Abstract

DO.16.11

The suprachoroidal space in glaucoma surgery – fluid mechanical model considerations for the development of a microstent

Guthoff R. F.¹, Buß D.¹, Schmidt W.², Schultze C.², Stachs O.¹, Sternberg K.², Klee D.⁴, Chichkov B.³, Schmitz K.-P.^2
1Universität Rostock, Medizinische Fakultät, Augenklinik, Rostock; ²Universität Rostock, Institut für Biomedizinische Technik; ³Laserzentrum Hannover e.V., Department of Nanotechnology; ⁴RWTH Aachen, Institut für Technische und Makromolekulare Chemie

Objective: Intraocular pressure (IOP) reducing implants in glaucoma therapy often were of little avail, since these implants drain subconjunctivally and could lead to scarring. Within the framework of the presented project and in consideration of the local pressure and flow features an adjustable micro stent is developed, that is using the natural existing uveoscleral route (out of the anterior chamber, through the ciliary body, into the suprachoroidal space, out through the sclera) and the nature of the suprachoroidal space as a potential cavity.
Methods: Based on literature concerning physiology of aqueous humor dynamics (pressure relationships, formation and outflow rates and anatomy) as well as own in vitro resp. ex vivo examinations a fluid mechanical model for the simulation of the future micro stent is developed. Flow resistances are being defined from experimentally detected pressure differences and flow rates. These are important for the constructional dimensioning of the micro stent and its outflow mechanism.
Results: Due to an aqueous humor production rate of 1,4 to 2,7 µl/min a maximum flow rate of 2,0 µl/min through the stent is being suggested, which leaves the glaucomatous eye through the uveoscleral route. The existing pressure difference between anterior chamber and posterior suprachoroidal space of about 4 to 10 mmHg allows a flow with this gradient through the stent lumen to be determined. The model shows the dependence of this pressure gradient on IOP, so a pressure controlled mechanism can be pictured. The model computations show a switch-barrier for the valves, which shift at a pressure difference of Δp = 1 – 5 mmHg.
Conclusions: The pathophysiological procedures within the recently little noticed suprachoroidal space were re-estimated, since modern technologies make it more interesting again to glaucoma treatment. Furthermore the concept of an regulating micro stent for suprachoroidal implantation seems to be an innovative approach for the further development in glaucoma surgery.
This project is supported by the SFB Transregio 37 "Micro- and Nanosystems in Medicine – Reconstruction of Biological Functions".

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