Also known as “dancing eyes”, nystagmus is an ocular condition in which the eyes make rapid, repetitive, involuntary to and fro movements, often resulting in blurry vision. Nystagmic movement might be side to side (horizontal), up and down (vertical), or in a circle (rotary or torsional).
The word “nystagmus” is derived from the Greek word “Nystazho” which means wobbly head movements of a sleepy of inebriated individual.
Most of the time, involuntary eye movement is seen in both eyes and rarely in a single eye. It might develop during infancy, or develop later in life. Similarly, based on the pattern of involuntary eye movements, it can be either jerky or pendular.
Jerky one is a very quick eye movement in one direction, immediately followed by a slower phase in the opposite direction. But, in pendular, there are phases of equal velocity movement in either direction.
According to Alexander’s law, the amplitude of jerk nystagmus is largest in the direction of fast component. Grades:
Grade I: present only in the direction of the fast component
Grade II: present only in primary gaze position
Grade III: present in all gazes.
Types and causes
On the basis of time of onset, the involuntary eye movement is categorized as follows:
It starts during infancy, usually at the age of 6 weeks to 3 months. It is common in both eyes. The exact cause of congenital nystagmus is not known and sometimes it is passed down from parents to children. It is classified as follows:
- Infantile nystagmus
Infantile nystagmus is not usually not noted at birth but becomes prominent during the first few months. It is a horizontal nystagmic movement with both pendular and jerk components. The eye movement increases with fixation and decreases with convergence. The patient tends to turn the head to achieve a null point.
It may be seen in isolation or in association with strabismus, and reduced vision. Base out prism and contact lens helps to induce convergence, dampens the eye movement, and may improve visual acuity.
- Spasmus nutans
Nystagmus, torticollis (head turn or tilt), and head-nodding is tried of symptoms seen in spasmus nutans. This benign type of nystagmic eye movement usually starts in the first year of life and disappears by 3-4 years of age.
- Infantile monocular pendular nystagmus
It occurs due to visual loss as in the case of optic neuropathy or chiasmal glioma. If the vision loss is bilateral, involuntary eye movement might be seen in both eyes.
This ocular condition happens later in life due to injury, diseases, neurological problems, alcohol, or drugs. It is of following types:
- Endpoint nystagmus
It becomes apparent in looking at the extreme lateral or upward gaze. It is a jerky eye movement.
- Vestibular nystagmus
It is also a jerky movement that occurs due to altered inputs from vestibular nuclei to PPRF (paramedian pontine reticular formation). It is demonstrated by the caloric test.
- Optokinetic nystagmus
This jerk nystagmus is induced by moving a full visual field stimulus. The slow phase in which the eye follows the target is known as a pursuit and the fast phase in which the eye fixates on the next target is known as a saccade. It is clinically used to test visual acuity in toddlers (rough estimate) and to detect malingering.
Associated with poor vision (sensory)
The nystagmus occurs due to poor vision as in cataract, aniridia, retinoblastoma, retinopathy of prematurity, and intrauterine infections.
Associated with neurological diseases (motor)
- Gaze paretic nystagmus
It is the most common type of nystagmic movement associated with neurological diseases. It doesn’t affect the vision because it is absent in the primary gaze. It beats in the direction of gaze and the major causes are cerebellar lesions, brainstem lesions, and anticonvulsants.
- Convergence-retraction nystagmus
This nystagmic movement is caused by the bilateral adducting saccades causing convergence of both eyes. It is prominently seen when the patient looks up. Midbrain lesions lead to convergence-retraction eye movement.
- Vestibular nystagmus
It occurs due to the disease of the vestibular system or the brainstem. Hearing loss occurs if it is associated with the disease of vestibular components and pursuit and saccadic defects are seen if it is associated with the disease of the brainstem. Mild to severe vertigo is accompanied by this type of eye movement.
- Nystagmus blockage syndrome
Nystagmus blockage syndrome has an inverse relationship with the esotropia as esotropia is an involuntary eye movement blocking mechanism. Face turn occurs in the direction of fixing eyes and the eyes preferred to be adducted to reduce the effect.
The list includes upbeat, downbeat, seesaw, periodic alternating, and nystagmus associated with strabismus.
Here, the ocular movements are not rhythmic regular. Following are the types of nystagmoid conditions:
- Oculopalatal myoclonus
- Ocular bobbing
Signs and Symptoms
Uncontrolled and rapid eye movement is the major symptom of the nystagmic condition. In additions to this, the following symptoms are common:
- Photophobia (sensitivity to light)
- Blurred vision
- Reduced depth of perception
- Abnormal head position (head tilt, face turn or chin up and down)
- Dizziness (oscillopsia)
Your eye doctor does a comprehensive eye exam to diagnose the involuntary eye movement. Nystagmus tests that are done to rule out the cause and type of nystagmic movement include:
Patient history is crucial to determine any general health problems, medications, and environmental factors contributing to involuntary eye movement. It is also necessary to determine whether the nystagmus is congenital or acquired.
Visual acuity test
A visual acuity test is an important nystagmus test. It tells the eye doctor about the visual status of patients with or without optical correction, and any possibility of vision improvement.
The refraction test determines the appropriate lens power that may contribute to achieve the best possible vision and to dampen the effect. Any type of refractive error myopia, hyperopia, or astigmatism should be corrected before starting any treatments.
Eye movement, eye teaming and focusing test
Eye movement, eye-focus, and ability of both eyes to work together (teaming) are necessary to achieve a clear, single vision. This nystagmus test looks for any problem related to ocular motility, vergence, phorias, or tropias. These tests help to determine the position of the null zone if any which is the main focus of treatment.
Treatment of Nystagmus
Treatment depends on whether the nystagmic condition is congenital, neurological, or pathological. Most of the cases of congenital nystagmus don’t require any treatment while non-neurological causes of acquired cases can be treated well with non-surgical methods. Similarly, for pathological involuntary eye movements, the underlying cause should be treated. Following treatment options are available:
Eyeglasses and contact lenses help to reduce the null zone (eye gaze position with no or minimum nystagmus) easily. Over minus eyeglasses stimulate the accommodative convergence and thus dampens the involuntary eye movement. Similarly, contact lenses give good visual stimulus for fusion control and help dampen nystagmus in high refractive errors.
Prism is useful mostly for diagnostic trials, but it is not effective as a therapeutic option in the treatment of nystagmic eye movement. Likewise, increased lighting in the house and workplace, and low vision devices including magnifying glasses help to make day-to-day activities easier in case of reduced vision due to nystagmus.
Conventional patching therapy has been found to be effective in treating nystagmus with amblyopia. As amblyopia gets treated and vision improves, the involuntary eye movements finally decrease.
The drugs are supposed to inhibit the excitatory neurotransmitters within the central nervous system. The drugs found to be effective against nystagmus in some patients include baclofen, carbamazepine, gabapentin, memantine, levetiracetam, 4-aminopyridine, acetazolamide, and 3,4-di aminopyridine.
Baclofen is found to be effective in treating congenital, seesaw, and periodic alternating nystagmus. Similarly, carbamazepine is widely used for superior oblique myokymia.
Botulinum toxin A blocks the neuromuscular transmission and is used to dampen nystagmus. It is administered in 2 distinct ways. A single large dose of the drug is applied into the retrobulbar space or 3 units of botulinum toxin are injected in all horizontal rectus muscle. The effect of this drug lasts for a few months.
The surgery is helpful in shifting the null position to the primary position, inducing extra convergence innervation by weakening medial recti, and reducing the amplitude of the nystagmus by weakening all recti muscles. The commonly used nystagmic surgeries are Kestenbaum surgery, Anderson surgery, and Parks surgery.
Sometimes, treatment is not necessary for acquired nystagmus. If the underlying cause of acquired nystagmic movement is treated, then it goes away. Ask your doctor about the available treatment options and useful resources about nystagmus. If you are looking for helpful articles, you can access the resources of the American Nystagmus Network.