Transorbital target localization with augmented ophthalmologic surgical endoscopy

Purpose Access to the space behind the eyeball is limited by the position of the globe anteriorly, the neurovascular structures embedded in fat posteriorly, and the tight bony confine of the orbit. These anatomical relationships have impeded application of minimally invasive procedures to the region, such as foreign body removal, tumor biopsy, or the administration of medical therapy directly to the optic nerve. An image-guided system was developed using a magnetically tracked flexible endoscope to navigate behind the eye, with the aim of enabling accurate transorbital surgery to user-specified target locations. Methods Targets were defined by microspherical bulbs containing water or gadolinium contrast, with differing visible coloring agent. Six living pigs were anesthetized and two microspheres of differing color and contrast content were implanted in the fat tissue of each orbit. Preoperative T1-weighted MRI volumes were obtained and registered intraoperatively. The system capabilities were tested with a series of targeted surgical interventions. The surgeon was required to navigate the endoscope to each lucent microsphere and identify it by color. For three pigs, 3D/2D registration was performed such that the target’s image volume coordinates were used to display its location on real-time endoscope video. Results The ophthalmologic surgeon was able to correctly identify every target by color, with average intervention time of 24.2 min without enhancement and 3.2 min with enhancement. This difference is highly statistically significant ( p < 0.02 ) for reduction in localization time. Conclusions Accurate transorbital target localization is possible in-vivo using image-guided transorbital endoscopy, while endoscopic enhancement through the use of video augmentation significantly reduces procedure time.