3-4 minutes. A shortened version of a full PAN cycle is shown here.
The duration of the PAN cycles can vary widely between subjects and in general congenital PAN consists of shorter cycles than acquired PAN. The time to reversal can also be different in each direction (asymmetric).