Background
Infantile nystagmus, (IN; also known as congenital nystagmus) is a clinical sign that may take many different forms. Involuntary, rhythmic eye movements are characteristic, as they are in acquired nystagmus. [1] Waveform, amplitude, and frequency can vary with changes in focal distance, direction of gaze, and under monocular or binocular viewing conditions. [2]
Oscillations usually are horizontal in direction but may be primarily vertical, torsional, or any combination of these three. Infantile nystagmus often is associated with other ocular conditions (eg, bilateral congenital cataracts) that impair visual acuity and occasionally can herald life-threatening conditions. [3] Other associated conditions include achromatopsia, Leber congenital amaurosis, anorexia, and ocular albinism. [4]
Pathophysiology
Few patients are noted to have nystagmus onset at birth. The term infantile is more accurate than congenital and includes nystagmus that presents within the first 6 months of life. This disorder classically has been divided into afferent (sensory deficit) nystagmus, which is due to visual impairment, and efferent (idiopathic infantile) nystagmus, which is due to oculomotor abnormality, with most cases being sensory in origin. It is believed that the nystagmus may reflect a failure of early sensorimotor integration. Although visual sensory defects are common in individuals with IN, a sensory defect is not a prerequisite for the development of nystagmus.
Data from eye movement recordings have conclusively shown that waveform alone is not a reliable method of distinguishing between these 2 entities. Therefore, it is essential that all infants with nystagmus be evaluated thoroughly for a primary sensory cause. In addition, it recently has been suggested that the following 3 additional subtypes of IN exist: (1) nystagmus associated with albinism, [4] (2) latent and manifest latent nystagmus, and (3) spasmus nutans.
Epidemiology
Frequency
United States
In one US study, the annual incidence of pediatric nystagmus was estimated to be 6.72 per 100,000 persons younger than 19 years, with IL comprising 87% of the study patients. [5]
International
Researchers conducted a review of medical records of children with infantile nysagmus born from 2010-2017 in Denmark to identify its causes. The overall prevalence of I was 6.1 per 10,000 live births, with a higher rate in premature children compared to term-born children. Ocular disease was the most common cause of nystagmus, followed by idiopathic nystagmus, neurological disorders, and genetic syndromes, with prematurity also being a contributing factor. Notably, a third of patients had no identified cause for their nystagmus. [6]
Mortality/Morbidity
Visual morbidity associated with nystagmus relates most closely to the underlying disorder affecting the visual or ocular motor system, which is responsible for the fixation instability. Infantile nystagmus rarely is associated with a life-threatening disorder.
Race
No reported racial predilection exists among patients with IN.
Sex
Infantile nystagmus may be more common in males. [7]
Age
Most patients with IN present within the first several months of life.
Nystagmus present at birth or prior to age 2 months is more likely to be idiopathic in nature or due to neurologic dysfunction. Sensory deficit nystagmus most commonly presents at age 2-3 months. Further investigation of the visual system is warranted in these cases. Nystagmus associated with albinism has characteristics similar to idiopathic nystagmus but usually is absent until after age 2 months. [4]
Nystagmus that presents after age 6 months is considered late infantile or childhood nystagmus and carries a graver prognosis. The exception is spasmus nutans, with onset in children aged 4 months to 3 years. Resolution of this condition usually occurs within a year of onset. Chiasmal glioma can present in an identical manner to spasmus nutans.
Latent or manifest latent nystagmus often is discovered after the first few months of life, but it most often is associated with infantile strabismus and can be identified by its unique characteristics.
Prognosis
Nystagmus intensity (frequency x amplitude) often improves spontaneously with increasing age but depends on etiology.
