Reduction Of Descemet's Membrane Endothelial Keratoplasty (Dmek) Corneal Grafts Elasticity By Proteolytic Enzymes

Descemet membrane endothelial keratoplasty (DMEK) is a well-established procedure for the treatment of corneal endothelial dysfunction. Grafts with higher elasticity are associated with technically challenging surgery and increased rate of postoperative graft detachment. The Descemet membrane determines the graft’s elasticity and is composed of glycoproteins, proteoglycans, collagen and elastin fibers. Enzymatic manipulation to reduce the elasticity of the graft could potentially lead to easier unfolding of the graft, shorten surgery time and reduce postoperative graft detachment.

Experimental surgery lab at a tertiary hospital 

An ex-vivo experimental study including 20 DMEK grafts. The grafts were immersed in proteolytic enzymes: Elastase, Hyaluronidase, Collagenase IV & VIII with their respective buffers. Measurements of graft scroll tightness as measured by maximal scroll width (MSW) was made by ImageJ software. The grafts width was compared to corntrol grafts that were immersed with the different buffers. Endothelial cells were evaluated for possible toxicity using histology with vital dyes. To estimate endothelial cell shedding from the grafts, post-immersion solution from each enzyme solution (after removing the immeresed grafts) were assessed by hemocytometer which counts free floating cells.

Collagenase 4 (N=6): Three grafts showed a mean increase of 43% in MSW (p<0.05). Two showed 10% decrease (p<0.05). One unchanged.
Collagenase 8 (N=2): No significant change in MSW.
Elastase (N=7): Five grafts showed a 15.5% decrease in MSW (p<0.01). One showed a 50% increase (p<0.05). One unchanged.
Hyaluronidase (N=4): Two grafts showed a 18.5% decrease in MSW (p<0.01). One showed 23% increase (p<0.01). One unchanged.
One graft immersed in a combination of Collagenase 4+Elastase showed 35% increase in MSW (p<0.01).
Post-immersion vital staining showed a mean of 30% injured endothelial cells.
Hemocytometer showed no significant difference in cellular shedding.

In this enzymatic panel, Collagenase 4 in the appropriate conditions showed the most promise in reducing the graft elasticity, without causing severe endothelial toxicity and shedding. Other enzymes were less potent for this matter.