History
There often is a known family history of this disorder. The pattern of heredity usually is sex-linked, with dominant being more common.
Establishing the precise age of onset is helpful in differentiating between sensory deficit and idiopathic infantile forms. Spasmus nutans rarely is seen prior to age 4 months. Onset prior to age 2 months, particularly in the setting of gaze-associated variable intensity and torticollis, strongly suggests idiopathic infantile nystagmus.
Patients with infantile nystagmus due to albinism may have a positive family history and often appear photosensitive. A history of infantile strabismus increases the likelihood of latent or manifest latent nystagmus.
A history of abnormal head movements (bobbing or nodding) or torticollis raises the possibility of spasmus nutans.
CNS disease can produce many other forms of nystagmus and always must be considered. A history of failure to thrive or other evidence of neurologic dysfunction should prompt immediate investigation.
Older children and adults with a history of infantile nystagmus typically deny oscillopsia but frequently may have signs and symptoms of accommodative dysfunction. These signs and symptoms include asthenopia, headaches, avoidance of near tasks, tearing, and blurry vision.
Both idiopathic infantile nystagmus and many forms of sensory deficit nystagmus have a familial pattern. X-linked, autosomal dominant, and autosomal recessive modes of inheritance have been reported.
Physical
Both sensory deficit nystagmus and idiopathic infantile nystagmus almost always are bilateral, symmetric, and conjugate. [5]
Eye movements usually are horizontal and remain so during vertical gaze (horizontal uniplanar) rather than changing to a gaze-evoked vertical nystagmus. The nystagmus disappears during sleep.
The nystagmus movements may be pendular or jerk in nature. The nystagmus may be intermittent or continuous. The patient with congenital nystagmus may have good vision or poor vision. There is no oscillopsia. There may be an inversion of the optokinetic reflex.
Nystagmus intensity (a product of the frequency and amplitude) often increases with fixation effort, attention, or anxiety, and diminishes with convergence.
Various waveforms have been described. Both pendular and jerk types have been documented to occur in idiopathic infantile and sensory deficit nystagmus. Nystagmus associated with albinism has characteristics similar to idiopathic infantile nystagmus. Latent and manifest latent nystagmus always are jerk-type with the fast phase in the direction of the fixing eye and decreasing velocity of the slow phase; the nystagmus is larger in the amblyopic or nonfixing eye, and amplitude decreases in adduction. Spasmus nutans classically is a triad of nystagmus, head nodding, and torticollis. The nystagmus is disconjugate, high frequency, small amplitude, pendular, and intermittent. It is suppressed with head nodding. A head tilt often is present. Spasmus nutans often disappears after a few years.
The hallmark of idiopathic infantile nystagmus is a gaze-dependent, variable intensity resulting in a "null zone" where nystagmus is least marked and visual acuity is maximized. This often corresponds to adoption of an anomalous head posture and frequently is the stated reason for referral.
In patients with nystagmus, visual acuity should be measured by fogging the contralateral eye with a +4 to +10 hyperopic lens over the patient's normal refractive error.
Slit-lamp examination should be performed to exclude iris transillumination defect. Funduscopy should be used to document the presence or absence of foveal hypoplasia, optic disc morphology, and any lack of fundus pigmentation.
Causes
Idiopathic infantile nystagmus is believed to be due to a primary abnormality in oculomotor control. Increasing evidence suggests a genetic mechanism with one gene mapped to the X chromosome and another gene mapped to band 6p12. Hackett et al have found evidence that mutations in the calcium/calmodulin-dependent serine protein kinase (CASK) gene are frequently associated with congenital nystagmus and X-linked mental retardation. [6]
Many ocular disorders have been associated with sensory deficit nystagmus. This is not meant to be an exhaustive listing. The variety of sensory causes suggests that the underlying cause is a failure of sensorimotor integration due to reduced vision and/or contrast sensitivity. See the following:
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Early (usually bilateral) visual deprivation (eg), congenital cataracts, severe glaucoma, Peters anomaly [7]
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Foveal hypoplasia (eg, aniridia, albinism [nystagmus associated with albinism has characteristics similar to idiopathic infantile nystagmus])
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Retinal disease (eg, Leber congenital amaurosis, achromatopsia, macular toxoplasmosis [especially if bilateral])
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Retinal detachment (eg, severe retinopathy of prematurity, posterior persistent hyperplastic primary vitreous, familial exudative vitreoretinopathy)
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Optic nerve abnormalities (eg, hypoplasia, coloboma, atrophy)
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Cortical visual impairment from perinatal insult or structural CNS abnormality
Nystagmus associated with albinism is the result of multifactorial visual impairment. Anatomical findings include abnormal ocular pigmentation, foveal hypoplasia, abnormally increased chiasmal decussation, and high cylindrical refractive errors. Several subtypes have been described. Most are autosomal recessive, but all modes of inheritance have been described.
Latent nystagmus is a conjugate, jerk nystagmus with the fast phase toward the side of the fixing eye. It is often seen in patients with congenital esotropia and following surgery for infantile esotropia, probably resulting from subnormal binocular interaction. Latent nystagmus can coexist with manifest nystagmus (in which case the nystagmus amplitude increases with occlusion). Latent nystagmus is a jerk nystagmus with the fast phase toward the side of the fixing eye. It often is seen following surgery for infantile esotropia and probably results from subnormal binocular interaction. Visual acuity measurement should be performed using the polarized vectograph or blurring one eye with a high plus lens to avoid iatrogenic reduction of acuity with occlusion. So-called manifest latent nystagmus can occur if monocular visual loss occurs in this setting.
The cause of spasmus nutans is unknown. Some studies have found an association with children from lower socioeconomic status, as well as coexisting strabismus and refractive error. Chiasmal glioma can present with an identical appearing nystagmus prior to affecting the anterior visual pathway. It may be more common in African Americans and in Latinos.
