Approach to the Examination and Classification of Nystagmus.

Abstract

Physical therapists caring for patients with neurologic or vestibular disorders must routinely examine and characterize nystagmus and other oscillatory eye movements. Often, the diagnosis hinges on proper interpretation of the nystagmus pattern. This requires understanding the terminology surrounding the numerous attributes and influencing factors of nystagmus, a systematic approach to the examination, and a classification structure that guides practitioners to the specific nystagmus type and subsequent evaluation and management. Nystagmus is an involuntary, rapid, rhythmic, oscillatory eye movement with at least 1 slow phase. Jerk nystagmus has a slow phase and a fast phase. Pendular nystagmus has only slow phases. Nystagmus is distinguished from other types of oscillatory eye movements, such as saccadic intrusions or oscillations. Characterizing nystagmus requires clearly describing its trajectory. This includes choosing a reference frame to describe the axes or planes and direction of eye movements. Several attributes are used to describe nystagmus: binocularity, conjugacy, velocity, waveform, frequency, amplitude, intensity, temporal profile, and age at first appearance. Several factors may influence nystagmus, including gaze position, visual fixation, vergence, and a variety of provocative maneuvers. Classification of nystagmus may be organized by physiologic or pathologic nystagmus versus other nystagmus-like movements. Pathologic nystagmus may be spontaneous, gaze-evoked, or triggered by provocative maneuvers. The combination of attributes allows differentiation between the many peripheral and central forms. Therapists should carefully examine and characterize the trajectory and other attributes and influencing factors of nystagmus to accurately classify it and arrive at the correct diagnosis.