Microscopic conjunctival plant foreign bodies—A seasonal cause of persistent corneal ulceration in UK horses

Summary Sixteen eyes from 15 horses in the south of England examined for nonhealing ulcers and/or persistent ocular pain between October 2022 and November 2024 were diagnosed with linear plant foreign bodies lodged in the palpebral conjunctiva. Surgical excision of the foreign bodies resulted in resolution of the ulcer and ocular pain in all cases. The cases showed a strong seasonal distribution (October–December), and most horses had known exposure to burdock ( Arctium lappa or Arctium minus ), with owners reporting burdock burrs tangled in the mane and forelock. Microscopic and histopathologic examination of the foreign bodies in five cases appeared consistent with pappus bristles of Arctium sp. ‘Burdock keratitis’ has been reported in horses in the USA, but as far as the authors are aware, this is the first report of seasonal conjunctival plant foreign bodies as a cause of nonhealing ulcers and ocular pain in the United Kingdom. The authors propose that burdock pappus bristles are the likely cause of ocular discomfort in these 15 horses. These foreign bodies were predominantly located in the palpebral conjunctiva of the upper eyelid, with a similar appearance to ectopic cilia and thus may be misdiagnosed. Standing conjunctivectomy is an effective treatment.