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Ophthalmic Pearls: Neuro-Ophthalmology
How to Assess and Treat Infantile Nystagmus
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.
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.
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.
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.
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.