By Marcello Cherchi, MD PhD
For patients
Drinking alcohol can cause short-term problems within minutes to hours, including problems with eye movements and balance; these effects are reversible by stopping alcohol intake. Drinking alcohol frequently and over a long period of time can cause permanent damage to parts of the nervous system that help maintain equilibrium.
For clinicians
Overview
Ethanol (the form of alcohol consumed by humans) has a broad range of short-term and long-term physiologic effects across multiple organ systems. From the otoneurological perspective, acute alcohol intoxication can affect a broad range ocular motor functions, including the vestibulo-ocular reflex, semicircular canal function, the velocity storage mechanism, optokinetic nystagmus, tracking, visual fixation suppression, saccades (saccadic velocity, pro-saccades and anti-saccades), smooth pursuit (including its gain and velocity), and post-rotatory nystagmus; it can also cause positional alcohol nystagmus, alcohol gaze nystagmus and spontaneous down beat nystagmus; finally, it can impair visual processing tasks such as motion parallax and depth perception. Acute alcohol intoxication also impairs cerebellar function. On computerized dynamic posturography, acute alcohol intoxication increases body sway. Longer-term effects of alcohol include damage to the cerebellum, cerebral white matter and peripheral nerves. Chronic alcoholism can cause lesions in the mammillary bodies, resulting in Wernicke-Korsakoff syndrome.
Introduction
Ethanol is the form of alcohol consumed by humans. Some of the effects of alcohol, particularly on cognition, have been recognized for millennia. But alcohol has a rather broad range of physiologic effects across multiple organ systems (Birkova et al. 2021). Robert Barany was one of the first vestibular physicians to study the otologic and neurologic effects of acute alcohol intoxication (Bárány 1911; Bárány and Rothfeld 1913). Here we will discuss some of the vestibular, ocular motor and neurological consequences of alcohol toxicity.
Acute alcohol intoxication: Ocular motor findings
Many articles describe the acute effects of alcohol on the ocular motor system (Aschan 1958; Howells 1952, 1956; Jozefowicz-Korczynska, Lukomski, Kurnatowski 1994; Umeda and Sakata 1978).
Alcohol can affect semicircular canal function (Money, Johnson, Corlett 1965). It can also affect otolith function (Hafstrom et al. 2007), though perhaps this effect is greater on ocular vestibular evoked myogenic potentials than for cervical vestibular evoked myogenic potentials (Rosengren et al. 2014).
Acute effects of alcohol can impair a variety of eye movements, including the function of the velocity storage mechanism (Choi et al. 2022), optokinetic nystagmus (Baloh et al. 1979; Mizoi, Hishida, Maeba 1969; Schroeder 1972), tracking (Schroeder et al. 1973), visual fixation suppression of vestibularly-driven nystagmus (Barnes 1984; Guedry et al. 1975; Harder and Reker 1995; Takahashi et al. 1989), saccadic velocity (Baloh et al. 1979; Roche and King 2010), both pro-saccades and anti-saccades (Roche and King 2010), smooth pursuit (Guedry et al. 1975; Takahashi et al. 1989), smooth pursuit gain (Roche and King 2010), the smooth pursuit velocity (Baloh et al. 1979; Barnes 1984), and post-rotatory nystagmus (Karlovsek and Balazic 2005).
Numerous studies have reported that acute alcohol intoxication can impair the vestibulo-ocular reflex (VOR) (Martellucci et al. 2021; Tianwu et al. 1995). One study (Choi et al. 2022) reported that mid-frequency VOR gain (as measured by slow harmonic acceleration in rotatory chair testing) was unaffected, whereas high-frequency VOR gain (as measured by video head impulse testing) was reduced, and time constants (as measured by step velocity testing in rotatory chair testing) were reduced.
A specific ocular motor abnormality related to acute alcohol intoxication is positional alcohol nystagmus, sometimes abbreviated PAN (Bergstedt and Kus 1968; Harris, Guedry, Graybiel 1962). (The reader should be aware that, somewhat confusingly, the phenomenon of periodic alternating nystagmus is also abbreviated PAN, though it is an entirely different pathology.) The underlying mechanism of positional alcohol nystagmus (PAN) is incompletely understood (Aschan and Bergstedt 1975; Han et al. 2020; Money, Johnson, Corlett 1965; Oosterveld 1973), but may be a consequence of the differential effect of alcohol on the specific gravity of endolymphatic fluid versus perilymphatic fluid. The manifestation of PAN goes through different phases depending on the latency from alcohol ingestion (Hill, Collins, Schroeder 1973; Odkvist 1975). PAN can be modulated by gravity (Oosterveld 1970) and other linear acceleration (Oosterveld, Meineri, Paolucci 1974).
Acute alcohol intoxication can also cause spontaneous down beat nystagmus (Costin et al. 1980; Zasorin and Baloh 1984) and “vertical velocity offset” (Fetter et al. 1999).
One paper suggested that alcohol leads to a “disturbance of the visual-oculomotor system” as a mechanism underlying poor performance on dynamic visual acuity testing (Schmal, Thiede, Stoll 2003).
One paper explored the effect that acute alcohol intoxication has on slow eye movements and concluded that this is the mechanism by which alcohol impairs motion parallax and thus depth perception (Nawrot, Nordenstrom, Olson 2004).
It has been observed that acute alcohol intoxication can affect the nystagmus evoked at the extremes of lateral gaze, and this was the basis for the so-called “alcohol gaze nystagmus” test (Goding and Dobie 1986) which has been used by law enforcement for some years as a proxy for blood alcohol concentration (Good and Augsburger 1986; Halperin and Yolton 1986). The pattern of alcohol gaze evoked nystagmus can resemble that of cerebellar degenerative processes (Romano et al. 2017). However, it appears that, for example, police officers certified in this technique do not always adhere to the guidelines and requirements for administering this test (Booker 2001). The validity of this test for law enforcement purposes has also come under scrutiny (Booker 2004).
The acute effects of alcohol on level of alertness are variable; some individuals find alcohol to be sedating, while others experience it as stimulating. The ocular motor effects of acute alcohol intoxication appear to be independent of the subjective state of sedation/stimulation (Holdstock and de Wit 1999).
It should also be pointed out that a minority of literature has concluded that, “there was no significant correlation between duration of alcohol dependence and abnormal ENG [electronystagmography]” (Verma et al. 2006).
Acute alcohol intoxication: posturographic findings
Some papers refer rather vaguely to the effects that acute alcohol intoxication can have on an individual’s balance (Belle, Sartori Sdo, Rossi 2007). Other papers have studied this more objectively, observing that acute alcohol intoxication tends to increase body sway, as measured by stabilometry (a form of posturography) (Kubo et al. 1990) and computerized dynamic posturography (Choi et al. 2022; Ledin and Odkvist 1991; Nieschalk et al. 1999).
Acute alcohol intoxication: cerebellar toxicity
Alcohol can affect numerous areas in the central nervous system. The cerebellum appears especially vulnerable to the effects of alcohol (Alekseeva et al. 2014).
Alcohol also, “delays the conduction of electric signals from the central nervous system to the muscles controlling posture and impairs the integration of sensory inputs required for maintaining vertical stance. Consequently, alcohol intoxication delays the ability to detect postural changes and enact the appropriate response” (Vassar and Rose 2014).
Longer-term effects of alcohol
Alcohol can also have longer-term deleterious consequences for ocular motor function (Nsamba and al-Marashi 1972), presumably due to permanent damage from the longer-term toxic effects of alcohol. However, there is also some evidence that several of the longer-term ocular motor sequelae of chronic alcoholism can improve over several years of abstinence (Sasa et al. 1981).
The cerebellum appears to be selectively vulnerable to the effects of chronic alcohol use. The mechanism of cerebellar dysfunction appears to involve impairment of synaptic plasticity of cerebellar Purkinje cells (Valenzuela, Lindquist, Zamudio-Bulcock 2010), and death of Purkinje cells and granule cells (Luo 2012).
Chronic alcohol use can cause damage in other areas of the central nervous system relevant for balance beyond cerebellar atrophy, including loss of cerebral white matter and peripheral nerves (de la Monte and Kril 2014).
There is modest evidence that alcohol can impair recovery from vestibular lesions (Zingler et al. 2004).
Acute on chronic manifestations: Wernicke-Korsakoff syndrome
The mamillary bodies are selectively vulnerable to thiamine deficiency, and chronic alcohol use often results in thiamine deficiency. Thiamine deficiency develops gradually, but beyond a certain threshold, its clinical effects may manifest abruptly in the form of Wernicke-Korsakoff syndrome. Relevant to equilibrium, Wernicke-Korsakoff syndrome can manifest with several eye movement abnormalities, including in the vestibulo-ocular reflex, gaze-evoked nystagmus, and ocular motor paresis (Kattah 2017; Kattah et al. 2013).
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