Classification of vestibular signs and examination techniques: Nystagmus and nystagmus-like movements

Abstract

This paper presents a classification and definitions for types of nystagmus and other oscillatory eye movements relevant to evaluation of patients with vestibular and neurological disorders, formulated by the Classification Committee of the Bárány Society, to facilitate identification and communication for research and clinical care. Terminology surrounding the numerous attributes and influencing factors necessary to characterize nystagmus are outlined and defined. The classification first organizes the complex nomenclature of nystagmus around phenomenology, while also considering knowledge of anatomy, pathophysiology, and etiology. Nystagmus is distinguished from various other nystagmus-like movements including saccadic intrusions and oscillations.View accompanying videos at http://www.jvr-web.org/ICVD.html.

Fig.1

Jerk nystagmus schematic notation. Representing the important attributes of three-dimensional eye movements on a two-dimensional page presents several challenges requiring care to avoid ambiguity. As with describing nystagmus, its schematic notation should document the direction and intensity in the 9 cardinal gaze positions. If the nystagmus is not conjugate, each eye’s characteristics can be documented separately. By convention, eye movements are drawn from the vantage point of the examiner in front of the patient. Text should indicate whether arrows represent the slow or fast phase direction. In A-C, the arrows denote the direction of the fast phases, with the boldness of the arrows reflecting the intensity of the nystagmus. The frame of reference must be specified in every schematic in order to clarify whether the arrows for a given gaze position refer to eye movements being described in head-fixed coordinates (as viewed face to face with the patient) or eye-fixed coordinates (as viewed along the patient’s visual axis). The frame of reference that most efficiently describes a given pathologic nystagmus is typically the one most closely linked to the mechanism or site causing the nystagmus. Examples are shown: (A) Spontaneous third-degree horizontal-torsional left-beating peripheral vestibular nystagmus. This mixed horizontal-torsional nystagmus in straight-ahead gaze that obeys Alexander’s law (increases when looking in the fast phase direction and decreases when looking in the slow phase direction) is typical for an uncompensated right unilateral vestibular lesion. In this case the nystagmus directional arrows are in head-referenced coordinates, reflecting the combined effect of injury to all three semicircular canals and producing nystagmus that remains in a fixed direction with respect to the head and labyrinths regardless of gaze position (see Fig. 3). (B) Left posterior semicircular canal benign paroxysmal positional nystagmus. Nystagmus elicited in the left Dix-Hallpike position consists of mixed upbeat and torsional nystagmus with the upper pole of the eyes beating toward the left ear in straight-ahead gaze. Since the nystagmus direction is fixed in the plane of the left posterior canal, it appears predominantly vertical in rightward gaze and predominantly torsional in leftward gaze when observed along the patient’s visual axis (as documented in each box representing eye-referenced coordinates in this schematic), as well as obeying Alexander’s law. Note that the torsional fast phases could be confusingly described as clockwise from the examiner’s perspective (incorrect, but commonly used) but counterclockwise from the patient’s perspective (correct, but inconsistently used). (C) Spontaneous downbeat and bilateral gaze-holding nystagmus. Low-intensity pure downbeat nystagmus in straight-ahead gaze increases in lateral and downgaze and is associated with pathologic bilateral gaze-holding nystagmus. This schematic uses head-referenced coordinates, indicating that the downbeat component appears to remain fixed to labyrinthine coordinates regardless of gaze position. This may imply that the downbeat nystagmus is coming from a vestibular tone imbalance of the vertical rotational vestibulo-ocular reflex.

Fig.2

Common nystagmus slow-phase waveforms. (A) Constant velocity (linear) waveform, with added fast phases producing a sawtooth appearance characteristic of vestibular or cerebral hemispheric disease. (B) Decreasing velocity waveform with a negative exponential time course typical of pathologic gaze-evoked nystagmus from an impaired neural integrator. (C) Increasing velocity waveform suggesting an unstable neural integrator. (D) Pendular nystagmus, consisting of only slow phases. Adapted from Leigh and Zee [109].

Fig.3

Nystagmus slow phases observed for excitation of individual semicircular canals. In the bottom row of each panel (A through F), shading indicates the excited canals. In the second row, a diagram of the extraocular muscles depicts which muscles are activated (darker shading indicates stronger activation). In the top row, the resultant yaw, pitch, and/or roll eye movements are indicated. (A) Excitation of the left horizontal (LH) canal causes rightward slow phases mainly as a result of strong activation of right lateral rectus (LR) and left medial rectus (MR). (B) Excitation of the left anterior (LA) canal causes upward/clockwise (from patient’s perspective) slow phase because of the combined action of the right inferior oblique (IO) and superior rectus (SR) and the left superior oblique (SO) and SR. (C) Excitation of the left posterior (LP) canal causes downward/clockwise (from patient’s perspective) slow phases as a result of the combined action of the right IO and inferior rectus (IR) and the left SO and IR. (D) Combined equal excitation of both the left anterior (LA) and right anterior (RA) canals activates bilateral SR and oblique muscles and causes purely upward slow phases since the torsional components from each canal cancel each other. (E) Combined equal excitation of left anterior (LA) and left posterior (LP) canals excites muscle activity that is the sum of each canal’s individual effect; upward and downward pulls cancel, which results in a purely torsional nystagmus. (F) Combined equal excitation of all three left canals causes a right-clockwise (from patient’s perspective) slow phase, the expected result of summing activity for each individual canal. (Modified from Cohen et al [37]; adapted from Cummings Otolaryngology: Head and Neck Surgery. Flint, Haughey (eds.). Sixth edition [61]. Chapter 163: Principles of applied vestibular physiology. Carey JP, Della Santina CC. ISBN: 978-1-4557-4696-5. Data adjusted to human head frame of reference.)

Fig.4

Schematic summary of the waveforms of ocular bobbing and its variants. Adapted from Leigh and Zee [109].