Sleeping in contact lenses raises the risk of a serious eye infection tenfold

Serious contact-lens eye infections are uncommon, but sleeping in lenses raises the risk of one roughly tenfold, making it the single largest modifiable risk factor a wearer controls [s1]. The infection in question, microbial keratitis, is an infection of the cornea that can progress quickly and, in its worst cases, scar the eye and permanently reduce vision [s1][s2].

What the numbers show

A population study of contact-lens-related microbial keratitis put the annualised incidence at 1.9 per 10,000 for daily-wear soft-lens users, 2.2 per 10,000 for soft-lens wearers who occasionally slept in them, and 19.5 per 10,000 for those on overnight (extended) wear — an order-of-magnitude jump for sleeping in lenses [s1]. Loss of vision occurred in about 0.6 per 10,000 wearers overall [s1]. Those absolute risks are low, which is the reason contact lenses remain a mainstream product; but the relative effect of overnight wear is large and consistent [s1].

The same study identified the behaviours that raise risk beyond wear schedule: overnight use, poor storage-case hygiene, smoking, buying lenses over the internet, less than six months of wearing experience, and higher socioeconomic class [s1]. Notably, newer lens materials marketed as safe for overnight wear had not reduced the incidence of disease compared with older ones — the risk tracks the sleeping, not the specific plastic [s1].

Why sleeping is the pivotal risk

The cornea has no blood vessels and gets much of its oxygen directly from the air; a lens sitting on the eye overnight, under a closed lid, reduces that oxygen and disrupts the tear film that flushes away microbes [s1][s2]. That combination lets bacteria — and in rarer, harder-to-treat cases, amoebae such as Acanthamoeba, associated with water exposure — establish an infection [s2]. Public-health guidance therefore concentrates on a few high-yield habits: not sleeping in lenses unless a clinician has specifically prescribed it, keeping lenses and cases away from water (including showers and swimming), replacing the case regularly, and using fresh disinfecting solution rather than topping up old solution [s2].

The limits of the evidence

The incidence figures come from a specific population and time, and rates vary with lens types and practices that have shifted since; they should be read as the shape of the risk, not a universal constant [s1]. The study establishes strong associations between behaviours and infection, but observational data cannot prove that any single habit caused a given case [s1]. And "microbial keratitis" spans a range from mild, fully treatable infections to rare sight-threatening ones, so a single incidence number blurs a spectrum of severity [s1].

What holds across the evidence and the public-health guidance is unambiguous: the absolute risk of a serious infection is low, overnight wear multiplies it substantially, and the protective behaviours are simple and within the wearer's control [s1][s2]. This is an informational summary, not medical advice; anyone with eye pain, redness or blurred vision while wearing lenses should remove them and seek prompt care.