Involuntary "Voluntary" Nystagmus

Voluntary nystagmus is a common phenomenon in the general population and is believed to be under voluntary control. Some patients have an eye movement disorder indistinguishable from voluntary nystagmus and yet have no control over these movements.

Original Contribution Section Editors: Clare Fraser, MD Susan Mollan, MD Involuntary “Voluntary” Nystagmus Michael L. Rosenberg, MD Background: Voluntary nystagmus is a common phenomenon in the general population and is believed to be under voluntary control. Some patients have an eye movement disorder indistinguishable from voluntary nystagmus and yet have no control over these movements. Methods: Four patients with involuntary eye movements consisting of spontaneous or induced bursts of saccadic eye movements with no intersaccadic interval are described. All eye movements were typical of “voluntary nystagmus,” yet they denied any control over the movements. In none of the patients was there any evidence of psychopathology or secondary gain. Results: Two types of patients with involuntary eye movements that were indistinguishable from voluntary nystagmus are presented. One group of 2 patients had clear neurological disease, whereas another 2 had no evidence of any neurological pathology. Conclusions: The patterns seen in these patients suggest that there is a spectrum of oculomotor saccadic instabilities that includes voluntary nystagmus on one extreme and ocular flutter on the other. In between these 2 are both normal and abnormal patients with eye movements indistinguishable from ocular flutter/voluntary nystagmus that may or may not be induced by convergence. It is suggested that involuntary “voluntary nystagmus” is a real condition and that psychopathology should be ruled in rather than simply assumed. Journal of Neuro-Ophthalmology 2021;41:e688–e691 doi: 10.1097/WNO.0000000000001196 © 2021 by North American Neuro-Ophthalmology Society V oluntary nystagmus is a common eye movement phenomenon that is said to occur in at least 8% of the normal population (1). The eye movements consist of a series of end on end saccades without any intersaccadic interval. It is considered to be under voluntary control. Patients reported in the literature as having voluntary nystagmus have generally fallen into one of 2 groups: subjects New Jersey Neuroscience Institute, Edison, NJ. The authors report no conflicts of interest. Address correspondence to Michael L. Rosenberg, MD, New Jersey Neuroscience Institute, 65 James Street, Edison, NJ 08818; E-mail: [e-mail] e688 who have learned or discovered that they have the ability to wiggle their eyes rapidly at will and another group who report no ability to control the movements. The latter are often suspected as being malingerers (1). It is suggested that involuntary “voluntary nystagmus” is a real condition and that psychopathology should be ruled in rather than simply assumed. METHODS Four patients are described with an eye movement disorder indistinguishable from voluntary nystagmus. All, however, denied having any control over the movements. None had any evidence of psychopathology or apparent secondary gain from the intermittent eye movements. RESULTS Normal Patients With Convergence-Induced “Voluntary Nystagmus” Case 1 A 21-year-old man, without any history of neurological, ophthalmologic, or psychological problems, developed intermittent oscillopsia which usually occurred while playing basketball. He was attending a technical school at the time and was doing very well. There were no identifiable stressful aspects to his life. He denied ever being aware of such symptoms in the past. On examination, there were no abnormalities except intermittent rapid end on end saccadic oscillations. His symptoms were present only during these oscillations, and they could be induced by having the patient converge. The spells would last 10–20 seconds and resolve spontaneously. He was asked to try and control the movements. After a week, he said he could induce the movements by following his fingers in toward his nose. He could not otherwise spontaneously induce the movement voluntarily nor could he prevent the episodes that occurred spontaneously. Electroencephalogram (EEG), visual evoked responses, and computed tomography (CT) scan were performed and were Rosenberg: J Neuro-Ophthalmol 2021; 41: e688-e691 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution normal. There was no attempt to use this abnormality to avoid any responsibilities. He concluded his schooling without problems. The only effect seemed to be decreased time in sports, an activity he enjoyed. Case 2 A 76-year-old woman was being seen in the neurology clinic for migraine headaches. As part of the routine examination, convergence was tested. Marked convergence induced a 5 second episode of saccadic oscillations typical of voluntary nystagmus. The patient appeared astonished and somewhat concerned. She asked “what happened?” On further questioning, she denied ever having had the sensation previously. She did not remember ever trying to cross her eyes as a child. The phenomenon could be repeated, although not every attempt at strong convergence induced a burst of eye movement. She said that the sensation was unpleasant and was associated with a significant oscillopsia. The patient had no obvious psychopathology and was not a management problem regarding her headaches. No secondary gain was apparent. She continued to be followed in the neurology clinic for several years on a routine basis with good control of her migraines and no change in her neurological condition. When seen by other physicians, the eye movements were often not documented in the notes. Over the 4– 5 years, she was seen by this author, on each occasion the movements could be induced with strong convergence. They were never noted to occur spontaneously. She did not like it and did not want it performed more than once per visit. She consistently denied any ability to bring on or stop the movements. No secondary gain was ever sought. Patients With Neurological Disease and Convergence-Induced “Voluntary Nystagmus” Case 3 A 23-year-old man was in excellent health until 2 weeks before admission, when he developed headaches and fever. The fever resolved but the headache continued. Examination was totally normal with the exception of a minimal decrease in elevation of the eyes and intermittent ocular oscillations typical of voluntary nystagmus. The bursts of eye movements were always preceded by a convergence movement and consisted of 10–30 seconds of back-to-back saccadic oscillations. The movements were associated with a marked oscillopsia. There was no suggestion of ataxia or other cerebellar signs. He stated that he was unaware of ever having had such eye movements in the past, either voluntary or involuntary. He vehemently denied any voluntary control over the current eye movements. Although an initial CT scan suggested a possible abnormality of the midbrain, a repeat study confirmed that the changes were artifactual. Based on the voluntary nystagmus–like eye movements, consisting of bursts of spontaneous end-to-end saccades Rosenberg: J Neuro-Ophthalmol 2021; 41: e688-e691 confirmed by eye movement recordings, he was initially believed to have a totally functional disorder. However, an EEG showed diffuse slowing in the theta range with occasional delta activity. A repeat EEG, a week later, was slightly slow with a background alpha rhythm of 7–8 Hz. One week later, the background rhythm was 9 Hz. A final EEG performed 2 weeks thereafter had a background rhythm of 10–11 Hz. At no time during his admission was he given any medications. During his hospitalization, the eye movements became more and more difficult to induce with convergence, and 5 weeks after the onset of his illness, no such movements could be induced at all. His family strongly denied any knowledge of his being able to move his eyes in any abnormal fashion. One year after discharge, he and his wife (in separate conversations) both denied any further episodes of unusual eye movements either voluntary or nonvoluntary. Case 4 A 32-year-old woman had been followed for several years in the neurology clinic for migraine headaches. They were well controlled, and she was seen on a yearly basis. When first seen for the headaches in by a general neurologist, she noted on review of systems that she had oscillopsia most of the time whenever she watched a moving target. A “shimmering nystagmus” was noted on examination. Workup for this problem included CT scan, EEG, pattern reversal visualevoked responses, and brainstem auditory–evoked responses, which were all normal. No diagnosis was made. She was seen thereafter on an annual basis for her migraine headaches. There was no suggestion that she ever pressured any of her physicians to evaluate this sign, and in fact over the next several years, it was mentioned only intermittently and in passing by the doctors in the records. No further tests were performed. Six years later, she was first seen by the author in routine follow-up for her headaches. The examination was normal with the exception of intermittent bursts of end on end saccades that would come on for varying time periods. She stated that she had no control over the movements. Based on the resemblance to voluntary nystagmus, she was informed that the movements were typically capable of being controlled. She was asked to try to control them voluntarily. After several weeks, she stated that she had tried but was been unable to prevent their occurrence. She noted that on most but not all attempts at convergence would induce an episode. Eye movement recordings confirmed the saccadic nature of the oscillations and the lack of an intersaccadic interval. The duration was typically short, but during sustained convergence, the movements could continue for long periods. One such episode was documented to last 10 minutes at which point the patient requested we stop. Although frequently induced with convergence, this was not necessarily present at the commencement of an episode. Pursuits would also often induce of the saccadic movements. There were no other e689 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution signs or symptoms of cerebellar disease nor any suggestion of secondary gain. When contacted by phone 10 years later, the patient stated that she had been diagnosed with clinically definite multiple sclerosis. DISCUSSION Oculomotor instabilities in the horizontal plane caused by unwanted saccades are classified on the basis of their intersaccadic intervals. Those with an intersaccadic interval are termed square wave jerks. Both ocular flutter and voluntary nystagmus show horizontal end on end saccades with no intersaccadic interval and are indistinguishable by eye movement recordings (1). They are usually distinguished by the types of associated abnormalities. Other evidence of cerebellar dysfunction by history, physical examination, or radiological evaluation is typically seen in patients with ocular flutter. By contrast, subjects with voluntary nystagmus have an otherwise normal examination. Zahn reviewed several other features from the literature that had been believed by various authors to distinguish voluntary nystagmus from “organic pathology.” (1) These include initiation only by convergence, presence only in the primary position, the inability to initiate the movements behind closed lids, conjugacy of the movements, inability to sustain the movements for more than a short time, larger amplitude, and higher velocity. Overall, the only feature he found that might best distinguish physiologic voluntary nystagmus from pathologic conditions was the duration. He mentions that subjects with voluntary nystagmus “on average” cannot continue the movements for more than 25 seconds (1). As neither pathologic flutter nor normal involuntary nystagmus are typically continuous for nearly this long, this finding would seem potentially useful as a screening test to separate an incidental finding of voluntary nystagmus from malingering in a patient who does not admit to being able to control his spells, but it would have clearly misclassified our last patient. Many of the articles written about this problem have emphasized that the disorder is voluntary and suggest that the patient who complains of symptoms from this is either hysterical or malingering (1,2) This would not, however, explain the findings in all cases as a number have been reported with clearly documented voluntary nystagmus yet still complained of additional episodes that were involuntary and symptomatic (3,4). Two such patients with involuntary spells of spontaneous “voluntary nystagmus” were treated successfully with base out prisms and + lenses (5,6). There are other cases in the literature similar to the above 4 patients, who were reported in the literature as having voluntary nystagmus but denied having any voluntary control of their eye movements (2,3). Although some had evidence of possible secondary gain, others did not. Although the authors assumed it was under voluntary cone690 trol, this remains unclear and nearly impossible to improve. It is therefore unknown how many of these patients truly had “voluntary” nystagmus that was under voluntary control. In none of our cases was there any suggestion of secondary gain. It is important to note that the family members of some of the patients in the literature, and in our case number 3, were unaware of the patients’ ability to move their eyes in an unusual way (7). One would suspect that it to be more typical for the patient to have used their abilities to amuse their friends and family by demonstrating their abilities, rather than to keep it as a hidden secret. Our case number 3 had all the parameters which have been said to suggest voluntary nystagmus. Spells seemed to be initiated by convergence and could only be sustained for short periods. In fact, the patient was initially diagnosed as having psychogenic voluntary nystagmus. However, neither the patient’s parents nor his wife was at all aware of any unusual eye movements before the hospitalization nor were any present afterward. The association of the headaches, fever, abnormal EEG, and improvement of the EEG coincident with and proportionate to the disappearance of the voluntary nystagmus–like eye movements clearly support a diagnosis of benign encephalitis with ocular flutter rather than a psychogenic origin. Other findings suggestive of a functional disorder might include frequent visits to the doctor; missed work, and emphasizing the disability to the physician. Our case numbers 2 and 4 were followed with migraines for several years. Only minimal symptoms related to the unusual eye movements were mentioned to the doctors during clinic visits. No additional attention had been paid to it after the initial neuro-ophthalmological evaluations. Again, had the nystagmus been voluntary, it seems much more likely that the patients would have used it to attract more attention by complaining more significantly or demanding further evaluation. The eye movements of voluntary nystagmus and those of ocular flutter are, as mentioned previously, indistinguishable by eye movement recordings, both showing end on end saccades. It is well known that while fixating a target, omnipause neurons are constantly inhibiting bursts cells. When uninhibited these bursts cells stimulate cells in the abducens nucleus and thereby generate a saccade. Shaikh et al have proposed that the sudden inhibition of omnipause cells needed to generate a saccade results in a rebound increase in the firing rate of the burst cells, potentially increasing the velocity of the saccade. They further postulate that this rebound increase in firing may lead to an imbalance between the excitatory input from burst cells and the inhibitor input from omnipause cells. This could in turn result in abnormal saccadic oscillations (8). Omnipause neurons are suppressed not only with saccades in any direction but also with saccade-related vergence movements (9). This would explain the Rosenberg: J Neuro-Ophthalmol 2021; 41: e688-e691 Copyright © North American Neuro-Ophthalmology Society. Unauthorized reproduction of this article is prohibited. Original Contribution FIG. 1. The spectrum of saccadic bursts. phenomena in both our normal and abnormal subjects as all had episodes induced by convergence. When convergence is tested clinically, little care is taken to insure that the eyes and both the near and far fixation points are perfectly aligned. Thus, although the clinician is attempting to evaluate only convergence when requiring the patient to look from distance to near, the likelihood that the 2 targets are perfectly aligned would be near zero. Thus, clinically looking at a near target is very likely to also require a superimposed saccade and therefore an increased likelihood of suppression of omnipause neurons and abnormal oscillations. It is conceivable, if not expected, that some people would have more “inhibitable” pause cells than average. This would explain the clinical spectrum described in this article of patients’ ability to influence these cells. A normal subject, in whom neither the subject normal the examiner, can elicit bursts of saccades is on one end of the spectrum. An abnormal patient with posterior fossa dysfunction who has uncontrollable episodes of ocular flutter would be on the other. Near the “normal” end are normal people with no spontaneous spells but in whom convergence can inhibit the pause cells and elicit the movements. Near the opposite end are patients with neurologic disease and no spontaneous bursts of saccades but in whom convergence and other eye movements such as voluntary saccades or pursuits can induce them (Fig. 1). It has always been assumed that all patients with “voluntary nystagmus–like eye movements” without evidence of Rosenberg: J Neuro-Ophthalmol 2021; 41: e688-e691 cerebellar problems have simple voluntary nystagmus. If such a patient said that he or she could not control their eye movements, it was assumed that the patient must be trying to deceive their physician and therefore was either malingering or hysterical. This is too simplistic an approach. Malingering must be a diagnosis confirmed by evidence of secondary gain and not thrust on a person because his eye movements are similar to those that can be duplicated by other “normal” patients. Such a mistake has been made repeatedly with other movement abnormalities such as dystonia and blepharospasm and should not be repeated in patients with unusual eye movements. REFERENCES 1. Zahn JR. Incidence and characteristics of voluntary nystagmus. J Neurol Neurosurg Psychiatry. 1978;41:617–623. 2. Coats AC, McCrary JA. Voluntary nystagmus masquerading as Tullio’s phenomenon. Arch Otolaryngol Head Neck Surg. 1979;105:288–289. 3. Jarrett A, Emery JM, Coats AC, Justice J Jr. Voluntary nystagmus. Ann Ophthalmol. 1977;9:853–859. 4. Cuiffredo KJ. Voluntary nystagmus: new findings and clinical implications. Am J Optom Physiol Opt. 1980;57:795–800. 5. Carlow TJ. Medical treatment of nystagmus and ocular motor disorders. Int Ophthalmol Clin. 1986;26:251–264. 6. Neppert B, Rambold H. 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