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Definition:

Nystagmus is a condition in which there are involuntary rhythmic oscillations of one or both eyes in any field of gaze. Parents frequently describe their infant’s eye as ‘shaking’. Nystagmus can be described according to its movements. It may described as:

  1. Pendular – where there is rhythmic oscillation of the eyes with no quick phase.
  2. Jerk Nystagmus – where there is a rapid movement of the eyes in one direct with a slow drift in the reverse direction.
  3. The oscillations of the eye may be horizontal, vertical or mixed
  4. The movements may be extremely fine and difficult to see or relatively coarse and easily observed.
  5. The movements may be rapid or slow

It is difficult to distinguish between the waveforms clinically. Recordings of eye movements can be made electro-

physiological

It must be remembered that nystagmus does occur in the normal state.

  1. Opticokinetic Nystagmus. This form of nystagmus occurs in everyday life.
  2. Evoked Vestibular Nystagmus.
  3. End Point Nystagmus.
  4. Voluntary Nystagmus

 Pathological Nystagmus:

Disorders of vision of eye movement control or the vestibular system can produce nystagmus. The occurrence of abnormal nystagmus suggests a pathological state of either the afferent visual pathway, that is the eye to the brain, or the efferent neurological pathways which control eye movement or position.llll

Spontaneous Nystagmus in Infants ::

Spontaneous nystagmus in infants is rarely present at the time of birth. It usually appears some time during the first six months. Nystagmus occurring within the first month of life can be divided into 3 types:

  1. Sensory Defect Nystagmus – In these patients there is an abnormality of vision.
  2. Congenital Idiopathic Nystagmus or Motor Nystagmus – These patients have no visual or neurological impairment on clinical examination.
  3. Neurological Nystagmus – Where abnormal neurological signs are present indicating cerebral dysfunction.

Nystagmus TableTable from:Casteels, Harris, Shawkat, Taylor – Nystagmus in Infancy BJO, 1992, 76, 434-437

All forms of nystagmus present in similar ways. It is extremely important to differentiate between these three forms of nystagmus because their management and investigation differ.llll

Congenital Ideopathic Nystagmus ::

This condition can be diagnosed only by exclusion of any neurological or ocular abnormality. Patients with congenital idiopathic nystagmus usually have relatively good vision.

Typical Congenital Ideopathic Nystagmus:

Usually this condition results in equal movement of each eye. Usually the movements are horizontal and remain horizontal even when the child looks upwards or downwards. It can be noted that the excursions of the eye decrease when the eyes converge to focus on a close target. It may also decrease when the eyelids are closed. Fixation on a visual target may have a variable affect, either increasing or decreasing the excursions of the eye. In this form of nystagmus there is often a decrease in the nystagmoid movements, in particular gaze direction, if this null point is not eccentric. Children may sometimes adopt an abnormal head position, that is turn their head to one side or the other, or even adopt a chin up or chin down position to improve their vision by decreasing the shaking of their eyes. It is interesting that some patients may have congenital idiopathic nystagmus with the null point in the primary position, that is looking straight ahead. Their nystagmus will only be noted on side gaze. In congenital idiopathic nystagmus the waveform may be variable. It may be pendula or jerk or a mixture of each. It may be variable in different gaze direction. It has been reported that congenital nystagmus often decreases with age.

Inheritance Patterns -

Congenital ideopathic nystagmus may be inherited as an X linked trait In these pedigrees there is normally variable expressivity and incomplete penetrance. In these patients there will be a strong family history of the condition.

It may occur sporadically. It should be considered that sporadic occurrence may possibly represent a recessive inheritance pattern

Patterns of Eye Movements - Patients with congenital ideopathic nystagmus normally have no recognisable opticokinetic nystagmus. Similarly the vestibulo-ocular reflex is often abnormal. Tracking of targets by infants with congenital idiopathic nystagmus is usually normal with a variable nystagmus waveform superimposed on the normal eye movements.

Congenital ideopathic nystagmus normally permits visual acuity of 6/18 or better. By definition patients with congenital ideopathic nystagmus have no other neurological or ocular defects. Not all patients with congenital ideopathic nystagmus have all of the described typical features. In these cases investigation must be undertaken to exclude any underlying abnormalities. Electro-physiological and neurological investigation should be performed in these cases, including Magnetic Resonance Imaging (MRI). Monocular nystagmus should be viewed with suspicion as it may be associated with serious intracranial pathology. When nystagmus is monocular or asymmetric and a headshake, with or without a head tilt or turn is present, the diagnosis of Spasmus Nutans can be considered. This is a benign condition which improves with time. Its diagnosis therefore is often retrospective.

Sensory Defect Nystagmus:

 Any condition which seriously affects vision can cause nystagmus. The defects are sometimes obvious, such as cataract or corneal opacities. Abnormality of the optic nerve, including optic atrophy, hypoplasia of the optic nerve, coloboma of the optic nerve and retinal disorders may permit a clinical diagnosis. In other patients the eyes appear normal to a clinical examination and visual electro-physiological testing may be necessary to permit the diagnosis of conditions such as cone dysfunction, achromatopsia, congenital stationary night blindness and Leber’s congenital amaurosis.

Ocular abnormalities such as aniridia or albinism and other conditions resulting in failure of the development of the macula or damage to the macula that can occur with retinopathy of prematurity are usually a clinical diagnosis.

Visual Electro-Physiology -

The electro-retinogram helps to distinguish retinal disorders and the visual evoked potential assists with assessment of macula and optic nerve function. This latter test also allows the objective assessment of visual acuity in infants and can be confirmatory in an uncertain diagnosis of albinism. Follow this link to see electrophysiology examples

 Neurological Nystagmus:

If the nystagmus is not symmetrical or unilateral or vertical, neurological disease should be suspected and a full neurological examination should be requested. Abnormalities of the visual pathway, which may result in nystagmus, include lesions of the optic chiasm or optic nerve by space occupying lesions such as optic nerve glioma, craniopharyngioma and optic nerve compression. Neurological nystagmus may be noted in patients who have marked neurological symptoms or signs and may be present with raised intra cranial pressure. A number of systemic disorders are listed which may have associated nystagmus. These include Downs Syndrome and Hypothyroidism. Monocular Nystagmus may be associated with epileptic seizures. Seesaw Nystagmus suggests a neurological abnormality.

 Latent Nystagmus:

 Latent nystagmus is binocular jerk nystagmus which is absent with both eyes open. It is usually detected on occlusion or blurring of vision of one eye. In latent nystagmus the fast phase always beats in the direction of the viewing eye. The curios term Manifest Latent Nystagmus is sometimes present in patients with alternating strabismus. In these cases again, the nystagmus fast phase will always beat towards the fixating eye.

 Management of Patients with Nystagmus in Infancy:

  1. A full paediatric examination may be indicated to exclude systemic causes.
  2. Ophthalmic examination. This examination should include refraction and full eye examination, including ophthalmoscopy to exclude the presence of any ocular abnormality which can produce sensory nystagmus.
  3. Visual Electro-Physiology. An electro-retinogram and visual evoked potential should be performed to exclude retinal or optic nerve dysfunction.
  4. If the nystagmus is atypical, imaging including MRI and neurological examination are indicated.

Treatment of Congenital Idiopathic Nystagmus:

 Spectacles should be prescribed if appropriate.

  1. Treat any associated squint or strabismus. In early infancy to use the dampening effect of convergence to decrease the ocular movement. It is important in these children to be aware of the possibility of amblyopia and to treat it appropriately.
  2. Correct abnormal head position. Surgery to adjust the null position to the primary position of gaze, that is looking straight ahead, can be performed on children who have an abnormal head posture. Various adjustments of the extra ocular muscles have been recommended initially by Anderson and Kestenbaum. Parkes recommended adjustment of four horizontal muscles. This surgery is frequently helpful. There can be regression and recurrence of the head turn. The extent of the surgery can be varied proportionately to the angle of the head turn. Similarly adjustment of vertical muscles is recommended in patients who have an abnormal chin up or chin down position with vertical nystagmus. Note the previous warning regarding vertical nystagmus. This should always be fully investigated prior to recommending adjustment of the extra ocular muscles.

 Summary: 

Infants and children presenting with nystagmus require a full history and clinical examination including family history. Added electro-physiological investigation and eye movement recordings may assist in the delineation of the form of nystagmus which is present. Neuro-radiological and neurological examination are to be recommended if the nystagmus is atypical and no sensory defect is discovered.

 

Reference:

 

Casteels, Harris, Shawkat, Taylor – Nystagmus in Infancy BJO, 1992, 76, 434-437