Nystagmus can be difficult to categorize, especially since the spectrum of this eye movement encompasses both normal physiology and serious (sometimes rare) underlying disease. With a prevalence ranging from one in 1,000 to one in 6,550, infantile nystagmus is likely to be encountered in a comprehensive or pediatric ophthalmology practice. It is important to recognize and follow up nystagmus in an infant, since it may be a manifestation of a serious condition. Also, in order to avoid a vision-related learning disability, treatment for nystagmus should be considered.
Defining the Condition
Nystagmus is a rhythmic oscillation of one or both eyes about one or more axes. It is further divided into jerk nystagmus and pendular nystagmus, according to the characteristics of the oscillation. In jerk nystagmus, there is slow movement in one direction followed by a rapid movement in the other direction. In pendular nystagmus, there is no obvious distinction between the speed of movement in either direction. Infantile nystagmus is defined by onset in the first few months of life. Although the term “congenital nystagmus” is often used synonymously, nystagmus is seldom diagnosed at birth. Infantile nystagmus has traditionally been divided into sensory (afferent) and motor (efferent) types. While this distinction may be conceptually correct, it does not always reflect the underlying pathophysiology. More clinically useful are the descriptive categories: congenital motor nystagmus, sensory defect nystagmus, periodic alternating nystagmus and latent nystagmus (see Table). While these forms of infantile nystagmus are benign, other forms, discussed in “Differential Diagnosis,” can signal serious CNS pathology.
The most characteristic form of infantile nystagmus is a jerk or pendular horizontal, uniplanar eye movement. The amplitude and frequency of the oscillations vary. The nystagmus frequently diminishes on convergence and is absent during sleep. The eyes are objectively normal. In many instances, a null zone (a position where the intensity of the oscillations is diminished and visual acuity improves) is present. Persons with a null zone often adopt abnormal head positioning to maximize vision.
Time of onset. While nystagmus is seldom diagnosed at birth, the timing of onset can offer clues. For example, spasmus nutans (see below) occurs in children age 3 to 15 months and typically disappears by age 3 to 4 years, while sensory defect nystagmus begins within the first 3 months of life if vision loss is present at birth.
Family history and examination of relatives. Congenital motor nystagmus has a strong hereditary component. The sex-linked dominant form is the most common pedigree; the sex-linked recessive form is also relatively frequent. Autosomal transmission, either dominant or recessive, is rarely seen. When a case is sex-linked recessive, other anomalies such as Leber’s optic atrophy or spastic paralysis are commonly associated.
Head positioning. With time, the child will adopt abnormal head positioning if there is a null position associated with the nystagmus.
Presence of photophobia. Albinism and oculocutaneous albinism can lead to nystagmus that presents as sensory defect nystagmus.
Visual acuity. Congenital motor nystagmus is associated with relatively good visual acuity (20/40 to 20/70), while sensory defect nystagmus is often associated with poor vision.
Color vision. Achromatopsia (red monochromatism), present at birth, is complete color blindness. The first signs may be the presence of sensory defect nystagmus and light sensitivity with squinting in bright light. An electroretinogram may show an abnormal photopic signal with maintenance of a normal scotopic signal.
Slit-lamp exam. A slit-lamp exam differentiates ocular albinism, optic nerve hypoplasia and congenital cataracts—all of which manifest sensory defect nystagmus.
CT scan and MRI. Imaging is important when it is necessary to rule out organic and neurologic causes of nystagmus.
It is important to catalog symptoms and rule out serious causes of infantile nystagmus. If a child’s presentation does not precisely fulfill the criteria for congenital motor nystagmus, neuroradiologic testing is necessary.
Spasmus nutans. Spasmus nutans is acquired, typically presenting between the ages of 3 and 15 months. The classic triad is 1) nystagmus, 2) head nodding and 3) torticollis. In its classic manifestation, the nystagmus is usually bilateral but sometimes monocular and can be horizontal, vertical or rotary. It can be described as shimmering, due to its small-amplitude and high-frequency nature. The diagnostic difficulty here is the similarity between spasmus nutans and the nystagmus that accompanies a chiasmal glioma or other suprachiasmal tumor. Therefore, neuroradiologic investigation is indicated with this triad of signs. Prognosis is excellent since spasmus nutans usually resolves by the age of 3 to 4 years.
See-saw nystagmus. This form is clinically unique, with both vertical and torsional components. True to its name, the eyes will alternate with one eye high and intorting and the other low and extorting. See-saw nystagmus is often associated with a lesion in the rostral midbrain or suprasellar area and, therefore, the patient also may show bitemporal hemianopia. Neuroradiologic investigation is indicated. Treatment is removal of the tumor. There is also a form of see-saw nystagmus that is not related to tumor.
Convergence retraction nystagmus. When associated with paralysis of upward gaze, defective convergence and light-near dissociation, this type of nystagmus is indicative of dorsal midbrain syndrome. Congenital aqueductal stenosis and pinealoma are the most common causes in children.
Opsoclonus. Opsoclonus is not a true nystagmus, but rather a rapid, high- frequency, low-amplitude, involuntary, multivectorial oscillation. It is often called “dancing eyes and dancing feet,” because of its association with acute cerebellar ataxia of childhood. Opsoclonus can herald neuroblastoma.
Vertical nystagmus. Vertical nystagmus is usually jerk and is named according to the direction of the fast beat. Downbeat nystagmus is associated with cervicocranial abnormalities, such as Arnold-Chiari malformation or spinal cerebellar degeneration.
Monocular nystagmus. Monocular nystagmus is pendular, usually vertical, and of irregular frequency. It occurs in severely amblyopic eyes, in blind eyes and as spasmus nutans.
Dissociated nystagmus. In dissociated nystagmus, the nystagmus is in the abducting eye. This nystagmus is seen with internuclear ophthalmoplegia, surgical weakening of the contralateral medial rectus muscle and myasthenia gravis.
First, significant refractive errors should be corrected, and amblyopia therapy provided, if needed.
If a head turn is present and disabling, medical and surgical options exist. Prisms for both eyes, with the apex pointing toward the eye deviation (or in the opposite direction to the head turn), can correct head positioning. Prisms can also be used after surgery if abnormal head position is still manifest.
The Kestenbaum (or Kestenbaum-Anderson) procedure is designed to correct a head turn or to improve visual function by shifting a null zone into primary position. Briefly, in a patient with a left face turn and a null zone in dextroversion, the left lateral and right medial rectus muscles would be recessed. If vertical torticollis is present, the vertical rectus muscles can also be recessed.
Asymptomatic eye movements do not require treatment. However, when nystagmus is associated with decreased visual acuity and oscillopsia, it can be treated pharmacologically. For example, gabapentin, baclofen, clonazepan, 3, 4-diaminopyridine and 4-aminopyridine can be used for downbeat nystagmus, and baclofen is preferred for periodic alternating nystagmus. ¹
Also, significant encouragement in learning is important. These children sometimes adopt unconventional reading positions. Experience suggests taht they learn to read much quicker if allowed to position the book however they please. As discussed above, convergance dampens the nystagmus, allowing the child to fixate longer on the words.
1 Rucker, J.C. Curr Treat Options Neurol 2005;7:69-77.
Katie Flickinger is a fourth-year medical student at the University of South Carolina. Jeramiah P. Tao, MD, is an oculoplastics fellow at Indiana University.
|Characteristics of Important Forms of Infantile Nystagmus|
Congenital Motor Nystagmus
- Binocular and conjugate
- Can be pendular, jerk, circular or elliptical
- Waveform typically exhibits increasing velocity in the slow phase.
- A null zone, with abnormal head positioning, is often present
- There is paradoxical inversion of optokinetic nystagmus
Sensory Defect Nystagmus
- All waveforms are present, but pendular is most common; may become jerk on lateral gaze
- Caused by an abnormality in the afferent visual pathway and failure to develop a normal fixation reflex
Periodic Alternating Nystagmus
- An unusual congenital motor jerk nystagmus
- Shows a 60- to 90-second one-sided jerk nystagmus, 10 to 20 seconds of no nystagmus, then 60 to 90 seconds of nystagmus in the opposite direction
- Changes the location of the null zone and the child’s preferred head position
- Associated with oculocutaneous albinism
- Horizontal and conjugate
- Occurs with monocular fixation.
- Fast phase in the direction of the fixating eye
- Waveform shows decreasing velocity in the fast phase
- Benign condition that occurs when one eye is occluded, or following surgery that leaves one eye with impaired vision
- May become manifest (manifest latent nystagmus) when only one eye is being used for vision (i.e., if one eye is amblyopic)