By Marcello Cherchi, MD PhD
For clinicians
Identification and characterization of eye movements comprise a crucial diagnostic tool in the fields of otoneurology, neuro-otology and neuro-ophthalmology. The interested reader is directed to the foundational compendium by Leigh and Zee (Leigh and Zee 2015), an invaluable reference work regarding the neurology, otology, physiology, basic science, and control systems analysis of eye movements. Leigh and Zee (Leigh and Zee 2015) organize eye movements into the following broad categories:
| Class of eye movement | Main function |
|---|---|
| Vestibular | Holds images of the visual world steady on the retina during brief head rotations or translations |
| Visual fixation | Holds the image of a stationary object on the fovea by minimizing ocular drifts |
| Optokinetic | Holds images of the visual world steady on the retina during sustained head rotation or translation |
| Smooth pursuit | Holds the image of a small moving target on the fovea; or holds the image of a small target on the retina that is close to the head, during linear motion with; with optokinetic responses, aids gaze stabilization during sustained head rotation |
| Nystagmus quick phases | Reset the eyes during prolonged rotation and direct gaze toward the ongoing visual scene |
| Saccades | Bring images of objects of interest onto the fovea |
| Vergence | Moves the eyes in opposite directions so that images of a single object are placed or held simultaneously on the fovea of each eye |
Table : Categories of eye movements. From Leigh and Zee (2015).
Our readers have probably noticed that the term “nystagmus” comes up very frequently in our discussions of diagnoses and testing. The term “nystagmus” has been defined in various ways (Eggers et al. 2019) and applied as a general term to a broad variety of eye movements, both normal (physiologic) and abnormal (pathologic). The Barany Society consensus document on this topic (Eggers et al. 2019) offers the following definition:
“Nystagmus is an involuntary, rapid, rhythmic, oscillatory eye movement with at least one slow phase. Jerk nystagmus is nystagmus with a slow phase and a fast phase. Pendular nystagmus is nystagmus with only slow phases” (Eggers et al. 2019).
Eggers and colleagues (Eggers et al. 2019) that an adequate characterization of nystagmus should include the following:
| Characteristic | Notes |
|---|---|
| Trajectory | Axis or plane of rotation and direction (horizontal, vertical, torsional components) |
| Binocularity | Is the eye movement binocular or monocular? |
| Conjugacy | Is the eye movement conjugate or dysconjugate? |
| Velocity | If the nystagmus includes both fast and slow phases, velocity refers to the slow phase |
| Waveform | Pendular (only slow phases) or jerk (alternating fast and slow phases) |
| Frequency | If there is a repetitive pattern, how many cycles per second? |
| Intensity | A qualitative combination of amplitude and frequency |
| Effect of direction of gaze | Does eccentric gaze modulate the eye movement? |
| Effect of convergence | Does convergence modulate the eye movement? |
| Effect of vision availability | Can the eye movement be modulated by permitting versus blocking visual fixation? |
| Effect of provocative maneuvers | Such as neck vibration, head shaking, hyperventilation, Valsalva |
| Temporal profile | Is the eye movement intermittent, continuous, or changing over time |
| Initial appearance | Patient’s age at the first appearance of the eye movement |
Table : Features of eye movements. From Eggers et al. (2019).
Ideally all of these features of an eye movement should be noted. However, in clinical practice one may see documentation of only the salient features (abnormal findings, pertinent normal findings).
References
Eggers SDZ, Bisdorff A, von Brevern M, Zee DS, Kim JS, Perez-Fernandez N, Welgampola MS, Della Santina CC, Newman-Toker DE (2019) Classification of vestibular signs and examination techniques: Nystagmus and nystagmus-like movements. J Vestib Res 29: 57-87. doi: 10.3233/VES-190658
Leigh RJ, Zee DS (2015) The neurology of eye movements, 5th edn. Oxford University Press, Oxford ; New York
