[Obseration clinical, diagnosis and treatment of microsporidial keratitis]

Objective: To investigate the clinical and etiological characteristics of microsporidial keratitis (MK). Methods: A retrospective case series study was conducted. Clinical data were collected from patients diagnosed with MK at Beijing Tongren Hospital, Capital Medical University between June 2023 and April 2025, including risk factors, time to diagnosis, clinical manifestations, laboratory findings, best-corrected visual acuity (BCVA) before and after treatment, and cure duration. In addition to routine microbiological smear cytology, specimens underwent in vitro Vero cell culture for isolation and identification. Polymerase chain reaction (PCR) targeting the small subunit ribosomal RNA gene of microsporidia was performed on corneal lesion secretions and parrot feces (suspected infection sources), followed by sequencing and strain identification to clarify the infection origin. Results: Ten patients (12 affected eyes) were enrolled, comprising 4 males and 6 females with a median age of 36 years (range: 7 to 77 years). Major risk factors included parrot contact (8/10), plant-induced trauma (1/10), and soil-related trauma (1/10). The median interval from symptom onset to diagnosis was 12.5 days (range: 3 to 56 days). At presentation, 2 eyes had BCVA<0.5, and 10 eyes had BCVA≥0.5. Typical manifestations included conjunctival follicular reaction and scattered multifocal punctate elevated epithelial lesions on the corneal surface with positive fluorescein staining. Stromal involvement presented as pseudo-dendritic epithelial defects, diffuse stromal infiltration/edema, neovascularization, and positive keratic precipitates. Microsporidial spores were detected in all 12 eyes via scraping cytology. Vero cell culture was positive in 4 eyes (33.3%), and all PCR assays were positive. In vivo confocal microscopy revealed scattered hyper-reflective puncta in the epithelium, central erosive lesions in epithelial cells, and rose-like aggregates of damaged epithelial cells. Densely arranged punctate structures were observed in the stroma upon stromal involvement. All 9 epithelial MK patients achieved clinical cure after pharmacotherapy, with a median treatment duration of 21 days (range: 10 to 40 days). Conclusions: MK presents as epithelial or stromal type, with the former having a favorable prognosis. Parrot contact and ocular trauma are key risk factors. Vero cells are suitable for microsporidial isolation/culture. The diagnosis relies on typical clinical signs, corneal scraping microbiology, and PCR analysis.