Understanding Nystagmus

Nystagmus is an involuntary rhythmic shaking or wobbling of the eyes. The term nystagmus is derived from the Greek word, “nmstagmos”, which was used to describe the wobbly head movements of a sleepy or inebriated individual. Nystagmus has also been described as “dancing eyes” or “jerking eyes”. Doctors and researchers classify nystagmus by the characteristics of the eye movements like do they move back and forth like a pendulum or do they move slowly in one direction and then rapidly in another.  Do the eyes move laterally or vertically and by how much? How fast do the eyes move?
There are various methods of classifying nystagmus. Traditionally nystagmus has been divided into two groups. Sensory nystagmus is related to vision loss and motor nystagmus is related to the control of muscle function.  There are over 45 types of nystagmus. To simplify our explanation of nystagmus, we will divide nystagmus into two basic types. The first is nystagmus that begins very early in life and is associated with vision loss. The second is called acquired nystagmus and is associated with neurological disorders occurring later in life.
Nystagmus from Early in Life
Early onset nystagmus often accompanies vision loss acquired at birth or soon after and may be one of the first signs that a child has a loss of vision. Studies suggest 1 in every 1000 children have nystagmus. In 80-90% of cases, it is a side effect of vision loss from eye diseases such as albinism, aniridia, optic nerve hypoplasia, achromatopsia congenital cataracts, coloboma or retinopathy of prematurity. This type of nystagmus is usually observed around the sixth to eighth week of life and is rarely seen before then. In about 10-20% of cases, it presents with mild vision loss not associated with other diagnosed ocular diseases. The discovery of nystagmus in a child is reason for an immediate examination!
The typical nystagmus related to vision loss during childhood is a pendular nystagmus. The eyes rotate back and forth evenly, much like a pendulum. Patients with early onset nystagmus do not notice the movement of their vision when their eyes shake. Although nystagmus is associated with early vision loss, it may vary from stress, emotional status and direction of view.  It is uncommon to permanently worsen over time. In fact, nystagmus often improves mildly from childhood to adulthood.
Most cases of early onset nystagmus are associated with ocular disease many of which are inherited conditions. Genetic counseling can help the patient and family understand the odds of passing the condition to their children. Not all cases of early onset nystagmus are hereditary.
Nystagmus Arising Later in Life
While vision loss before birth will result in nystagmus, loss of vision occurring later in life does not usually cause nystagmus. Thus, a patient with age related macular degeneration would not show nystagmus while a child with achromatopsia would develop this condition.
Nystagmus can be acquired later in life due to neurological dysfunction such as a head injury, multiple sclerosis or brain tumors. Unlike nystagmus acquired from early in life, patients with late onset nystagmus usually notice movement in their vision related to the movement of their eyes. This is called oscillopsia. Oscillopsia causes a person to have vertigo or dizziness related to the new movement they experience in their vision.
Late onset nystagmus is more likely to be directional. The eye will move slowly in one direction, then quickly move back.  The nystagmus may change as the patient looks in different directions. The unexplained onset of nystagmus in an adult may indicate a serious neurological disorder and an immediate examination is indicated!
Medications and Nystagmus
Some medications may cause nystagmus. For example, Dilantin and Phenobarbital, medications given to prevent seizures, may cause nystagmus. This acquired condition may cause the patient to experience oscillopsia, a sensation of movement in their vision that causes a vertigo effect.  When it occurs vertically, the patient may describe a rolling of the vision in front of them.
Fluctuations in Vision
Nystagmus patients often experience fluctuations in their vision.  A change in the speed of the nystagmus leading to a decrease in vision can be related to stress, the patient’s emotional state, fatigue, the direction of view or when one eye is covered. Understanding these issues allows the patient and teachers to create a better environment.
The Null Position:  Unusual Head and Eye Positions
Patients with nystagmus often find a unique position of their head and eyes that slows the nystagmus allowing them to have better vision. This is called a null position and varies with each person. Teachers, friends and family must understand and support the patient’s unusual head or eye position.
Balance and Binocular Vision
Patients with nystagmus may report problems with balance. Impairment to binocular vision is common with early onset nystagmus and depth perception is indirectly impaired in many patients. Nystagmus acquired later in life may cause vertigo or dizziness like effects from the sensation of motion in the vision.  Nystagmus may decrease when the eyes converge to read.  Low vision specialists can add prism to induce convergence artificially and thus reduce the nystagmus in some patients.
Examining the Nystagmus Patient
Patients with nystagmus have many unique problems that should be evaluated by a low vision specialist or eye doctor skilled in treating nystagmus. Simple tests like visual acuity can be misleading as the vision may decrease if the patient is under stress or has latent nystagmus which causes an increase in nystagmus in both eyes when one eye is covered. The visual acuity testing requires special steps to insure an accurate measurement.
Low Vision specialists also use special testing techniques during the refraction to measure the eyeglass prescription and prevent inaccurate results from latent nystagmus. Reducing stress during testing is another method used by Low Vision Specialists to obtain the best results.
Nystagmus and Eyeglasses
Patients with nystagmus frequently have other vision problems such as astigmatism that require prescription eyeglasses. This is particularly true of patients with albinism and  retinopathy of prematurely.  Eyeglasses, however, do not cure nystagmus. Prisms may be added to the eyewear to improve the patient’s cosmetic appearance by changing the null position to a slightly more normal position.  Prisms may also be used to induce more convergence, turning in of the eyes, which may reduce nystagmus slightly. When bifocals are prescribed, the null position must be considered. Placing a small bifocal in the normal position may not be usable in a patient who must turn his or her eyes far to the left to have the best vision.
Nystagmus and Contact Lenses
Contact lenses have been shown to aid some nystagmus patients. One theory is that the tactile feedback of feeling the contact lenses on the eyes may lead to better control of the movement and allow the patient better vision.  Another benefit of contact lenses is that they move with the eyes and thus providing better image quality.
Medical and Surgical Treatments
Several surgical procedures have been developed to reduce null positions and thus improve a patient’s cosmetic appearance. Botox, botulinum toxin, has been used to paralyze ocular muscles and thus reduce nystagmus. It has not become a practical treatment since the effect of this drug lasts only three to four months and requires injection into the ocular muscles under general anesthesia. Baclofen has also been used to lessen certain forms of nystagmus. Additionally, biofeedback has also been used to treat nystagmus.
Social Issues
Not only do nystagmus patients have vision loss, but they also are faced with cosmetic problems from the constant eye movements and often an unusual head/eye position. Patients may be teased about their appearance or chastised and told to hold their head correctly.
School Issues
The teacher of a child with nystagmus needs to understand how to aid a child with nystagmus and associated vision loss. Timed tests may create emotional stress that can cause the nystagmus to increase and the child’s vision to temporarily decrease. The teacher must understand the need for the child to turn his eyes or head in a specific manner.  Allowing the child to sit at the front of the classroom is also needed. Depending on the level of vision, low vision adaptation may be required including large print books, closed circuit television, optical low vision aids, etc.  Low vision children should always have their own books and worksheets. Sharing materials is difficult for low vision patients. Materials should be enlarged and of high contrast. A simple clear yellow acetate sheet with a black line across it may be helpful in keeping one’s place especially when looking away to the chalkboard or to a computer screen.
Summary
Nystagmus, an involuntary shaking or jerking of the eyes is a very complex ocular condition. It can occur early in life secondary to various ocular diseases or can be acquired later in life in patients who have neurological disorders. Patients with nystagmus often have an abnormal head position called a null position in which their vision is improved. Low vision specialists or other nystagmus specialists may be able to provide special care, eyewear and contact lenses to help patients with nystagmus.