Eosinophilic keratitis in horses resident in the United Kingdom

Summary Background Eosinophilic keratitis (EK) is considered an emergent ocular condition in horses, although to date, the condition has not been reported in detail in the United Kingdom. Objectives The purpose of this study was to describe the clinical appearance of EK cases in the United Kingdom; to compare the clinical findings to those described for horses with EK outside the United Kingdom; and to describe key differences between cases of non‐eosinophilic ulcerative keratitis and eosinophilic keratitis. Study design A prospective multi‐centre descriptive study involving equine veterinary practices throughout the United Kingdom was performed between June 2022 and April 2024. Methods Samples for corneal cytology were obtained from horses with ulcerative keratitis. EK was diagnosed by identifying the presence of eosinophils in submitted corneal samples. Information regarding signalment, lesion appearance and treatment was gathered. Follow‐up information was obtained to determine outcome and duration to healing. Comparisons between horses with EK and those without were made using univariable nonparametric statistical analyses. Results EK was diagnosed in 18 horses ( n = 18/85) affecting 23 eyes ( n = 23/94); these represented 21.2% and 24.5% of the total number of sampled horses and eyes, respectively. The condition was more common in the warmer months, and more likely to simultaneously affect both eyes compared to non‐EK ulcerative lesions. Corneal plaques were identified in 11/23 (47.8%) eyes diagnosed with EK. Time to healing was significantly longer in EK eyes (median time 42 days, IQR 27–76 days) than non‐EK ulcerative lesions (median 21 days, IQR 10–35 days; p < 0.001). Main limitations Convenience sample and potential selection bias. Multiple clinicians submitted samples, increasing the likelihood of incorrect categorisation. Conclusions EK in horses in the United Kingdom has many similarities to the condition described in other areas of the world. Lesions in horses diagnosed with EK may take longer to heal than horses with non‐EK ulcerative keratitis.