The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017

Nystagmus

Nystagmus is an ophthalmic disorder that is characterized by involuntary, repetitive movements of one or both eyes. The condition presents with the eyes shifting up and down, side to side, or in a circular manner. Some even describe nystagmus as the eyes appearing to be “dancing.” There are many possible etiologies of nystagmus, and removal of an identifiable cause remains the most effective form of management.

Pathophysiology

Nystagmus occurs due to a dysfunction in the areas of the brain and inner ear that regulate eye movement. When the head rotates, organs within the vestibular system of the inner ear detect the movement and send signals to the brain initiating appropriate eye adjustment. This process allows for the eyes to adapt to the motion and maintain a stable line of vision. A disruption in this signaling pathway is what leads to the inappropriate ocular muscle movements associated with nystagmus.

Based on its etiology, there are two main classifications of nystagmus: infantile nystagmus syndrome (INS) and acquired nystagmus. INS is a condition that patients are born with, typically presenting within six weeks to three months of age. The disorder is genetically inherited, and a family history will increase the likelihood of development. Conversely, acquired nystagmus occurs later in life as a result of causative factors. Several diseases and injuries in the inner ear and brain have been implicated in the development of acquired nystagmus, due to these organs’ role in proper eye movement. Additionally, the presence of existing vision problems such as cataracts (cloudiness of the lens) and myopia (nearsightedness) can contribute to faster progression of nystagmus. Common medications associated with nystagmus are antiseizure drugs, such as phenytoin. Furthermore, excess use of alcohol and sedatives can lead to the condition, as a result of their effects on balance within the inner ear. Despite the multitude of implicated diseases, a cause of nystagmus cannot be identified in some patients, and this is termed idiopathic nystagmus.

Presentation

The severity of nystagmus can vary greatly between patients and from day to day, with movements of the eyes changing in speed and duration. The condition can present continuously or in intermittent episodes that occur spontaneously or are triggered by factors such as stress and fatigue. The movements associated with nystagmus can be classified as pendular, where the eyes move at the same speed in either direction, or jerk, where the eyes drift slowly in one direction and quickly in the other. Symptoms of nystagmus include oscillopsia, when objects in the visual field appear shaky. This can lead to significant vision impairment, as surroundings are viewed as blurry. Other visual defects include light sensitivity and difficulty seeing in the dark. Patients with nystagmus often feel the need to tilt their heads, as this has been known to help improve visual focus. Due to the effects on inner ear balance, patients may also experience dizziness and vertigo.

Diagnosis and Treatment

Diagnosis of nystagmus should be done with a thorough eye examination to rule out all other conditions. Tests that detect the disorder may involve the patient spinning around for several seconds, stopping, and attempting to stare at an object. When focusing on the object, the eyes will move quickly in different directions if the patient has nystagmus. Visual acuity tests can be used to determine the impact of nystagmus on a patient’s vision.

When managing nystagmus, it is important to establish what is causing the disorder and treat the underlying disease. Removal of offending agents can result in spontaneous return to normal eye movement. When all etiologies have been accounted for, the only treatment options for nystagmus are to improve symptoms. Certain medications such as baclofen (a muscle relaxant) and gabapentin (a nerve-modifier) have been used in practice with variable success. Botulinum toxin injections (commercially known as Botox) have been useful in mildly paralyzing eye muscles in patients who experience severe shakiness. Prisms are corrective factors that can be added to eyeglasses to help keep the eyes in fixed positions for better visual focus. Finally, surgery is an option for severe nystagmus to alter the positions of ocular muscles, although this procedure has shown inconsistent results. Importantly, none of these therapies has demonstrated complete reversal of nystagmus, and the need for more effective treatment options remains a future area of clinical study.

Vidya Pugazhenthi

See also: Dizziness; Vestibular System; Visual System

Further Reading

American Academy of Ophthalmology. (2013). What is nystagmus? Retrieved from www.geteyesmart.org/eyesmart/diseases/nystagmus.cfm

Bradley, Walter G. (2004). Neurology in clinical practice. Philadelphia, PA: Butterworth-Heinemann.

Medline Plus. (2013). Nystagmus. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/article/003037.htm