Incision of the pre-Descemet layer and Descemet membrane affects outflow facility: ex-vivo studies on a human eye perfusion model

Purpose: The collagen and elastin fibres of the pre-Descemet layer or Dua layer (PDL) fan out to become the beams of the trabecular meshwork (TM), indicating similarities in the structural elements in the PDL and TM. This study evaluated the effects of disruption of the PDL and Descemet membrane (DM) on the facility of aqueous outflow from the anterior chamber, using human eyes and an anterior segment perfusion model (ASPM). Methods: The ASPM was established using human donor eyes. The PDL and DM in the experimental eyes were half incised circumferentially along an 8 mm diameter circle for 180°, and the other half was left non-incised. Results: The experimental eyes in the ASPM model exhibited a decrease in the outflow rate, indicating an increased outflow resistance. In the TM, the expressions of fibronectin, myocilin and alpha-smooth muscle actin were increased in incised compared to non-incised and control samples. The outflow perfusates in the experimental eyes showed a significant increase in the level of active MMP-9 on day 4 and a subsequent decrease on day 9 compared to the control eyes. Myocilin was only detected in the perfusate on day 9 in the experimental eyes. Conclusion: Our study suggests that surgical disruption of the PDL and DM results in decreased outflow, which can be due to an alteration in biomechanical properties, with consequent molecular changes in the TM, adversely affecting the resistance to outflow. This could explain why the incidence of raised pressure is greater with penetrating keratoplasty compared to deep anterior lamellar keratoplasty.