Nystagmus is a condition where there is involuntary eye movement that is acquired resulting in limited or reduced vision. It has also been called “dancing eyes”. Normally, when the head rotates in an axis, the distant visual images are maintained by the eyes rotating in the opposite direction of the axis. Angular acceleration is sensed by the semicircular canals in the vestibule sending signals to the nuclei for eye movement. This signal is then relayed from the brain to the extraocular muscles, so the gaze fixates on the object as the head moves. In patients with nystagmus, the semicircular canals are stimulated although the head is not in motion.
There are two types of nystagmus known as pathological and physiological nystagmus. Both these types of nystagmus have different variations within these types. While nystagmus is easily noticeable, it is rarely recognized. It can be investigated using the caloric reflex test where an ear canal is irrigated with warm or cold water. The difference in temperature gradient triggers the stimulation of the horizontal semicircular canal resulting in nystagmus. The movements of the eyes can be quantified and recorded using devices such as electronystagmography (ENG). It is a form of electrooculography where an electrical method is used to measure the eye movements using external electrodes. Nystagmus can also be assessed by a physical therapist who uses certain movements of the patients head and body to induce the eye movements.
To assess the patient’s eye movements, orthoptists may also use electrooculography or an optokinetic drum. In medicine, a nystagmus can be benign or indicate an underlying neurological or visual problem. There are many causes of nystagmus. Some of the examples are as follows.
Cause #1: Benign Paroxysmal Positional Vertigo
Benign paroxysmal positional vertigo or BPPV is a condition where the main issue arises from the inner ear. It results in symptoms such as vertigo, nausea, nystagmus, vomiting, and more. It can be a debilitating issue which greatly affects daily activities of patients.
BPPV can be due to a head injury or simply occur among older patients. It is thought to be due to a small calcified otolith that moves around in the inner ear. The diagnosis is achieved when the Dix-Hallpike test leads to a nystagmus. While it is not a serious condition and resolves in a week or two, it can be recurring.