Nystagmus

Introduction

A nystagmus in general is a jerky eye movement, which is performed in very short intervals from left to right or from right to left. On the one hand, a nystagmus has a biological function, but under certain circumstances it can also be a sign of illness. Nature has created the nystagmus in order to improve the absorption and processing mechanism of visual effects in the brain.

This mechanism can be illustrated particularly well using the example of a view from a moving train. Looking out of the window of a moving train and observing the landscape passing by, one has the impression of a whole picture. In reality, however, this picture consists of many individual images that the brain collects through the restoring movement of the eye and then puts them together to form an overall picture (in this case the landscape picture).

If you look outside from a moving train, the eye fixes on a certain point. This happens unconsciously. The eye now follows this point until it has disappeared from the field of vision.

Then it chooses a new point. For this purpose, the eye moves back very quickly to the starting position. This fast, involuntary movement is called nystagmus.

Cause

There are two forms of nystagmus: physiological nystagmus, or normal, congenital, and pathological nystagmus, or pathological nystagmus. The physiological nystagmus has been established by nature to stabilize the perception of images. Through fast, trembling eye movements, a landscape, for example, which passes by quickly, is perceived as a whole, stable image.

The eye collects different fixed points of view. It sticks to one point until it has disappeared from the field of vision and then immediately looks for a new point. This causes the eye to return very quickly to its initial position.

This eye return movement is not actively perceived. An observer who looks at it, however, does. The rapid eye reset movement is coordinated and controlled by the cerebellum and parts of the brain stem.

In the so-called jerk nystagmus, the eye slowly follows a certain object and then makes a rapid jerky movement in the opposite direction. The direction of the nystagmus is indicated by the fast phase. In the pendulum nystagmus, the eye’s positioning movements are the same in both directions.

The nystagmus that occurs to stabilize the retinal image (moving train and looking outside) is also called optokinetic nystagmus (OKN). The so-called vestibulo-ocular reflex enables the stabilization of the retinal image during one’s own head movement, i.e. if someone turns his head in a certain direction, the eyes are automatically guided in the opposite direction and then jump to the center of the eye with a jerk. This measure is also needed to stabilize the image.

Disturbances of this vestibulo-ocular reflex indicate damage to the vestibular nerve. Pathological nystagmus includes sudden, undirected nystagmus. It occurs suddenly without the need for point tracking.

Another pathological form of nystagmus is congenital nystagmus. This is a congenital eye fibrillation that increases with the fixation of certain points. It has an irregular form of flapping, which is attenuated in certain directions of vision, but can also be intensified by others.

Congenital nystagmus is a sign of a congenital disorder of the eye muscle motor function. Another possible cause may be a severe congenital visual impairment. A disease of the central nervous system or a tumor are practically never present.

Latent nystagmus occurs when one eye is covered and disappears when both eyes are uncovered again. It is a sign of early childhood squint syndrome. Another pathological nystagmus is the so-called vestibular nystagmus.

In the event of a failure of one of the organs of equilibrium, such as in Menière’s disease, a suddenly occurring eye tremor occurs, which the patient perceives as severe dizziness. The dizziness attacks, which are usually attacks of rotary vertigo, sometimes become so severe that the patient also suffers from balance problems, severe nausea and even vomiting. If the patient fixes a certain point, the nystagmus is usually inhibited.

Severe dizziness after changing position (e.g.B. from lying to sitting or from sitting to standing) is sometimes also associated with a nystagmus. The reasons for this are probably calcification and increasing immobility of the small beads, also called otoliths, which are present in the organ of equilibrium of the ear.

Possible causes of a pathological nystagmus are not only a failure of the organ of equilibrium and calcification of the otoliths but also injuries or damage to the brain stem. Here, for example, a bleeding or a tumor could trigger this disorder. Appropriate imaging, such as CT or MRT, should be performed in any case if the nystagmus is unclear.