Advances in corneal preservation using an active storage machine

Abstract

Since the 1980s, corneal storage has been carried out by eye banks throughout the world, mainly by two methods: short‐term storage at 4°C (America, India), and medium‐to‐long‐term organoculture at 31–34°C (Europe, Australia). In these two techniques, known as passive, the cornea is simply immersed in a storage medium. However, the control of corneal hydration in vivo depends both on the proper functioning of the corneal endothelial cells (responsible for the imbibition pressure IP) and on the presence of a normal intraocular pressure (IOP), both of which are opposed to the stromal swelling pressure (SP): IP = SP‐IOP. By restoring IOP ex vivo in an active storage machine (ASM) that separates an endothelial chamber from an epithelial chamber, corneal hydration is better controlled, thus preventing the formation of deep endothelial folds responsible for endothelial over mortality. The active control of corneal hydration eliminates the need to add macromolecules to deswell the cornea (continuously for cold storage or during the last 48–72 h for organoculture). The toxicity of this forced deswelling has been demonstrated for organ culture.We performed two successive preclinical studies comparing ASM and organoculture with paired human corneas having more than 2000 cells/mm2 at the time of the first endothelial count. The organoculture medium (CorneaMax, Eurobio, les Ulis, France) was identical in both groups. The ASM was an experimental version from our laboratory, including a PEEK (polyetheretherketone) corneal support, a peristaltic pump, an Edwards pressure sensor, a microsolenoid valve and a microcontroller managing the flow rate (2.6 μL/min) and the IOP (21 mmHg). In the first study, for 52 pairs of corneas stored for 4 weeks, the ASM corneas had, at the end of storage, +23% viable endothelial cells compared to passive organoculture. Furthermore, ASM also significantly increased Na+/K+/ATPase protein expression by 3.8 ± 1.4. In the second study, for 12 pairs of corneas stored for 3 months, the ASM corneas had +53% viable endothelial cells at the end of storage compared to passive organoculture. One third of corneas still had 2000 cells/mm2 or more in ASM versus none in organoculture. The ASM significantly increased Na+/K+/ATPase protein expression by 2.9 ± 0.8.The ASM has 2 transparent windows which allow all quality controls to be performed without deconditioning the cornea, and in particular to perform endothelial counting by specular microscopy on a cornea which remains thin. The ASM thus combines the advantages of both methods of storage: long‐term storage without massive oedema and without toxic dextran and a closed system allowing non‐invasive controls. As with the perfusion machines for vascularized organs, the restoration of near‐physiological conditions improves grafts' quality.We have transferred this innovation to THEA laboratories (Clermont‐Ferrand, world specialist in ophthalmology) which is industrializing the ASM via its spin‐off SINCLER. The industrial version will take the form of a single‐use cassette incorporating a flow/pressure regulator, a media reservoir and a waste bin. The cassette will be plugged into a computer‐controlled multi‐place incubator for IOP and media flow management. The ASM could revolutionize eye banking worldwide.