Eye movements in cocaine abusers

The Effects of Substance Misuse on Auditory and Vestibular Function: A Systematic Review

BACKGROUND

Chronic substance misuse is an ongoing and significant public health concern. Among a myriad of health complications that can occur, substance misuse potentially causes ototoxic effects. Case reports, retrospective chart data, and a few cohort studies suggest that certain prescription opioids and illicit drugs can have either temporary or permanent effects on auditory and/or vestibular function. Given the steady rise of people with a substance-use disorder (SUD), it is of growing importance that audiologists and otolaryngologists have an insight into the potential ototoxic effects of substance misuse.

OBJECTIVES

A systematic review was conducted to (1) synthesize the literature on the illicit drugs, prescription opioids, and alcohol misuse on the auditory and vestibular systems, (2) highlight common hearing and vestibular impairments for each substance class, and (3) discuss the limitations of the literature, the potential mechanisms, and clinical implications for clinicians who may encounter patients with hearing or vestibular loss related to substance misuse, and describe opportunities for further study.

DESIGN

Systematic searches were performed via PubMed, Scopus, and Google Scholar, and the final updated search was conducted through March 30, 2022. Inclusion criteria included peer-reviewed articles, regardless of study design, from inception until the present that included adults with chronic substance misuse and hearing and/or vestibular complaints. Articles that focused on the acute effects of substances in healthy people, ototoxicity from already known ototoxic medications, the relationship between hearing loss and development of a SUD, articles not available in English, animal work, and duplicates were excluded. Information on the population (adults), outcomes (hearing and/or vestibular data results), and study design (e.g., case report, cohort) were extracted. A meta-analysis could not be performed because more than 60% of the studies were single-case reports or small cohort.

RESULTS

The full text of 67 studies that met the eligibility criteria were selected for the review. Overall, 21 studies reported associations between HL/VL related to illicit drug misuse, 28 studies reported HL/VL from prescription opioids, and 20 studies reported HL/VL related to chronic alcohol misuse (2 studies spanned more than one category). Synthesis of the findings suggested that the misuse and/or overdose of amphetamines and cocaine was associated with sudden, bilateral, and temporary HL, whereas HL from the combination of a stimulant and an opioid often presented with greater HL in the mid-frequency range. Reports of temporary vertigo or imbalance were mainly associated with illicit drugs. HL associated with misuse of prescription opioids was typically sudden or rapidly progressive, bilateral, moderately severe to profound, and in almost all cases permanent. The misuse of prescription opioids occasionally resulted in peripheral VL, especially when the opioid misuse was long term. Chronic alcohol misuse tended to associate with high-frequency sudden or progressive sensorineural hearing loss, or retrocochlear dysfunction, and a high occurrence of central vestibular dysfunction and imbalance.

CONCLUSIONS

Overall, chronic substance misuse associates with potential ototoxic effects, resulting in temporary or permanent hearing and/or vestibular dysfunction. However, there are notable limitations to the evidence from the extant literature including a lack of objective test measures used to describe hearing or vestibular effects associated with substance misuse, small study sample sizes, reliance on case studies, lack of controlling for confounders related to health, age, sex, and other substance-use factors. Future large-scale studies with prospective study designs are needed to further ascertain the role and risk factors of substance misuse on auditory and vestibular function and to further clinical management practices.

Effects of Antisocial Personality, Cocaine and Opioid Dependence, and Gender on Eye Movement Control

Substance-dependent patients have been reported to exhibit abnormal smooth pursuit and saccadic eye movements. However, contrasts of the effects of different substances and the effects of comorbid psychiatric symptoms such as antisocial personality have rarely been performed. Separate analyses examined the effects of cocaine dependence, opioid dependence, or antisocial personality disorder. In each analysis, sex was included as an additional grouping factor. The dependent measures were the gain of smooth pursuit eye movement and the delay and accuracy of saccadic eye movement. Analyses of covariance indicated that both cocaine dependence and antisocial personality, but not opiate dependence, were associated with a significant reduction in gain of smooth pursuit eye movement. Cocaine dependence and antisocial personality also slowed the onset of saccadic eye movements, but only in men. No group differences were found in the accuracy of saccadic eye movements. The results suggest that the neurophysiological effects of cocaine dependence and antisocial personality overshadow the effects of heroin. The significance of these findings for visual attention and reading skill has yet to be assessed.

Biological markers of cocaine addiction: implications for medications development

The search for effective medications for cocaine addiction has been elusive. The failure to find such medications so far could be due to poor understanding of the underlying biology both in the premorbid condition and following the disease state of chronic cocaine use. Population heterogeneity could be a major factor in response to medications. In an attempt to highlight the issue of biomarkers we reviewed physiological, neuroendocrine and neuroimaging studies to identify specific biological changes/markers that could be used to characterize subgroups among chronic cocaine users. Merging the biology within medications studies of cocaine abusers could prove useful for targeting specific pharmacological agents to subgroups of patients, prediction of response to medication and relapse to use.

Smooth pursuit eye movement dysfunction in substance-dependent patients: mediating effects of antisocial personality disorder

Smooth pursuit eye movements were evaluated in 21 healthy volunteers and 126 patients meeting criteria for one of the following DSM-III-R dependence diagnoses: alcohol (n = 10), cocaine (n = 44), heroin (n = 34), or dual alcohol and cocaine (n = 38). A significant reduction in tracking accuracy was found in the heroin and the dually dependent groups relative to controls. Interestingly, the eye movement dysfunction in the drug-dependent groups was no longer detectable when the effects of antisocial personality disorder were statistically removed. The magnitude of the dysfunction also correlated with several antisocial personality-related features, including an increased number of criminal charges and months of incarceration, increased problems associated with drug abuse, and lower intellectual functioning. The relationship demonstrated presently between antisocial personality disorder and eye movement dysfunction may have implications beyond studies of substance dependence.

Effects of vestibular and cerebellar deficits on gaze and torso stability during ambulation

We measured gaze, head, and torso stability during ambulation to determine how vestibulo-ocular reflex dysfunction caused by unilateral vestibulopathy, bilateral vestibulopathy, and cerebellar dysfunction might affect image stabilization on the retina. Subjects were tested during standing, walking, and running on a treadmill. Gaze velocity, vestibulo-ocular reflex gain, and head velocities were calculated from angular positions of the eye and head, as well as linear positions of the head and trunk. Mean gaze velocity with a visible, distant target was below 4 degrees /second for all measurement conditions in control and vestibulopathic subjects. The performance of unilaterally vestibulopathic subjects was indistinguishable from that of control subjects except that the former had less vertical translation during walking. Bilaterally vestibulopathic subjects demonstrated less head translation than control subjects but had higher gaze velocity. In subjects with cerebellar dysfunction, gaze velocity was elevated by pathologic nystagmus, but head movements were similar to those of control subjects.

Anticipatory smooth eye movements of high velocity triggered by large target steps: normal performance and effect of cerebellar degeneration

We studied frequencies and dynamic characteristics of anticipatory smooth eye movements (ASEM) in humans who were tracking step target movements of 20-70 deg amplitude. During presentation of periodic steps of constant amplitude healthy subjects showed frequent high velocity ASEM reaching maximal peak velocities of 5-40 deg/sec. There was no effect of ASEM on the frequency of anticipatory saccades. Randomization of target step amplitude or onset reduced the frequency of ASEM but did not completely abolish fast ASEM. In patients with cerebellar degeneration who exhibited impaired smooth pursuit, fast ASEM were absent and the number of slow ASEM was minimal. In conclusion, large sequential target steps can elicit much higher ASEM velocities than typically described in the literature. Similar to slow ASEM triggered by small steps, these fast ASEM do not require specific training and are not canceled by unpredictable step target motion. However, fast ASEM depend on the intact function of the cerebellum which gives further evidence of their generation by the smooth pursuit oculomotor subsystem.

Eye movements in recovering substance abusers: a prospective study

Smooth-pursuit (SPEM) and saccadic (SEM) eye movements were studied in 11 cocaine-dependent and 4 alcohol-dependent patients after 1, 3, and 12 weeks of verified abstinence. Sixteen non-drug-dependent controls were studied after comparable intervals. SPEM tracking accuracy, estimated by the Ln (S/N) statistic, was higher among cocaine-dependent patients than among alcohol-dependent patients and normal controls. A microanalysis of SPEM tracking revealed that the superior accuracy of the cocaine-dependent group was due to a small increase in eye movements at the target frequency (0.4 Hz) and a small compensatory decrease in higher frequency eye movements (i.e., saccades). In contrast to the findings of the SPEM study, the findings of the SEM study revealed that alcohol-dependent patients constituted the only abnormal group. Alcohol-dependent patients exhibited slower saccade onset latencies than the other groups. There were no significant differences among the groups with respect to saccade velocity, amplitude, or duration.