NYSTAGMUS IN NORMAL PERSONS
C. Hain, MD
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March 9, 2021
Nystagmus is involuntary movement of the eyes. A little bit of nystagmus is common in otherwise normal subjects, and as equipment has improved in recent years to register nystagmus, smaller amounts of nystagmus can now be detected. Below we are discussing jerk nystagmus only.
There have been just a few studies of nystagmus in normal subjects over the years. There also also often been studies of evoked nystagmus, wherein a baseline recording of nystagmus is reported. This has resulted in a general opinion that normal subjects have little to no nystagmus, when looking straight ahead in the dark. There is also a general impression that there can be small amounts of positional nystagmus elicited by supine, head-right or head-left. The general opinion is that nystagmus in the light is not normal.
The degree of nystagmus that is considered "OK" has gone down over time, as methodology has improved. In the past, 5 deg/sec of nystagmus was accepted as normal when using "ENG" methods. These are now obsolete. With the newer infrared video systems, a typical value is just 2 deg/sec. It is also generally felt that horizontal nystagmus is more acceptable than vertical or torsional. In the authors opinion, there are roughly 10 times as many people having horizontal nystagmus (defined as 2 deg/sec or more) as vertical nystagmus. Torsional nystagmus is difficult to see and nearly impossible to quantify. The author's opinion is that torsional spontaneous nystagmus in the upright position is about 1000 times less common than even horizontal nystagmus. Supine, we think about 10 times less common than vertical nystagmus, and 100 times less common than horizontal. Accordingly,, when torsional nystagmus is seen upright, the clinician generally assumes that there a very unusual pathology such as a CNS lesion or congenital nystagmus. When positional torsional nystagmus is seen, the clinician usually assmes a some pathology (such as BPPV).
Studies of "normal" spontaneous nystagmus:
- Geisler et al (2000), using video recordings in 25 normal subjects, reported "Two subjects had spontaneous nystagmus, but nystagmus after head-shake was not found in any. No subject had torsional nystagmus in the Dix-Hallpike positions. In the elderly subjects horizontal nystagmus in head hanging position was a frequent finding."
- Grohman and Meissner (1983) reported "In the observation of a nystagmus in registration corresponding to the fluorescent spectacles, a definite nystagmus was registered in less than 10% of the normal subjects. In visual fixation, this number was reduced to less than 5%. The results of these registrations do not justify postulation of a physiological spontaneous nystagmus. " Here we think the most important word is "definate".
- Mulch, G. and W. Lewitzki (1977). Made an opposite conclusion: "When the ENG was registered with open eyes in darkness, 63 out of the 102 test persons had a horizontal spontaneous or positional nystagmus, however, under the Frenzel glasses there was a nystagmus in only 2 out of these test persons. With open eyes in darkness, the frequency and intensity was the same in all age groups. With this, we believe to have proved that a physiological horizontal vestibular nystagmus does exist." These authors combined upright and positional ("spontaneous or positional"), and used a noisy method (ENG). We think that there is some truth to this paper in that there often is some nystagmus in normal subjects, but the 63/102 figure seems a bit high to us.
- Takahashi, J., et al. (1996). These authors used ENG which has more noise than video methods. They found "Spontaneous nystagmus was detected in 5 (16.7%) of 30 subjects." This is reasonable but this method is now obsolete.
Not so reasonables studies:
Young et al (2020), using a portable system of their own design, recently reported on this question. Recordings were made at home. They stated that "there was no lower limit placed on the nystagmus SPV (slow phase velocity". They studied 101 subjects, with a mean age of 44. They found small (i.e. about 1 deg/sec) amounts of nystagmus in about 30.7% of these subjects. As they had no lower limit for SPV, we are not entirely clear how they came up with the 30.7% number, as one would think that there might be people with, lets say, 0.01 deg/sec of nystagmus, and likely rather few with 0.0 deg/sec of nystagmus.
A small amount of positional nystagmus (mean of 2.2 deg/sec) was registered in more than 50% of subjects, and in fact 11 (normal) subjects displayed persistent positional nystagmus with velocities > 10 deg/sec. We wonder if these subjects were looking straight ahead.
- Geisler, C., et al. (2000). "Nystagmus findings in healthy subjects examined with infrared videonystagmoscopy." ORL J Otorhinolaryngol Relat Spec 62(5): 266-269.
- Grohmann, R. and R. Meissner (1983). "[Evaluation of electronystagmographically registered spontaneous nystagmus in healthy persons]." Laryngol Rhinol Otol (Stuttg) 62(11): 508-511.
- Likhachev, S. A. and I. P. Mar'enko (2010). "[Spontaneous and provoked nystagmus in healthy subjects: on the so-called "vestibular" form]." Vestn Otorinolaringol(6): 21-25.
- Mulch, G. and W. Lewitzki (1977). "Spontaneous and positional nystagmus in healthy persons demonstrated only by electronystagmography: physiological spontaneous nystagmus or "functional scar"?" Arch Otorhinolaryngol 215(2): 135-145.
- Takahashi, J., et al. (1996). "Spontaneous nystagmus in normal subjects." ORL J Otorhinolaryngol Relat Spec 58(1): 42-45.
- Young, A. S., et al. (2020). "Nystagmus characteristics of healthy controls." J Vestib Res 30(6): 345-352.