The Miami InnFocus Drainage Implant ("MIDI") Membrane Spacer for a Novel Micro Drainage Tube

Abstract

Purpose:: To investigate the effect and biocompatibility of a thin novel thermoplastic elastomer called poly(styrene-block-isobutylene-block-styrene;"SIBS") membrane.

Methods:: Twelve NZW rabbits were implanted with MIDI tube shunts and MIDI shields 50-70 µm in thickness and 6-8 mm in diameter. After making a fornix based conjunctival flap dissection, a track 2mm from the limbus was made into the AC using a 27G needle. Using an inserter, the MIDI tube (100µm ID) was deployed through the track inside the AC with distal end of tube on the sclera. The MIDI shield was then placed under the tube such that the distal end laid on the shield and the conjunctiva was closed with a 7-0 vicryl suture. Four rabbits received a 70µm thick soft shield (without suturing of the shield). Another 4 rabbits received a 70µm thick hard shield impregnated with fluorescein to assist in visualization using blue light. In another 4 rabbits the 50 µm shield with fluorescein was sutured in place. The rabbit’s eyes underwent slit lamp exam, pachymetry, tonometry, funduscopy immediately preop and postop and at POD 7, 14, 28 and monthly thereafter with euthanasia at 3 months.

Results:: Slit-lamp exams showed a quiet ocular surface normal, a normal anterior chamber, and in many instances a bleb formation. No hypotony was found and the IOP was normalized to the contralateral eye and was found normal. No extrusion or erosion occurred. No trend was observed between soft and hard MIDI shields. A trend was observed where shields with fluorescein had smaller blebs. In two instances the shield displaced from the tube. Therefore, in subsequent implants the MIDI shield was sutured in place. Three shields curled and folded onto the tube. Although the cause of curling of the shield is unknown at this time, it is postulated that it could be some post-surgical healing contracture forces acting on the thin shield or simply rubbing of the eye. Histology is underway.

Conclusions:: The MIDI micro shunt and shield combination appears to improve bleb formation by creating an artificial surface for aqueous to disperse. The thin SIBS membrane-shield may have other ophthalmic applications such as a subconjunctival patching due to the high degree of biocompatibility.

Keywords: wound healing • conjunctiva • sclera