When we think of testing for nystagmus, medical personnel and lay people alike, we tend to think of the horizontal gaze nystagmus test performed by police officers as part of the standard field sobriety test (SFST). It’s true that the police have taken this useful neurological exam and put it to good use to identify folks who may have had to much to drink. There are other good uses for the nystagmus test as well.
I use the horizontal gaze nystagmus test as a part of the basic neurological exam that I do any time I’m uncertain of how well a patients brain is talking with their body. Head injuries, altered mentation, syncope, dizziness and headaches are some of the common complaints that make me want to check out how well the patients brain is doing its job. So this test gets pulled out of the tool box frequently. But what is nystagmus anyway? How do you really test for it and what does it tell you when you find it?
What is nystagmus?
Imagine that I took a large drum and I painted it white with black stripes running evenly down it. Then I set the drum on an axis and spun it slowly in one direction. As you watched the drum your eyes would focus on a black stripe and follow it across the surface of the drum until the stripe moved out of visual range. Then your eyes would jump backward to acquire a new stripe and follow it. This repetitive cycle of smooth eye pursuit interrupted by fast twitches (saccadic movement) is what we call nystagmus.
This peculiar tracking of the eye can be induced by spinning in a chair, riding on a roller coaster or observing a spinning object like in the example above (AKA Opticokinetic nystagmus). It can also be caused by a wide variety of medical and pharmocological conditions. Most causes of nystagmus point to an abnormal condition within the nervous system. It is a physical finding that calls us to pay attention and look deeper.
How do we assess for nystagmus?
The observe for nystagmus we need to present the patient’s eyes with a smoothly moving object and see if they are capable of tracking it with normal “smooth pursuit” ocular motion.
- First, make sure the patient knows what they’re supposed to be looking at … before you move it. It’s not helpful to have the patient’s eyes jumping around trying to figure out where they need to be looking. Hold up something small and specific. I’m usually holding my pen light while I’m doing my eye exam. It’s white. I also wear blue gloves. So I tend to hold out my pen light and poke my index finger just a half inch above it. Then I say something like, “Look right at the tip of my finger and don’t take your eyes off of it. Follow my finger with your eyes without moving your head.”
- I tend to place my other hand gently on the patient’s forehead to emphasize the point of not moving the head. If the patient can’t distinguish between eye movement and head movement that is a sign of possible significant impairment, however it is not positive nystagmus.
- Important point here. You need to move the object that the patient is focused on smoothly. Imagine that slowly rotating drum. Smooth motion back and forth within the patients visual range. If you zip the object back and forth like a fire fly you won’t be able to recognize nystagmus even if the patient does have it. You’re only going to see their eyes jump all over trying to track down your object.
- You can also move the object up and down at the midline (in front of the nose) to look for vertical nystagmus. I find vertical nystagmus harder to evaluate and less diagnostically useful than horizontal nystagmus.
- Keep in mind that everyone has mild nystagmus at the outer edges of their visual range. If you swing the object way out towards 90 degrees all patients will present with some nystagmus-like switches as their ocular muscles strain to keep the object in sight.
- It has been suggested that the onset of nystagmus within 50 degrees of midline (0 degrees) indicates a greater degree of impairment in our intoxicated and drug induced nystagmus patients. This study has never been duplicated.
Note the estimated angle of nystagmus onset
Yup, my patient has nystagmus. What does that mean?
Big picture … it means that there’s something abnormal about the patient’s nervous system. There are a few major reasons to consider.
Drugs and alcohol
Yes, that old roadside sobriety test is a useful indicator of alcohol intoxication. People begin having nystagmus with blood alcohol levelsas low as .04%. But alcohol isn’t the only drug that can cause nystagmus. Other central nervous system depressants like barbiturates, Lithium and benzodiazepines like Valium will also induce nystagmus. Some other prescription meds like SSRIs and Dilantin may be responsible as well.
One quick related note if you encountered the nystagmus test during a roadside sobriety test or you’re concerned about alcohol or drug addiction. Drug and alcohol detox centers are available and treatment centers can help.
Neurological and balance disorders
Disease processes that involve the nervous system can induce nystagmus. These include Multiple Sclerosis, Wernicke’s encephalopathy, brain tumors, ocular nerve or macular degeneration and stroke. Also, balance and inner ear disorders can be a culprit. Consider vertigo and Meniere’s Disease.
Idiopathic and congenital causes
Lastly, we should keep in mind that there are some benign and congenital causes of nystagmus. There are folks who just walk around with nystagmus and we don’t know why. Down Syndrome and Noonan Syndrome patients can have benign nystagmus. Some reports estimate as many as 1 in 5,000 adults have ongoing benign nystagmus without a known etiology.
Try putting a basic nystagmus evaluation in your neurological examination tool kit and see what you think. It’s useful for more than just roadside sobriety checks. It may help you catch something important about your patient.