Nystagmus

Nystagmus is a rhythmic and involuntary movement of one or both eyes that may occur at any age. The rhythmic movement has two phase: a rightward-moving quick phase and a leftward-moving quick phase. A pendular nystagmus is when the two phases are symmetrical in speed, and a jerk nystagmus when they are asymmetrical, meaning that the nystagmus is quicker towards one side than the other. 

The defining characteristics of a nystagmus are: direction, range, frequency and intensity. 

• Direction: horizontal, vertical, torsional and mixed
• Amplitude: the route both the eyes do in each phase recorrido 
• Frecuency: expresses the number of oscillations per minute
• Intensity: is the product of the amplitude multiplied by the frequency

The most common conjugate nystamus.

We talk about when they eyes move simultaneously in the same direction, amplitude and frequency in the different eye positions. It is a disconjugate or disassociated nystagmus when the previously mentioned characteristics are not present.

Some patients present a neutral or blockage zone. This is an eye position where the nystagmus diminishes or disappears and that causes torticollis to move the eyes into the blockage position.

There are multiple classifications.

According to age of onset:

• Infantile nystagmus: appears before the age of 6 months
• Acquired nystagmus: appears after the age of 6 months

According to the cause:

• Physiological nystagmuses are considered normal. They are called:

1. Optokinetic: It is caused by following moving objects
2. Extreme gaze
3. Induced vestibular: It stimulates the labyrinth (the inner ear) by breaking the head or irrigating the external auditory canal.

• Pathological nystagmus: due to eye and/or neurological lesions. 

1. Infantile nystagmus syndrome 
2. Fusion maldevelopment fusion nystagmus syndrome
3. Nystagmus blockage syndrome
4. Spasmus Nuntans syndrome: It manifests itself with nodding, nystagmus and torticollis and usually goes away itself in 1-2 years in the majority of cases.
5. Central vestibular nystagmus: It is caused by damage to brainsteam and cerebellum.
6. Perifpheral vestibular nystagmus: It is caused by a lesion to the vestibular nerve or labyrinth.
7. Nystagmus associated with neurological disorders

• Idiopathic nystagmus or of an unknown cause: It occurs with children with relatively good visual acuity without a demonstrable cause.

Poor vision, photophobia, amblyopia (lazy eye), strabismus and torticollis point to infantile nystagmus associated with an eye pathology.

Oscillopsia (the feeling that the enviroment is moving), nausea, vomitting, loss of balance, ataxia and oculomotor nerve paralysis point to nystamus associated with a neurological pathology.

The causes are multifactorial. Among children they are many and varied in addition to being complicated to assess and diagnose. In general, we can differentiate between two large groups: 

Nystagmus of eye origin 

• Congenital cataracts
• Diseases of the retina and optic nerve
• Retinal dystrophies
• Albinism
• Aniridia
• Others

Nystagmus of neurological origin

• Hydrocephalus
• Demyelenating diseases, encephalitis, meningitis
• Tumours of the central nervous system and cerebellum
• Optic nerve tumours, chiasma, hypophysis
• Haemorrhages and cerebral infarctions
• Periventricular leukomalacia

In some nystagmuses, ocular and neurological causes coincide which is suitable for getting a correct diagnosis.

The aims of treatment are to improve visual acuity, reduce the amplitude and frequency of the nystagmus and correct or improve torticollis.

Medical treatment

• Drugs: Do not yield good results.
• Optical: Glasses and contact lenses.
• Prisms: They are used in horizontal nystagmus with torticollis to improve the cooperation of both eyes in the primary gaze position (looking straight ahead).
• Botulinium toxin: In acquired nystagmus. It is injected into the horizontal muscles of both eyes to relax them. The downside is that their benefit is temporary and may cause double vision and droopy eyelids. 
• Amblyopia treatment: via optical or pharmacological penalization in the eye with better vision. 

Surgical treatment

Before considering it, you must consider whether the nystagmus has improved over time. The indication, the approach and muscles to be operated on, will vary depending on the type of nystagmus and torticollis induced. The surgery aims to moe the eyes from a blocked peripheral area to a central gaze position to avoid torticollis. Nystagmus is a complex clinical case which must be personalised for each patient.

There are different techniques based on the same principle:

• Anderson technique: The muscles that contract in the blockage position become are weakened in both eyes. It is useful if the horizontal torticollis is 20 degrees. If, for example, the patient presents torticollis with the face turned to the left because the blockage position (neutral zone, where the nystagmus diminishes or disappears) is in dextroversion (looking towards the right) the lateral rectus muscles of the right eye and rectus medialis muscle of the left eye (which are the opposite muscles that we strengthen) should be weakened.
• Kestenbaum technique: Indicated if the horizontal torticollis is 25-40 degrees. It adds the strengthening of the antagonistic muscles to the weakening of the muscles that contract in both eyes in the blockage position.
• Parks technique: It uses the rule of personal dosification, weakening and strenghtening in both eyes, following the principles applied in the Kestenbaum technique and depending on the degree of torticollis. 

Vertical torticollis

In torticollis with an elevated chin and blockage in depression, the inferior muscles are weakened. If the torticollis is greater than 25 degrees, resection of the antagonistic muscles must be required. We must rule out the fact that the torticollis is not induced by A V patterns or alphabet syndrome which would require another specific technique.

In torsional torticollis 

They have a poor prognosis meaning that the surgical indication is usually for exceptional cases given the risk of undesired complications.

In nystagmus with torticollis and strabismus

We must opt for correcting both symptoms simultaneously. The fixating eye is operated on to reduce the torticollis and the non-dominant eye is operated on to correct the strabismus.