Categories
Ocular System

Nystagmus

Involuntary (or voluntary, in rare cases) oscillation of one/both eyes about one/more axes, acquired in infancy or later in life, that may result in reduced or limited vision.

Involuntary (or voluntary, in rare cases) oscillation of one/both eyes about one/more axes, acquired in infancy or later in life, that may result in reduced or limited vision.


Classification

Types of nystagmus
Types of nystagmus | Abadi, R. V. (2002). Mechanisms underlying nystagmus. Journal of the Royal Society of Medicine, 95(5), 231–234. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/11983762

Physiological nystagmus:

Physiologically nystagmus occurs during self-rotation in order to hold images of the visual world steady on the retina and maintain clear vision.
  • Optokinetic nystagmus (involuntary, conjugate, jerk nystagmus that is seen when a person gazes into a large moving field) | Fig (d)
    • Cortical and subcortical pathways contribute to the response, which is driven by the retinal image slip velocity.
  • Vestibular nystagmus (occurs during self-rotation even in darkness) | Fig (d)
    • Vestibular labyrinth (which project to the vestibular nuclei and cerebellum) contribute to the response
    • Can also be induced by irrigating the ears with warm or cold water

Infantile nystagmus:

Oscillations are typically conjugate, horizontal and jerky.
Classification for infantile nystagmus
A schematic classification for infantile nystagmus based on the possible association with one of two nystagmus waveforms (congenital nystagmus (CN) and manifest-latent nystagmus (MLN)) and various associated anomalies. | Abadi, R. V, & Bjerre, A. (2002). Motor and sensory characteristics of infantile nystagmus. British Journal of Ophthalmology, 86(10), 1152 LP-1160. https://doi.org/10.1136/bjo.86.10.1152
  • Congenital nystagmus (CN) (slow phases are of an increasing exponential velocity form)
  • Manifest latent nystagmus (MLN) (slow phases are decreasing/linear)
    • In addition to its distinguishing slow phase, the fast phase of MLN always beats toward the viewing eye.
    • MLN is also closely associated with presence of strabismus and dissociated vertical divergence
    • Strongly visually driven
    • Largely dependent on the attentional state of the patient

Acquired nystagmus:

Many forms of acquired nystagmus can be attributed to disturbances of the three mechanisms that normally ensure steady gaze—visual fixation, the vestibulo-ocular reflex, and the mechanism that makes it possible to hold the eyes at an eccentric eye position (e.g. far right gaze)

Pathophysiology

3 main control mechanisms for maintaining steady gaze:

  • Fixation
  • Vestibulo-ocular reflex
  • Gaze-holding system (neural integrator) (operates whenever the eyes are required to hold an eccentric gaze position)
Schematic diagram depicting cortical and optokinetic pathways
Schematic diagram depicting cortical and optokinetic pathways: Cortical input to temporally directed movement,which is present only in frontal-eyed animals, requires the establishmentof normal binocular cortical connections. This input is absent in humans withcongenital strabismus. Direct crossed pathways from the eye to the nucleusof the optic tract provide nasalward subcortical optokinetic responses evenwhen binocular cortical connections are absent (R and L represent monocularcortical cells corresponding to the right and left eyes, respectively). Note: Nucleus of the optic tract (NOT) relays horizontal visuo-vestibularinformation to the vestibular nucleus (VN), where it is integrated with horizontalvestibular input from the labyrinths to establish horizontal extraocular muscletonus. LGN indicates lateral geniculate nucleus; CC, corpus callosum; V1,abducens nucleus; III, oculomotor nucleus; LR, lateral rectus muscle; MR,medial rectus muscle; AC, anterior canal; PC, posterior canal; and HC, horizontalcanal. | Brodsky, M. C., & Tusa, R. J. (2004). Latent Nystagmus: Vestibular Nystagmus With a Twist. Archives of Ophthalmology, 122(2), 202–209. https://doi.org/10.1001/archopht.122.2.202
Supranuclear centers for controlling eye movements
Supranuclear centers for controlling eye movements: These allow exact topographical determination: lesions in the region of the interstitial nucleus of Cajal (INC) lead to a vertical gaze-holding defect, lesions in the region of the rostral interstitial nucleus of the the medial longitudinal fasciculus (rilMF) leads to impairments of vertical saccades, lesions of the paramedian pontine reticular formation (PPRF) result in impairments of the horizontal saccades, lesions of the nucleus prepositus hypoglossi (NPH) are characterized by a horizontal gaze-holding defect | Strupp, M., Hüfner, K., Sandmann, R., Zwergal, A., Dieterich, M., Jahn, K., & Brandt, T. (2011). Central oculomotor disturbances and nystagmus: a window into the brainstem and cerebellum. Deutsches Arzteblatt International, 108(12), 197–204. https://doi.org/10.3238/arztebl.2011.0197

Failure of any of these control systems will bring about a disruption of steady fixation.

2 types of abnormal fixation can result:

  • Nystagmus: Essential difference between them lies in the initial movement that takes the line of sight off the object of regard. In nystagmus, a slow drift or ‘slow phase’ often due to a disturbance of one of the three mechanisms for gaze stability occurs
  • Saccadic intrusions/oscillations: Inappropriate fast movement that moves the eyes off target

Nystagmus

Characterized by the degree of conjugacy, the plane or planes of the oscillation, the direction or directions of gaze at which it is present, and the waveform, its amplitude and its frequency.

Types:

  • Pendular nystagmus: Eyes oscillate like a sine wave
  • Jerk nystagmus: Drifts in one direction with corrective fast phases
A schematic illustration of nystagmus waveforms (A) pendular nystagmus, (B) an accelerating velocity exponential slow phase jerk nystagmus (CN), (C) a decelerating exponential slow phase jerk nystagmus (MLN), (D) a linear or constant velocity slow phase jerk nystagmus (MLN). In (A) a slow phase is followed by a slow phase while in (B)–(D) a slow phase is followed by a fast phase. | Abadi, R. V, & Bjerre, A. (2002). Motor and sensory characteristics of infantile nystagmus. British Journal of Ophthalmology, 86(10), 1152 LP-1160. https://doi.org/10.1136/bjo.86.10.1152
f2.medium
A schematic illustration of nystagmus waveforms (A) pendular nystagmus, (B) an accelerating velocity exponential slow phase jerk nystagmus (CN), (C) a decelerating exponential slow phase jerk nystagmus (MLN), (D) a linear or constant velocity slow phase jerk nystagmus (MLN). In (A) a slow phase is followed by a slow phase while in (B)–(D) a slow phase is followed by a fast phase. | Abadi, R. V, & Bjerre, A. (2002). Motor and sensory characteristics of infantile nystagmus. British Journal of Ophthalmology, 86(10), 1152 LP-1160. https://doi.org/10.1136/bjo.86.10.1152

Presentation

Common symptoms:

In isolation/combination
  • Blurred vision
  • Double vision
  • Oscillopsia (jumping images)
  • Rotatory vertigo
  • Postural vertigo
  • Tendency to fall
  • Brainstem-related symptoms (for example, swallowing or speaking difficulties)
  • Cerebellar symptoms (for example, coordination problems of the extremities)
  • Inner ear symptoms (for example, hearing loss or tinnitus).

Diagnosis

Clinical examination

Leave a Reply