New insights into persistent corneal subepithelial infiltrates following epidemic keratoconjunctivitis: The first case report with ultrastructural and immunohistochemical investigations

Epidemic keratoconjunctivitis (EKC) is one of the most severe clinical manifestations of human adenovirus ocular surface infection, which may lead to the formation of subepithelial infiltrates (SEIs) in the anterior corneal stroma in 20-50 % of cases. SEIs may be asymptomatic or give rise to corneal aberrations and visual impairment for months or years after acute infection, despite treatments. Here, we describe the ultrastructural and immunophenotypic features of the anterior corneal stroma of a patient who underwent superficial anterior lamellar keratoplasty (SALK) surgery to remove corneal opacities related to clinically significant and steroid-unresponsive, long-lasting SEIs after adenoviral EKC. Before femtosecond laser-assisted SALK surgical intervention, the patient underwent in vivo confocal microscopy that showed a cluster of hyperreflective inflammatory cells within the basal epithelium, associated to an abnormal sub-basal nerve plexus with a fragmented nervous component appearance. The areas corresponding to the SEIs appeared as roundish hyperreflective spots with undefined borders. Transmission electron microscopy analysis of the excised anterior corneal button revealed the presence of giant stromal cells displaying myofibroblast-like features immediately beneath the Bowman's layer. Such abnormal cells exhibited ultrastructural signs of endoplasmic reticulum stress and autophagy, and were positive for markers of activated fibroblasts/myofibroblasts at immunofluorescence analysis. The deeper stroma was instead populated by normal stromal cells (i.e., keratocytes). This case report provides the first morphological evidence that persistent SEIs could be the macroscopic expression of subepithelial giant stromal cells with myofibroblast-like characteristics. Such a novel observation might pave the way toward a better targeted therapeutic management of SEIs.