In vitro Testing of the Orbital Tissue Expander (OTE)

Abstract

Purpose: : To determine the safe inflation range of the Orbital Tissue Expander (OTE). The OTE is an inflatable polymeric globe which uniformly delivers pressure to the boney structures of the orbital cavity as a means of stimulating orbital growth for the prevention of facial asymmetry caused by anophthalmia, microphthalmia and early enucleation. A previous in vivo study conducted in the feline model demonstrated the safety and efficacy of the OTE implant for the treatment of anophthalmia and microphthalmia (ARVO 2005). This study presents in vitro results of a "softer" version of the OTE, which demonstrates safety within the normal operating range in the growing enucleated orbit.

Methods: : The OTE was made using a silicone rubber globe with a shore Hardness of 40A. Previously reported OTE’s had a Shore Hardness of 70A. Maximum burst volume and the failure mode of the device were determined by inflating 20 samples after EtO sterilization in 1mL increments using a 30 gauge needle to approximately 15mL. If the device failed, the method of failure was recorded. Statistical analysis was performed on the results to determine the safe operating volume and the method of failure.

Results: : The testing performed showed that 100% of the samples passed the 5mL inflation point, which is the maximum recommended inflation volume. This volume is equivalent to an anterior posterior diameter of 23.7 ± 0.4mm, and a lateral diameter of 21.9 ± 0.4mm. The OTEs began to fail at a volume of 11mL which is more than twice the recommended volume of use. At 11mL the measurements of the device were 26.03mm in antero-posterior diameter and 27.48mm in lateral diameter. The maximum inflation volume exceeds the average diameter of a normal adult human eye ball by 6% in the antero-posterior and 14% in the lateral or nasal-temporal quadrant. 100% of the units passed a safety range of more than twice the recommended volume of the device. The predominant failure mode was identified as fracture of the silicone globe at the junction with the inflation port. Fragmentation of the silicone material was not observed.

Conclusions: : The OTE is safe in the operating range of 0-5mL, which is required for normal development of the orbit in the infant. The maximum volume attained by the OTE is 11mL - 12mL and rupture of the device occurs by fracture of the silicone globe without fragmentation.

Keywords: anatomy • orbit • wound healing