Ocular Surface Changes After Sulfur Mustard Exposure in Rabbits, Monitored by Impression Cytology

Purpose: Ocular injuries after exposure to sulfur mustard (SM) are characterized by acute corneal erosion and inflammation of the anterior segment that may be followed by delayed corneal neovascularization and epithelial defects, associated with limbal stem cell deficiency in part of the exposed eyes. This study aimed to further clarify the mechanism of the late injury by monitoring SM-induced cytological alterations in the ocular surface, in relation to the clinical symptoms, using impression cytology (IC). Methods: Rabbit eyes were exposed to SM vapor (n = 20) and were clinically observed up to 4 weeks. Samples for IC were collected simultaneously from the upper bulbar conjunctiva, limbus, and cornea and then fixed and stained with periodic acid-Schiff and hematoxylin. At 1 month, animals were killed and eyes dissected and processed for histology. Results: Concomitant with clinical symptoms of SM ocular toxicity, IC showed significant long-term loss of conjunctival goblet cells shortly after exposure, followed by abnormal differentiation toward squamous metaplasia. Simultaneously with corneal erosion, apoptotic bodies and cellular debris were seen in the corneal epithelium, followed by regeneration at 1 week. Migration of conjunctival goblet cells toward the cornea was noted in neovascularized eyes, as early as 1 week, indicating limbal stem cell deficiency. The IC findings were supported by histological evaluation. Conclusions: Continuous monitoring of the ocular surface after SM exposure by IC enables earlier detection of pathology and therapeutic intervention, therefore, is recommended for routine follow-up of casualties. Prolonged loss of goblet cells may point toward the role of mucin in the pathogenesis.