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This is a non-comparative retrospective observational case series from India from 1 October 2020 to 31 January 2021. The inclusion criteria were: (1) presence of nummular / coin shaped lesions with at least one >2mm in size and / presence of a complete or incomplete ring / disciform shaped cellular infiltration, (2) anterior segment optical coherence tomography (OCT) with focal thickening due to stromal oedema, (3) microscopic diagnosis of microsporidial keratitis based on spores detection, or microsporidial DNA in polymerase chain reaction (PCR) of corneal scrapings. Real-time PCR for adenovirus (ADV), Epstein-Barr virus (EBV), herpes simplex (HSV) and varicella-zoster (VZV) was performed. Twenty out of 152 (13%) were diagnosed. The mean age and duration of symptoms were 35.7 years and 46.3 days respectively. Half had predisposing factors (e.g., trauma) and 30% had prior recurrences. Clinical presentations included disciform keratitis (n=12), incomplete / complete ring (n=5), and combination (n=3), or variable subepithelial infiltrates (n=14). All cases had stromal oedema with intact epithelium and pigment dusting on endothelium. Microsporidia spores were found in smears of 17/20 (85%), pan-microsporidial DNA in 14/20 (70%), and Vittaforma cornea by sequencing in 11/20 (55%). ADV in 70%, VZV 10%, EBV 5% and HSV 5% were detected. Resolution of inflammation and oedema was achieved within two weeks of topical steroid treatment.

Microsporidia-induced stromal keratitis: a new cause of presumed immune stromal (interstitial) keratitis.
Mohanty A, Behera HS, Barik ME, et al.
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Jonathan Chan

Royal Hallamshire Hospital, Sheffield, UK.

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