Contact Lens Cultures Lead to Optimal Antibiotic Selection

Additional cultures of contact lenses or cases are of value when microbes are absent from corneal scraping.

Clinicians are now facing the challenge to specifically tailor antibiotics to individual contact lens-associated keratitis cases at a time when the use of contact lenses is increasing. Researchers at the University of Pittsburgh, University of Michigan, and Stanford University assert that culturing both the patient’s cornea and contact lens will optimally inform practitioners’ choices of antibiotics, according to a chart review published in the British Journal of Ophthalmology.

In a retrospective observational study, investigators analyzed the microbiological data of patients who visited the University of Pittsburgh Medical Center for contact lens-related keratitis between April 2006 and May 2019. The final population sample included 72 patients (80 eyes) whose electronic records included both corneal scrapings and contact lens cultures. 

“In our study, it is noteworthy that treatment in at least half of these cases was based on the microbiological yield from contact lens cultures,” according to the study. “This reiterates the importance of obtaining contact lens cultures especially in patients with no yield on corneal scrapings.”

Cultured samples comprised 135 total incidences of microbial growth. The researchers divided the participants into 3 groups. Group 1 consisted of patients for whom the microbial growth on both corneal and contact lens cultures agreed (6.7% of samples, 7 subjects). Group 2 consisted of those whose microbial growth on corneal and contact lens cultures disagreed (44.4% of samples, 34 subjects). Group 3 consisted of those whose microbial growth was noted only on the contact lens cultures (close to 49% of samples, 31 participants).

Investigators isolated bacteria including Pseudomonas spp, Stenotrophomonas maltophilia, Serratia sp, and other microbes including Acanthamoeba, but the most frequently found organism in both corneal and contact lens cultures was Pseudomonas. For subjects with corneal cultures showing no growth, the most prevalent contact lens-isolated bacteria was Pseudomonas spp (n=25). Further, 50% of the participants in group 3 were treated based on contact lens culture results, according to the study.

Because Pseudomonas spp was among the most frequently cultured microorganisms, 29% of incidences (n=39), researchers formed an additional subgroup and found that 89% (n=35) of the subgroup’s corneal and contact lens cultures did not agree. “In 35 incidences, Pseudomonas grew from contact lenses,” they added. Of note, several of the participants in the Pseudomonas isolates subgroup acknowledged leaving contacts in while sleeping, or inadequately cared for their lenses.

Participants experienced no difference in outcomes for visual acuity, number of antibiotic drops, or complications whether they were treated based on results of corneal or contact lens culture. Limitations of the study included a relatively small sample size across the 13-year study period. In addition, investigators did not differentiate between cultures of the contact lens or lens case.

Previous studies list detractors for culturing, such as less specific results when multiple microorganisms are produced, as well as increased laboratory costs. “However, our experience is quite different, as culture data almost always help to narrow antibiotic selection especially in refractory cases,” the researchers concluded.


Mukhtar S, Atta S, Durrani A, et al. Microbiological evaluation of corneal and contact lens cultures in contact lens-associated bacterial keratitis. Bri J Ophthalmol. Published online December 23, 2020. doi:10.1136/bjophthalmol-2020-317832