Since June, the police have used nearly 2,000 rounds of tear gas on protesters in Hong Kong. As a Part 1 optometrist, I would like to express my concern. Tear gas is considered effective as a “non-lethal” form of crowd control. Today, the most commonly used agents are chloroacetophenone (CN), o-chlorobenzylidene malononitrile (CS) and oleoresin capsicum (OC). The Hong Kong police uses CS, which is considered less toxic than CN. One systematic review reported that, among the 90 cases of exposure to CS, 57 per cent showed ocular clinical effects, such as lacrimation (secretion of tears), blepharospasm (involuntary tight closure of the eyelids), conjunctivitis and reduced vision. However, serious ocular morbidity or even blindness can result when the charge of tear gas is fired at close range. Besides, CS has been associated with more serious pulmonary complications and allergic reactions. Researchers discovered that subjects have a significantly higher risk of acute respiratory illnesses after exposure to CS. Respiratory tract injuries and even deaths were reported after exposure to high concentrations of tear gas or exposure in enclosed spaces. To manage the effects of tear gas: 1. Withdraw from the contaminated area and move to a well-ventilated space 2. Attempt to stay on higher ground because lacrimating agents are several times heavier than air. Patients should be lifted off the ground whenever possible 3. Thoroughly flush the affected areas of the body with water or saline for 10 to 20 minutes 4. Seek medical help for persistent symptoms. An extensive ophthalmological examination is required to search for retained particles and corneal erosion. Topical anaesthetics are not recommended for the treatment of conjunctivitis. To conclude, tear gas can result in severe complications or even death. Regulation and training in the use of tear gas is essential to protect the lives of protesters. Charles Li, Sai Wan Ho