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Tear Gas in Ophthalmology – More than Just Tears

  • Tear gas is being used by police to quell protests in various countries around the world at present.
  • The chemical attacks various parts of the body but most notably the eyes, hence its name.
  • We examined research into the ophthalmological implications of tear gas and its potential long-term effects.

Imagine the scene: It’s 2 p.m. on a Saturday and you’ve popped out for lunch. It’s been a long day and you’re hungry. You make it halfway to the restaurant before you notice a sulphuric smell and taste wafting on the air. All of a sudden your eyes begin to burn.

That was my first experience with tear gas. I was living in Bethlehem, Palestine, when Donald Trump announced his Middle East peace plan. Major protests followed. Tear gas was fired by the Israeli army at a demonstration taking place more than a kilometer from my apartment.

The gas traveled downwind and caught me completely off guard. The pain became so intense I found myself incapable of ordering my legs to go forward and I had to beat a hasty retreat back. My eyes were streaming, it was difficult to breathe — and all from gas released some distance away.

Many Names but the Same Pain

Tear Gas in Ophthalmology - More than Just Tears
Unlike pepper spray, tear gas isn’t 100% organic.

Tear gas sucks, something that protestors in a number of countries have discovered over the last year. Hong Kong police deployed tear gas to control pro-democracy protests and now their American counterparts are using it with great alacrity. And though tear gas is not designed to be  lethal, it can still kill and cause serious injuries.

Tear gas (which is actually a white powder that becomes aerosolized when mixed with a solvent) is similar to pepper spray in its effects but there is a subtle difference. Pepper spray is made from naturally occurring oleoresin capsicum whereas tear gas contains 0-Chlorobenzylidenemalononitrile (CS) or 2-chlorobenzalmalononitrile (CN). The former variety is more prevalent, hence the term CS gas or spray.

Tear gas is classified as a chemical weapon and was added to the Geneva Protocol on chemical weapons in 1997. This means that its use is banned in warfare. As the Geneva Protocol only applies to military law, tear gas is allowed to be used by civilian agencies like police forces.

That’s not to say that every law enforcement force uses tear gas routinely. For example, police forces in the mainland U.K. tear use gas for riot control. However, some officers use much weaker pepper spray individually. The tear gas we are currently seeing used in the U.S. is usually fired into crowds as a canister.

Indeed, tear gas manufacturers place warnings on the canisters warning against firing them from close range into crowds or at people’s faces. In light of the injuries protesters are suffering in the U.S. it appears likely that police officers are ignoring these warnings. 

Tears and Sweat but Usually Not Blood

Tear Gas in Ophthalmology - More than Just Tears
Churchill offered blood, sweat and tears. Luckily, tear gas usually only includes the last two.

Regardless of its form, tear gas affects the eyes the same way. It causes severe irritation and conjunctival infection, complete corneal epithelial defects, pseudopterygium, corneal neovascularization, persistent conjunctivalization, corneal opacities and reduced visual acuity.1 These symptoms are usually observed in conjunction with a burning sensation in the throat and nose, increased nasal secretions, chest tightness, sneezing, coughing and retching.2

These thoroughly unpleasant symptoms usually dissipate on withdrawal from the affected area. However, the canisters that release the gas are often more deadly — if one strikes an individual’s eyes it can cause blindness. And if someone is hit with enough force to the head, it can cause a fatal skull fracture.

The long-term effects of exposure to tear gas are still being studied. However, there is evidence that it can have a significant impact. One study examined a group of individuals who were attacked with concentrated CS gas on a bus, some reporting direct contact. They were re-examined at one hour, one month and 10-month intervals.2

Ocular injury was reported by most participants at the one hour mark and was the most common reported injury. After one month, ocular injury was still the most reported complaint. However, the incidence rate declined by up to 50%. The rate of ocular injury declines considerably at 10 months. Respiratory complaints are the most likely long-term complications. This includes asthma, in which two participants reported significant worsening over the recorded time frame.

Got Milk?

Tear Gas in Ophthalmology - More than Just Tears
Please don’t pour milk into your eyes.

Social media currently abounds with images of protestors having their eyes doused with milk to lessen the effects of tear gas. However, washing the eyes with milk will at best create a placebo effect and is not endorsed by tear gas experts like Professor Sven Jordt at Duke University. Washing the eyes with purified water can alleviate some of the symptoms.

Many of those affected by tear gas frequently do not submit for treatment as they may be concerned about arrest or harassment by security personnel. In Ukraine, during the 2014 Euromaidan revolution — which saw the widespread deployment of tear gas by police units —anecdotal evidence showed that there was an upsurge in clinical admissions for conjunctivitis. Simply put: It is difficult to gather peer-reviewed evidence when goons are breathing down your neck.

As protests continue both in the U.S. and in other countries, we are highly likely to see more people receive tear gas injuries. The American Academy of Ophthalmology (AAO) recommends wearing proper eye protection at protests.


1. Kim YJ, Payal AR, Daly MK. Effects of Tear Gases on the Eye. Surv Ophthalmol. 2016;61(4):434-442. 

2. Karagama YG, Newton JR, Newbegin CJR. Short-term and long-term physical effects of exposure to CS spray. J R Soc Med. 2003;96(4):172–174.

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