Contact lens hygiene: rules, risks and warning signs

Contact lenses are medical devices that sit directly on the cornea, and the US Centers for Disease Control and Prevention (CDC) is clear that they are not risk-free. Small lapses in lens care can lead to infections that, in rare cases, permanently affect your sight. The good news is that many of these risks can be reduced with a few well-supported habits. Here is what the CDC and the American Academy of Ophthalmology (AAO) recommend – and what studies show about the risks.

Why hygiene matters with contact lenses

The main concern is an infection of the cornea known as microbial keratitis. According to a 2022 review in Deutsches Ärzteblatt International, contact lens wear accounts for 52 to 65 per cent of new cases, and the risk for lens wearers is around 80 times higher than for people who don’t wear lenses. Bacteria are the usual cause – in Europe, the review reports, in 91 to 100 per cent of cases, with Pseudomonas aeruginosa by far the most common; acanthamoebae account for 1 to 5 per cent.

In absolute terms, such an infection remains rare. In a nationwide study from Australia published in 2008, around 2 in 10,000 people a year developed one if they wore conventional soft (hydrogel) lenses during the day only or used daily disposables; with silicone hydrogel lenses worn during the day only, the figure was 11.9 in 10,000. Risky habits, on the other hand, are widespread: in a 2014 CDC survey of about 1,000 lens wearers in the US, roughly 99 per cent reported at least one hygiene lapse. 55 per cent had at some point topped up the solution in their case instead of replacing it, and 82 per cent replaced their case less often than recommended. And nearly a third had needed to see a doctor because of a red or painful eye.

Sleeping in lenses: a strong risk factor

According to the CDC, sleeping in contact lenses increases the risk of a lens-related eye infection six- to eightfold. The CDC adds that the risk is raised whether it happens by accident, occasionally or as part of a prescribed wearing schedule. Even so, it happens a lot: in the CDC survey, around half had slept overnight in their lenses at least once and 87 per cent had napped in them. In a 2018 report, the agency described six serious corneal infections after sleeping in lenses; in two patients the cornea perforated and had to be replaced with a transplant.

In the Australian study, the size of the effect depended on the type of lens and how it was worn. People who regularly wore conventional soft lenses overnight developed an infection about ten times as often (19.5 cases per 10,000 wearers per year) as those who wore them during the day only (1.9). With silicone hydrogel lenses, overnight wear roughly doubled the rate (25.4 versus 11.9). Occasional overnight wear of daily disposables doubled the rate from 2.0 to 4.2. Exactly why sleeping raises the risk has not been fully explained, the CDC notes. What is clear, though: only sleep in your lenses if your eye care professional has explicitly told you to.

Water: why showering and swimming are risky

Water and contact lenses don’t mix – according to the AAO, not even sterile water. Acanthamoebae play a part here: single-celled organisms that, according to the Ärzteblatt review, are widespread and found mainly in watery environments. The CDC counts tap water and homemade solutions in lens care, as well as swimming, showering or using a hot tub with lenses in, among the risk factors for Acanthamoeba keratitis.

In the CDC survey, 85 per cent had showered in their lenses, 61 per cent had swum in them and more than a third had rinsed them in tap water. A 2023 case-control study from England suggests that showering is no minor matter. It compared 83 patients with 122 controls, including 20 patients who wore daily disposables. Among the daily disposable wearers, those who showered with their lenses in had around 3.3 times the odds of Acanthamoeba keratitis. Because this subgroup is small, the direction is clear but the exact size of the effect is uncertain. Saliva is off limits too – the AAO points out that it is not sterile.

Acanthamoeba keratitis: rare but serious

According to the Ärzteblatt review, more than 85 per cent of Acanthamoeba infections of the cornea occur in contact lens wearers, mostly those who use soft lenses. The CDC describes pain that is out of proportion to the rather unremarkable clinical findings as a classic feature. Diagnosis is often difficult: on average it takes 2.8 months to get it right, the review reports, and almost half of cases are initially mistaken for a herpes infection of the cornea. Treatment can last 6 to 12 months or longer, according to the CDC. According to the Ärzteblatt review, at least one in five cases requires a corneal transplant, and around a third of those affected are left with permanently reduced visual acuity.

Everyday lens care rules

These points are based on recommendations from the CDC and the AAO; also follow the instructions for your care solution and the advice of your eye care professional.

• Wash and dry your hands: wash them with soap and water before every contact with your lenses and dry them thoroughly with a clean, lint-free towel.
• Rub and rinse: rub and rinse your lenses with solution – according to the AAO, even if the product is labelled ‘no-rub’.
• Always use fresh solution: never top up or reuse old solution in the case; replace it completely every time.
• No water, no saliva: don’t rinse or store your lenses in water, don’t wet them with saliva, and take them out before showering or swimming.
• Look after the case: rinse it with solution rather than tap water and, as the CDC recommends, leave it to air-dry upside down with the caps off.
• Replace the case: at least every three months, and straight away if it is cracked or damaged.
• Stick to wearing times: wear and replace your lenses only as prescribed.
• Keep your check-ups: have the fit of your lenses and your cornea checked regularly by your eye care professional. In the study from England, infrequent check-ups were the strongest modifiable risk factor among daily disposable wearers.
• Keep glasses as a backup: carry a pair with an up-to-date prescription so you can take your lenses out whenever you need to.

If your lenses often feel dry at the screen, you’ll find tips in our article on dry eyes and screen work.

Daily disposables or monthly lenses?

Daily disposables are thrown away after a single use, so no case or solution is involved. For corneal infections overall, the Australian study found hardly any difference between daily disposables (2.0 cases per 10,000 wearers per year) and conventional soft hydrogel lenses worn during the day only (1.9). With silicone hydrogel lenses worn during the day, however, the rate was 11.9. The authors concluded that newer lens types had not reduced how often these infections occur.

Acanthamoeba keratitis is a different story. In the 2023 study from England, the odds were around 3.8 times higher with reusable soft lenses – such as monthly or two-weekly lenses – than with daily disposables, and around 4.6 times higher with rigid gas-permeable lenses, although the latter figure is statistically very uncertain. The researchers estimate that 30 to 62 per cent of cases could be prevented if wearers of reusable soft lenses switched to daily disposables.

Daily disposables are no free pass, though. In the small group of daily disposable wearers, the odds were higher for those who attended check-ups less often (around 10 times), reused lenses (around 5.4 times), wore them overnight (around 3.9 times) or wore them in the shower (around 3.3 times). Which type of lens suits you is something to discuss with your eye care professional.

Warning signs: when the lens must come out

Redness, pain, watery eyes, sensitivity to light, blurred vision or discharge: if you notice any of these, the CDC and AAO advise taking your lenses out and contacting an ophthalmologist straight away. The CDC also lists pain in or around the eye that gets worse – even once the lens is out – as a warning sign. According to the Ärzteblatt review, bacterial corneal infections often develop within a few days and can worsen quickly.

A red, painful eye while wearing contact lenses is not something to sit out: take the lens out and have your eye examined by an ophthalmologist straight away.

A tip from the review: bring the lenses you were wearing and your lens case to the examination – they can help identify the pathogen.

If contact lenses become a hassle in the long run, laser eye surgery or an implantable contact lens (ICL) may be an alternative, depending on your eyes. Both are procedures with their own requirements and risks that need careful assessment. At My Laser Vision in Wallisellen, a free pre-assessment of around 30 minutes is available for this.