Neuroretinal Dysfunctions in Regular Cannabis Users: An Impact of Cannabis on Retinal Neurotransmission?

Abstract

Introduction

Although cannabis is very widespread worldwide, its brain toxicity is poorly understood. The neuroretina is an accessible extension of the brain and could be a relevant site for investigating neurotransmission abnormalities in neuropsychiatric disorders. The retina has a functional endocannabinoid system involved in the regulation of retinal neurotransmission. In animals, the modulation of this system led to retinal dysfunctions measured with the electroretinogram (ERG).

Objectives

To assess whether the regular cannabis use could affect the neuroretinal function.

Aims

Assessments of the neuroretinal function in cannabis users compared with controls.

Methods

Recordings of pattern, flash and on-off ERG were performed in 55 cannabis users and 29 controls. The amplitude and implicit time of the following waves were evaluated: N95 (pattern); a – and b – (flash); a –, b- and d1 – (on-off).

Results

Cannabis users showed a significant increase in implicit time of the waves N95 (P = 0.0001), a- (P = 0.029) and b – (P = 0.002) for the flash ERG and b – (P = 0.016) and d1 – (P = 0.027) for the on-off ERG, compared with controls. No significant difference was found between groups in terms of wave's amplitudes.

Conclusions

These results show a delay in the response of cones, bipolar and ganglion cells of the on and off pathways to constitute a delay of ≈ 6 ms in the transmission of information from the retina to the brain in cannabis users. Cannabis could disrupt the regulatory role of the cannabinoid system and impair retinal glutamatergic neurotransmission. The consequences on visual perception should be explored in future studies.

Disclosure of interest

The authors have not supplied their declaration of competing interest.