Like most contact lens wearers, my entire body recoiled in disgust when I read about doctors pulling 27 contacts out of a woman's right eye.
The case, which is recounted in a recent issue of the BMJ medical journal with the innocuous title "Retained contact lenses," tells the story of a 67-year-old British woman who arrived in hospital for routine cataract surgery. That's when surgeons discovered a "blueish mass" of 17 lenses welded together by mucus in her right eye, quickly followed by another 10 contacts in the same eye.
There are so many questions about this story. How do you fit 27 lenses in one eye? Why didn't her left eye have any? But as someone who has worn contacts since age 11, my disgust was immediately tempered by a chilling sense of recognition: This could be me.
Any contact lens user will recognize the following scenario: You've passed out at home, drunk or tired or both, and woken up squinting and unable to see. Did you take your contacts off before you fell asleep? Who knows, but now it's time to play a fun game of Hunt for the Lens Without Scratching Your Cornea!
Watch: Is It Worth Your Time and Money to Freeze Your Eggs?
So how likely is it that we could all end up like the 67-year-old woman in the UK? Might you already have 27 lenses in your right eye without knowing it?
"I have found three disposable lenses in an elderly gentleman's eye during a routine check-up but 27 is extreme," says Ceri Smith-Jaynes, an Association of Optometrists spokesperson and an optometrist herself. "Occasionally someone will insert two on top of each other and wonder why their vision is blurred."
Read more: Why You Hate the Sound of Your Own Voice
According to Smith-Jaynes, the most common symptoms of leaving your lenses in are dry, tired, and red eyes, and irritation. It also depends on the type of lens and its material—there are even some fancy lenses designed for extended wear that can be worn overnight.
However, she cautions, "most are not designed for this and must be removed at night to avoid depriving the cornea of oxygen; this causes the cornea to swell slightly and vision to become foggy, a temporary effect."
She adds: "A lens may stick to the cornea and be difficult to remove in the morning and the risk of infection is increased. The wearer risks an eye ulcer which can be sore and in extreme cases can be sight threatening."
Fortunately, the woman in the BMJ case didn't develop a severe eye infection and lose her sight. But what about the apocryphal horror story that every contact lens wearer has heard—the one about a guy who fell asleep with their contacts in and had to go to hospital to get them removed from the back of their eyeball?
"Lenses cannot slip behind the eye," Smith-Jaynes says. "There is a membrane called the conjunctiva which covers the white of the eye and doubles back over the back of the eyelid, forming a pocket. A lens can only slip under the top or bottom lid about as far up or down as where the crease of your eyelid is."
Phew. So what happens if you accidentally put in a new pair of contacts while there's already a rogue lens sliding around under your eyelid?
"In some cases nothing will happen. However, you are likely to feel the lens irritating under the top lid. It may work its way out or it may need to be removed by an optician or optometrist. Again the risk of infection is slightly increased if it is there a long time but usually nothing really happens other than it being uncomfortable."
According to Smith-Jaynes, it's all down to the individual contact lens wearer and their unique physiology. In fact, the BMJ speculates that the woman's deep-set eyes helped provide an optimal cubby-hole for her lost lenses. This means that what works for one person—like having 27 lenses with relatively little fallout—will lead to excruciating pain and potential blindness for another.
So, always make sure to go for regular check-ups with your optician to find out how long you can leave your lenses in for. "It depends on the quality of the lens and the quality of the tears that coat the particular wearer's eye," she explains. "Your optician or optometrist will tailor the wearing time advice accordingly. For some people this may be just a few hours, for others in a modern lens this could be 7 AM to midnight."
And for God's sake, remember to take them off before you go to bed.