Toxicology – Acute Visual Loss and Visual Disturbances

Core Concept

Acute visual disturbance after a toxic exposure can result from injury anywhere along the visual pathway, including:

• Cornea and conjunctiva
• Lens
• Retina
• Optic nerve
• Central visual pathways
• Extraocular muscles and their innervation

Symptoms can range from mild blurring or abnormal color perception to visual-field loss or complete blindness.

Sudden visual loss is an ophthalmologic emergency until a serious ocular, neurologic, vascular, or toxic cause has been excluded.

Major Toxicologic Causes

Methanol

Methanol is one of the most important toxicologic causes of acute visual impairment.

Methanol is metabolized to formic acid, which produces metabolic acidosis and is particularly toxic to the retina and optic nerve.

Visual complaints may include:

• Blurred vision
• Reduced visual acuity
• Central visual defects
• Photophobia
• “Snowfield” or “snowstorm” vision
• Severe visual loss or blindness

Systemic findings may include:

• Headache
• Nausea/vomiting
• Abdominal discomfort
• CNS depression
• High-anion-gap metabolic acidosis
• Tachypnea

Severe poisoning can progress to seizures, coma, cardiovascular instability, and permanent blindness.

Methanol: Important Diagnostic Pattern

A particularly concerning combination is:

Visual disturbance + unexplained high-anion-gap metabolic acidosis

The osmolal gap may be elevated early but can become normal later as methanol is converted to toxic metabolites.

Therefore:

A normal osmolal gap does not exclude late methanol poisoning.

Direct methanol measurement is preferred when available.

Methanol Management

Important treatment principles include:

• Stabilization and supportive care
• Inhibition of toxic alcohol metabolism with fomepizole
• Correction of clinically important acidosis
• Folate-related adjunctive therapy in appropriate cases
• Hemodialysis for selected severe poisoning

Visual symptoms are an important marker of serious methanol toxicity and warrant urgent toxicology involvement.

Quinine and Related Drugs

Quinine toxicity can cause significant ocular toxicity.

Possible manifestations include:

• Blurred vision
• Reduced visual acuity
• Constricted visual fields
• Altered color vision
• Scotomas
• Severe visual impairment

Systemic features of quinine toxicity may include:

• Tinnitus
• Hearing disturbance
• Dizziness
• Nausea/vomiting
• Headache
• Dysrhythmias

The combination of tinnitus and visual abnormalities can be an important clue.

Chloroquine and Hydroxychloroquine

These agents can affect vision through different mechanisms depending on the exposure pattern.

Severe acute chloroquine/hydroxychloroquine poisoning is primarily characterized by:

• Hypotension
• Hypokalemia
• QRS/QT abnormalities
• Ventricular dysrhythmias
• Seizures
• Cardiovascular collapse

Long-term hydroxychloroquine exposure can produce retinal toxicity, potentially causing:

• Paracentral visual defects
• Reduced visual acuity in advanced disease
• Altered color vision
• Progressive retinal damage

Chronic retinal toxicity differs from the cardiovascular emergency of acute overdose.

Digoxin and Cardiac Glycosides

Digoxin toxicity can produce characteristic disturbances in visual perception.

Possible complaints include:

• Blurred vision
• Photophobia
• Halos
• Altered color perception
• Yellow or yellow-green vision

These findings may accompany:

• Nausea/vomiting
• Confusion
• Bradycardia
• AV block
• Other dysrhythmias

Visual symptoms support the diagnosis but are not required for digoxin toxicity.

Anticholinergic Agents

Antimuscarinic drugs may cause blurred vision through:

• Marked mydriasis
• Cycloplegia
• Loss of accommodation

Patients may have difficulty focusing on near objects.

Associated findings include:

• Tachycardia
• Dry mouth
• Dry, flushed skin
• Reduced bowel sounds
• Urinary retention
• Agitation or delirium

Topical ophthalmic anticholinergics can produce particularly prominent ocular findings.

Botulism

Botulism causes presynaptic inhibition of acetylcholine release.

Early neurologic manifestations frequently involve the cranial nerves.

Visual complaints can include:

• Blurred vision
• Diplopia
• Difficulty focusing
• Ptosis

These may be followed by:

• Dysarthria
• Dysphagia
• Facial weakness
• Descending symmetric paralysis
• Respiratory failure

The patient is generally alert unless another process is present.

Ethambutol

Chronic ethambutol exposure can cause optic neuropathy.

Possible manifestations include:

• Reduced visual acuity
• Central visual defects
• Impaired color discrimination
• Bilateral visual symptoms

Early recognition and medication review are important because recovery is more likely when toxicity is recognized promptly.

Deferoxamine

Prolonged or excessive exposure can occasionally produce ocular toxicity, including:

• Reduced visual acuity
• Visual-field abnormalities
• Altered color perception
• Retinal or optic-nerve dysfunction

Visual abnormalities may improve after appropriate modification of therapy.

Mercury

Significant chronic mercury exposure can cause neurologic and visual abnormalities.

Possible manifestations include:

• Visual-field constriction
• Tremor
• Paresthesias
• Ataxia
• Neurobehavioral changes

The exact clinical pattern depends on the chemical form and exposure route.

Thallium

Thallium poisoning primarily produces gastrointestinal and neurologic toxicity but may occasionally affect the visual system.

Other clues include:

• Painful peripheral neuropathy
• Weakness
• Gastrointestinal symptoms
• Delayed alopecia

Vitamin A Toxicity

Excess vitamin A can increase intracranial pressure.

Possible findings include:

• Headache
• Nausea
• Diplopia
• Papilledema
• Visual disturbance

Chronic toxicity may also produce skin and hepatic abnormalities.

Chemical Eye Injury

Direct exposure to corrosive substances can damage:

• Conjunctiva
• Corneal epithelium
• Corneal stroma
• Anterior chamber
• Deeper ocular structures

Important exposures include:

• Strong alkalis
• Strong acids
• Phenolic chemicals
• Other corrosive agents

Symptoms may include:

• Severe pain
• Blepharospasm
• Tearing
• Redness
• Photophobia
• Blurred vision
• Corneal clouding

Alkali Versus Acid Injury

Alkali injuries are often particularly dangerous because they can penetrate deeply and continue damaging ocular tissue.

Severe alkali exposure may cause:

• Corneal opacification
• Limbal ischemia
• Anterior-segment injury
• Scarring
• Permanent visual impairment

Acids often cause more superficial coagulation injury, although concentrated acids can also cause severe ocular damage.

Important Principle: Pain Does Not Equal Severity

A painless eye after chemical exposure is not necessarily reassuring.

Severe chemical injury can damage sensory nerve endings and reduce pain despite extensive tissue injury.

Irritant Eye Exposures

Lacrimators and irritant chemicals may cause:

• Burning
• Tearing
• Conjunctival redness
• Blepharospasm
• Temporary blurred vision

Examples include:

• Pepper spray
• Tear gas
• Chlorine
• Other irritant gases or aerosols

Most uncomplicated irritant exposures improve after effective decontamination, but persistent symptoms require examination for corneal injury.

Immediate Management of Chemical Eye Exposure

The priority is:

Begin irrigation immediately.

Do not delay irrigation while trying to identify the exact chemical.

General principles include:

• Remove contact lenses when possible.
• Irrigate copiously with available clean fluid.
• Ensure the eyelids and conjunctival spaces are adequately exposed.
• Remove retained particulate material when appropriate.
• Check ocular pH in significant acid/alkali exposures.
• Continue irrigation until pH remains near physiologic range.

The clinical endpoint and normalization of ocular pH are more important than an arbitrary fixed irrigation volume.

Eye Examination

Assessment should include:

• Visual acuity in each eye
• Pupil size and reactivity
• Extraocular movements
• Visual fields when possible
• Eyelid and conjunctival examination
• Corneal clarity
• Fluorescein examination
• Slit-lamp examination when available

Intraocular pressure should be measured when glaucoma or other pressure-related pathology is suspected and when doing so is safe.

Fluorescein Examination

Fluorescein helps identify:

• Corneal epithelial defects
• Abrasions
• Ulceration
• Chemical injury

Significant chemical burns generally require ophthalmologic assessment.

Nontoxicologic Differential Diagnosis

Do not attribute acute visual loss automatically to poisoning.

Important alternatives include:

• Central retinal artery occlusion
• Retinal detachment
• Vitreous or retinal hemorrhage
• Acute angle-closure glaucoma
• Optic neuritis
• Ischemic optic neuropathy
• Stroke
• Intracranial hemorrhage
• Migraine
• Orbital disease
• Giant cell arteritis in the appropriate age group
• Raised intracranial pressure

Sudden painless monocular visual loss is particularly concerning for a retinal or vascular emergency.

Key Diagnostic Tests

Depending on the presentation, consider:

• Visual acuity testing
• Slit-lamp/fluorescein examination
• Ocular pH after chemical exposure
• Electrolytes and bicarbonate
• Anion gap
• Blood gas
• Serum osmolality/osmolal gap
• Methanol concentration
• ECG
• Digoxin concentration when indicated

Additional ophthalmologic or neurologic testing depends on the suspected cause.

Disposition

Systemic poisoning with visual abnormalities often requires admission or prolonged monitored treatment.

Chemical eye injuries require ophthalmologic follow-up, with urgent specialist evaluation for:

• Reduced visual acuity
• Significant epithelial injury
• Corneal clouding
• Limbal ischemia
• Persistent abnormal pH
• Severe pain
• Suspected penetrating injury

Key Points

• Visual toxicity may arise from corneal injury, retinal injury, optic neuropathy, neurologic dysfunction, or altered accommodation.
• Methanol + visual symptoms + high-anion-gap metabolic acidosis is a major toxicologic emergency.
• A normal osmolal gap does not exclude late methanol poisoning.
• Fomepizole is preferred for inhibiting methanol metabolism; severe cases may require dialysis.
• Quinine can produce tinnitus together with severe visual disturbance.
• Digoxin may cause halos and altered yellow-green color perception.
• Anticholinergics commonly blur vision through mydriasis and cycloplegia.
• Botulism can begin with diplopia, blurred vision, ptosis, and bulbar weakness.
• Chronic ethambutol exposure can produce optic neuropathy and impaired color vision.
• Chemical eye exposure requires immediate irrigation.
• Severe alkali burns may penetrate deeply and threaten vision.
• Lack of pain does not exclude severe ocular injury.
• Sudden visual loss always requires consideration of nontoxic ophthalmologic and neurologic emergencies.

187. Toxicology – Withdrawal Syndromes

Core Concept

Withdrawal occurs when a person who has developed physiologic adaptation to a substance experiences symptoms after:

• Abrupt cessation
• Rapid dose reduction
• Falling drug concentrations
• Administration of an antagonist
• Administration of certain partial agonists in susceptible opioid-dependent patients

Withdrawal syndromes differ substantially according to the drug class.

The most important distinction is:

Alcohol and sedative-hypnotic withdrawal can be life-threatening.

Typical opioid and stimulant withdrawal are usually not directly life-threatening in otherwise healthy adults, although complications and coexisting illness can still be serious.

General Principle

Withdrawal often produces physiologic effects roughly opposite to those produced during intoxication.

Examples:

CNS depressant intoxication → sedation

CNS depressant withdrawal → CNS hyperactivity

Similarly:

Opioid intoxication → miosis, reduced GI activity, CNS/respiratory depression

Opioid withdrawal → mydriasis, diarrhea, autonomic activation

This is useful conceptually but should not replace clinical assessment.

Alcohol Withdrawal

Chronic alcohol exposure causes neuroadaptation involving:

• Reduced inhibitory GABAergic function
• Increased excitatory glutamatergic activity

When alcohol concentrations fall abruptly, this adapted nervous system becomes excessively excitable.

Clinical severity ranges from mild tremulousness to seizures and delirium.

Early Alcohol Withdrawal

Possible findings include:

• Anxiety
• Tremor
• Insomnia
• Nausea
• Diaphoresis
• Tachycardia
• Hypertension
• Headache
• Agitation

Importantly:

Withdrawal can begin while measurable alcohol remains in the blood.

A rapid decline from a chronically high concentration may be sufficient to trigger symptoms.

Alcohol Withdrawal Seizures

Withdrawal can cause generalized seizures.

They often occur relatively early in the withdrawal course.

Important alternative causes should still be considered, including:

• Hypoglycemia
• Hyponatremia
• Head trauma
• Intracranial hemorrhage
• Infection
• Coingestion
• Primary epilepsy

Repeated or atypical seizures require broader investigation.

Alcohol Withdrawal Delirium

The most severe alcohol withdrawal syndrome is alcohol withdrawal delirium, historically called delirium tremens.

Features include:

• Severe agitation
• Confusion
• Disorientation
• Hallucinations
• Tremor
• Marked autonomic hyperactivity
• Tachycardia
• Hypertension
• Diaphoresis
• Hyperthermia

Complications can include:

• Dehydration
• Electrolyte abnormalities
• Rhabdomyolysis
• Dysrhythmias
• Aspiration
• Cardiovascular collapse

This is a medical emergency.

Sedative-Hypnotic Withdrawal

Withdrawal from GABAergic sedative medications can resemble alcohol withdrawal.

Important substances include:

• Benzodiazepines
• Barbiturates
• Certain older sedative-hypnotics

Possible manifestations include:

• Anxiety
• Tremor
• Insomnia
• Agitation
• Tachycardia
• Hypertension
• Perceptual disturbances
• Delirium
• Seizures

Severe withdrawal can be fatal.

Benzodiazepine Withdrawal

Withdrawal risk depends on:

• Duration of use
• Dose
• Degree of physiologic dependence
• Drug half-life
• Speed of discontinuation

Shorter-acting agents may produce earlier symptoms, while withdrawal from long-acting agents may be delayed.

Abrupt discontinuation after substantial chronic exposure can cause seizures or severe autonomic instability.

GHB Withdrawal

Chronic heavy gamma-hydroxybutyrate use can produce a particularly severe withdrawal syndrome.

Possible findings include:

• Severe agitation
• Insomnia
• Tremor
• Tachycardia
• Hypertension
• Hallucinations
• Delirium

The syndrome can progress rapidly and may require intensive management.

Alcohol/Sedative Withdrawal Differential Diagnosis

Conditions that can resemble severe withdrawal include:

• Sympathomimetic poisoning
• Anticholinergic toxicity
• Serotonin syndrome
• Neuroleptic malignant syndrome
• MAOI toxicity
• Hyperthyroidism
• Sepsis
• Heat stroke
• Intracranial hemorrhage
• CNS infection
• Primary psychiatric disease

Do not automatically attribute agitation and tachycardia to withdrawal simply because a patient has a history of substance use.

Treatment of Alcohol Withdrawal

Benzodiazepines are first-line therapy.

Treatment aims to control:

• Agitation
• Tremor
• Autonomic hyperactivity
• Seizures
• Progression to severe withdrawal

Medication should be titrated according to clinical severity and monitoring.

Phenobarbital is also used in selected patients and protocols, particularly for severe or difficult-to-control withdrawal.

Thiamine and Supportive Care

Patients with chronic heavy alcohol use may have thiamine deficiency.

Thiamine should be provided when clinically indicated, particularly when malnutrition or Wernicke encephalopathy is a concern.

Also assess and correct:

• Hypoglycemia
• Dehydration
• Potassium abnormalities
• Magnesium abnormalities
• Other nutritional deficiencies

Urgent glucose treatment should not be delayed in a hypoglycemic patient while waiting to administer thiamine.

Withdrawal Seizure Treatment

Benzodiazepines are central to treatment of alcohol or sedative-hypnotic withdrawal seizures.

Phenytoin is generally ineffective for preventing recurrent seizures caused purely by alcohol withdrawal because it does not correct the underlying withdrawal physiology.

It may still be appropriate when the patient has a separate seizure disorder requiring it.

Opioid Withdrawal

Opioid withdrawal results from loss of opioid receptor stimulation after physiologic dependence has developed.

It may follow:

• Abrupt opioid discontinuation
• Major dose reduction
• Naloxone administration
• Inappropriately timed partial-agonist therapy

Clinical Features of Opioid Withdrawal

Typical findings include:

• Anxiety
• Restlessness
• Yawning
• Lacrimation
• Rhinorrhea
• Mydriasis
• Piloerection
• Diaphoresis
• Myalgias
• Abdominal cramping
• Nausea/vomiting
• Diarrhea
• Increased bowel sounds
• Tachycardia

Patients may feel extremely unwell despite the syndrome usually not being directly fatal in otherwise healthy adults.

Complications of Opioid Withdrawal

Severe vomiting and diarrhea may cause:

• Dehydration
• Electrolyte disturbances
• Acute kidney injury

Risk can be greater in:

• Frail patients
• Pregnant patients
• Patients with major comorbidities
• Neonates

Return to opioid use after loss of tolerance also increases subsequent overdose risk.

Opioid Withdrawal Treatment

Modern treatment generally favors opioid agonist therapy when appropriate.

Important options include:

• Buprenorphine
• Methadone

These can relieve withdrawal and support ongoing treatment of opioid use disorder.

Non-opioid medications such as:

• Clonidine
• Lofexidine

may reduce autonomic symptoms but generally do not treat opioid use disorder itself.

Additional symptomatic treatment may address:

• Nausea
• Diarrhea
• Pain
• Dehydration

Precipitated Opioid Withdrawal

An opioid antagonist can rapidly displace opioid agonists and produce abrupt withdrawal.

Similarly, initiating buprenorphine at an inappropriate point after certain opioid exposures can precipitate withdrawal because of its high receptor affinity and partial agonist activity.

This syndrome can be much more abrupt than spontaneous withdrawal.

Stimulant Withdrawal

Withdrawal can occur after cessation of chronic use of:

• Cocaine
• Amphetamines
• Methamphetamine
• Other stimulants

The syndrome differs substantially from alcohol withdrawal.

Stimulant Withdrawal Features

Typical symptoms include:

• Fatigue
• Increased sleep
• Dysphoria
• Depressed mood
• Irritability
• Reduced motivation
• Poor concentration
• Increased appetite
• Drug craving

Some patients experience marked psychomotor slowing.

Unlike severe alcohol or sedative withdrawal, stimulant withdrawal generally does not cause the same autonomic hyperexcitable seizure syndrome.

Mental Health Risk in Stimulant Withdrawal

Although the physical withdrawal syndrome is usually not directly life-threatening, severe depression may occur.

Assessment should include:

• Suicidal thoughts
• Severe depression
• Psychosis
• Ability to care for oneself
• Coexisting substance use

Psychiatric risk may therefore be more important than physiologic instability.

Nicotine and Caffeine Withdrawal

These generally produce milder syndromes.

Nicotine withdrawal

May cause:

• Irritability
• Anxiety
• Difficulty concentrating
• Increased appetite
• Restlessness
• Craving

Caffeine withdrawal

May cause:

• Headache
• Fatigue
• Sleepiness
• Reduced concentration
• Irritability

These syndromes are generally self-limited.

Neonatal Withdrawal

Neonates exposed chronically to certain substances before birth may develop withdrawal after delivery.

Modern terminology for opioid-related neonatal withdrawal includes neonatal opioid withdrawal syndrome (NOWS).

Manifestations may include:

• Irritability
• Tremor
• Abnormal sleep
• Feeding difficulty
• Gastrointestinal symptoms
• Autonomic abnormalities

Management is specialized and differs from adult withdrawal care.

The older source’s recommendation of paregoric as the drug of choice is obsolete and should not be carried into modern study notes.

Diagnostic Evaluation

Withdrawal is primarily a clinical diagnosis supported by exposure history.

Important questions include:

• Substance used
• Duration of use
• Typical amount
• Last use
• Recent dose reduction
• Formulation/half-life
• Other substances
• Previous severe withdrawal
• Previous withdrawal seizures
• Medical comorbidities

Laboratory Evaluation

Testing should be guided by severity.

Potential studies include:

• Bedside glucose
• Electrolytes
• Magnesium
• Renal function
• Liver tests
• CBC
• CK when severe agitation, seizures, or hyperthermia occur

Additional testing may be necessary when altered mental status or seizures have an uncertain cause.

When to Consider Brain Imaging or Other Workup

Withdrawal should not be assumed to explain every neurologic abnormality.

Consider further investigation when there is:

• Head trauma
• Focal neurologic deficit
• Unusual seizure pattern
• Persistent altered mental status
• Fever or meningismus
• Concern for intracranial hemorrhage
• Clinical suspicion of infection

Decontamination

Gastrointestinal decontamination has no routine role in withdrawal because withdrawal results from declining drug exposure rather than an ongoing ingestion.

An exception would be a separate acute ingestion occurring at the same time.

Monitoring

Patients with severe alcohol or sedative-hypnotic withdrawal require monitoring for:

• Mental status
• Agitation
• Seizures
• Respiratory status during sedative therapy
• Heart rate
• Blood pressure
• Temperature
• Hydration
• Electrolytes

Severe withdrawal may require ICU-level management.

Timing of Withdrawal

The onset and duration depend heavily on the substance’s pharmacokinetics.

General principle:

Shorter-acting drug → earlier withdrawal

Longer-acting drug → potentially delayed withdrawal

Therefore, fixed timelines should not be applied rigidly.

Important Pitfalls

• Withdrawal does not require complete abstinence; a substantial fall in drug concentration may trigger it.
• Alcohol withdrawal can begin despite a measurable blood alcohol concentration.
• Long-acting sedative withdrawal may be delayed.
• Do not mistake stimulant intoxication for alcohol withdrawal.
• Do not mistake opioid intoxication for stimulant withdrawal-related sleepiness.
• Phenytoin does not correct the underlying mechanism of uncomplicated alcohol-withdrawal seizures.
• Beta-blockers, clonidine, and antipsychotics may sometimes be adjuncts but do not replace adequate GABAergic treatment for severe alcohol withdrawal.
• Severe agitation should not automatically be attributed to withdrawal; infection, intracranial disease, metabolic disorders, and poisoning must remain in the differential.
• Avoid dismissing reported withdrawal as drug-seeking behavior; assess the syndrome objectively and treat clinically significant findings.

Key Points

• Withdrawal follows cessation, dose reduction, or antagonism after physiologic adaptation.
• Alcohol and sedative-hypnotic withdrawal can cause seizures, delirium, hyperthermia, and death.
• Benzodiazepines are first-line treatment for clinically significant alcohol withdrawal.
• Phenobarbital has an important role in selected severe alcohol/sedative withdrawal protocols.
• Phenytoin is generally ineffective for uncomplicated alcohol-withdrawal seizures.
• Withdrawal can begin while blood alcohol remains measurable.
• Opioid withdrawal typically causes mydriasis, yawning, lacrimation, rhinorrhea, piloerection, myalgias, vomiting, and diarrhea.
• Typical adult opioid withdrawal is usually not directly life-threatening, but dehydration and other complications can occur.
• Buprenorphine or methadone are important modern treatments for opioid withdrawal and opioid use disorder.
• Clonidine or lofexidine can reduce autonomic opioid-withdrawal symptoms.
• Stimulant withdrawal mainly causes fatigue, hypersomnia, dysphoria, depression, and craving.
• Suicide risk and severe depression should be assessed during stimulant withdrawal.
• Long-acting drugs may produce delayed withdrawal, so onset cannot be predicted from a single universal timeline.
• Treatment should address the specific withdrawal syndrome and its complications, while continuing to consider alternative diagnoses.