Thermomechanical stability of sclera after glyceraldehyde crosslinking

Recently, glyceraldehyde-induced crosslinking was proposed by us for the treatment of progressive myopia, increasing significantly the biomechanical rigidity of sclera. The aim of the present study was to investigate the changes in thermo-mechanical stability after scleral glyceraldehyde crosslinking, allowing a better evaluation of the efficacy of crosslinking.

One hundred and twenty six porcine eyes were retrieved from the local abattoir. Using hot saline solution, the threshold shrinkage temperature (Ts) was determined for both equatorial scleral strips and whole eye globes incubated with glyceraldehyde for 4 days. Untreated control samples and specimens crosslinked with formaldehyde for 4 days were tested for comparison. In the globes, a small 6 mm limbus-parallel scleral strip was excised 5 mm behind the limbus to allow extrusion of the vitreous, facilitating heat-induced globe contraction. After heat exposure, the eyes were examined histologically by light microscopy.

There was significant Maillard browning of the sclera after incubation with glyceraldehyde. The contraction temperature determined in the glyceraldehyde group was 78°C for both scleral strips and globes, in the formaldehyde group 88°C for scleral strips and 92°C for globes, and in non-crosslinked controls 62°C for scleral strips and 68°C for globes. Interestingly, the eye balls contracted in an implosion-like manner, leading to an abrupt reduction in eye volume by about one third. On light microscopy, scleral thickening, heat denaturation of collagen fibers, and loss of birefringence were noted.

Scleral collagen crosslinking by glyceraldehyde proved very efficient in increasing the scleral thermomechanical stability by at least 10°C in Ts, stabilizing the eye shape and preventing the shrinkage of the eye in all dimensions. There is hope that, in a similar manner, glyceraldehyde crosslinking can stabilize the scleral collagen crosslinks and eye shape in myopia, stopping progression of scleral thinning and stretching.