Development of a glaucoma microstent with drainage into the suprachoroidal space. Fluid mechanical model approach

Background. The purpose of this study was to develop a microstent with valve function, which normalizes the intraocular pressure (IOP) and drains into the suprachoroidal space. In comparison to the subconjunctival space the suprachoroidal space is attributed with less fibroblast colonization and activity. Methods. Different glaucoma drainage devices were idealized as tubes and the flow rates were calculated according to Hagen-Poiseuille. The dimensions of the ideal glaucoma implant were modified with respect to an aqueous humor production of 2 mu l/min and the different outflow pathways. Specific components of glaucoma drainage devices at the inlet and outlet were not included. Results. The volume flow calculation of the tested glaucoma implants showed that the dimensions of all lumina were too large to prevent postoperative hypotension. A maximum inner tube diameter of 53 pm was calculated for drainage into the suprachoroidal space based on an intra-ocular pressure (IOP) of 20 mmHg. Conclusion. The glaucoma microstent has to guarantee an aqueous humor flow for physiological IOP. An increase of IOP has to be regulated to physiological pressure conditions by the microvalve.