Introduction: Lowering of intraocular pressure in deep sclerectomy (DS) is often explained by outflow via Schlemm's canal (SC). Earlier we showed quantitatively that the main drainage does not happen via SC due to its high hydraulic resistance. Improvement of outflow was clinically observed when inserting a tube in SC adjacent to the scleral lake (SL).
Methods: We developed a biomechanical model to calculate implant parameters. Computer simulation (Mathlab 5.2) was applied. Perimeter of the cross-section of the implant should not be larger than the natural perimeter of SC in order not to compromise its inner wall. Outflow parameters of cross-sections of different geometrical shape with the same perimeter were calculated.
Results: A round cross-section has the lowest hydraulic resistance. Aque-ous could exit via an implant with a radius r=0.11mm at a maximum rate of ~2mm3/min if the operating length of the implant is 1.4mm and the pressure gradient between the aqueous veins and the SL is 5mmHg. Thus the whole outflow could be accommodated via SC. Other dimensions of tube design yielded lower maximal outflow rates.
Conclusion: The positioning of a round porous tube implant into both sides of SC adjacent to the SL is a possibility to ensure outflow after DS. We calculated the dimensions of an implant able to accommodate the volume necessary for sufficient drainage.