What the wear schedules actually mean, how to clean reusable lenses properly, why water and lenses must never meet, and the one symptom that means removing them and getting seen the same day.
The terms, which get muddled
Three different things are often described interchangeably, and they carry very different risks.
Daily disposables are worn once and thrown away at the end of the day. There is no cleaning, no solution and no case, which removes most of the ways things go wrong.
Reusable lenses are taken out each night, cleaned, stored in solution and worn again, typically for a fortnight or a month before replacement. These need the full cleaning routine.
Extended or continuous wear means lenses designed to be slept in, for anything up to a month without removal. This is the category that deserves its own warning, below.
A fourth phrase, “daily wear”, confusingly means lenses removed daily rather than replaced daily, which is not the same as a daily disposable. The useful questions to ask at a fitting are how long each lens is worn before replacement, and whether it may be slept in.
Sleeping in lenses
Older writing presents overnight wear as a convenience for people with demanding jobs and irregular hours. That undersells the trade-off considerably.
The cornea has no blood supply of its own and takes its oxygen from the air through the tear film. A lens sits in the way of that, and closing the eye for a night reduces the supply further. Modern silicone hydrogel materials pass far more oxygen than older ones, which is what made overnight wear possible at all, but material alone does not remove the problem: sleeping in lenses measurably increases the risk of microbial keratitis, an infection of the cornea that is painful and can scar it.
That does not make continuous wear indefensible. It makes it a decision to take deliberately, with an optometrist, understanding what is being traded for the convenience — and it is a reason for keeping aftercare appointments rather than skipping them.
Napping in lenses that are not approved for it counts. So does falling asleep in them by accident, which is worth planning around rather than hoping about.
Cleaning reusable lenses
The routine is short and the shortcuts are what cause problems.
Hands are washed and dried before touching a lens. Each lens is rubbed gently in the palm with solution and then rinsed with solution, even where the product is marketed as no-rub — rubbing physically removes deposits and the film of organisms that disinfectant alone does not reliably clear.
The case is emptied, rinsed with solution, and left to air dry face down on a tissue rather than refilled and closed wet. Solution is replaced fresh every time; topping up what is already there does not disinfect. The case itself is replaced regularly, since the biofilm that builds up inside it cannot be scrubbed out.
Solutions are not interchangeable. Their disinfecting ability varies, and switching on the strength of a supermarket offer is a change worth asking about first.
Water
This is the single clearest rule in contact lens care, and the British Contact Lens Association puts it without qualification: water should never come into contact with lenses or with the storage case.
The reason is an organism called acanthamoeba, which lives in tap water, bottled water, chlorinated swimming pools and hot tubs. In a lens wearer it can cause acanthamoeba keratitis — rare, extremely painful, and capable of taking sight. Caught early it may clear quickly; recognised late it can need intensive treatment for up to a year, and it can recur.
In practice that means lenses and cases are never rinsed in tap water, and lenses are out before showering, swimming or getting into a hot tub. Swimming in lenses is a particular risk without well-sealed goggles, and prescription goggles or wearing glasses poolside are the better answers. If a lens or case has been exposed to water, both are replaced rather than disinfected again.
The daily details
Lenses go in before makeup and come out before it is removed. Hairspray and aerosols are best used before lenses are inserted, or with eyes closed.
Lenses are not worn for longer than the hours agreed at fitting, and not worn at all when the eye is already red, sore or watering. A lens that feels wrong is taken out and inspected rather than pushed back into place; a torn lens is replaced.
Nobody should be wearing a lens that has been kept past the replacement date because it still seems fine, and nobody should be reusing a daily disposable.
Keeping a pair of up-to-date glasses is part of wearing lenses safely rather than an admission of defeat. There will be days with a sore eye, and an alternative is what makes it easy to do the right thing.
When to take them out and get seen
One combination matters more than any other: a red, painful eye in a contact lens wearer, particularly with light sensitivity, watering, blurred vision or a feeling of something in the eye.
The lenses come out and stay out, and it needs looking at the same day — by an optometrist, an eye casualty department or a GP. It is not something to sleep on, and it is not a situation for putting a lens back in to get through the working day. Keep the lenses and the case, since they may be useful in identifying what is causing it.
Most red eyes in lens wearers turn out to be something minor. The reason for treating this one seriously is that the serious version looks much the same at the start and the difference in outcome depends on how quickly it is treated.
Aftercare
Contact lenses in the UK are supplied against a valid specification from a fitting, and aftercare appointments are part of the arrangement rather than an upsell. They are when the fit is checked, the cornea is examined for the early changes that have no symptoms yet, and the wear schedule is reviewed.
Anyone wearing lenses they were fitted with years ago, without having been back, is the most common version of a problem waiting to happen.
The comparison with glasses and the different dry eye question are covered separately.
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