Objective measurement of motion in the orbit

Abstract

The research described in the thesis had two major aims: to find methods for objective measurement of motion in the orbit, and to determine the clinical use of these methods in patients with orbital disorders. This implied that a number of research questions had to be answered in the fields of both image science and of ophthalmology and orbitology. The results have established that measurement of the two- and three-dimensional motion of tissues in the orbit is feasible in humans. It can be imaged in 2-D and 3-D with Magnetic Resonance Imaging (MRI) sequences. It can be calculated objectively from these sequences using optical flow methods. First order techniques were found to be superior for this purpose as they are less sensitive to noise, partial volume effects and aliasing. A new first-order 3-D optical flow algorithm was developed for robust and computationally efficient three-dimensional optical flow estimation. A number of techniques were developed to visualize 2- and 3-D motion combined with the anatomy in 3-D space, using color-coding. The results of two clinical studies have established the clinical use of objective measurement of motion in the orbit in a number of orbital and motion disorders. The studies have resulted in an explanation for the persistent pain that may occur after enucleation of the globe, based on motion measurements in patients after enucleation. They have also shown that orbital tumors can be differentiated using motion studies. The results have also shown that the position of the rectus muscle pulleys is the same in patients with Graves disease and in normals. After surgical decompression of the orbit, the muscles and their pulleys are usually not displaced, except in cases where specific muscle paths and pulleys are displaced in specific patterns, resulting in specific motility disturbances. Thus, a new explanation has been found for the motility disturbances that may occur in some patients after decompression surgery for Graves orbitopathy. These last findings have led to the notion central to this thesis, namely that the orbital tissues are an organ in their own right, the organ of gaze, and do not need their bony orbit to function normally.