What could be more festive than a spell of beetle-borne corneal ulceration? That’s the seasonal treat that visits parts of Australia each year as a very small beetle causes a lot of pain in the eyes of unlucky residents in northeast Victoria and southern New South Wales, Australia. The culprit is a tiny beetle, and the excruciating condition it causes is known as “Christmas Eye”. Not as fun as it sounds, clearly.

First coined by C S Colvin in the late 1970s, Christmas Eye has afflicted the peepers of Australians under the names seasonal corneal ulcer, Albury-Wodonga syndrome, harvester's eye, and harvester's keratitis. It earned its rather more festive nickname as cases predominantly kick off around Christmas, but here its similarities with the jovial holiday end.

Christmas Eye is a monocular condition, meaning it typically only affects one eye at a time. For a long time, its origin was a mystery – but further presentations of the painful condition eventually revealed it’s caused by Orthoperus, a minuscule group of beetles native to Australia. Patients typically present the day after some kind of outdoor activity such as mowing the lawn or gardening, which is where they meet this tiny ocular saboteur.

Orthoperus are what’s known as vesicating beetles, meaning they’re associated with vesicles and blisters. Some beetle species cause this kind of irritation on the skin, but Orthoperus has been linked specifically to itching and burning in the eyes which can develop into ulcerating lesions on the cornea.

The irritation comes in response to chemicals released by the beetles when disturbed or crushed. The offending irritant is thought to be Pederin, a powerful blistering agent that has a dramatic effect on the corneal epithelium. Being less than one millimeter in size, a person may never know they've come into contact with the beetles and could easily transfer them and their excretions by rubbing their eyes.

As for the symptoms, Christmas Eye is quite the doozy.

“The pain associated with Christmas Eye has achieved folkloric status,” said Victoria optometrist Robert Holloway to Good Vision For Life. “Sufferers describe it as ‘torturous’ and ‘on par with giving birth’.”

Patients who fall folly to Christmas Eye are often woken early in the morning by the pain, and after being unable to remedy it at home, present to clinicians in a considerable state. Fortunately, while its symptoms may be severe, the treatment for Christmas Eye is fairly simple. Anesthetic eye drops can ease the pain, while the epithelium recovers which takes around seven to 10 days.

If you’re local to southeastern Australia, the good news is that Christmas Eye is relatively uncommon – but if you wake up with excruciating eye pain, it’s worth getting checked out by an optometrist.