A Novel Orbital Tissue Expander (OTE): From Concept to in vitro Testing

Abstract

Abstract: : Purpose: Congenital anophthalmic and microophthalmic patients require a pressure stimulus for orbital expansion and ideally need an implant whose volume can be stepwise adjusted in an outpatient setting. Insertion of currently available orbital tissue expanders is quite time–consuming and technically difficult in an infant. Furthermore, controlling the direction of expansion and maintaining rigid fixation of the implant in the orbit for uniform expansion remains problematic. The OTE was conceptualized by one of us (DT) to solve these problems. Methods: The OTE consists of a 9.3mm diameter silicone rubber expandable globe joined to a 9.3x4.8mm cylindrical titanium puncture chamber with a needle guard. The OTE slides on a 3.0mm wide titanium "T" bone plate secured to the temporal bone with 1mm titanium screws. Inflation self–aligns the OTE in the horizontal plane of the growing orbit. 30 OTEs were fabricated for in vitro testing which included: injection volume versus diameter measurements to determine consistency between devices, static and dynamic (flex fatigue), weight change in isotonic saline to determine leakage with time, sealability after repeated injection punctures, burst and sterility testing and ex–vivo implantation in kittens. Results: Less than a 5% diameter variance was observed between different OTEs at 0.5cc volume injection increments to 5.0cc (n=4). Less than a 5% weight change was observed in isotonic saline at 37°C over 7 weeks (n=6). Less than a 3% weight change was measured over 14 months (>40 million flex cycles) in the fatigue tester (n=3). No quantifiable leakage (<1mg) was measured after 65 consecutive 30ga needle punctures (n=4). Globes burst by splitting along their length without fragmentation, at greater than 7.0cc (n=4). The OTEs were effectively sterilized by autoclave and easily secured in the orbit of 3 weeks old cats. Conclusions: The OTE can be manufactured reproducibly to fit orbits larger than 9.3mm in diameter, and can be sequentially and controllably inflated via a 30ga transconjunctival puncture until its diameter reaches 6cc, the normal orbital volume in human. Support: NIH–1R43–EY015016–0; NIH center grant P30–EY014801; Innovia LLC, Miami FL; Florida Lions Eye Bank; Research to Prevent Blindness; the Henri and Flore Lesieur Foundation.

Keywords: orbit