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Wearing contact lenses is a common cause of infectious keratitis. At the 131st International Congress of the French Society of Ophthalmology in Paris, held from May 10 to 12, 2025, Pierre Labalette, MD, PhD, of Lille University Hospital, Lille, France, emphasised that not replacing the lens case regularly is a major risk and the main source of fungal and amoebic infections.

A multicentre case-control study led by Pierre-Henri Becmeur, MD, from the Department of Ophthalmology, Strasbourg University Hospital in Strasbourg, France, and colleagues found that failure to replace the case, continuous wear of contact lenses (day and night), lack of handling instruction, use of generic disinfecting solutions, and mixing solutions all increased the risk for infectious keratitis.

“Disinfectant solutions are not 100% reliable. They have been tested on certain strains of microorganisms, but resistance can occur,” said Labalette. Regular case replacement and choosing daily disposable contact lenses are key preventive measures.

“Visual health with contact lenses demands absolute rigor, particularly regarding hygiene. Patients with keratitis often report that they were not advised to avoid rinsing the case with tap water,” Labalette said.

In high-income countries, contact lens wear is the leading risk factor for infectious keratitis. Up to two thirds of severe corneal infections are linked to contact lenses, which increase the risk for corneal abscesses or infections 10-fold.

Bacterial infections account for 71%-88% of cases of infectious keratitis. Pseudomonas species are the most common, followed by Staphylococcus species. Fungal infections — mainly Fusarium — make up nearly 5% of cases, while amoebae account for about 4%.

The risk levels vary according to the lens type. Extended-wear lenses carry a higher risk than daily disposables. Soft lenses are riskier than rigid lenses, although silicone hydrogel lenses with greater oxygen permeability have reduced this risk. Researchers identified modifiable risk factors in nearly 500 contact lens wearers who developed infectious keratitis.

Occasional overnight lens use carried the highest risk for corneal infection (odds ratio [OR], 6.3), followed by failure to replace the case (OR, 3.95), lack of training in handling the contact lens (OR, 4.47), use of optician-branded disinfecting solution (OR, 5.55), and mixing solutions (OR, 4.68).

Other modifiable factors included extended wear, poor case hygiene, infrequent lens replacement, noncompliance with hygiene rules, smoking, and online purchases. Nonmodifiable risks included recent purchases within 6 months, lower socio-economic status, and male sex.

Labalette warned that online purchases can include counterfeit lenses, particularly cosmetic contact lenses used to change eye colour, which may carry an infection risk and are sometimes shared.

“The state of the case is critical. Poor case hygiene and infrequent replacement are the main causes of contamination, notably by amoebae and fungi,” he stated. “The case should be replaced whenever the disinfectant solution is renewed.”

Fungal infections occur more often in patients with corneal surface damage — after keratoplasty, for example — or in hot weather. Amoebic infections are most often linked to tap water exposure, whether rinsing the case under running water, showering, or swimming while wearing lenses.

Rinsing the case under tap water also risks contamination by pathogenic bacteria, such as Pseudomonas aeruginosa, which thrive in warm water tanks. “This is a heat-loving bacterium found in hot water tanks,” he explained.

Labalette noted that bacterial infections establish quickly and are easier to treat than fungal or amoebic infections. “Once fungi penetrate deep into the cornea, fungal infections become inaccessible to treatment — and the same goes for amoebae.” Corneal transplantation may be required.

“Treatment response for bacterial infection is rapid — often a few weeks — whereas fungal infections can take several months,” he said. Amoebic keratitis, which can cause serious complications, may require years of treatment.

“To prevent these infections, patients must be educated to avoid contact with tap water. Amoebae are inevitably present in tap water,” Labalette said.

This story was translated from Medscape’s French edition.