What is nystagmus?

Nystagmus is an involuntary ocular oscillation of the eyes. Typically it has a pathologic slow eye movement followed by a fast eye movement. The movements can be exclusively horizontal, exclusively vertically, exclusively torsional, or a combination of all three. Congenital nystagmus may present in early childhood. Acquired cases may develop in adulthood or childhood.

Do affected patients see the world moving constantly?

Oscillopsia is the symptomatic perception of the visual world moving from variable eye movements. In early-onset nystagmus, most patients do not experience oscillopsia. In some forms of adult acquired nystagmus and in other irregular-eye-movement disorders (such as opsoclonus) there may be symptomatic oscillopsia.

Why do nystagmus patients not experience oscillopsia?

It is not entirely clear what mechanisms are in place that eliminate symptomatic oscillopsia in early onset nystagmus. It had been speculated that retinal information was sampled during foveation only and then suppressive mechanisms were in place during eye motion—like a strobe light effect. Studies have shown that there is indeed processing of retinal information continuously. Based on this information, there is speculation of “extraretinal signals” that somehow cancel out the visual information during eye movement. Changes in nystagmus waveforms (by new pathology, surgical or medical intervention) can result in oscillopsia in some nystagmus patients.

Are patients with well-adapted nystagmus (i.e., no oscillopsia or diplopia) able to see their own eyes move when they look in a mirror?

No, they cannot see their own eyes move in a mirror. The presumption is that the eye movements match the mirrored image so they do not see it. To show a patient what he or she looks like to others, you must make a video of the eye movements.

Why don’t many nystagmus patients see well?

Many of these patients have underlying eye pathology that causes decreased acuity and then leads to the development of nystagmus. In those that do not have other eye disease, the nystagmus itself limits fixation time (foveation) and thus decreases acuity.

What are the classifications of nystagmus?

The National Eye Institute has reclassified eye-movement disorders in the Classification of Eye Movement Abnormalities (CEMAS). See Table 28-1 .

What is the infantile nystagmus syndrome?

Typically this is binocular conjugate horizontal nystagmus, but can have vertical or rotary components. It tends to also be uniplanar, staying horizontal in all gazes. Infantile nystagmus syndrome (INS) can be primary motor nystagmus, unrelated to any other eye pathology. It can also be primary sensory nystagmus-related poor vision associated with optic nerve hypoplasia, albinism, congenital cataracts, or other intraocular pathology.

What is the typical waveform of the nystagmus seen in infantile nystagmus syndrome?

Onset of the nystagmus is typically within the first 6 weeks of life, with wide pendular movements and apparent poor visual behavior. By 6 to 8 months of age, it converts to smaller pendular waveforms. Between 18 and 24 months of age, the waveform progresses to more jerk-type movements and with possible formation of a null point.

What is the null point in nystagmus?

The null point is the direction of gaze in respect to orbital coordinates that minimize the amplitude and frequency of nystagmus. Because a position of gaze that minimizes the nystagmus allows better vision, it is common for patients to seek out the null point with an anomalous head position.

Is the null point the same for each eye?

Yes, but there is an exception—nystagmus blockage syndrome. See question [CR] .

What is nystagmus blockage syndrome?

Patients find that convergence dampens their nystagmus and manifest a large-angle esotropia as their null point. They may manifest a face turn toward the fixating adducted eye and may alternate face turn with alternating fixation.

Do patients with infantile nystagmus syndrome associated with poor vision (congenital sensory nystagmus) also have the same natural history of the nystagmus waveform evolution?

Yes. Care must be taken to look for albinism, achromatopsia, Leber’s congenital amaurosis, hypoplasia of the optic disc, and delayed visual development.

Is a distinctive nystagmus associated with specific ocular pathology?

To date, only the unique nystagmus of achromatopsia seems somewhat distinctive as it evolves to an oblique direction from a horizontal pendular direction.

Does infantile nystagmus syndrome ever disappear spontaneously?

Rarely, yes. More commonly the patient has spasmus nutans, which is not recognized, and, of course, by its very definition the spasmus nutans disappears after a year or so.

What is spasmus nutans?

Spasmus nutans is acquired in the first 2 years of life and consists of the triad of nystagmus, head nodding, and torticollis. It is a benign condition that generally resolves by 3 to 4 years of age. Magnetic resonance imaging (MRI) is indicated, as midbrain pathology can mimic these findings.

What is the hallmark of the nystagmus seen in spasmus nutans?

Most often, there is binocular small-amplitude high-frequency “shimmering” nystagmus. It can be monocular or asymmetric and multiplanar.

Does nystagmus mean that the patient is blind?

No, to the contrary. You must have or have had some vision to develop nystagmus. Many patients with sensory nystagmus have significant visual impairment, though, depending on their pathology.

Are some types of nystagmus present at birth?

Yes, physiologic bidirectional jerk nystagmus can be seen soon after birth. This includes vestibular and optokinetic nystagmus and eccentric “end gaze” nystagmus. These are normal and typically are associated with normal vision.

Does a patient need vision to have nystagmus?

Yes, but the vision may be poor. The retinal or systemic conditions may worsen or cause blindness, and the typical INS persists.

If one sees what seems to be the natural history of infantile nystagmus syndrome, should an MRI be obtained?

A full ophthalmologic examination should be performed, looking for underlying pathology that would cause the nystagmus. If an intraocular cause for sensory nystagmus can be found, then no imaging is indicated (except for optic nerve hypoplasia, for which imaging should be ordered to evaluate for other midline central nervous system defects). If there is optic atrophy or pallor found, then MRI is indicated to look for midbrain lesion. If spasmus nutans is considered, then an MRI should be obtained (see question [CR] .)

If the nystagmus is vertical, will the patient develop a preferred chin-up or chin-down head position?

Yes. Patients may develop a head position in relationship to the null point in the same fashion as patients with horizontal nystagmus. The null point is in the direction of the slow phase of the nystagmus. Therefore, if the patient has obvious downbeat nystagmus, it will be worse on upgaze and the null zone will be downward, with a preferred chin-up head position.

Do patients with torsional infantile nystagmus syndrome exhibit a head tilt in respect to torsion?

Occasionally. The physician needs to examine the infant with torticollis carefully with the slit lamp to look for torsional nystagmus if no other etiology for the torticollis is found.

How can torsional nystagmus be observed and diagnosed?

Slit lamp observation of the iris is the most sensitive test. Eye-movement recordings can be used, but these are more involved and may be difficult to obtain.

Is the pivot of the torsional nystagmus always on the visual axis?

No, and exceptions may cause some difficulty in diagnosis. If the pivot is on the visual axis, the eye rotates clockwise and counterclockwise about the visual axis—the object of fixation (visual axis)—and vision is only modestly degraded. In fact, the nystagmus often is not noted unless an examiner studies the iris or disc. If, however, the pivot is to the left (e.g., on the left brow), the patient will have a component of horizontal and vertical nystagmus. This combination results in a “windshield wiper” nystagmus in which the radii of each eye varies much like an automobile windshield wiper when the pivot of rotation is located asymmetrically.

Do patients develop torsional nystagmus late in childhood or later in life?

Both. If the nystagmus is asymmetric, it is most likely caused by midbrain pathology. More commonly, the torsional nystagmus was present all along, but not observed.

What is alternating in periodic alternating nystagmus (central vestibular instability nystagmus by CEMAS terminology)?

The mostly horizontal (may have a torsional component) nystagmus will alternate in the direction of the fast phase. Patients may develop alternating head turns toward the fast phase to compensate for the changing direction of the null position.

What is the time cycle of periodic alternating nystagmus?

The time cycle is 60 to 90 seconds with intervals of 10 to 20 seconds without nystagmus in between alternations.

Is congenital periodic alternating nystagmus commonly associated with any other ocular problem?

Yes. Oculocutaneous albinism is the most common association—and most commonly overlooked. Look for it carefully.

Does acquired periodic alternating nystagmus imply central nervous system pathology?

Yes, but be careful. Often the nystagmus is overlooked if the patient compensates well by changing head position. If it is truly acquired, midbrain pathology is most common.

Does acquired periodic alternating nystagmus respond to pharmacologic treatment?

Yes. Baclofen may work.

Does congenital infantile nystagmus respond to any pharmacologic treatment?

Gabapentin (600 to 2400 mg/day) and memantine (10 to 40 mg/day) have been studied, with some results showing improved visual acuity with decreased nystagmus intensity.