Increases in Retinal Nerve Fiber Layer Thickness May Represent the Neuroprotective Effect of Cannabis: An Optical Coherence Tomography Study

Although optical coherence tomography (OCT) has been used in many neuropsychiatric disorders, data on substance use disorders (SUD) are not available. The aim of this study was to evaluate ganglion cell layer (GCL), inner plexiform layer (IPL), retinal nerve fiber layer (RNFL), and choroidal layer thickness in patients diagnosed with SUD especially cannabis use disorder (CUD). RNFL, GCL, IPL, and the choroidal layers of 111 patients diagnosed with SUD and 45 healthy controls were retrospectively analyzed. Fifty patients were diagnosed with CUD and 50 patients had multiple drug use (MDU). The mean age of the patient and control groups were 23.39 ± 5.53 and 28.48 ± 5.21 years, respectively. The mean duration of substance use was 3.53 ± 2.95 years. The patients had not used any substance for a mean of 121.45 ± 116.99 days. When the RNFL values of the SUD, MDU, and control groups were compared, no significant difference was found except for such components. However, there were significant differences in terms of right naso-superior (p = 0.020), right temporo-inferior (p = 0.024), right temporo-superior (p = 0.002), left naso-superior (p= 0.005), left naso-inferior (p = 0.043), and left temporo-superior (p = 0.008) between CUD and control groups. That is, RNFL values were higher in the CUD group than in the control group. Cannabis has medical uses because of its possible neuroprotective properties. Our study supports the possible neuroprotective effects associated with cannabis through RNFL data. According to our best knowledge, this is the first study investigating the association between RNFL and drugs, particularly cannabis.