Introduction:
Nystagmus is a condition in which the eyes of the person make uncontrolled movements in various directions. These signs are repetitive and are involuntary. The brain controls eye movements. When a person moves their head, the eyes move naturally to adjust. This results in stabilizing the image and helps the person see clearly. For people having nystagmus, the areas of the brain that influence eye movements do not function proficiently. Spontaneous nystagmus symbolizes the movement of the eyes without visual, cognitive, or vestibular stimulation. Most commonly, vestibular imbalance (vestibular balance helps a person keep balance and stay oriented) is the reason for spontaneous nystagmus. When the vestibular balance is lost, spontaneous nystagmus can be observed. The spontaneous nystagmus test decides if there is any presence of the nystagmus in the patient with or without fixation when sitting while keeping the head and eyes in a neutral position.
What Is Spontaneous Nystagmus?
Spontaneous nystagmus can be defined as an uncontrolled movement of the eye with a fixation at a central gaze when the person is stationary in position, neutral or upright position. There are various types and sub-classifications of nystagmus. Spontaneous nystagmus is detected and confirmed by performing the spontaneous nystagmus test. There are certain sub-classifications of spontaneous nystagmus given in the following:
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Spontaneous nystagmus.
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Spontaneous vestibular peripheral nystagmus.
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Spontaneous vestibular central nystagmus.
All healthcare team members must be familiar with the nature and type of nystagmus. According to the specialty, they should be capable of changing degrees of arrangement of the nystagmus. Nonetheless, the ability to identify the condition plays a vital role, as then the patient can be referred to an appropriate clinician for further diagnosis and the management of the condition. It must be documented in the patient's record so that all healthcare team members are well-familiarized with the situation, and proper action can be taken, leading to a more precise diagnosis and good patient prognosis.
Why Is the Spontaneous Nystagmus Test Performed?
The spontaneous nystagmus test decides if the person has any nystagmus, without or with fixation, when sitting with the eyes and the head in a neutral position. The existence of spontaneous nystagmus can impact all other VNG tests. Therefore, it is important to identify the presence of spontaneous nystagmus previously to perform any other VNG (videonystagmography) tests.
The following are some reasons behind performing spontaneous nystagmus test:
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The primary reason is that recorded spontaneous nystagmus can be a decisive indicator of a vestibular lesion (a vestibular lesion can be indicated by postural instability, and intolerance for head movement.). The direction and strength of nystagmus can help uncover this lesion.
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Another reason is to document any underlying eye movements that can be present during subsequent tests. By knowing what these eye movements are, they can be corrected in the other tests.
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The last documented reason is that by adding a fixation target in the goggles, the examiner can have an estimation of central vestibule involvement. If there is the presence of spontaneous nystagmus and the fixation light does not suppress it, then there is central vestibular involvement, and that may need detailed investigation.
How Is the Assessment of Spontaneous Nystagmus Test Done?
The following information will explain the assessment of normal and abnormal spontaneous nystagmus tests:
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Normal Spontaneous Nystagmus Test: When the spontaneous nystagmus is absent in the patient, the graph will yield a tracing that is a straight line virtually. The two eyes are differentiated with different colors so that the origin of the nystagmus can be studied. The right eye is depicted by the red line, and the blue line symbolizes the left eye. The presence of the nystagmus will be pinpointed by triangles on the graph that symbolize each detected nystagmus beat. The average slow phase velocity value(s) will be counted in the bar graphs to the tracings on the right side. When both a fixation and fixation-free section have been assembled in the spontaneous test, a percentage value known as a fixation index (FI) will also be estimated. A yellow bar in the tracing will indicate the fixation section.
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Abnormal Spontaneous Nystagmus Test: An abnormal spontaneous test result would reveal the existence of nystagmus in the horizontal and vertical channels or one of the channels. When the average slow phase velocity surpasses the threshold value of six degrees per second, the bar graph will be present in gray shade, and a diamond in red color will appear close to the bar graph to characterize an out-of-threshold response.
Why Is It Necessary to Perform the Nystagmus Tests?
The first concern with finding out about pathological nystagmus is detecting the abnormal brain or ear apparatus structures affected and the underlying etiology. The tests performed for detecting nystagmus help the doctor to diagnose any underlying major condition causing it. For example, acquired nystagmus, which forms later in adulthood or adolescence, can prove a central nervous system issue like head injury, multiple sclerosis, brain tumor, metabolic disorder, hyperventilation (reacting exaggeratedly or panicking), medication side effects, or even drug or alcohol toxicity. The differential diagnosis of nystagmus also contains oculogyric crises (oculogyric crises is a spasmodic movement of eyeballs into a set position, usually in an upward direction) and ocular bobbing (ocular bobbing is a distinguishing eye movement disorder observed in patients with pontine) (pontine means pons is an anatomical structure in the brain) or (related to pons dysfunction). Oculogyric crises can be distinguished from nystagmus by declaring a lack of a specific rhythm or slow degree of eye movements. This type of eye movement most typically presents with intoxication of phenothiazine. Ocular bobbing is more distinctive than nystagmus and often occurs in locked-in syndrome.
Conclusion:
Sometimes, the objective failure of the fixation suppression of spontaneous nystagmus is noticed in patients with vestibular strokes concerning the cerebellum or brainstem; yet, the accuracy of this test for the differentiation between the central and the peripheral causes in patients with an acute vestibular syndrome (AVS) is not known. Spontaneous nystagmus is a pivotal clinical sign in patients suffering from acute vestibular syndrome, and hence, the spontaneous nystagmus test is important to diagnose the syndrome as soon as possible.
