CHAPTER 9

The Patient With Nystagmus or Spontaneous Eye Movement Disorders

Introduction

A variety of diseases, drugs, or other factors may disrupt the systems that provide ocular stability. Abnormal eye movements may occur because of inability to maintain fixation, loss of the normal inhibitory influences on eye movement control, or loss of the normally symmetric input from one of the vestibular pathways to the ocular motor nuclei. One form of excessive eye movements is nystagmus, a term that should be reserved for rhythmic, to-and-fro eye movements (eg, horizontal, vertical, torsional, or mixed) that incorporate a slow phase. Jerk nystagmus has 2 phases: (1) a slow-phase drift from the visual target, followed by (2) a corrective saccade (fast phase) back to the target. Pendular nystagmus describes back-and-forth slow-phase movements that occur without a fast phase (Fig 9-1). Abnormal saccadic movements may also adversely affect visual fixation. Collectively, these pathologic eye movements are termed saccadic intrusions or saccadic oscillations; because they have no slow phase, they do not conform to the definition of nystagmus.

Figure 9-1 Nystagmus waveforms are named for their slow-phase velocity profile. From top to bottom: linear velocity is typical of vestibular nystagmus; increasing velocity exponential typifies congenital nystagmus; decreasing velocity exponential typifies gaze-evoked nystagmus; and pendular velocity typifies congenital or acquired nystagmus.

Kline LB, Bajandas FJ. Neuro-Ophthalmology Review Manual. 6th ed. Thorofare, NJ: Slack; 2008.)

Patients with acquired nystagmus often report oscillopsia, a sensation of environmental movement. Oscillopsia is usually absent in children with congenital nystagmus. Nystagmus in primary position may degrade visual acuity. Patients should be asked about any associated neurologic symptoms (eg, vertigo, ataxia, motor weakness, or sensory weakness) and any family history of abnormal eye movements or strabismus.

Examination of ocular motility begins with assessing ocular stability in primary gaze. Any abnormal eye movements in the cardinal positions should be examined to determine if they are

monocular or binocular

conjugate (ie, the eyes behave similarly) horizontal, vertical, torsional, or mixed in pattern continuous or induced by a particular eye position

characterized by slow phases only (ie, pendular nystagmus), fast-and-slow phases (ie, jerk nystagmus), or fast phases only (ie, saccadic intrusion)

reduced at a null point (ie, the field of gaze at which the nystagmus is minimal)

By convention, the direction of jerk nystagmus is reported as the direction of its fast-phase component; however, the slow-phase component indicates the pathology. Dissociated nystagmus