Noxious effects of riot control agents on the ocular surface: Pathogenic mechanisms and management

Abstract

Riot Control Agents (RCAs) are chemical compounds used by law enforcement agencies to quell violent demonstrations as an alternative to lethal force and as part of police/military training. They are also known as tear gases because of the hallmark ocular irritation and lacrimation they cause. The most common RCAs include oleoresin capsicum (contained in Mace and pepper spray), chlorobenzylidene malononitrile, dibenzoxazepine, and chloroacetophenone (previously the main content of Mace); some of which have been in use for decades. Their immediate incapacitating effects are mediated through polymodal afferent fibers innervating the corneal surface, inducing the release of peptides that cause neurogenic inflammation. Although previously thought to have only transient effects on exposed patients more severe complications such as corneal stromal opacities, corneal neovascularization, neurotrophic keratopathy, conjunctival necrosis, and pseudopterygium can occur. Concerningly, the lack of research and specific therapies restrict the current management to decontamination and symptom-tailored support. This manuscript will provide an overview of the toxic mechanisms of RCAs, their clinical manifestations, and current therapy after exposure to tear gases.

Keywords: chlorobenzylidene malononitrile; neurogenic inflammation; ocular surface; oleoresin capsicum; riot control agents; tear gas; toxicity.

FIGURE 1

Mechanism of action of Riot Control Agents. OC activates TRPV1 channels; while CS, CN, CR activate TRPA1 channels in corneal sensory neurons, inducing Ca²⁺ influx. With orthodromic stimulation, the impulse travels through the trigeminal pathway to the somatosensory cortex and elicits the pain sensation. In antidromic stimulation, TRP channel activation triggers an impulse that travels to adjacent nerve fibers, inducing the release of additional neuropeptides (i.e., SP, CGRP) to propagate inflammation. CGRP, Calcitonin-Gene Related Peptide; CN, chloroacetophenone; CR, Dibenzoxazepine; CS, chlorobenzylidene malononitrile; TRPA1, Transient Receptor Potential Ankyrin 1; TRPV1, Transient Receptor Potential Vanilloid 1. Created with Biorender.com.