Purpose: To describe and analyze the microstructural changes in herpetic stromal keratitis (HSK) observed in vivo by spectral-domain ocular coherence tomography (SD-OCT) at different stages of the disease. Methods: A prospective, cross-sectional, observational, and comparative SD-OCT analysis of corneas with active and inactive keratitis was performed, and the pathologic differences between the necrotizing and non-necrotizing forms of the disease were analyzed. Results: Fifty-three corneas belonging to 43 (81.1%) women and 10 (18.8%) men with a mean age of 41.0 years were included for analysis. Twenty-four (45.3%) eyes had active keratitis, and 29 (54.7%) had inactive keratitis; the majority (83.0%) had the non-necrotizing form. Most corneas (79.1%) with active keratitis showed stromal edema and inflammatory infiltrates. Almost half of the active lesions affected the visual axis, were found at mid-stromal depth, and had a medium density. By contrast, corneas with inactive keratitis were characterized by stromal scarring (89.6%), epithelial remodeling (72.4%), and stromal thinning (68.9%). In contrast to non-necrotizing corneas, those with necrotizing HSK showed severe stromal scarring, inflammatory infiltration, and thinning. Additionally, most necrotizing lesions (77.7%) affected the visual axis and had a higher density (P = 0.010). Conclusion: Active HSK is characterized by significant epithelial and stromal thickening and the inactive disease manifests epithelial remodeling at sites of stromal thinning due to scarring. Necrotizing keratitis is characterized by distorted corneal architecture, substantial stromal inflammatory infiltration, and thinning. In vivo SD-OCT analysis permitted a better understanding of the inflammatory and repair mechanisms occurring in this blinding corneal disease.

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