Corneal calcification of acellular porcine corneal stroma following lamellar keratoplasty.

PURPOSE To describe the corneal calcification of acellular porcine corneal stroma (APCS) following lamellar keratoplasty (LKP) and identify risk factors. METHODS Two cases of APCS calcification were evaluated by slit-lamp photography and anterior segment optical coherence tomography (AS-OCT). von Kossa staining and scanning electron microscope/energy-dispersive spectrometry (SEM/EDS) were performed on pathologic tissue. Associated graft and postoperative risk factors were analysed. Acellular porcine corneal stroma (APCS) cleanliness and element content after rinsing with sterilized water were observed by SEM/EDS and inductively coupled plasma mass spectrometry. Calcium metabolism-related proteins were analysed by protein mass spectrometry. Corneal epithelial defects and postoperative medications were reviewed. RESULTS Two cases of APCS calcification occurred at 23 and 22 days postoperatively. Anterior segment optical coherence tomography (AS-OCT) and von Kossa staining demonstrated calcium deposition in the superficial stroma composed of calcium, phosphorus and oxygen conforming to the Ca/P ratio of hydroxyapatite. Phosphate crystals were present on the APCS surface and decreased with number of rinsing times. The phosphorus content of APCS was minimal after rinsing 10 times and avoiding excessive corneal swelling. Calcium metabolism-related proteins were downregulated in APCS. Patients with corneal calcification had 1-week postoperative corneal epithelial defects and were treated with three types of phosphorous eyedrops. CONCLUSIONS Acellular porcine corneal stroma (APCS) calcification occurs in the superficial corneal stroma about 1 month after LKP. The application of AS-OCT, von Kossa staining and SEM/EDS provides a basis for the clinical and pathological diagnosis of corneal calcification. The associated risk factors were mainly high phosphorus content and downregulated calcium metabolism-related proteins in APCS. Postoperative epithelial defects, inflammation and use of phosphorous eyedrops may promote corneal calcification.