Like other drugs, the mode of methamphetamine consumption can be variable. Smoking is the most common route, followed by injection and inhalation or snorting (Pro et al., 2022). Regardless of how it is consumed, many harmful effects of methamphetamine can be attributed to its sympathomimetic effects, which leads to diffuse vasoconstriction (Hazin et al., 2009). This can present as toxicity of multiple organ systems, some of which are described below.

Methamphetamine elicits a harmful vasoconstrictive effect that can directly cause cardiovascular, cerebrovascular, hepatic, renal, neurologic, and ocular complications. Cardiovascular injuries include arrhythmias or ischemia with or without infarction (Ahmad et al., 2017). Narrowing or frank occlusion of cerebral vessels leads to cerebral ischemia with stroke or hemorrhagic stroke arising from intracerebral hemorrhage (Schep et al., 2010) and may also cause transient cortical blindness (Gospe, 1995; Edinoff et al., 2022). Intoxicated patients who are agitated and hyperthermic are at risk for rhabdomyolysis, which could result in liver damage and renal failure with resultant electrolyte abnormalities (Richards et al., 1999). Individuals may exhibit psychological and neurologic manifestations such as anxiety, depression, psychosis, and deficits in memory and executive functioning (Rusyniak, 2013).

Indirectly, methamphetamine use may contribute to behavioral and immunologic factors that harm the health of an individual. Methamphetamine users engage more frequently in high-risk sex behaviors, increasing avenues for transmission of infectious diseases such as hepatitis and HIV (Hittner, 2016). Behaviors such as unprotected sex, anal sex, use of commercial sex venues, and having multiple concurrent partners are more prevalent in methamphetamine users of the men-who-have-sex-with-men (MSM) population and are associated with a high incidence of sexually transmitted infections (STIs) such as Chlamydia, gonorrhea, and syphilis (Taylor et al., 2007; Reback and Fletcher, 2018). Needle or syringe-sharing behavior among users who inject contributes to a higher prevalence of infections (Wada et al., 1999). Methamphetamine may play a role in the immunopathogenesis of HIV and HCV infectivity as well. In vitro studies with human cells and animal models have shown that methamphetamine use is associated with higher viral loads, immune dysfunction, antiretroviral resistance, and accelerated progression to AIDS (Marcondes et al., 2010; Harms et al., 2012; Passaro et al., 2015; Skowronska et al., 2018; Liu et al., 2021). Methamphetamine may also damage the integrity of the blood brain barrier, thereby increasing likelihood of CNS involvement during HIV infection (Silverstein et al., 2011). It was also found to enhance replication of HCV in human hepatocytes in vitro (Ye et al., 2008).

The methamphetamine epidemic has had significant socioeconomic repercussions, costing the nation an estimated $23.4 billion in 2005 (The RAND Corporation, 2005). This amount was comprised of costs associated with morbidity and mortality, criminal justice and social welfare services, environmental clean-up from methamphetamine production, and lost productivity and quality of life burden due to drug dependence (Nicosia et al., 2009). Methamphetamine users are more likely to have unstable housing, low income, and residence in rural areas (Shearer et al., 2020) with populations of lower socioeconomic status being disproportionately affected. Multiple barriers may prevent these individuals from receiving medical care, as evidenced by higher rates of missed appointments, decreased compliance, and factors that interfere with effective substance use disorder treatment (Marquez et al., 2009; Lai et al., 2020). Additionally, high frequency of co-occurring addiction and mental health problems may lead to a higher risk of treatment non-adherence and missed appointments (Morasco et al., 2014). Children of methamphetamine users are exposed to a myriad of risk factors, including maltreatment, exposure to violence, and criminal behaviors. This environment negatively impacts a child’s psychological development and perpetuates a cycle of neglect and abuse (Gonzales et al., 2010; Messina et al., 2014).

Immediately following methamphetamine use, the user may experience blurred vision, mydriasis, disturbances in perception, or visual hallucinations. (Grant and Thomas, 1987; Srisurapanont et al., 2003). Following the acute phase of intoxication, additional ocular complaints may arise if corneal damage occurs. Patients with keratitis may experience days to weeks of decreased vision, eye pain, photophobia, and redness (Franco et al., 2022). They may also describe irritation or a foreign body sensation. Due to hyperstimulation from the drug, the user may fixate on the ocular discomfort and repeatedly rub or pick at the eye, increasing risk for corneal epithelial defects (Poulsen et al., 1996). On exam, focal opacification of the cornea often indicates a corneal ulcer, and severe cases of infection may present with a hypopyon or accumulation of white blood cells that settles in the anterior chamber.

Less frequently reported ocular symptoms arising from the vasoconstrictive effects of methamphetamine include amaurosis fugax, which manifests as short episodes of transient vision loss spontaneously resolving without treatment (Shaw et al., 1985). Similarly, sudden onset of painless vision loss hours after intranasal methamphetamine use may suggest a central retinal artery occlusion (CRAO) or non-arteritic ischemic optic neuropathy (NAION) (Wallace et al., 1992; Wijaya et al., 1999). The presence of blurred vision or visual field defect such as a scotoma may suggest intraretinal hemorrhages (Wallace et al., 1992). Less frequently described ocular findings include painful lid edema, proptosis, chemosis, and corneal melt, which may indicate panophthalmitis (Reed et al., 2021).

A spectrum of ophthalmic manifestations associated with methamphetamine use is reported in the literature (Table 1). These infectious or inflammatory processes affect various parts of the ocular anatomy, such as the conjunctiva, sclera, cornea, retina, optic nerve, or orbit.

In addition to consumption-related smoking or thermal injury, production-related causes of ocular involvement include direct injury, exposure to caustic chemicals during production, or exposure to toxic impurities used to dilute the methamphetamine (Heer et al., 2020). This is especially relevant amidst the rise of illicit methamphetamine production, which uses low-cost ingredients, some of which are dangerous and caustic (Movahedan et al., 2015). A “shake and bake” methamphetamine lab explosion resulted in combined thermal and alkali ocular injury (Chan et al., 2011). While “shake and bake,” also known as the one-pot method for cooking meth, simplifies the cooking process, this particularly dangerous method confers a high risk of fire and explosions with resultant chemical burns, and poisoning (Village, 2022).

Three individuals suffered ocular injuries after using a technique involving combination of ephedrine or pseudoephedrine, sodium or lithium, and anhydrous ammonia (Lee et al., 2003). Ocular complications resulting from an explosion accident include ocular surface failure, symblepharon, ankyloblepharon, and foreshortening of fornices (Movahedan et al., 2015). Nearby individuals such as children and first responders have also been reported to suffer from injury (Watanabe-Galloway et al., 2009; Melnikova et al., 2011). Patients who suffer from methamphetamine production-related burns typically have a larger burn size, higher incidence of inhalation injury, and increased morbidity from injuries (Spann et al., 2006). Patients may be dishonest about the cause of injury, which further confounds the diagnosis. Therefore, it is reasonable to consider the likelihood of a methamphetamine production-related accident when constructing a differential for the presentation of chemical and thermal ocular injuries (Charukamnoetkanok and Wagoner, 2004).