Overview

Eye movements that are either spontaneous or provoked and start with a gradual phase shift are known as nystagmus. There are important social and psychological repercussions that result from nystagmus. 

Seesaw nystagmus (SSN) is an uncommon ocular motor condition marked by cyclic eye movements that include a conjugate torsional component and a dissociated vertical component. 

In the second half of the cycle, the movement pattern is inverted, with one eye rising and intorting while the other depresses and extorts.¹

Numerous therapy approaches are currently available and must be evaluated individually following a thorough examination of the underlying aetiology of nystagmus. The best way to improve eyesight and treat strabismus and AHPs are through surgery and refractive correction using glasses or contact lenses, possibly with prisms included.

Introduction

An involuntary rhythmic oscillation of the eyes is known as nystagmus, and it is quite simple to demonstrate by eye movement recordings or direct eye observation. Nystagmus, a common ailment in clinical practice, impairs visual acuity by causing images on the retina to shift excessively and images to migrate away from the fovea.²

There are few known causes for seesaw nystagmus (SSN), an uncommon and debilitating neurologic disease.
Maddox originally described seesaw nystagmus (SSN) in 1913. SSN is a rare type of nystagmus that is typified by irregular eye movements, one eye rises and intorts at the same time as the other eye extorts and depresses.

In nystagmus, an eye movement disorder, a slow phase can cause abnormal, involuntary rhythmic oscillation in one or both eyes.³

A very uncommon kind of nystagmus seems to happen when there are brainstem lesions, especially if the superior portions of the medial longitudinal fasciculus are affected, possibly around the posterior commissure.

Children with nystagmus may have almost normal visual acuity (VA) or be severely visually impaired, depending on the underlying disorder.⁴

Prevalence

According to estimates, there are 24 cases of nystagmus for every 10,000 people in the general population, with a slight tendency towards European ancestry. Also, there are 14 cases of infantile nystagmus for every 10,000 people.²

Pathophysiology

SSN is observed in conditions affecting the optic chiasm and other visual pathways. In the literature, SSN has been linked to parasellar lesions like congenital absence of the optic chiasma, brainstem infarcts, pituitary macroadenoma, and multiple sclerosis (MS).

The interstitial nucleus of cajal (INC), located in the anterolateral superior colliculus, regulates the rotation of the ocular muscle. The pathogenesis of SSN is believed to be associated with the disturbance of the graviceptive pathway between the vestibular nucleus and INC.

A mass lesion or vascular accident is thought to be the cause of the disruption of the posterior commissure, the interstitial nucleus of cajal (INC), which includes the area of the rostral interstitial nucleus of the medial longitudinal fasciculus, and the medial mesencephalic reticular formation.²

These dorsal midbrain regions are essential for regulating the movements of the vertical eyes. The ocular tilt reaction involves the INC. The vestibular nuclei provides information to the medial longitudinal fasciculus, which generates vertical saccades.

The posterior commissure allows the fasciculus to project this information to the oculomotor and trochlear nuclei ipsilateral and contralateral. This kind of nystagmus might have a jerk (hemi-seesaw) or pendular (seesaw) waveform. Lesions in the INC region are linked to jerk SSN, while parasellar or chiasmal mass lesions are linked to pendular SSN.³

Symptoms of seesaw nystagmus

Because foveal vision deteriorates when pictures travel quickly across the retina, nystagmus causes a decline in visual acuity and motion sensitivity.
While both IN and AN patients have decreased vision, AN patients are more likely to experience oscillopsia, which is the appearance of continuous movement in the environment, and may be more affected by the disease.

Clinical signs of sellar lesions, bitemporal hemianopia, and see-saw nystagmus frequently co-occur.⁷

Causes

The following conditions can cause seesaw nystagmus: radiation, chemotherapy, congenital abnormalities (such as Arnold Chiari malformation), stroke, trauma, multiple sclerosis, parasellar or mesodiencephalic masses/disease, and severe vision loss from cone-rod dystrophies or retinitis pigmentosa.³

Characteristics

When the child first enters the room, the clinical examination starts by looking for signs of photophobia, eye rubbing for retinal stimulation, head postures (variable, alternating, or consistent), and/or head shaking (both frequently, but not always, after 1 year of age), skin and hair tone, especially in relation to other systemic and neurological features. After that, the examination can be divided into two sections: the ocular (+/- systemic) examination and the eye movements.⁴

The eyes move vertically in opposition to one another; that is, one eye travels up and the other down.⁵ A conjugate torsion of the eyeball to the left accompanied the upward and downward movements of the right and left eyes, whereas a corresponding conjugate torsion to the right accompanied the upward and downward movements of the right and left eyes, respectively.

Underlying lesions

Depending on the nystagmus's waveform, seesaw nystagmus can have different causes.

Patients with lesions involving the optic chiasm (such as parasellar tumours, chiasmal trauma, or congenital abnormalities like septo-optic dysplasia/achiasma) are more likely to experience pendular waveform seesaw nystagmus, while those with midbrain-thalamic lesions involving the interstitial nucleus of cajal (the neural integrator for vertical-torsional eye movements) are more likely to experience jerk waveform seesaw nystagmus (hemi-seesaw nystagmus).⁶

Multiple sclerosis, congenital hindbrain abnormalities, and lower brainstem lesions can also cause hemi-seesaw nystagmus.

It is frequently linked to the ocular tilt reaction, which is typified by ocular torsion towards the side of the lower eye and skew deviation with head tilt. Serious oscillopsia can result from either type of seesaw nystagmus.

While gabapentin and memantine (class II) can dampen the jerk form, alcohol and clonazepam (Class IV) can dampen the pendular form.⁶

Suprasellar/ parasellar lesions

Craniopharyngiomas and pituitary adenomas are the causes of compressing the mesodiencephalic region.

Mesiodiencephalic lesions

This includes lesions affecting the interstitial nucleus of the cajal, which helps in eye movement.

Brainstem and cerebellar lesions

Other different brainstem and cerebellar lesions can also cause see-saw nystagmus.