Ocular Manifestations of Crystal Methamphetamine Use

Bioinformatics-driven untargeted metabolomic profiling for clinical screening of methamphetamine abuse

PURPOSE

Amphetamine-type stimulants are very common, and their usage is becoming a very big social problem all over the world. Thousands of addicts encounter several health problems including mental, metabolic, behavioral and neurological disorders. In addition to these, there are several reports about the elevated risk of tendency on committing criminal cases by addicted persons. Hence, methamphetamine addiction is not only an individual health problem but also a social problem. In our study, we aimed to investigate the pathogenesis of chronic usage of methamphetamine via untargeted metabolomics approach.

METHODS

38 plasma samples were carefully collected and extracted for untargeted metabolomics assay. A liquid-liquid extraction was performed to get as much metabolite as possible from the samples. After the extraction procedure, samples were transferred into vials and they were evaluated via time of flight mass spectrometry instrument.

RESULTS

Significantly, altered metabolites were identified by the fold analysis and Welch's test between the groups. 42 different compounds were annotated regarding to data-dependent acquisition method. Pathway analysis were also performed to understand the hazardous effect of methamphetamine on human body.

CONCLUSION

It has been reported that drug exposure may affect several metabolic pathways for amino acids, fats, energy metabolism and vitamins. An alternative bioinformatic model was also developed and validated in order to predict the chronic methamphetamine drug users in any criminal cases. This generated model passes the ROC curve analysis and permutation test and classify the controls and drug users correctly by evaluating the metabolic alterations between the groups.

Branch retinal artery occlusion in a 49-year-Old woman taking phentermine

Purpose

This report describes the presentation of a 49-year-old woman with a branch retinal artery occlusion of the right eye in the setting of taking phentermine, a commonly used weight loss medication.

Observations

A 49-year-old woman presented with acute painless vision loss in her right eye and was found to have a branch retinal artery occlusion after taking prescribed dosages of phentermine for weight loss therapy. Fundus examination revealed retinal whitening in the distribution of the superior temporal branch retinal artery, and spectral domain optical coherence tomography demonstrated macular edema. Systemic evaluation was negative for cardiovascular, infectious, or autoimmune etiologies. Based on the retinal findings, the patient was diagnosed with phentermine associated branch retinal artery occlusion. She was followed for nine years with no further complications and her vision remained stable in the right eye.

Conclusions and Importance

This case highlights that phentermine, a commonly used weight loss medication, could be associated with ischemic retinopathies. Thus, clinicians should be aware that retinal vascular occlusions may not only occur in those who use recreational amphetamines but also in patients taking the prescribed dosages of a weight loss medication like phentermine.

Rapid Separation and Detection of Drugs in Complex Biological Matrix Using TD-CDI Mass Spectrometer

The drug detection technology plays a pivotal role in the domains of pharmaceutical regulation and law enforcement. In this study, we introduce a method that combines thermal desorption corona discharge ionization (TD-CDI) with mass spectrometry for efficient drug detection. The TD-CDI module, characterized by its compact and simple design, enables the separation of analytes within seconds and real-time presentation of one or two analyte peaks on the mass spectrum most of the time, which reduces matrix interference and improves detection performance. Through experimental investigation, we studied the characteristics of TD-CDI for analyte separation and detection, even with the same mass number, and optimized the TD-CDI approach. TD-CDI-MS was employed for the rapid detection of drugs in various traditional medicine, food products, and human samples. Additionally, by utilizing TD-CDI for segmented hair direct analysis, it becomes possible to trace the drug usage cycle of individuals. This underscores the feasibility of the proposed analytical method within the realm of drug detection.

Lentiform Fork Sign on Magnetic Resonance Imaging After Methamphetamine and Alcohol Misuse

This case report describes a patient with a 3-day history of acute blindness after using alcohol and methamphetamine for 3 consecutive nights before onset of visual impairment.

Vision health perspectives on Breaking Bad: Ophthalmic sequelae of methamphetamine use disorder

Methamphetamine use has become a rampant public health issue that not only causes devastating consequences to the user but also poses a burden to surrounding communities. A spectrum of ophthalmic sequelae is associated with methamphetamine use and includes episcleritis, scleritis, corneal ulceration, panophthalmitis, endophthalmitis, retinal vasculitis, and retinopathy. In many instances, prompt recognition of the condition and associated infectious process and early initiation of antimicrobial therapy are crucial steps to preventing vision loss. In this review, we summarize the reported ocular complications that may result from methamphetamine use in addition to several postulated mechanisms regarding the ocular toxicity of methamphetamine. The increasing prevalence of methamphetamine use as a public health threat highlights the need for continued investigation of this ophthalmologic issue.

Long-term effects of methamphetamine abuse on visual evoked potentials

PURPOSE

To compare visual evoked potential (VEP) components in normal individuals and those with long-term methamphetamine and crystal methamphetamine use.

METHODS

In this study, monocular pattern-reversal VEPs were recorded in 40 methamphetamine and crystal methamphetamine users and 38 normal individuals. Visual stimuli were high-contrast (99%) checkerboard patterns at 15 and 60 min of arc with a reversal rate of 1.53 reversals per second.

RESULTS

A significant difference was seen between the two groups for the P100 peak time for the 60 min of arc checks (p = 0.002, d = 0.75, 4.61% higher peak time in the addicted group) and the 15 min of arc checks (p = 0.004, d = 0.73, 4.78% higher peak time in the addicted group). However, other VEP components were not significantly different between the two groups.

CONCLUSIONS

The higher P100 peak time at both 15 and 60 min of arc in methamphetamine-dependent users reveals that VEPs are highly sensitive for the diagnosis of retinal and visual pathway lesions.

Sex-Dependent Alterations in the mRNA Expression of Enzymes Involved in Dopamine Synthesis and Breakdown After Methamphetamine Self-Administration

Sex differences have been reported in methamphetamine (METH) use disorder in humans and in animal models of METH exposure. Specifically, animals that self-administer METH show sex-related dissimilarities in dopamine (DA) metabolism. To better understand the molecular bases for the differences in DA metabolism, we measured the levels of mRNAs of enzymes that catalyze DA synthesis and breakdown in the prefrontal cortex (PFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and hippocampus (HIP) of rats that had self-administered METH. There were significant sex differences in control rats, with males having higher basal levels of Th in the PFC and dSTR, Ddc in the NAc, and MaoB in the HIP. In contrast, female controls showed higher basal levels of Comt in the HIP. Male and female METH SA rats also showed some distinct responses to the drug. Specifically, female METH rats exhibited increased expression of Ddc and MaoB, whereas male METH animals showed higher levels of Comt mRNA in the PFC compared to their respective controls. In the NAc, male METH rats displayed decreased Th and Ddc mRNA levels. Together, our results identified sex-dependent and region-specific changes in the mRNA expression of several enzymes involved in DA synthesis and breakdown in response to METH SA, with the majority of differences being observed in the mesocorticolimbic dopaminergic system. These findings are of significant translational importance providing further support for the inclusion of sex as an important variable when planning and evaluating therapeutic interventions against METH use disorder in human clinical studies.

Ophthalmic complications associated with methamphetamine use disorder

Purpose

To describe the devastating ophthalmic sequelae of methamphetamine use disorder in two patients who developed vision loss from ocular complications, including keratitis and endophthalmitis.

Observations

Case 1 is a 26-year-old male with hepatitis C, poorly controlled type 1 diabetes, and chronic methamphetamine use who presented with a corneal ulcer in the left eye. Corneal culture grew Staphylococcus aureus and Streptococcus viridans, prompting antibiotic therapy. Follow-up exam showed peripheral corneal ulceration OD and diffusely vascularized and scarred cornea OS, although nonadherence was reported. Vision eventually worsened to hand motions OD and light perception OS.

Case 2 is a 44-year-old woman with hepatitis C, acute myeloid leukemia, dry eye syndrome secondary to chronic graft-versus-host disease (GVHD), and chronic methamphetamine use who presented with a diffuse corneal infiltrate and hypopyon. She underwent emergent corneal transplantation, vitrectomy, and broad-spectrum intravitreal and intravenous antibiotics. Vitreous cultures were positive for Streptococcus pyogenes. However, progressive disease eventually required enucleation despite initial globe salvaging measures.

Conclusions and importance

These two patient cases highlight the risk of vision loss or blindness due to the detrimental effects of chronic methamphetamine use on the eye, including the potential for keratitis and endophthalmitis. Given the increasing prevalence of methamphetamine use disorder in the United States, further understanding of these toxicities and preventive strategies are needed.

Macula and optic disk features in methamphetamine and crystal methamphetamine addicts using optical coherence tomography

PURPOSE

Methamphetamine and crystal methamphetamine abusers were compared with healthy subjects using optical coherence tomography to assess their retinal nerve fiber layer, macula, and optic disk characteristics.

METHODS

Forty-one methamphetamine and crystal methamphetamine abusers and 42 healthy subjects (mean ± SD of age: 35.82 ± 8.6 and 37.76 ± 9.1 years, respectively) were incorporated in this cross-sectional study. The drug abusers had a history of at least five years of substance use through smoking. Fourier-domain optical coherence tomography was used to image and assess the characteristics of retinal nerve fiber layer, macular thickness, and optic disk in the study groups.

RESULTS

The retinal nerve fiber layer thickness was significantly lower in the superior and temporal retinal quadrants of drug abusers than healthy subjects (P = 0.008 and P = 0.028, respectively). This study did not find a significant difference between drug abusers and healthy controls regarding optic to disk ratio, rim area, and disk area (P > 0.05). The comparison between the study groups showed that the reductions in perifovea and the superior quadrant of parafoveal thickness were statistically significant (P < 0.001 and P = 0.029, respectively).

CONCLUSION

Fourier-domain optical coherence tomography measurements showed that the retinal nerve fiber layer and macular thickness were different between methamphetamine and crystal methamphetamine abusers and healthy subjects, which should be considered in clinical practice. It seems that these drug abuses can cause alterations in retinal morphology.

Changes in corneal and anterior chamber indices due to methamphetamine abuse

CLINICAL RELEVANCE

Considering the significant relationship between methamphetamine abuse and some anterior segment indices, methamphetamine abuse should be considered in differential diagnosis especially in the case of angle closure glaucoma.

BACKGROUND

To investigate the effect of inhaled methamphetamine (meth) and crystal methamphetamine (crystal meth) on the quantitative indices of the cornea and anterior chamber using pentacam and anterior segment optical coherence tomography.

METHODS

In this cross-sectional study, the participants were (crystal) meth addicts living in Zahedan. The participants were transported to the examination site to undergo imaging and optometric tests. Pentacam and anterior segment optical coherence tomography imaging were then conducted so as to evaluate corneal and anterior chamber quantitative indices.

RESULTS

A total of 42 (crystal) meth addicts and 42 healthy subjects with matching age and gender were examined. Out of 42 subjects in the case group, 6 were female and 36 were male (mean age: 35.7 ± 8.6 years). The mean dose of drug used was 0.0074 ± 0.0034 g, and the mean duration of drug use was 6.9 ± 2.6 years (5-12 years). Based on the images of both devices, corneal curvature was significantly steeper in both meridians of anterior and posterior surfaces compared to the control group (p = 0.01). Among the anterior chamber parameters, the anterior chamber depth and volume were lower in the cases than the controls (p < 0.01). However, the lens rise was higher in addicts than controls (p = 0.01).

CONCLUSION

Quantitative changes in corneal and anterior segment indices including dilated pupils, shallower anterior chamber depth and higher lens rise in addicted cases compared to the control group may precipitate the risk of closed-angle in these individuals.

Retinal hypoxia and angiogenesis with methamphetamine

Central retinal artery occlusion, retinopathy, and retinal neovascularization have been reported in methamphetamine (METH) abusers. In the current study, we investigated whether METH induces retinal neovascularization in a mouse model, and if so, whether the neovascularization is associated with increased hypoxia, hypoxia-inducible factor 1α (HIF-1α), and vascular endothelial growth factor (VEGF). Mice were administrated METH by intraperitoneal injection over a 26-day period, or injected with saline as a vehicle control. The number of retinal arterioles and venules were counted using in vivo live imaging following infusion with fluorescein isothiocyanate-dextran. Excised retinas were stained with griffonia simplicifolia lectin I and flat mounted for a measurement of vascularity (length of vessels per tissue area) with AngioTool. Retinal hypoxia was examined by formation of pimonidazole adducts with an anti-pimonidazole antibody, and HIF-1α and VEGFa protein levels in the retina were detected by immunoblot. METH administration increased vascularity (including the number of arterioles) measured on Day 26. Retinal VEGFa protein level was not changed in METH-treated mice on Day 5, but was increased on Day 12 and Day 26. Hypoxia (pimonidazole adduct formation) was increased in retinas of METH-treated mice on Day 12 and Day 26, as were HIF-1α protein expression levels. These results indicate that METH administration induces hypoxia, HIF-1α, VEGFa, and angiogenesis in the retina.

Psychostimulant use disorder emphasizing methamphetamine and the opioid -dopamine connection: Digging out of a hypodopaminergic ditch

BACKGROUND

Approved food and drug administration (FDA) medications to treat Psychostimulant Use Disorder (PUD) are needed. Both acute and chronic neurological deficits related to the neurophysiological effects of these powerfully addictive drugs can cause stroke and alterations in mood and cognition.

OBJECTIVE

This article presents a brief review of the psychiatric and neurobiological sequelae of methamphetamine use disorder, some known neurogenetic associations impacted by psychostimulants, and explores treatment modalities and outcomes.

HYPOTHESIS

The authors propose that gentle D2 receptor stimulation accomplished via some treatment modalities can induce dopamine release, causing alteration of D2-directed mRNA and thus enhanced function of D2 receptors in the human. This proliferation of D2 receptors, in turn, will induce the attenuation of craving behavior, especially in genetically compromised high-risk populations.

DISCUSSION

A better understanding of the involvement of molecular neurogenetic opioid, mesolimbic dopamine, and psychostimulant connections in "wanting" supports this hypothesis. While both scientific and, clinical professionals search for an FDA approved treatment for PUD the induction of dopamine homeostasis, via activation of the brain reward circuitry, offers treatment for underlying neurotransmitter functional deficits, potential prophylaxis, and support for recovery efforts.

CONCLUSION

Dopamine regulation may help people dig out of their hypodopaminergia ditch.

Effects of chronic methamphetamine abuse on the retinal nerve fiber layer, ganglion cell layer and Bruch's membrane opening minimum rim width

BACKGROUND

Methamphetamine (Meth) is a highly addictive and hallucinogenic agent which is used as the second most common illicit drug globally. Meth could affect the retina and optic nerve by inducing the release of vasoconstrictive agents such as endothelin 1 and induction of severe oxidative stress with accumulation of reactive oxygen species.

AIM

To evaluate the effects of chronic Meth abuse on the retinal nerve fiber layer (RNFL), ganglion cell layer (GCL) and the Bruch's membrane opening minimum rim width (MRW).

METHOD

In this case-control study, we recruited 55 Meth abusers and 49 healthy individuals with mean age of 44.63 ± 0.97 and 43.08 ± 0.91 years, respectively. RNFL thickness, GCL thickness and MRW were evaluated using optical coherence tomography.

RESULTS

We found statistically significant decrease in RNFL, MRW thickness in Meth abusers (P: 0.002 and P: 0.006, respectively). We did not detect statistically significant difference regarding GCL thickness between the groups (P = 0.320). Our results showed a weak but statistically significant correlation of Meth dose increment and decrement of RNFL thickness ((P: 0.005, r = -0.193) and MRW (P: 0.013, r = -0.174). We found no correlation between duration of Meth consumption with RNFL and MRW thickness (P: 0.205, r= -0.124; P: 0.771, r= -0.029, respectively).

CONCLUSION

We found a statistically significant adverse association in meth abusers with RNFL thickness and MRW. These two parameters were also statistically associated with the meth dose as measured by daily dose of Meth. Although we found a decrease in the GCL thickness, it did not reach statistical significance.

Methamphetamine causes acute toxicity in the retina of Balb/c mice

Purpose: As a powerful psychostimulant with high potential for abuse, methamphetamine (Meth) could cause neurological diseases. METH-induced ophthalmic complications are present, but its underlying mechanism has not been completely elucidated, specifically on the retina. This study was to investigate effects of Meth treatment on the retina. Methods: Balb/c mice were treated with Meth at progressively increasing doses (0-6 mg/kg) intraperitoneally four times per day for five days, mice treated with saline as negative control. Electroretinography (ERG) was used to test the function of retina after Meth treatment. Pathological changes were examined by haematoxylin and eosin staining and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) assay. Enzyme-linked immunosorbent assay (ELISA) was used to measure the norepinephrine and tumour necrosis factor alpha (TNFα). Real-time PCR and western blot were used to measure expression changes of genes and proteins, respectively. Results: Our data showed that Meth treatment caused photoreceptor cell death and decreased the thickness of retina. Meth treatment also elevated norepinephrine levels in plasma and increased TNFα in the retina. Moreover, Meth treatment decreased platelet endothelial cell adhesion molecule-1 (PECAM-1) protein expression and increased protein expression of matrix metalloproteinases (MMPs) in the retina.Conclusions: Our study indicated that short-term intraperitoneal treatment of Meth induced retinal degeneration of Balb/c mice due to a vascular loss of PECAM-1 and an increase of MMPs.

Illicit drugs: Effects on eye

There is a myriad of changes that can be produced in the eye by toxic drugs ranging from mild/no symptoms to severe loss of vision from endophthalmitis. The routes of administration include oral ingestion, smoking, nasal inhalation, intravenous injection, topical application or application to other mucosal surfaces. It is important to recognize certain clinical signs and symptoms in the eye produced by these toxins. This article describes in brief some of the ocular effects of commonly abused drugs. For identification of a particular poisoning, in addition to the clinical presentation, pulse, blood pressure, respiration and body temperature, pupillary size, pupillary reaction to light, ocular convergence and nystagmus can be useful indicators of the type of drug the patient is exposed to. Unmasking these features help the clinician in an early and accurate diagnosis of the offending drug as well as timely management.

Retinal vasculitis: A framework and proposal for a classification system

Retinal vasculitis, a poorly understood process involving inflammation or ischemia of the retinal vessel wall, may occur in association with a systemic process, although it can also be isolated to the retina. Because of the limited ability to perform histopathological studies on retinal vessels, there is no gold standard for diagnosis. Thus, there is utility in creating a classification system for retinal vasculitis and improving diagnostic strategies for this disease. We provide a framework for understanding retinal vasculitis based on size, location, and etiology. We hope that this information can be implemented in the clinical setting to provide some diagnostic strategies for this often confusing entity.

Acute changes in the retina and central retinal artery with methamphetamine

Methamphetamine (METH), an addictive stimulant of neurotransmitters, is associated with cardiovascular and neurological diseases. METH-induced ophthalmic complications are also present but have been insufficiently investigated. The purpose of this study is to investigate the retinal effects of METH. C57BL/6 mice were administrated progressively increasing doses of METH (0-6 mg/kg) by repetitive intraperitoneal injections for 5 days (4 times per day). Retinal degeneration was examined by morphological changes and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling (TUNEL) assay. Norepinephrine levels were measured by ELISA, protein expression levels were determined by immunoblot and immunostaining, and gelatinase activity was examined by zymography. The thickness of the retina and the number of nuclei in the inner and outer nuclear layers were decreased by METH. Retinal cell death and astrocyte activation by METH treatment were confirmed by TUNEL assay and glial fibrillary acidic protein expression, respectively. Increased tumor necrosis factor-α protein in the retina and elevated norepinephrine levels in plasma were found in METH-treated mice. Platelet endothelial cell adhesion molecule-1 (PECAM-1) protein expression level was decreased in the retina and central retinal artery (CRA) by METH treatment, along with the endothelial proteoglycans glypican-1 and syndecan-1. Moreover, a regulator of the extracellular matrix, matrix metalloproteinase-14 (MMP-14) in the retina, and MMP-2 and MMP-9 in plasma, were increased by METH treatment. In conclusion, METH administration is involved in retinal degeneration with a vascular loss of PECAM-1 and the glycocalyx in the CRA and retina, and an increase of MMPs.

Bilateral methamphetamine-induced ischemic retinopathy

Purpose

To describe the multimodal imaging and treatment of a 37-year-old male presenting with bilateral ischemic retinopathy induced by methamphetamine abuse.

Observations

A 37-year-old male presented with progressively deteriorating vision and was found to have branch retinal artery occlusion and central retinal vein occlusion in both eyes along with secondary vitreous hemorrhage in the left eye following seven years of intermittent intranasal methamphetamine abuse. Fundus fluorescein angiography and optical coherence tomography angiography revealed large areas of non-perfusion in the peripheral retina along with peripapillary neovascularization. Systemic evaluation revealed ischemic foci scattered in the deep brain on magnetic resonance angiography scanning. Based on the retinal findings, the patient was diagnosed with methamphetamine-induced ischemic retinopathy. He received panretinal photocoagulation, which improved the vision in the right eye and vitreous hemorrhage in the left eye. The vision in the left eye remained stable.

Conclusions and importance

This case highlights that intranasal methamphetamine abuse is associated with bilateral simultaneous central retinal vein occlusion and branch retinal artery occlusion. To our knowledge, extensive bilateral ischemic retinopathy has not been documented previously with newer modalities. In addition, PRP may be considered for the treatment of ischemic retinopathy induced by methamphetamine abuse.

Long-Term Systemic Treatment With Methamphetamine Causes Retinal Damage in CD1 Mice

As a powerful psychostimulant with high potential for abuse, methamphetamine (Meth) could cause long-lasting abnormalities in retinas. The purpose of this study was to investigate the effects of systemic administration of Meth at low dose on retinal damage and understand the underlying mechanisms of pathology. CD1 mice were treated with 0.5 mg/kg or 1 mg/kg Meth by intraperitoneal injection daily for 2 months, mice treated with saline were used as negative control. Electroretinography (ERG) reflects the mass response of photoreceptor cells and was used to test the outer retinal function after Meth treatment. Toluidine blue staining was used to show the retinal morphology and evaluate the photoreceptor cell loss. Inflammatory factors were measured by enzyme-linked immunosorbent assay to show the inflammatory response. Terminal deoxynucleotidyl transferase dUTP Nick end labeling assay was used to detect the apoptosis-positive cells. Real-time polymerase chain reaction and Western blot were applied to measure the gene and protein change to explore the underlying mechanisms. Results demonstrated that retinal damage was caused by Meth treatment after 2 months, evidenced by loss of rod photoreceptor cells; decreased ERG amplitude; increased apoptotic photoreceptor cells, cytochrome-c release, caspase-3 activity, caspase-9 activity, and apoptosis-related protein expression; increased malondialdehyde level as well as nicotinamide adenine dinucleotide phosphate oxidase 4 protein expression; decreased anti-oxidative agents glutathione as well as superoxide dismutase levels; and increased production and gene expression of inflammatory factors. Our study indicated that systemic administration of Meth caused neurotoxic effects on CD1 mouse retinas, providing the potential mechanisms for the retina damage caused by Meth abuse.

Methamphetamine Causes Photoreceptor Cell Damage Through Promoting Polarization of Macrophages and Inducing Inflammatory Response

Classically activated macrophages (M1) are proinflammatory effectors and closely related to the progression of neurotoxicity. As a powerful psychostimulant and addictive drug, methamphetamine (Meth) abuse could result in long-lasting abnormalities in retina. This study investigated the effect of Meth at nontoxic concentration on macrophage activation state and its resultant toxicity to photoreceptor cells. Results showed that cytotoxicity was caused by Meth on 661 W cells after coculturing with RAW264.7 macrophage. RAW264.7 cells tended to switch to the M1 phenotype, releasing more proinflammatory cytokines after treatment with Meth. Meth could also upregulate the M1-related gene and protein expression. Our study demonstrated that Meth promoted macrophage polarization from M0 to M1 and induced inflammatory response, providing the scientific rationale for the photoreceptor cell damage caused by the Meth abuse.

Ocular manifestations of drug and alcohol abuse

PURPOSE OF REVIEW

The purpose of this study is to review commonly encountered adverse ocular effects of illicit drug use.

RECENT FINDINGS

Drug and alcohol abuse can produce a variety of ocular and neuro-ophthalmic side effects. Novel, so-called 'designer', drugs of abuse can lead to unusual ocular disorders. Legal substances, when used in manners for which they have not been prescribed, can also have devastating ophthalmic consequences.

SUMMARY

In this review, we will systematically evaluate each part of the visual pathways and discuss how individual drugs may affect them.

Oxidative stress response in the adult rat retina and plasma after repeated administration of methamphetamine

Methamphetamine (MA) is a psychostimulant that target the sensory systems, with the neurosensory retina having been shown to be affected. In the brain, MA-related toxicity can be linked to oxidative stress; the same relationship has yet to be established for the retina. The aim of this study, therefore, was to evaluate the effects of repeated exposure to MA on oxidative stress parameters in the rat retina. Oxidative stress parameters in the blood plasma were also assessed. Male Wistar rats were given 5mg/kg MA every 2h for a period of 6h (i.e., 4 injections) daily between postnatal day (PND) 91 and 100. Evolution of body weight was registered. Rats were sacrificed at PND 110. Blood plasma was collected and immediately frozen for storage at -70 degrees C. The eyes were enucleated, and the retina and choroids rapidly dissected on ice under dim light also to be stored at -70 degrees C. Lipid peroxidation activity was measured by the thiobarbituric acid (TBA) test. Total antioxidant status, superoxide dismutase (SOD) activity, catalase (Cat) activity, and nitrogen oxides contents were also determined. Lipid peroxidation was significantly higher in the retina and blood plasma of the MA-treated rats. Total antioxidant levels were significantly lower in both retina and blood plasma of the MA-treated rats. The activity of SOD was significantly increased in the retina and blood plasma of MA-treated rats. Catalase activity did not differ between groups in either the retina or the blood plasma. Nitric oxide production was significantly higher in both the retina and blood plasma in the MA-treated animals. The overall findings show that the oxidative stress defence mechanisms in the retina are compromised by MA toxicity. The results are similar to those found in the brain, and, moreover, showed some correlation with the blood plasma.