Risks associated with wearing contact lenses
Written by Javier Cabrerizo
Quick answers
Are contact lenses dangerous?
Contact lenses are safe for most people when used correctly, but they can increase the risk of dry eyes, corneal damage and infections.
Can you sleep with your contact lenses?
As a general rule, you shouldn’t. Sleeping in contact lenses significantly increases the risk of serious corneal infections.
What is Acanthamoeba keratitis?
It is a rare but serious infection of the cornea, which is particularly associated with contact lens use. In severe cases, it can lead to permanent loss of vision.
Which contact lenses are the safest?
If contact lenses are the right choice, daily disposable lenses generally carry a lower risk of infection than reusable lenses.
Can contact lenses cause dry eyes?
Yes. Contact lenses can affect the tear film and increase evaporation, which can lead to dryness, irritation and reduced comfort.
What if I can no longer tolerate contact lenses?
Glasses are one option, and for suitable patients, vision-correcting treatments such as Aqua PRK, ICL or RLE may be other options.
At the Copenhagen Eye Institute, we view contact lenses for what they are: a truly useful visual aid for many people — and a medical device that carries real, well-documented risks when worn beyond the limits that your eyes can tolerate.
It usually starts with dry eyes
The most common reason why people stop wearing contact lenses is not infection — it is dryness. A lens rests directly on the tear film on the surface of the cornea and disrupts it after several hours of wear: it absorbs moisture, thins the tear film and increases evaporation. Dryness is consistently cited in the ophthalmological literature as the main reason why people stop wearing contact lenses. For most people, this manifests as a mild, temporary irritation towards the end of the day. But dryness is not just a matter of comfort — a compromised tear film and ocular surface also make the cornea more vulnerable to everything that follows: micro-scratches, breakdown of the epithelium and, ultimately, a gateway for microorganisms.
From irritation to infection: what the figures actually show
- For soft disposable contact lenses worn correctly, the annual incidence of microbial keratitis is around 2 per 10,000 wearers.
- For reusable soft contact lenses intended for daily wear (e.g. monthly lenses that are removed at night), the incidence roughly doubles.
- When worn at night or for longer periods, the incidence rises to approximately 10–15 times that of daytime-only wear — mainly because sleeping with lenses in deprives the cornea of oxygen and prevents the tear exchange that normally washes away bacteria.
These are population averages from large case-control studies carried out in Europe and Australia. The microorganisms involved also vary depending on usage patterns: infections associated with daily use are typically caused by slower-growing staphylococci, whilst prolonged use or overnight use is disproportionately associated with Pseudomonas aeruginosa — a fast-growing pathogen that can potentially threaten eyesight.
Acanthamoeba keratitis: rare, but one of the most feared complications in our field
If there is one infection that keeps cornea specialists awake at night, it is Acanthamoeba keratitis (AK) — a parasitic infection that is difficult to diagnose, painful to an extent that is out of proportion to the clinical signs, and notoriously resistant to treatment. Acanthamoeba is by no means an exotic organism. It is found everywhere — in tap water, showers, swimming pools and soil — and most of us have antibodies against it. What makes wearing contact lenses dangerous is that a lens can trap the organism against the cornea, giving it time to invade a compromised epithelium. The figures give pause for thought regarding a condition that many patients have never even heard of:
- Contact lens use accounts for up to 93 per cent of AK cases in the developed world (StatPearls / NCBI clinical review).
- A nationwide Dutch surveillance study (2009–2015) showed that the incidence among soft contact lens wearers had risen to approximately 1 in 21,000 per year, and that the number of cases had tripled over the study period.
- Reusable lenses carry approximately three to four times the risk of AK as disposable lenses (Carnt et al., case-control study, Ophthalmology), and the overall risk of AK is estimated to be around 20 times higher among contact lens wearers than in the general population.
- In the same Dutch cohort, 39 per cent of patients experienced treatment failure – meaning significant, permanent vision loss and/or the need for a corneal transplant.
This is a rare condition. But ‘rare’ is not the same as ‘irrelevant’ when the consequence is an infection that can lead to blindness in an otherwise healthy, young eye — and the age group most frequently affected is 20–40 years, precisely the section of the population most likely to wear contact lenses purely for reasons of convenience.
When contact lenses end up on the operating table for the wrong reasons
Corneal transplantation (keratoplasty) is one of the most effective treatments in the entire field of ophthalmology — but it is a major operation that carries lifelong risks of graft rejection, wound dehiscence and the need for further surgery. In specific case series on Acanthamoeba keratitis, approximately 1 in 5 affected eyes ultimately required a penetrating keratoplasty. Comparative data on complications requiring corneal transplantation also suggest that visual outcomes following infection-related complications associated with contact lenses are, on average, significantly poorer than those following complications from laser surgery. We are not saying this to frighten our patients, but because it is the honest clinical picture: in a small but real number of cases, an optional corrective aid can trigger a chain of events that culminates in a corneal transplant — something that has essentially never occurred following a well-chosen refractive treatment.
Practical advice that we give to our own patients
- Daily wear time: Most manufacturers’ instructions and the clinical consensus state that safe daily wear is within the range of 8–12 hours, although individual adjustments may be made by your optician or optometrist based on the lens material and the condition of your ocular surface. Lenses with lower oxygen permeability (older hydrogel lenses) should generally be limited to the lower end of this range.
- Chronic dry eyes are a relative – and sometimes absolute – contraindication. If you already have a compromised tear film, wearing lenses increases both discomfort and the risk of infection. This should be assessed and must not simply be assumed to be absent.
- Never sleep in your contact lenses unless they are specifically designed and prescribed for extended wear under close supervision.
- If a contact lens is not designed for single use, you must never reuse it beyond the prescribed replacement period, and you must never top up or reuse lens solution.
Not all contact lenses pose the same risk
If contact lenses are the right choice for you, the type of lenses is crucial:
- Soft, disposable daily wear contact lenses are the preferred choice if you wear contact lenses at all. As a fresh, sterile lens is used only once and then discarded, this prevents biofilm formation, contamination of the case and hygiene issues associated with reuse – factors which account for a large part of the increased risk seen with reusable lens types.
- Newer silicone hydrogel materials allow approximately five times more oxygen to reach the cornea than older hydrogel lenses (Dk values now regularly exceed 100 barrers), which significantly reduces oxygen-deficiency-related complications such as corneal neovascularisation. This is a genuine and welcome advance. However, it is important to be precise about what it does and does not do: large-scale case-control data show that silicone hydrogel material in itself has not been shown to significantly reduce the overall risk of microbial keratitis compared with conventional soft lenses — better oxygen supply is not the same as eliminating the risk of infection, and some silicone hydrogel materials are more prone to lipid deposition and reduced wetting ability, which in itself can cause dryness and intolerance.
What are the alternatives?
- Spectacles remain the lowest-risk option for vision correction and carry virtually none of the infection risks mentioned above.
- Refractive surgery — including Aqua PRK, implantable Collamer lenses (ICL) and refractive lens exchange (RLE) — can, in suitably selected patients, permanently reduce or completely eliminate dependence on contact lenses, thereby removing the daily risk of infection and oxygen deprivation rather than merely managing it.
Every patient is different, and refractive surgery has its own selection criteria and risk profile, which should be assessed on a case-by-case basis by a cornea specialist or a specialist in refractive surgery. However, for patients who still need to wear contact lenses despite recurring signs of intolerance, it is entirely reasonable to request such a consultation. Our view: Contact lenses are a legitimate and valuable tool for many people, but wearing contact lenses is a medical decision involving real, measurable risks that deserve the same careful consideration as any other treatment. There is a wealth of scientific evidence suggesting that tolerance to contact lenses decreases with age. If your eyes are signalling that they are struggling, it is worth heeding that message and seeking a specialist’s assessment.
References
- Dart JKG, Radford CF, Minassian D, Verma S, Stapleton F. Risk Factors for Microbial Keratitis with Contemporary Contact Lenses: A Case-Control Study. Ophthalmology. 2008;115:1647–1654.
- Stapleton F, Keay L, Edwards K, et al. The Incidence of Contact Lens–Related Microbial Keratitis in Australia. Ophthalmology. 2008;115:1655–1662.
- Carnt N, et al. Acanthamoeba Keratitis Risk Factors for Daily Disposable and Reusable Contact Lens Users: A Case-Control Study. Ophthalmology. Summarized in American Academy of Ophthalmology, EyeNet, “Risk of Acanthamoeba Keratitis in Contact Lens Users,” 2023.
- Verani JR, et al. / van Meer B et al. The Rising Incidence of Acanthamoeba Keratitis: A 7-Year Nationwide Survey in the Netherlands. Acta Ophthalmologica / associated cornea literature, 2009–2015 cohort, PMC6731013.
- Acanthamoeba Keratitis. StatPearls, NCBI Bookshelf, updated 2023.
- Acanthamoeba Keratitis. EyeWiki, American Academy of Ophthalmology.
- Evaluation of Acanthamoeba Keratitis Cases in a Tertiary Medical Care Centre Over 21 Years. PMC7806847.
- Complications Leading to Keratoplasty Among Contact Lens Users and LASIK Patients: A 10-Year Cross-Sectional Analysis. PMC8380166.
- Daily Disposable and Silicone Hydrogel Contact Lenses and Risk of Microbial Keratitis. American Academy of Ophthalmology, Editor’s Choice summary, 2013.
- Young G. Why One in Four Contact Lens Wearers Doesn’t Achieve Optimum Vision: An Evaluation of Field Trial Data of Multifocal Contact Lenses. (Cited widely as the basis for dryness as the leading cause of contact lens discontinuation), 2011.
- Manufacturer prescribing/fitting guidance (Alcon DAILIES TOTAL1, Johnson & Johnson 1-DAY ACUVUE TruEye) on maximum daily wearing schedules, accessed via published clinical trial protocols, ClinicalTrials.gov.