Purpose:To report the histologic findings of penetrating keratoplasty buttons in decompensated corneas with toxic anterior segment syndrome (TASS) after a cataract surgery is performed.Methods:We evaluated the histologic findings of 16 corneal buttons of 16 patients who exhibited decompensation findings because of TASS by means of light microscopy. The patients were classified into 3 groups: The first group consisted of 5 corneal buttons with mild symptoms in which the central corneal thicknesses (CCTs) were 650 m, and the visual acuities (VAs) were 0.1. The second group consisted of 7 corneal buttons that exhibited moderate symptoms in which the CCTs were between 650 and 750 m and the VAs were between 0.1 and 0.03. The third group consisted of 4 corneal buttons that had severe symptoms in which the CCTs were 750 m and the VAs were 0.03.Results:Light microscopy showed endothelial cell loss, vacuolated and thinned epithelial cell layers, disturbed collagen bonds, and Descemet membrane invaginations in patients in group I. Group II corneal buttons exhibited inflammatory cells (lymphocytes) and extended intercellular space between the epithelial cells, wrinkled Bowman membrane separated from the stroma in some local areas, stromal edema, and early vascularization. In group III, endothelial and epithelial cell layer loss, wrinkled Descemet and Bowman membranes, inflammatory cells, and structurally disturbed collagen bonds located beneath the Bowman membrane, and a greater amount of vascularization in the area of inflammation were observed.Conclusions:The results of the histologic evaluation of the decompensated corneas caused by the TASS are compatible with the clinical severity of the disease. In mild cases, the histologic findings were insignificant; however, when the clinical situation deteriorated, histologic findings became increasingly worse.