Surgical management of nystagmus

All nystagmus degrades visual acuity by reducing the stability of fixation and lessening foveation time. In addition, adults with acquired nystagmus may complain of oscillopsia, a subjective impression of movement of the perceived world. Surgery may be performed for congenital nystagmus (CN), for latent or manifest-latent nystagmus (LN, MLN) or for acquired nystagmus. Nystagmus surgery aims to reduce the amplitude of nystagmus with either improvement of visual acuity or a reduction of a bothersome head posture. The commonest reason for patients' seeking surgical treatment is to allow them to acquire a driving licence. Regrettably, this is frequently not possible.

SURGERY FOR CONGENITAL NYSTAGMUS

Congenital nystagmus can occur in patients with no other ocular abnormality (idiopathic motor nystagmus), or may be associated with other ocular conditions such as oculocutaneous or ocular albinism, early visual deprivation or retinal dystrophies. All patients require a careful ophthalmological examination to exclude other ocular abnormalities, a cycloplegic refraction and, if a refractive error is detected, a trial of optical correction with spectacles or contact lenses. Recession of a rectus muscle is the commonest operation to reduce its action. The muscle insertion is moved to a more posterior point on the eye, usually 5-7 mm from its original insertion, where it reattaches. Resection is the commonest strengthening operation. A segment of muscle (5-8 mm) is removed and the shortened muscle reattached at its original insertion.

Four main surgical strategies have been advocated in management of congenital nystagmus—Kestenbaum surgery for compensatory head posture with null zone; artificial divergence surgery; maximum recession of horizontal rectus muscles; and rectus muscle anterior tenotomy.

Kestenbaum surgery

It has never been adequately explained why certain patients with congenital motor nystagmus (CN) have a position of gaze where the intensity of their nystagmus is minimal. Such patients discover that their vision is at its best when their eyes are placed in the position of least ocular instability, and commonly demonstrate a compensatory head malposition to bring the zone of best vision into the straight-ahead position. In contrast, patients with manifest-latent nystagmus (MLN), who typically fix with only one eye, may find that their latent nystagmus, which invariably involves a nasalward drift of the fixing eye, is minimized by adopting a face turn towards the fixing eye.

In 1953, Anderson1 and Kestenbaum2 independently suggested that an abnormal head posture related to nystagmus could be alleviated by surgery. In the following year Goto3 made similar suggestions. Anderson's proposal was for recession of the pair of rectus muscles whose action was in the direction of the face-turn. Goto suggested resection of the antagonist muscles, and Kestenbaum favoured surgery on all four muscles, although he also suggested the two eyes should have sequential surgery. It is the Kestenbaum strategy, with modifications, that is normally performed today, and his name tends to be attached to this surgical approach to nystagmus.

Types of head posture

Face-turns to one side or the other are the commonest type of posture, although minor degrees of head tilt or chin elevation or depression are seen. Large degrees of chin up/down or head tilt are unusual. The typical head posture is in moderately but not extremely eccentric gaze, and nystagmus intensity will often increase again in gaze beyond this ‘null zone’.

Care should be taken to identify, by history or examination, patients with variable head-turns, as these do not benefit from active treatment. Some patients find that pushing their eyes into either position of extreme horizontal gaze helps to stabilize the eyes. Others have the rare condition of periodic alternating nystagmus, or the even rarer periodic alternating null zone.

Measurement of compensatory head positions is notoriously difficult. The most extreme head positions are often adopted only when the patient is making a maximum effort to read a distant test-type. Frequently there is no head posture for near, and when vision is not critical the head tends to be kept in the most comfortable position, usually straight ahead. Various methods have been adopted. Many authorities make a subjective estimate. Sradj4 has devised a ‘torticollometer’. Others5 have used eccentric fixation on an array of light emitting diodes. Mitchell et al.6 utilized an orthopaedic goniometer.

Assessment before surgery

All cases require careful refraction, with cycloplegia if indicated, since astigmatism and anisometropia are not rare. Even apparently trivial refractive errors should be corrected, as such correction may occasionally produce spectacular improvement in ocular stability. Contact lenses move with the eye and therefore offer an improvement in potential best visual acuity.

Prisms will allow the eyes to be placed in the eccentric null position while the head is straight (i.e. change the direction of gaze). They should be placed with the base towards the head-turn. Prisms may be very useful as a guide to likely benefit from surgical treatment, but have little to offer as a definitive therapy, since most head-turns are of 30° or more, requiring around 60▵ of prism. If they are ordered as Fresnel membrane prisms, acuity will be degraded. Solid glass prisms are unacceptably heavy and obvious; they will also cause chromatic aberration.

Surgical treatment

The principle underlying surgical treatment is to rotate the eyes in the direction of the head-turn—in other words, to produce a relative gaze palsy towards the side to which the eyes are normally directed. The technique is essentially that advocated by Kestenbaum. However, he advocated recessions and resections of only 5 mm, and this is not adequate to improve the head position in the typical case. Parks7 in 1973 suggested his popular (and memorable) ‘5, 6, 7, 8’ procedure. This dosage is based on the amounts felt to represent maximal surgery without sacrificing rotations—i.e. recession of one medial rectus of 5 mm, and one lateral rectus 7 mm, with appropriate resections of the other medial rectus 6 mm and lateral rectus 8 mm. Calhoun and Harley8 and later Nelson et al.9 suggested ‘augmented Parks’ surgery. Where the head-turn is up to 30°, the surgical amounts are increased by 40%—i.e. 7, 8.4, 9.8, 11.2 mm. Where the turn equals or exceeds 45°, they advocate 60% augmentation—i.e. 8, 9, 11.2, 12.8 mm. On the other hand, Pratt-Johnson10 obtained excellent results by making all recessions and resections 10 mm. Other authors11,12,13 have suggested various surgical dosages.

Most authorities agree that the early response to surgery wears off in some cases, with recurrence of the head posture. Reoperation—for example, re-resection of the previously resected muscles by 5 mm and a posterior fixation procedure on the previously recessed pair of muscles—is safe and effective.

Vertical postures and head tilts are much less common, although many face-turns are accompanied by minor degrees of vertical head displacement. When chin elevation or depression is the main feature, the principle of rotating the eyes in the direction of the head posture should be followed. Therefore for chin depression, both inferior recti should be resected 4-6 mm and both superior recti recessed a similar amount. For pure head tilt, the intortor on the side of the tilt (e.g. the superior oblique) should be weakened and the extortor on the other side (e.g. the inferior oblique) strengthened. Conrad and de Decker14 operate on all four oblique muscle insertions, slanting the insertions to either increase or decrease their cyclotorsional effect. An alternative approach has been described by Spielmann15, who slants the insertions on all the rectus muscles of each eye. Both approaches seem logical.

The benefit of surgery is largely cosmetic, but Dell'Osso and Flynn5 have shown ‘broadening of the null zone’ postoperatively. Best corrected visual acuity is usually unchanged.

Artificial divergence surgery

This surgical approach is based on the common observation that many patients with congenital nystagmus show a significant reduction in its amplitude on convergence. Their near visual acuity is therefore frequently disproportionally better than distance acuity. In some patients, base-out prisms suppress nystagmus and improve vision. The aim of surgery is to induce a latent divergent ocular position (exophoria), which the patient will then overcome by exerting fusional convergence, thereby damping the nystagmus. Patients must have adequate fusional reserves to overcome the induced deviation, so preoperative testing with prisms is mandatory. Sedler et al.16reported 26 patients assessed preoperatively with prisms. 20 responded to prism adaptation and of these 17 did well with artificial divergence surgery; 3 patients required a combination of artificial divergence surgery with the classic Kestenbaum procedure. 6 patients who did not respond to prisms had Kestenbaum surgery as a primary procedure. Zubcov et al.17 reported 18 cases treated with combinations of artificial divergence surgery and Kestenbaum surgery with particular reference to visual acuity. 6 had artificial divergence surgery alone: 2 gained one line of Snellen visual acuity, and one gained four lines. 7 patients had standard Kestenbaum surgery: one gained a single Snellen line of vision. 5 had a combined approach: 4 gained two or more lines of Snellen acuity.

Maximum recession of horizontal rectus muscles

This procedure is designed to symmetrically weaken the horizontal rectus muscles and reduce the amplitude of the nystagmus, all congenital nystagmus being either purely or largely horizontal in direction. It was first suggested by Bietti and Bagolini in 196018, but was then revived by von Noorden19 and Helveston20 in 1991.

All four horizontal recti are recessed to around the equator of the globe, the medials being 10 mm from their insertions, and the laterals at 12 mm. The procedure causes remarkably little reduction in horizontal rotations of the eye and distinctly improves vision. The Snellen acuity is only slightly improved, but nearly all patients report a decrease in the time taken to identify an object of regard. This has been studied by Sprunger et al.21.

Anterior tenotomy of rectus muscles

Dell'Osso et al.22 have recently reported some studies in an animal with naturally occurring nystagmus, the achiasmatic Belgian sheepdog. Their thesis is that removal of the tendon organ responsible for proprioception abolishes the nystagmus. Anterior tenotomy of all rectus and oblique muscles certainly reduced nystagmus in two animals, but the results in man are still awaited.

Neurosurgery

In 1988 Funahashi23 reported a series of 106 patients with congenital nystagmus of whom 10 (aged 18-42, mean 27) underwent stereotactic neurosurgical superior colliculectomy. 7 showed a reduction of nystagmus amplitude by 40%. There has been no replication of this study

SURGERY FOR MANIFEST-LATENT NYSTAGMUS

Most patients with latent and manifest-latent nystagmus have no important visual symptoms as long as both eyes are open. A small group, however, have a significant face-turn towards the fixating eye in order to damp the nystagmus, which typically increases on abduction and decreases on adduction. If surgery is contemplated it should be directed at the fixing eye to prevent it drifting in a nasalward direction. Typical surgery would involve recession and posterior fixation of the medial rectus of the dominant eye. Many cases of manifest-latent nystagmus have esotropia and a face-turn. Here the amount of surgery for the face-turn and that for the esotropia should be summed. Typically, a standard recession of the medial rectus and resection of the lateral rectus on the dominant eye will be required. If patients are unhappy about surgery on their ‘good’ eye, it is possible to demonstrate the expected effects of surgery by means of an injection of botulinum toxin to the medial rectus of the dominant eye

NYSTAGMUS SURGERY IN CHILDREN

Although congenital nystagmus is usually present by the age of 3 months, and children may be referred at quite an early age, surgery is normally deferred until the child is around 7-8 years old. There seems no evidence of permanent skeletal change due to an intermittently adopted head posture, and young children do not as a rule complain of the cosmetic defect. In binocular cases, there is a small risk in visually immature children of inducingstrabismus, especially if the surgery is on vertical recti. In cases with manifestlatent nystagmus, amblyopia treatment should take priority and there is no urgency in surgical treatment since such cases are rarely if ever binocular.

SURGERY FOR ACQUIRED NYSTAGMUS

Regrettably, little can be done surgically for most patients with acquired nystagmus. Sometimes the causal lesion can be removed, as shown by the reports by Senelick25 who improved down-beat nystagmus secondary to basilar impression and Arnold—Chiari malformation by transoral removal of the odontoid process, and Spooner and Balogh26, who reported reduction of nystagmus in 4 of 5 cases of Arnold—Chiari malformation following suboccipital decompression. Roberts et al.27 operated on 7 patients with nystagmus (acquired in 3 cases) and an abnormal head posture with extreme chin elevation or depression; the patients with acquired nystagmus improved by one or two Snellen lines.

Patients, especially adult patients, with nystagmus are seeking a therapy for an inherently incurable condition. They are understandably keen to try any therapy that might help. The condition can be very variable, with emotion, tiredness and stress all known to have effects on its severity. The placebo effect of any treatment, especially surgery, must be very great, and randomized trials of treatment are difficult to design. One should therefore try not to raise hopes of radical improvement with any therapy.

CONCLUSIONS

Patients with congenital nystagmus and a compensatory head posture should be fully assessed medically and ophthalmologically. All cases require careful refraction and a trial of spectacle or contact lens treatment. Prisms may be of value in assessment and selection of cases for surgery, but are of little value for long-term therapy. The modified Kestenbaum surgical approach to congenital nystagmus with an abnormal head posture has proved its worth over the past 47 years. Additional amounts of surgery may be beneficial in cases with exceptionally large face-turns. Recurrence of head position may be managed by reoperation. Artificial divergence surgery and maximal recession of the horizontal rectus muscles may benefit patients who do not adopt a compensatory head posture. In most cases of acquired nystagmus surgical treatment is unlikely to be of value.

Nystagmus and Driving

This may be one of the most sensitive topics for people with nystagmus. As you can imagine, anything that affects your vision may affect your ability to operate a vehicle. Let’s talk about driving and nystagmus in general, and then I’ll tell you a little more about my experiences.

Can people with Nystagmus drive?

It depends on three things:

1. How extreme the nystagmus is. It may be that a shifty eyed person needs to get a note from their optometrist/ophthalmologist saying that it is safe for them to drive.
2. General vision. Many times nystagmus is accompanied by low vision. A person with nystagmus will need to take the same eye exam at the DMV as any other person would do. This test can be taken with glasses on, but that will mean that the driver would need to wear the glasses at all times while driving.
3. Where the person lives. It’s my understanding that in the UK, the driving requirements are much stricter than they are here in the US, and it’s much more difficult for people with nystagmus to get a license there. Also, every state in the US has different driving requirements.

Do I Drive?

No, I do not. Can I drive? Technically, yes. In the past I have gotten my permit, and have driven a great deal. However, I have never gotten my license. Just because I can drive does not mean that I am comfortable driving. Because of the way my particular nystagmus reacts to movement, fast glances and checking blind spots are challenging. I’ve been in some close calls before. My worst nightmare is not seeing someone in time, making a movement, and then getting into a huge accident on a freeway that kills somebody.

So, for this reason (and others not having to do with nystagmus) I have chosen not to drive for the moment. This may change someday, especially if I have kids and need to drive them around. But even if I do get my license, I will probably keep driving at a minimum

Does not driving affect my life?

Yes, it does. This is probably the single greatest nystagmus-related challenge for my personal life. I live in Los Angeles, which is probably one of the biggest pro-driving societies in the world. Not driving can be seen as being irresponsible. It also means that the public transportation system is often times lacking. In order to have any kind of personal life, I depend on getting rides from other people. My friends have been great about this, but I know that sometimes it can be frustrating for other people. I try to pitch in for gas if I’m being toted around a lot.

I do have a fantastic boyfriend who is very understanding about my not driving. I won’t lie though; it has come up as an issue. I can imagine how frustrating it is when there is a family event at his house that he has to pick me up and drive me back for. It also affects how much he can drink when we go out, which isn’t fair to him. He is very kind about it, and has let me taken my time with the driving issue. He never complains to me, and for most of the time, it’s not a problem. But I can see that it’s frustrating sometimes. I struggle with a lot of guilt about this.

As far as work goes, luckily, I work just blocks away from my house, so I have avoided the challenge of getting to work for now. Whew!

So yes, driving is an issue all shifty-eyed people have to deal with. It’s a sensitive topic. No body likes to think they can’t do something simply because of the way they were born. We appreciate all the understanding and shifty-eyed love from all the “normal” sighted folks out there

Nystagmus and fighting blindness

Overview

Nystagmus is an uncontrolled movement of the eyes, usually from side to side, but sometimes the eyes swing up and down or even in a circular movement.

Most people with nystagmus have vision which is worse than average.

Nystagmus that appears in the first months of life is called ‘early onset nystagmus’ or ‘congenital nystagmus’. The condition may also develop later in life when the term ‘acquired nystagmus’ is used.

Causes

Nystagmus in early childhood may be caused by a defect in the eye or the visual pathway from the eye to the brain. It occurs in a wide range of eye disorders of childhood such as cataract, glaucoma, some disorders of the retina and albinism (see Related eye conditions below). It may also be found in children who have multiple disabilities such as Down’s syndrome.

Many children with nystagmus do not have eye, brain or other health problems. In this case the condition is called ‘congenital idiopathic nystagmus’ or ‘idiopathic nystagmus’, meaning that the condition starts very early on in life and the cause is unknown.

Several types of nystagmus can be inherited. To find out the chances of someone passing on nystagmus to the next generation, a specialist must first make an accurate diagnosis of the underlying condition. A clinical geneticist can provide detailed information. Your eye specialist will be able to refer you to one. Acquired nystagmus, which develops later in life, may be a symptom of another condition such as stroke, multiple sclerosis or even a blow to the head. There are many causes. Nystagmus is not infectious or contagious.

Because nystagmus may be the first sign of serious disorder of the eye or the brain, it is vital that when nystagmus first develops the child or adult is referred to an ophthalmologist (eye specialist) or a neurologist.

It is not known accurately how common the condition is, but nystagmus is believed to affect around 1 in 1,000 individuals.

Symptoms

Nystagmus affects people in many ways and the effects vary from person to person. In all cases, the vision will be blurred. Here are some of the ways the condition can affect people.

Most people who have had the condition since childhood are not affected by a constantly moving image (known as ‘oscillopsia’), as their brain adapts to the movement of the eyes. However, people who acquire nystagmus later in life are unlikely to adjust so well and will be affected much more by oscillopsia. Nystagmus is often associated with reduced sight. The degree of sight loss varies from mild to very poor vision and is related to the underlying condition. Many people with the condition are eligible to be registered partially sighted or blind.

Please note that very few people who are registered are totally blind. Most have very poor vision.

Vision varies during the day and is likely to be affected by emotional and physical factors such as stress, tiredness, nervousness or unfamiliar surroundings. People with nystagmus may tire more easily than other people because of the extra effort involved in looking at things.

Many people with nystagmus can read very small print if it is close enough to their eyes. Some find a visual aid such as a magnifier helpful. However, large print material should always be made available and all written matter should be clear. It is very difficult to share a book because it will probably be too far away or at the wrong angle.

People with nystagmus may be slow readers because of the extra time needed to scan. This should not be taken as a sign of poor reading ability, but students or school children with nystagmus may need extra time studying and when sitting exams.

Many people with nystagmus use computers, as they can position screens to suit their own needs and adjust brightness, character size, and so on. However, some people find it difficult to read computer screens for more than a few minutes. Experimenting with different colour combinations and using large screens may help. The angle of vision is important. Many people with the condition have a ‘null point’ where the eye movement is reduced and the vision is improved. They will often turn their head to one side to make the best use of their vision. Sitting to one side of a screen or blackboard often helps. Children with nystagmus should be allowed to adopt the head posture which gives them best vision.

Uncontrolled head nodding helps concentration probably because the head movement compensates somewhat for the eye movement.

Depth perception is usually considerably reduced. This may sometimes make people seem a little slower or clumsier than normal.

Balance may be affected, possibly because of poor depth perception, which may make it difficult to use stairs or cross uneven surfaces.

Confidence may be reduced because of poor vision and maintaining eye contact may be difficult.

Getting about can also be affected, especially in unfamiliar and busy surroundings such as supermarkets, railway stations and airports. Crossing roads is more difficult too. Orientation (knowing where you are) and mobility (moving from place to place safely) training can help. Very few people with nystagmus are legally able to drive a car.

Treatments

Nystagmus cannot be cured but there are several treatments which can help.

Glasses and contact lenses do not correct nystagmus although they may help a little and should certainly be worn to correct other sight problems. A child or adult may be diagnosed as being ‘short sighted’ or ‘long sighted’ as well as having nystagmus. Long or short sightedness occurs because the eye itself is not exactly the right shape for focusing.

The focusing problems can be corrected with glasses or contact lenses, but the nystagmus will still affect the person’s eyesight. Being long sighted does not mean that someone with nystagmus has good distance vision. Ask your ophthalmologist or optician to explain more.

Very occasionally, surgery is performed to alter the position of the muscles, which move the eye. The purpose of this is to reduce the amount the head has to turn to try and see better.

Researchers have explored ways of trying to reduce the nystagmus by making the patient aware of the eye movement and encouraging them to control it.

These techniques rely on visual and audio signals (known as biofeedback) to the patient. For example, the patient might listen to an electronic signal, which goes higher when the eye movement is greater. Some people have said that they benefit from this type of treatment.

However, the evidence is not conclusive and many of questions remain unanswered such as: “Do these techniques bring about a real improvement in vision and do the possible effects last?”

The good news is that nystagmus is not painful and does not lead to total blindness. Vision tends to improve until it stabilises around the age of five or six.

Giving children plenty of stimulation in the early years does seem to help them make best use of the vision they have. Toys which encourage the child to follow a moving object, such as marbles or train sets, are helpful. So are games which are designed to develop hand-to-eye coordination.

It is not possible to say which type of school is best for the child with nystagmus – each child has his / her special requirements. However, most children with nystagmus go to mainstream schools. Many go on to college and most adults lead fulfilled, independent lives.

How can the effects be minimised?

Much can be done to reduce the effects of nystagmus and make sure that people with the condition have the same access to the same opportunities as fully sighted people.

Accurate information and support, during the early years in particular, can and do make a big difference. In the worst cases, without a clear explanation of the effects of nystagmus, some children are mistakenly thought to have learning difficulties. This means that the real problems caused by their poor vision are not addressed. With the support of teachers trained in visual impairment, an understanding school and the help of parents, most of the difficulties presented by nystagmus can be overcome.

Related eye conditions

Albinism

Albinism is the name given to a group of inherited conditions in which there is a lack of pigmentation (colour) in the eyes and usually in the skin and hair as well. This causes most people with albinism to have a very fair, almost white, appearance, although in some people albinism affects the eyes only. People with albinism find their greatest problems arise on sunny days and in brightly lit environments. Virtually everyone with albinism has nystagmus.

Cone dystrophy

Cone dystrophy is an impairment to vision which can be caused by any one of a number of eye disorders. These disorders may or may not be inherited. Some dystrophies appear later in life, sometimes as late as 50. Other types may appear in early childhood or even be present at birth. Cone dystrophy may cause problems with seeing in bright light, seeing detail and seeing colours.

Childhood (or ‘juvenile’) cataract

Cataract is a clouding of the lens of the eye which causes sight to become blurred or dim, because light cannot pass through to the back of the eye. Not all cataracts impair sight so badly that an operation is required. Some babies are born with cataracts and some develop them later in childhood. Childhood cataract may be inherited or may be caused by injury or illness. However, in some cases the cause cannot be identified.

Down’s syndrome

Down’s syndrome is a genetic condition caused by the presence of an extra chromosome. People with Down’s syndrome have 47 chromosomes instead of the usual 46. It is amongst the most common forms of learning disability. Nystagmus is a common side effect of Down’s syndrome.

How to Assess and Treat Infantile Nystagmus

Nystagmus can be difficult to categorize, especially since the spectrum of this eye movement encompasses both normal physiology and serious (sometimes rare) underlying disease. With a prevalence ranging from one in 1,000 to one in 6,550, infantile nystagmus is likely to be encountered in a comprehensive or pediatric ophthalmology practice. It is important to recognize and follow up nystagmus in an infant, since it may be a manifestation of a serious condition. Also, in order to avoid a vision-relatedlearning disability, treatment for nystagmus should be considered.

Defining the Condition
Nystagmus is a rhythmic oscillation of one or both eyes about one or more axes. It is further divided into jerk nystagmus and pendular nystagmus, according to the characteristics of the oscillation. In jerk nystagmus, there is slow movement in one direction followed by a rapid movement in the other direction. In pendular nystagmus, there is no obvious distinction between the speed of movement in either direction. Infantile nystagmus is defined by onset in the first few months of life. Although the term “congenital nystagmus” is often used synonymously, nystagmus is seldom diagnosed at birth. Infantile nystagmus has traditionally been divided into sensory (afferent) and motor (efferent) types. While this distinction may be conceptually correct, it does not always reflect the underlying pathophysiology. More clinically useful are the descriptive categories: congenital motor nystagmus, sensory defect nystagmus, periodic alternating nystagmus and latent nystagmus (see Table). While these forms of infantile nystagmus are benign, other forms, discussed in “Differential Diagnosis,” can signal serious CNS pathology.

Clinical AppearanceThe most characteristic form of infantile nystagmus is a jerk or pendular horizontal, uniplanar eye movement. The amplitude and frequency of the oscillations vary. The nystagmus frequently diminishes on convergence and is absent during sleep. The eyes are objectively normal. In many instances, a null zone (a position where the intensity of the oscillations is diminished and visual acuity improves) is present. Persons with a null zone often adopt abnormal head positioning to maximize vision.

HistoryTime of onset. While nystagmus is seldom diagnosed at birth, the timing of onset can offer clues. For example, spasmus nutans (see below) occurs in children age 3 to 15 months and typically disappears by age 3 to 4 years, while sensory defect nystagmus begins within the first 3 months of life if vision loss is present at birth.

Family history and examination of relatives. Congenital motor nystagmus has a strong hereditary component. The sex-linked dominant form is the most common pedigree; the sex-linked recessive form is also relatively frequent. Autosomal transmission, either dominant or recessive, is rarely seen. When a case is sex-linked recessive, other anomalies such as Leber’s optic atrophy or spastic paralysis are commonly associated.

Head positioning. With time, the child will adopt abnormal head positioning if there is a null position associated with the nystagmus.

Presence of photophobia. Albinism and oculocutaneous albinism can lead to nystagmus that presents as sensory defect nystagmus.

Exam Findings
Visual acuity. Congenital motor nystagmus is associated with relatively good visual acuity (20/40 to 20/70), while sensory defect nystagmus is often associated with poor vision.

Color vision. Achromatopsia (red monochromatism), present at birth, is complete color blindness. The first signs may be the presence of sensory defect nystagmus and light sensitivity with squinting in bright light. An electroretinogram may show an abnormal photopic signal with maintenance of a normal scotopic signal.

Slit-lamp exam. A slit-lamp exam differentiates ocular albinism, optic nerve hypoplasia and congenitalcataracts—all of which manifest sensory defect nystagmus.

CT scan and MRI. Imaging is important when it is necessary to rule out organic and neurologic causes of nystagmus.

Differential DiagnosisIt is important to catalog symptoms and rule out serious causes of infantile nystagmus. If a child’s presentation does not precisely fulfill the criteria for congenital motor nystagmus, neuroradiologic testing is necessary.

Spasmus nutans. Spasmus nutans is acquired, typically presenting between the ages of 3 and 15 months. The classic triad is 1) nystagmus, 2) head nodding and 3) torticollis. In its classic manifestation, the nystagmus is usually bilateral but sometimes monocular and can be horizontal, vertical or rotary. It can be described as shimmering, due to its small-amplitude and high-frequency nature. The diagnostic difficulty here is the similarity between spasmus nutans and the nystagmus that accompanies a chiasmal glioma or other suprachiasmal tumor. Therefore, neuroradiologic investigation is indicated with this triad of signs. Prognosis is excellent since spasmus nutans usually resolves by the age of 3 to 4 years.

See-saw nystagmus. This form is clinically unique, with both vertical and torsional components. True to its name, the eyes will alternate with one eye high and intorting and the other low and extorting. See-saw nystagmus is often associated with a lesion in the rostral midbrain or suprasellar area and, therefore, the patient also may show bitemporal hemianopia. Neuroradiologic investigation is indicated. Treatment is removal of the tumor. There is also a form of see-saw nystagmus that is not related to tumor.

Convergence retraction nystagmus. When associated with paralysis of upward gaze, defective convergence and light-near dissociation, this type of nystagmus is indicative of dorsal midbrain syndrome. Congenital aqueductal stenosis and pinealoma are the most common causes in children.

Opsoclonus. Opsoclonus is not a true nystagmus, but rather a rapid, high- frequency, low-amplitude, involuntary, multivectorial oscillation. It is often called “dancing eyes and dancing feet,” because of its association with acute cerebellar ataxia of childhood. Opsoclonus can herald neuroblastoma.

Vertical nystagmus. Vertical nystagmus is usually jerk and is named according to the direction of the fast beat. Downbeat nystagmus is associated with cervicocranial abnormalities, such as Arnold-Chiari malformation or spinal cerebellar degeneration.

Monocular nystagmus. Monocular nystagmus is pendular, usually vertical, and of irregular frequency. It occurs in severely amblyopic eyes, in blind eyes and as spasmus nutans.

Dissociated nystagmus. In dissociated nystagmus, the nystagmus is in the abducting eye. This nystagmus is seen with internuclear ophthalmoplegia, surgical weakening of the contralateral medial rectus muscle and myasthenia gravis.

Treatment
First, significant refractive errors should be corrected, and amblyopia therapy provided, if needed.

If a head turn is present and disabling, medical and surgical options exist. Prisms for both eyes, with the apex pointing toward the eye deviation (or in the opposite direction to the head turn), can correct head positioning. Prisms can also be used after surgery if abnormal head position is still manifest.

The Kestenbaum (or Kestenbaum-Anderson) procedure is designed to correct a head turn or to improve visual function by shifting a null zone into primary position. Briefly, in a patient with a left face turn and a null zone in dextroversion, the left lateral and right medial rectus muscles would be recessed. If vertical torticollis is present, the vertical rectus muscles can also be recessed.

Asymptomatic eye movements do not require treatment. However, when nystagmus is associated with decreased visual acuity and oscillopsia, it can be treated pharmacologically. For example, gabapentin, baclofen, clonazepan, 3, 4-diaminopyridine and 4-aminopyridine can be used for downbeat nystagmus, and baclofen is preferred for periodic alternating nystagmus. ¹

Also, significant encouragement in learning is important. These children sometimes adopt unconventional reading positions. Experience suggests taht they learn to read much quicker if allowed to position the book however they please. As discussed above, convergance dampens the nystagmus, allowing the child to fixate longer on the words.

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1 Rucker, J.C. Curr Treat Options Neurol 2005;7:69-77.

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Katie Flickinger is a fourth-year medical student at the University of South Carolina.  Jeramiah P. Tao, MD, is an oculoplastics fellow at 

Indiana University

.

Characteristics of Important Forms of Infantile Nystagmus

Congenital Motor Nystagmus Uniplanar Horizontal Binocular and conjugate Can be pendular, jerk, circular or elliptical Waveform typically exhibits increasing velocity in the slow phase. A null zone, with abnormal head positioning, is often present There is paradoxical inversion of optokinetic nystagmus Sensory Defect Nystagmus All waveforms are present, but pendular is most common; may become jerk on lateral gaze Caused by an abnormality in the afferent visual pathway and failure to develop a normal fixation reflex Periodic Alternating Nystagmus An unusual congenital motor jerk nystagmus Shows a 60- to 90-second one-sided jerk nystagmus, 10 to 20 seconds of no nystagmus, then 60 to 90 seconds of nystagmus in the opposite direction Changes the location of the null zone and the child’s preferred head position Associated with oculocutaneous albinism Latent Nystagmus Horizontal and conjugate Jerk Occurs with monocular fixation. Fast phase in the direction of the fixating eye Waveform shows decreasing velocity in the fast phase Benign condition that occurs when one eye is occluded, or following surgery that leaves one eye with impaired vision May become manifest (manifest latent nystagmus) when only one eye is being used for vision (i.e., if one eye is amblyopic)

Medical treatment of nystagmus and its visual consequences

In some cases of acquired nystagmus, stopping a medication or eliminating alcohol or drug abuse can end the problem. However, nystagmus is often a permanent condition. Its severity may be reduced through different treatments. Improving vision with spectacles or contactlenses is an important part of treating nystagmus.
Medications have been used to lessen the severity of nystagmus, but their use is often limited because of the side effects they cause. Injections of botulinum toxin may be helpful for some individuals who experience severe shakiness in their vision

Surgery on the eye muscles may be appropriate for some people with nystagmus. The goal of the surgery is to alleviate a significantly abnormal head position or to ease the severity of the nystagmus. While the surgery may improve vision, it does not totally eliminate nystagmus.

For us to see clearly the details in our visual world, images must be held quite still upon the retina, especially the central part (the fovea). For reading, which concerns detection of high spatial frequencies, image motion must be less than about 5° / second1. If image drift substantially exceeds this limit, visual acuity will decline and we may experience the illusion that the world is moving (oscillopsia). In health, three main mechanisms hold the line of sight steady so that our view of the world is clear and stable2. The first is ‘fixation’, which has two distinct components—the visual system's ability to detect retinal image drift and programme corrective eye movements, and the ability to suppress unwanted eye movements that would take the eye away from the target. The second mechanism is the vestibulo-ocular reflex, by which the motion detectors of the inner ear promptly initiate eye movements to compensate for head perturbations, such as occur during locomotion. The third mechanism is the gaze-holding system, which makes it possible to hold the eyes at an eccentric position (e.g. in lateral gaze).

If any of the three mechanisms that normally act to hold gaze steady malfunctions, the eyes may start to drift away from the object of regard, and corrective rapid eye movements may be made. Thus, nystagmus may be defined as repetitive to-and-fro involuntary eye movements that are initiated by slow drifts of the eye. It is important to realize that some forms of nystagmus are normal. Thus, nystagmus that occurs during rotation of the body in space acts topreserve clear vision. In pathological nystagmus, however, drifts of the eyes away from the target degrade vision. In one form, pendular nystagmus, the drifts consist of a to-and-fro sinusoidal oscillation. More commonly, nystagmus consists of alternation of unidirectional drifts away from the target and corrective fast movements (saccades) which momentarily bring the visual target back to the fovea; this is jerk nystagmus.

Nystagmus should be distinguished from inappropriate saccades that disrupt steady fixation. Saccades produce high-speed movement of images upon the retina—too high for clear vision—and several physiological mechanisms exist to prevent perception of the smeared retinal signal due to the saccade. However, patients in whom inappropriate saccades repeatedly misdirect the fovea often complain of difficulty with reading.

Box 1 Medical strategies for treating nystagmus and its visual consequences

• Methods that place the eye in a position in which nystagmus is minimized
• Optical and electronic methods for negating the visual consequences of the nystagmus
• Procedures for weakening the extraocular muscles
• Application of somatosensory or auditory stimuli to suppress nystagmus
• Drugs that suppress some forms of nystagmus.

Five main approaches to treating pathological nystagmus and its visual consequences are summarized in Box 1. For a fuller discussion of the clinical features, pathogenesis and treatment of nystagmus, the reader is referred to a recent textbook on eye movements2.

METHODS THAT PLACE THE EYE IN A POSITION IN WHICH NYSTAGMUS IS MINIMIZED

In patients whose nystagmus is suppressed by viewing a near target, convergence prisms will often improve vision. This is especially the case in some patients with congenital nystagmus, when the improvement of vision may be appreciable. An arrangement that is often effective is 7.00 diopter base-out prisms with — 1.00 diopter spheres added to compensate for induced accommodation3. The spherical correction is not usually required in presbyopic individuals. Some patients with acquired nystagmus also benefit4, and in patients whose nystagmus is worse during near viewing, base-in prisms may help. In patients whose nystagmus is quieter when the eyes are moved into a particular position in the orbit (the ‘null region’) prisms only rarely help, since most patients use head-turns to bring their eyes to the quietest position.

OPTICAL AND ELECTRONIC METHODS FOR NEGATING THE VISUAL CONSEQUENCES OF THE NYSTAGMUS

Rushton and Cox described an optical system that stabilizes images upon the retina5. This system consists of a high-positive-power spectacle lens worn in combination with a high-negative-power contact lens. The system rests on the principle that stabilization of images on the retina is achieved if the spectacle lens focuses the primary image close to the centre of rotation of the eye. Such images, however, are defocused, and a contact lens is required to extend back the focus onto the retina. Since the contact lens moves with the eye, it does not negate the effect of retinal image stabilization produced by the spectacle lens. With such a system it is possible to achieve up to 90% stabilization of images upon the retina. There are several limitations to this system6. The first is that it disables all eye movements (including the vestibulo-ocular reflex and vergence), so that it is only useful while the patient is stationary and views monocularly. Another limitation is that the field of view is limited. A third is that patients with ataxia or tremor (such as those with multiple sclerosis) have difficulty inserting the contact lens. We have found that, in selected patients, a modification of the device, which uses soft contact lenses and attempts to provide lower amounts of retinal image stabilization, may prove useful for limited periods of time—for example, if the patient wishes to watch a television programme6.

A more recent innovation is to use an electronic circuit to distinguish between the nystagmus oscillations and normal eye movements7. This approach is most useful in patients with pendular nystagmus. Eye movements are measured with an infrared sensor and fed to a phase-locked loop that generates a signal similar to the nystagmus but is insensitive to other eye movements, such as saccades. This electronic signal is then used to rotate Risley prisms, through which the patient views the world. When the Risley prisms rotate in synchrony with the patient's nystagmus, they nullify the visual effects of the ocular oscillations. Improvement and miniaturization of a prototype device may eventually yield spectacles that selectively cancel out the visual effects of pathological nystagmus7.

MEDICAL PROCEDURES FOR WEAKENING THE EXTRAOCULAR MUSCLES

Injection of botulinum toxin into either the extraocular muscles or the retrobulbar space has been reported to reduce nystagmus and improve vision in some patients8,9,10,11. Limitations of this approach are the short period of action (2-3 months), ptosis, and diplopia, which may be more annoying to patients than visual symptoms due to the nystagmus. In some patients, the nystagmus may become worse in the non-injected eye, if the patient prefers to view with the injected eye. This is because botulinum toxin weakens all types of eye movement, not just the nystagmus. This paresis of normal movements stimulates the brain to make adaptive changes by increasing innervation that may worsen the nystagmus in the non-injected eye.

APPLICATION OF SOMATOSENSORY OR AUDITORY STIMULI TO SUPPRESS NYSTAGMUS

Various alternative treatments have been suggested for congenital nystagmus. Contact lenses can be beneficial, an effect that is not due to the mass of the lenses but is probably mediated via trigeminal afferents3,12. Electrical stimulation or vibration over the forehead or neck may suppress congenital nystagmus13, again possibly by an action on the trigeminal system, which receives extraocular proprioception. Similarly, acupuncture administered to the neck muscles may suppress congenital nystagmus in some patients14. Biofeedback has also been reported helpful. The role of any of these treatments outside the laboratory, during natural activities, has yet to be demonstrated.

DRUG TREATMENTS FOR NYSTAGMUS

Several drugs have been reported to suppress various forms of nystagmus and improve vision (Box 2), though the studies have mostly been uncontrolled or non-masked. Current concepts of the neurobiology of eye movements provide a rationale for three specific treatments, each of which has met with some success.

Box 2

Some current drug treatments for nystagmus (for details see Ref. 1)

For us to hold the eyes steadily at an eccentric position (e.g. turned into right gaze), the brain must programme a tonic contraction of the extraocular muscles, otherwise the orbital tissue will pull back the eyes towards the centre2. This gaze-holding mechanism depends mainly on a network of neurons that lie in the medulla for horizontal gaze17 and in the midbrain for vertical gaze18. Pharmacological inactivation of the neural network in the medulla causes the eyes to drift to the centre and cause ‘gaze-evoked nystagmus’. These studies have indicated that two neurotransmitters are important in this gaze-holding process: gamma-aminobutyric acid (GABA) and glutamate19,20. Theoretical and experimental evidence has suggested that some forms of nystagmus, such as the pendular nystagmus that occurs in multiple sclerosis, may arise from an instability in the gaze-holding mechanism21. The information served as the impetus for a controlled, double-blind trial of two agents with GABA effects—gabapentin and baclofen22. Most patients with pendular nystagmus benefited from gabapentin and elected to continue with this drug after the trial was completed. An open trial of a drug with glutamate effects, memantine, was also reported to offer improvement in patients with pendular nystagmus due to multiple sclerosis

In two rarer disorders, an understanding of pathogenesis suggested effective treatments. One is familial episodic vertigo and ataxia type 2 (a disorder of calcium channels), which responds to acetazolamide and calcium channel blockers24. The second is periodic alternating nystagmus, which follows lesions of the nodulus (vestibular cerebellum) and responds to baclofen

With improved knowledge of the pharmacology of the ocular motor system, further drug treatments are likely. Some agents, such as cannabis and alcohol, are not viable treatments during everyday activities because of their side-effects; however, they may provide clues leading to new drug strategies. Before any agent can be regarded as an effective treatment for nystagmus, a controlled masked trial is essential.