Nystagmus

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton, Kim Jackson, Alyssa Brooks-Wells, Jonathan Wong and Uchechukwu Chukwuemeka  

Introduction

Image 1: Left eye of male with congenital nystagmus in a rapid horizontal motion.

Nystagmus refers to rapid and rhythmic involuntary movements of the eye that may cause one or both eyes to move from side to side, up and down, or rotate. These movements can reduce vision, and affect depth perception, balance, and coordination

Some underlying conditions which cause nystagmus can be treated, especially childhood cataracts and strabismus and there are therapies for some neurological conditions and otologic conditions.

Triggers

Nystagmus can be triggered by head positioning, positional tests such as the Hall-pike dix, or gaze. Nystagmus on positional tests can suggest Benign Paroxysmal Positional Vertigo.

Classifications

Nystagmus can be classified by whether it is physiological, or pathological. Physiological nystagmus is a normal finding of oculomotor function which occurs naturally to maintain a clear and steady image of the environment, whereas pathological nystagmus refers to nystagmus caused by underlying pathology.

Physiological

• Physiologic end-point nystagmus - horizontal jerk nystagmus results from oculomotor movements in a maximal lateral direction
• Per-rotational nystagmus - horizontal jerk nystagmus occuring from sustained head rotations, with fast phases ipsilateral to the rotation
• Post-rotational nystagmus - reflexive horizontal nystagmus from a rapid brake to a unidirectional head rotation, with a contralateral fast phase and a subjective rocking boat sensation
• Optokinetic or pendular nystagmus - multi-direction (e.g.vertical, torsional, or horizontal) nystagmus in response to moving or rotating visual fields or objects, the slow phase is ipsilateral to the visual stimuli, and it does not have a fast phase.
  • Asymmetry is abnormal, and the lesion can localize to the parietal-occipital cortex.
• Optokinetic after-nystagmus - persisting ipsilateral optokinetic nystagmus after the visual stimulus has extincted, can persist for seconds and dissipates.
• Vestibular ocular reflex - occurs when the patient sees a fixed image, and a rapid head rotation is elicited in either direction.
• Caloric nystagmus - VOR reflex elicited by stimulating the tympanic membrane and horizontal semicircular canals with either warm or cold water.
  • Cold stimulus - eyes will turn slowly towards the cold water stimulation with rapid nystagmus away. Absence may indicate brain death.
  • Warm stimulus - eyes will turn slowly away with rapid nystagmus toward the side of the stimulus. Absence may indicate brain death.
• Magnetic vestibular stimulation-induced nystagmus - nystagmus that occurs while the patient is undergoing an MRI depends on the strength and direction of the field. It results from an interaction between the MRI field currents with the ionic currents in the endolymph fluid.

Pathological:

• Central or peripheral nervous system diseases affecting the peripheral vestibular apparatus, cortex, anterior visual tracts, brainstem and/or cerebellum

Nystagmus may also be defined by the type of movement observed:

• Jerk nystagmus: a slow beat in one direction and a fast beat in the other
• Pendular nystagmus: the same speed and amplitude in both directions
• Rotary nystagmus: rotational beat on the Z-Axis

Etiology

There are two categories for the etiology of pathological nystagmus:

1. Infantile nystagmus usually develops by three months of age and the most common types include congenital and manifest latent nystagmus. It is characterized by a horizontal movement and has correlations with conditions such as albinism, congenital iris absence, underdeveloped optic nerves, or congenital cataracts.
   • Congenital nystagmus often lessens with convergence or certain angles of gaze which may be used for future interventions
   • Although there are theories, there are no definitive reasons proven for why infantile nystagmus occurs
2. Acquired nystagmus may develop later in life and entails a disturbance to any portions of the mechanisms controlling gaze stabilization such as:
   • Visual system - diseases of this system may lead to nystagmus due to the loss of visual fixation
   • Vestibular organ - diseases or dysfunction of this system leads to an imbalance causing mixed horizontal-torsional nystagmus, commonly associated with vertigo
   • Central connections - diseases of the central nervous system and its connections to the vestibular system may cause up or down-beat, torsional, periodic alternating, and/or see-saw nystagmus.
   • Side effects of drugs (sedatives, alcohol, anticonvulsants) may also produce gaze-evoked nystagmus

Clinical Presentation

Nystagmus may be asymptomatic, however it commonly presents with other symptoms such as:

• Blurred or jumpy vision - complaints of difficulty with reading or watching television
  • Oscillopsia: the illusory sensation the stationary visual world is moving
  • Oscillopsia with head movement is indicative of abnormal vestibuloocular reflex (VOR)
• Dizziness
  • Vertigo: a type of dizziness that is often described as feeling that you are spinning or that the world is spinning around you
• Loss of balance
• Abnormal head posture -Some people find that their eye movements reduce in certain positions, and they may move their head to maintain this position. This can result in neck and shoulder problems.

Diagnosis

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Image 2: testing for the Horizontal Gaze Nystagmus

• When nystagmus is a new symptom and occurs with new dizziness or vertigo, the patient should get prompt medical attention.

• People experiencing pendular nystagmus for the first time should see a neurologist or neuro-ophthalmologist. Although it is not typically an emergency, pendular nystagmus should be assessed promptly.
• Depending on associated symptoms, the medical practitioner may:
  • Order tests such as a brain MRI or blood tests to rule out a potentially dangerous cause e.g. stroke
  • Perform an ocular exam
  • Perform a vestibular exam
• The type and direction of the nystagmus may be indicative of the cause and help to diagnose individuals

Treatment

Medical Treatment	Convergence prisms - viewing a near target with a convergence prism lens may suppress nystagmus and improve visual input, mostly for congenital nystagmus High positive and negative power spectacle contact lenses - may stabilize images on the retina, although multiple downsides include the patient must be stationary, limited field of view, and a patient with tremor may have difficulty with inserting a contact lens Electronic Circuit - may be useful for pendular nystagmus. An infrared sensor measures the nystagmus and then sends feedback to rotate Risley prisms, synchronizing with the nystagmus to negate the visual disturbance Medications - various drugs may be utilized to manage the condition depending on its origin Botulinum toxin injections have been shown to help some people with the acquired form of nystagmus (not usually effective in people with congenital nystagmus). The drugs gabapentin, baclofen, and memantine have also proved to have some success at reducing the effects of acquired nystagmus in some people, and they are also being trialed for people with congenital nystagmus. They do not work for everyone and can have unpleasant side effects.
Surgical Treatment	In rare cases eye muscle surgery can be performed which reduces the extent of the eye movement
Physical Therapy	Canalith Repositioning Maneuvers - if testing is positive for benign paroxysmal positional vertigo (BPPV),repositioning maneuvers for the affected canal can be used by a trained practitioner to treat nystagmus and vertigo Vestibular Rehabilitation Therapy (VRT) - if testing is positive for vestibulopathy or inner ear pathology, VRT may be used to help restore balance and vision through central compensation
Other Conservative Treatment	Electrical stimulation or vibration - this somatosensory stimulus may suppress congenital nystagmus by means of stimulating the trigeminal nerve Acupuncture - for the cervical musculature may suppress congenital nystagmus Biofeedback Relaxation techniques, meditation, Yoga, Pilates, and/or Tai Chi - can help indirectly by reducing stress and helping to stay calm. It has been found that, with both congenital and acquired nystagmus, the calmer and more rested a person is, the less the impact of their nystagmus on their sight and general well-being. People with acquired nystagmus also find that the worst effects of oscillopsia are alleviated if they are free from anxiety, fatigue, and stress.