“Sensory” and “Motor” Nystagmus

Abstract

ost patients with infantile nystagmus syndrome (INS) 1 (formerly known as congenital nystagmus) exhibit nystagmus with several of the waveforms first identified in 1975. 2 The past 45 years of recording and analyzing nystagmus waveforms have repeatedly demonstrated that most INS waveforms result from the same deficit in one of the several ocular motor subsystems, specifically smooth pursuit. 3-6 This applies to all patients with INS whether they have associated visual sensory deficits, are familially predisposed to have INS (ie, there is a true genetic anomaly), or exhibit INS without an associated ocular or central nervous system deficit (so-called idiopathic). Despite this eye-movement data, textbooks in ophthalmology, neuro-ophthalmology, and neurology as well as current peer-reviewed literature continue to use the terms sensory and motor nystagmus to describe the ocular oscillations of INS. Those descriptions imply not only that there are at least 2 different types of nystagmus but also that they have independent pathophysiology caused by different primary developmental deficits; both implications are unsupported by decades of ocular motor electrophysiological data. The adoption of this terminology and its presumed ability to clinically differentiate pendular from jerk waveforms are responsible for the misdiagnosis of many cases of INS. Ocular motor recordings demonstrate that owing to the complexity of INS waveforms, clinical differentiation is impossible in many patients. These recordings also show that another type of nystagmus of infancy, fusion maldevelopment nystagmus syndrome (formerly known as latent/manifest latent nystagmus), cannot be differentiated from INS with a latent component; Alfred Kestenbaum, MD, first noted the existence of these 2 clinically similar types of nystagmus in his 1946 textbook and its expanded 1961 second edition. 7

The Developmental Eye Movement Test Does Not Detect Oculomotor Problems: Evidence from Children with Nystagmus

“…The cause can be unknown (idiopathic) or associated with ocular disease or neurological syndromes. 29 Nystagmus can manifest along different planes, waveforms, amplitude, and conjugacy, but all variations are characterized as oculomotor deficiencies. 30 Fusion maldevelopment nystagmus syndrome is characterized as a jerk nystagmus that primarily occurs when one eye is closed.…”

“…Infantile nystagmus is congenital or acquired in the first 12 months of life. The cause can be unknown (idiopathic) or associated with ocular disease or neurological syndromes 29 . Nystagmus can manifest along different planes, waveforms, amplitude, and conjugacy, but all variations are characterized as oculomotor deficiencies 30 .…”

Evaluation of the Role of Displacement Surgery in the Management of Congenital Nystagmus

“…A high changeability of the eye position during the foveations, encumbers a stable placement of the target image on the intermediary fovea and consequently reduces visual acuity ( 1 ). Cogan has categorized congenital nystagmus into two principal types, termed sensory defect nystagmus and motor defect nystagmus ( 2 ). Motor defect nystagmus is a type of congenital nystagmus in which the main defect is in the efferent mechanism with possible involvement of the centers or pathways for conjugate oculomotor control, and the amplitude and frequency may lessen, or the nystagmus can completely disappear in a random position of gaze.…”

Infantile nystagmus syndrome: An observational, retrospective, multicenter study

“…7 Of note, the pathogenetic mechanism underlying infantile nystagmus syndrome is independent from the possible association with additional sensory system disease. 5,8 Idiopathic infantile nystagmus syndrome is the most common type in clinical practice. It typically occurs in the absence of other ocular or systemic disorders, and it is clinically characterized by a horizontal oscillation that remains horizontal in the different eye gaze positions and a direction consistent with the gaze way.…”

“…1,2 Particularly, infantile nystagmus syndrome includes the idiopathic form and infantile nystagmus syndrome associated with ocular diseases, such as albinism, aniridia, achromatopsia, optic nerve hypoplasia, fovea hypoplasia, and other retinal diseases. [3][4][5][6] Infantile nystagmus syndrome onset is within 6 months of life. 7 Of note, the pathogenetic mechanism underlying infantile nystagmus syndrome is independent from the possible association with additional sensory system disease.…”