A novel orbital tissue expander (OTE): design, in vitro, and in vivo studies

Purpose: To assess the efficacy of a novel orbital tissue expander (OTE) in treating congenital anophthalmic and microphthalmic infants. Methods: The OTE implant is an inflatable (0.5 to >6cc) silicone rubber globe sliding on a titanium T-shaped bone plate secured to the temporal bone with 1mm titanium screws. In vitro testing was performed to assess injection volume versus diameter measurements to determine consistency between devices, flex fatigue for durability of the implants when compressed, weight change in isotonic saline at 37°C to mimic human body temperature, seal durability by puncturing the globe numerous times while inflating, capacity before rupture to determine the maximum amount of saline it is able to contain, and effective sterilization. Ex-vivo testing was performed for adjustments prior to in vivo study. An OTE was then implanted in five 2-week old kittens (OS only) and inflated in 0.5cc increments. Three control animals received enucleation alone. All 8 animals were followed for 18 weeks and underwent euthanasia for morphological and histopathological analysis. Results: In vitro testing confirmed a <5% diameter variance between different OTEs inflated in 0.5cc increments up to 5.0cc, <5% weight change in isotonic saline at 37°C over 7 weeks, <3% weight change over 14 months in the fatigue tester, and no quantifiable leakage (<1mg) after 65 consecutive 30ga needle punctures. The OTEs were successfully sterilized by autoclave and easily secured in the orbit of postmortem kittens. The in vivo study demonstrated biocompatibility of the implant which stimulates orbital bone growth resulting in almost no difference between the implanted socket and the control eye of the cat. There were no adverse effects in the normal maturation, weight gain, and food intake of the cats. Light microscopy showed no signs of foreign body reaction. Pictures of the implants were obtained by using a shadow-photogrammetry system to compare the explanted OTE with the OD control eye. Conclusion: In vitro and in vivo studies show the implant's potential to safely treat anophthalmic and microphthalmic infants.