Application Of Orbit～(TM)1.8 Biomechanics Simulation For Incomitant Strabismus Diagnosis And Treatment

Part I . Application of Orbit M1.8 biomechanics simulation for incomitant strabismus diagnosis and treatmentPurpose: To simulate incomitant strabismus with Orbit?.8 biomechanics simulation, thereby clarify diagnostic and treatment possibilities. We want to discuss the methods of different simulations and evaluate the clinical value of Orbit?1.8.Methods: Eighteen patients with congenital superior oblique paresis, one with traumatic medial rectus disinsertion, one with six nerve paresis and one with Brown's syndrome were enrolled. Hess Test and other strabismus tests were performed before and after surgery. In Orbit?1.8, which was designed by Miller JM from the United States, parameters such as contractile force, elasticity, innervation of extraocular muscles were modified to simulate the preoperative disorder. In experimenting with diagnosis we incorporated whatever we know or suspect: not only changes of the paresis muscle, but also secondary changes in other muscles should be considered. As Orbit?s simulated alignment matched clinical data well, preoperative biomechanical strabismus models were created. Surgical manipulations were then applied to the models, so postoperative outcomes could be predicted. After surgery, simulated and actual outcomes were compared. Results: 1. In all the 21 patients, preoperative simulations clarified the diagnosis orhypotheses. As for the 20 patients who had strabismus surgery, their simulated and actual postoperative alignments matched well. 2. In the 18 patients with congenital superior oblique paresis, the mean error of simulation in all gaze positions tested was less than two degree. 3. In some individual gaze position, the simulated deviation was less typical than clinical measurements. 4. OrbitTM1.8 was employed to compute theoretical binocular alignment and muscle paths, under conditions including or omitting the pulleys. In the absence of pulleys, transposition of the superior and inferior rectus muscles to the medial rectus insertion for traumatic medial rectus disinsertion would result in bizarre ocular misalignment not observed clinically.Conclusion: OrbitTM1.8 biomechanics simulation is a helpful tool for diagnosis and treatment of ocular motility disorders. It can be used to reflect supposed causes of strabismus and proposed treatments, thus test the diagnosis and predict the outcome of surgery. In addition, we wonder if the difference between simulation and clinical measurement in some individual gaze position is due to disadvantage of Orbit?1.8. We will clarify that through testing more cases. Finally, with Orbit?1.8, we clarified the theoretical effects of pulleys on the outcome of rectus transposition surgery...