Ocular Effects of Synthetic Cannabinoids: A Case-control Study

MATERIAL AND METHODS Participants This study was designed as cross-sectional, observational, case-control study. Upon referral from the judiciary-supervised probation unit of Alcohol and Substance Research, Treatment and Training Centre (AMATEM) of the relevant tertiary psychiatry hospital between March 2015 and January 2016, 60 eyes of 60 consecutive male patients with past synthetic cannabinoids (SC) use and 30 eyes of age-matched 30 male healthy control subjects were enrolled in the study in 3 groups: a control group (n=30) included eyes of subjects with no history of use of any substance including tobacco, a seronegative SC group (n=30) included eyes of patients declaring no present use of any substance, as verified by three consecutive negative urine toxicology tests performed two weeks apart, and a seropositive SC group (n=30), including eyes of patients with positive urine toxicology tests proving present use of SC.

SCs and relevant metabolites in urine samples were screened with a direct ELISA kit (K2 Enzyme Immunoassay, Immunalysis Corp., Pomona, CA, USA). This kit was able to detect relevant metabolites, such as JWH-018, JWH-073, and AM-2201, with a cut-off level of 20 ng/mL and over for positive results. Exposures to classical cannabinoids, ecstasy, amphetamines, opioids, and ethylene glycol were also screened.

Regarding SC use, the patients were asked about the duration and the last time of use. In addition, the previous use of other substances was questioned in detail.

Ophthalmic Assessments All eyes underwent ophthalmic examinations, including autorefraction, best-corrected visual acuity (BCVA) testing, biomicroscopy, non-contact IOP measurement, and dilated fundus examination.

An experienced technician performed spectral-domain optical coherence tomography (SD-OCT) imaging of all eyes following pupil dilatation (1% tropicamide) and systolic/diastolic blood pressure measurements (SBP/DBP). All SD-OCT assessments were conducted between 14:00 and 16:00 to minimize the potential effect of diurnal variation. Only high-quality SD-OCT images with a signal strength index (SSI) greater than 50 were sent for analysis. The parafoveal retinal thickness (parafoveal RT) and central foveal thickness (CFT), CT, peripapillary RNFL thickness, and macular GCC thickness measurements were performed with an RTVue-100 OCT device (Optovue Inc., Fremont, US), which had a 5 µm axial image resolution with a speed of 27,000 A-scans per second.