Inadvertent Viscoelastic Separation of the Pre-Descemet (Dua) Layer in Deep Anterior Lamellar Keratoplasty With Structural Features Revealed by Polarization Microscopy.

Introduction: Deep anterior lamellar keratoplasty (DALK) is a corneal transplant technique that removes the host stroma down to either the pre-Descemet (Dua) layer or Descemet membrane. It is most common for the big bubble technique to create a cleavage plane between the posterior stroma and the pre-Descemet layer. This is advantageous because the pre-Descemet layer has been found to be much stronger than Descemet membrane, and makes the procedure easier to perform. In this report, we present an uncommon viscoelastic-related complication of DALK that resulted in excising the pre-Descemet layer and allowing it to be studied using polarization microscopy.

Methods: DALK was performed using a standard big bubble technique. Postoperatively, a double anterior chamber was found to have been created by the inadvertent passage of an ophthalmic viscoelastic device (OVD) through the pre-Descemet layer. This resulted in the OVD being trapped between the pre-Descemet layer and Descemet membrane. The pre-Descemet layer was then resected in a subsequent operation. The pre-Descemet layer and posterior stroma were studied by polarization microscopy using Sirius Red histochemical staining to elucidate the orientation of the collagen fibers.

Results: The pre-Descemet layer is composed of lamellar arrays of collagen that have consistent polarization properties within each layer but show variable polarization of the strands, indicative of anisotropic strand orientation. The degree of variable polarization of the pre-Descemet layer is distinct from the overlying posterior stroma.

Conclusions: Injecting an OVD into a big bubble in DALK may result in it being trapped between the pre-Descemet layer and Descemet membrane. The pre-Descemet layer shows alternating layers of varying polarization of collagen. This anisotropic structure helps explain the basis for the additional strength that the pre-Descemet layer is known to have.