Introduction

Nystagmus is a condition where the eyes move rapidly, uncontrolled. The types of nystagmus can vary based on how someone acquires the condition and the direction and pattern of eye movement. Both children and adults can have nystagmus. You are either born with nystagmus, known as congenital or infantile nystagmus, or you acquire it after at least 6 months of age.

Upbeat nystagmus is when the uncontrolled eye movement jerks in the upward direction.¹ The key characteristics of upbeat nystagmus are a quick phase of upward vertical eye movement and a slow phase of downward gaze.²

While nystagmus is not dangerous, it is likely a symptom of another medical condition. These underlying conditions can affect the brain, eyes, or ears, but are not limited to those areas. Associated health conditions can include stroke, brain tumours, trauma and inflammation. The brain, along with the vestibular system, a collection of organs in the inner ear that maintain your sense of balance, work together to control eye movement. In people with nystagmus, there is interference in how the brain and vestibular system coordinate eye movement.³ 

Basic eye movement control

The brain controls both voluntary and involuntary eye movement. Cranial nerves–nerves emerging from the brain–send signals from the brain to the muscles that control eye movement. The muscles that control eye movement are called extraocular muscles. Aside from coordinating muscle movement, the brain also controls other aspects of eye movement, such as how you perceive vision and the stabilisation of gaze when you move your head. 

The cerebellum is the part of the brain located in the back of the head. It lies above and behind the area of the spinal cord connecting to the brain. The cerebellum has various roles in maintaining brain and bodily functions, including coordinating motor movements and balance. The cerebellum acts as a network for ensuring the precision of eye movements and is important for real-time control of eye movement.^4,5 Cerebellum disorders have been associated with various types of nystagmus.⁶

The brainstem, the structure that connects the brain to the spinal cord, relays messages between the brain and other parts of the body to help regulate the body’s involuntary actions. It also plays a role in regulating eye movement.^{5, 7}

Causes of upbeat nystagmus

Nystagmus can be caused by underlying conditions affecting the eyes, brain or inner ear (vestibular system). Idiopathic nystagmus is nystagmus with an unclear cause.³ Below, we will cover the various causes of upbeat nystagmus.

Brainstem lesions

A clinical study found that lesions, areas of brain tissue that have been damaged from disease or injury, in the brainstem were responsible for upbeat nystagmus. These lesions were mainly in the medulla and pons, which are both parts of the brainstem.⁸ Possible causes of upbeat nystagmus involve damage to the neural pathways that control the involuntary eye movement called the vestibulo-ocular reflex (VOR), which keeps your eyes centred during head movements, and vertical gaze control.⁸

Cerebellar involvement

Degeneration of the cerebellum and strokes or tumours in the cerebellum region are known causes of upbeat nystagmus. ⁹ Damage to the cerebellum can have significant negative impacts on balance, coordination and movement of the body. This can affect eye movements, leading to nystagmus.^6,10 Upbeat nystagmus is rarer than downbeat nystagmus.¹¹ Cerebellar involvement in downbeat nystagmus has been attributed to impairments in different regions of the cerebellum (vermis, floccus, and nodulus).¹¹ In comparison, lesions or damage to the anterior vermis of the cerebellum have been reported in patients with upbeat nystagmus.^8,12 One clinical study reported that lesions in the brainstem (particularly in the medulla) are more associated with upbeat nystagmus, while lesions in the cerebellum commonly occur in downbeat nystagmus.¹²

Neurological conditions

Upbeat nystagmus has been reported in patients with other neurological conditions. In addition to cerebellar involvement, the following neurological conditions can cause upbeat nystagmus:

• Multiple sclerosis^3,8,9,11
• Wernicke’s encephalopathy (thiamine/vitamin B12 deficiency) – some patients with Wernicke’s encephalopathy have experienced transition from upbeat to downbeat nystagmus^8,9,11,13
• Brain tumours¹¹
• Brain ischaemia^3,11 – insufficient blood flow to the brain
• Cerebral hemorrhage⁹
• Cerebral infarction or ischaemic stroke^3,11
• Creutzfeld-Jakob disease^8,14
• Crossed eyes (strabismus)³
• Hydrocephalus (water in the brain)⁸ – buildup of cerebrospinal fluid in the ventricles of the brain
• Behcet syndrome^8,9 
• Chiari malformation⁸
• Meningitis^8,9
• Brain encephalitis^8,9
• Disorders of the retina or optic nerve³

Drugs and toxins

Temporary or transient upbeat nystagmus can be caused by side effects of drugs or toxins, including:

• Antiseizure medications (anticonvulsants) – e.g. phenytoin, carbamazepine^9,11,15
• Organophosphate poisoning from anticholinesterase insecticides^8,9,16
• Alcohol^8,17
• Barbiturates⁸
• Tobacco^8,18

Congenital and idiopathic nystagmus

Congenital upbeat nystagmus is upbeat nystagmus that you are born with. This condition is rare and can be associated with Leber’s congenital amaurosis. A transient form of upbeat nystagmus can occur in infants at 6 to 8 weeks of age and go away after a few months to a year.¹⁹ Idiopathic nystagmus is nystagmus where the cause is unknown.

Symptoms and diagnosis

Symptoms of upbeat nystagmus

Symptoms of upbeat nystagmus include:³

• Dizziness
• Vertigo – feeling like you’re spinning 
• Balance problems
• Light sensitivity
• Trouble seeing in the dark
• Shaky vision
• Blurry vision
• Oscillopsia – feeling as if your surroundings are constantly moving

While upbeat nystagmus is not life-threatening, it can make daily life more difficult by affecting your vision and sense of balance. It is important to communicate with your healthcare provider if you have symptoms of upbeat nystagmus, as the nystagmus may be a sign of another potentially serious health condition.

Diagnosis

Diagnosis of upbeat nystagmus is usually performed by eye care specialists called ophthalmologists. They will use eye exams to check for symptoms and related eye problems. Other specialists, such as brain doctors (neurologists) or ear doctors (otolaryngologists or ENTs) can perform examinations for neurological or ear-related issues contributing to upbeat nystagmus.³ 

Here are some methods doctors may use to diagnose upbeat nystagmus:³

• Physical examinations
• Neurological examinations
• Ear examinations
• Imaging tests such as a CT (computed tomography) scan or an MRI (magnetic resonance imaging) – to find structural lesions in the brain
• Eye movement recordings (video-nystagmography, electronystagmography)
• Genetic tests – to screen for genetic mutations (alterations in the DNA) that contribute to congenital nystagmus

Management and treatment

There is no definitive treatment for upbeat nystagmus, since treatment of nystagmus depends on the medical condition causing it. Treatment of the underlying condition can correct acquired nystagmus.^3,19 

Treatments for symptomatic upbeat nystagmus include:

• Glasses or contact lenses – improving vision may help manage rapid eye movements
• Vision correction surgery (e.g. LASIK) – while this doesn’t cure nystagmus, it improves vision to reduce nystagmus symptoms
• Medications such as baclofen and 4-aminopyridine,^11,20 as directed by your healthcare provider

Depending on the cause of upbeat nystagmus, your healthcare provider will determine what treatment or interventions are best for addressing upbeat nystagmus and its symptoms.

Summary

Upbeat nystagmus is a condition of uncontrolled vertical eye movements primarily in the upward direction. Eye movement is controlled by the brain and structures in the inner ear called the vestibular system. The main areas of the brain that control eye movements are the brainstem and cerebellum. Brainstem lesions, cerebellum lesions, and other neurological conditions cause upbeat nystagmus. Cerebellar damage, in particular, can lead to nystagmus, though cerebellar involvement is more commonly noted in downbeat nystagmus, while brainstem lesions are more associated with upbeat nystagmus. Drugs and toxins can cause temporary upbeat nystagmus. Congenital upbeat nystagmus is rare and occurs in infants; It usually disappears within 1 year after birth. Idiopathic upbeat nystagmus occurs from unknown causes. 

Upbeat nystagmus can make daily life more difficult since it affects a person’s vision and balance. While upbeat nystagmus is not life-threatening, it is important to consult a healthcare provider about its symptoms because it is likely that an underlying health condition is responsible for upbeat nystagmus. These health conditions can be neurological or affect the ears. Healthcare professionals can use neurological and ear examinations or other methods to diagnose upbeat nystagmus and its potential causes.