Clinical study on bicarbonate-free corneal storage medium

Purpose. Previous studies demonstrated that corneas stored in hypertonic media with NaHCO₃ remained thin and clear although endothelial degeneration occurred. It is speculated that the degeneration may be due, at least in part, to the instability of NaHCO₃ buffer. We investigated whether preservation of the endothelium could be improved if NaHCO₃ buffer is replaced by an internal HCO₃^--generating system. Methods. The study was carried out using 13 donor corneas stored in two different media: Chen Medium (isotonic, without NaHCO₃ buffer, with HCO₃^- generated from oxidation of β-hydroxybutyrate) and Optisol (hypertonic, with NaHCO₃ buffer). The study with corneas procured by Venice Eye Bank were paired, and those from Lions Eye Bank of Delaware Valley were not. The corneas had these characteristics: donor age: 47.3 ± 17.7 yr; postmortem time: 6.1±3.5 hr; and storage time: 3.1 ± 0.4 days. The study was monitored in terms of graft clarity and post-operative changes in corneal thickness and endothelial cell density estimated from specular micrographs. Results. Using the corneas stored in the NaHCO₃ buffer-free media, the grafts became clear and thin in 1-2 weeks after surgery, with evidence of a well preserved endothelium at the first specular microscopic examination 2-4 months after surgery. Two years after surgery (paired study), endothelial cell density was 57.3 ± 53.8% higher than that grafted with the corneas stored in the media containing NaHCO₃ buffer. All the grafts studied remained clear. Conclusions. The study showed that using β-hydroxybutyrate as substrate, the media without NaHCO₃ buffer is at least as effective as Optisol for preservation of the endothelium. The findings suggest that HCO₃^- generated from oxidation of high energy substrate is adequate for corneal storage. More studies are needed to determine whether a NaHCO₃-free media may provide a better storage environment for the cornea.