Page last modified: August 24, 2020
Unscrupulous individuals sometimes produce unusual eye movements in an attempt to feign illness. Often this involves an attempt to use a "parlor trick" type of eye movement, in the hopes of winning disability, attention from a loved one, or a greater financial settlement from an insurance company or lawsuit.
As about 8% of the college age population can produce voluntary nystagmus, and as it is somewhat dramatic, voluntary nystagmus is a popular form of ocular malingering.
Supplemental material : Video of voluntary nystagmus.
The first movie is a very large file (27 meg) for a mere 20 seconds of nystagmus. The file needs to be large because it must use a fast frame rate and large screen size to capture the tiny/rapid movement. Note how the pupil constricts during the rapid horizontal shimmering. This man was asked to produce this nystagmus and he could do it at will.
Voluntary nystagmus can be detected fairly easily by watching for the characteristic pupillary constriction that accompanies the nystagmus.
Even more primative than blinking all the time (which might be attributed to anxiety), is wildly looking all over the place. When this is noticed when the patient is wearing the video goggles, but not when talking to you in the broad daylight, think -- why are they doing this ? Could it be to make it harder for me to diagnose them ? Could they be confusing nystagmus with looking all over the place ?
A variant on this is vertical square wave jerks. Horizontal square wave jerks are common. Vertical, very rare.
Convergence and Blinking:
Unsophisticated malingerers often adopt a strategy based on making things difficult for the examiner, apparently in the hope that he/she will give up and accept the malingerer's story. While the person may appear perfectly normal when not being examined, as soon as they sit on the exam table, there suddenly is a paroxysm of blinking, generally attributed to light sensitivity. However, this behavior does not vanish in the dark (under video Frenzel goggles), but generally becomes even more pronounced as they perceive a greater threat of discovery.
Eye crossing (convergence) is often also displayed. The eyes will suddenly dive inward, accompanied by pupillary constriction, for no obvious reason, or the person may choose to cross their eyes only in particular situations, such as positional testing or on being asked to track. These patterns are harder to spot. A clue is that the pupils constrict when the strange oculomotor behavior is being displayed.
Rarely convergence excess accompanied by pupillary constriction can be due to an organic cause, but we know of no organic disorder that combines blinking and convergence.
Alcohol Induced Positional Nystagmus:
Occasionally one can be confused by the very strong horizontal direction changing positional nystagmus that accompanies extreme inebriation. This can closely resemble lateral canal BPPV. This is most easily detected by a blood alcohol level. Another strategy is to simply wait until the alcohol distributes into the inner ear -- have the patient sit out in the waiting room for a couple of hours and then re-examine. Alcohol induced positional nystagmus does not fatigue like BPPV, but this is not always a reliable sign. As alcohol is a cerebellar toxin, positional alcohol nystagmus is accompanied by ataxia, poor pursuit and gaze evoked nystagmus.
With a little practice, most people with latent nystagmus, a type of congenital nystagmus, can learn to look out of either eye, and produce a nystagmus at will, as well as sometimes one that can be made to go in either direction. Needless to say, this can be very alarming to their physicians. The clue here is that these people will have decreased vision in one eye (amblyopia) and esophoria or esotropia.
Supplemental material : Video of latent nystagmus
There are also other persons with other types of congenital nystagmus who can turn it on and off at will. These people are rare and difficult to spot.