Water Exposure While Wearing CLs Remains Leading Risk Factor for AK

While authors of this recent study found that in vivo confocal microscopy is the most sensitive diagnostic tool to diagnose Acanthamoeba keratitis, its limited availability means that clinical judgment in the context of relevant risk factors remains essential for timely diagnosis and treatment. Photo: Nicole Carnt, BOptom, PhD. Click image to enlarge. Prompt diagnosis and appropriate management of Acanthamoeba keratitis can be challenging due to indistinct signs of the condition early in its course, before hallmark findings like a ring infiltrate can develop. In a recent study, researchers from Moorefields Eye Hospital in London analyzed the risk factors, clinical features and diagnostic tests for AK and evaluated clinical outcomes with polyhexanide (PHMB) 0.06% monotherapy. They found that water exposure to contact lenses is the most common risk factor, PHMB 0.06% monotherapy is the most effective treatment and in vivo confocal microscopy (IVCM) is the most sensitive diagnostic tool. The findings were reported in Cornea.This study was a retrospective case series of eyes with AK presenting at Moorefields between January 2020 to April 2023. All patients were investigated with smear microscopy, microbial culture, polymerase chain reaction (PCR) and IVCM and were started on PHMB 0.06% monotherapy.This study found a year-on-year increase in the number of AK cases, with an average of 44 new ones every year. This represents a steady increase from the nine cases per year between 1984 and 1992 and 16 cases per year between 2000 and 2012.Of the 149 eyes included, 93.2% were contact lens wearers. Water exposure to lenses was the most common risk factor (71.2%).Only 6.7% of eyes were correctly diagnosed with AK at presentation, with the most common alternative diagnosis being bacterial keratitis (48.3%). The median time from symptom onset to diagnosis was 30 days.IVCM was the most sensitive diagnostic tool (87.2% positive rate, 0.97 sensitivity), followed by PCR (45.6% positive rate, 0.49 sensitivity) and microbial culture (9.4% positive rate, sensitivity 0.13). The relatively low positive culture result may be from poor yield from the corneal scrapes due to suboptimal technique, as they are performed by clinicians of varying levels of experience. “Our guidance now specifically states that clinicians should debride and plate the corneal epithelium on a nonnutrient agar plate in cases of suspected AK,” the researchers wrote in their paper.Corneal scrapes did not contribute to any additional diagnoses of AK that would not have been made with IVCM and PCR, the authors noted. “This study thus provides strong evidence that IVCM and PCR are the most vital investigations to optimize yield of AK cases to aid in diagnosis and management,” they explained in their paper. “Nevertheless, corneal scraping remains important as epithelial debridement may help reduce the microbial load by removing Acanthamoeba trophozoites. Clinicians who currently only have access to smear microscopy and culture should be aware of the real-world limitations of this investigation regarding sensitivity for AK.”PHMB 0.06% monotherapy was successful in nearly 92% of eyes. The authors also found a statistically significant correlation between duration of treatment and best-corrected final visual acuity. “While this has not been previously reported as a predictor of outcomes, it is most likely that patients requiring longer treatment courses of initial PHMB 0.06% monotherapy are infected with more resistant strands of Acanthamoeba,” the authors wrote.They noted that beyond the initial standardized PHMB 0.06% regimen, subsequent treatment decisions, including adjustments to antiamoebic therapy and initiation of corticosteroids, were made at the discretion of the treating consultant. “While each patient remains under the care of the same consultant throughout follow-up, some interclinician variation in timing and thresholds exists, which may have influenced treatment exposure and outcomes,” the authors explained.This is lower than the 86.6% medical cure rate at 12 months found in a prospective study at the same unit that compared PHMB 0.02% + propamidine 0.1% with PHMB 0.08% and followed a more standardized treatment protocol of PHMB therapy. “This study followed a much stricter treatment protocol, and as such, this may be a reason why there was a higher medical cure rate,” the authors explained in their paper. “This hypothesis has been suggested in a recent article that demonstrates higher cure rates when clinicians use a predefined treatment protocol.”Only five patients went on to have corneal transplantation surgery, suggesting that patients with AK are being diagnosed earlier and managed optimally, leading to less stromal scarring.Prediagnosis steroid use, AK relapse, scleritis, ring infiltrate at diagnosis and delayed diagnosis (more than 14 days from symptom onset) were all poor visual prognostic factors. Persistent epithelial defect, corneal perforation and scleritis were identified as the strongest independent predictors of poorer final visual acuity.Click here for the journal source. Arun K, Nderi K, Hoffman J, Koay S-Y. Acanthamoeba keratitis: analysis of risk factors, diagnostic modalities and clinical outcomes at a tertiary referral ophthalmic unit. Cornea. September 7, 2025. [Epub ahead of print.] This article was developed by the editorial staff in conjunction with experts in the field. In the process, AI may have been among the editorial tools used to meet the goals of human editors, who approved all content.