Does Esotropia (ET) Cause Globe Retraction In Adduction Similar to Primary Open Angle Glaucoma (POAG) with Normal Intraocular Pressure (IOP)?
Joseph L. Demer, M.D., Ph.D.; Robert A. Clark, M.D.; Soh Y. Suh, M.D.; JoAnn A. Giaconi, M.D.; Kouros Nouri-Mahdavi, M.D.; Simon K. Law, M.D.; Laura Bonelli, M.D.; Joseph Caprioli, M.D.
Stein Eye Institute, University of California, Los Angeles
Los Angeles, California, USA
Introduction: It has been proposed that optic nerve (ON) tethering in adduction causes repetitive strain to the ON, creating an IOP-independent mechanism for optic neuropathy in POAG without elevasted IOP. We investigated whether ET is associated with similar globe retraction in adduction.
Methods: We acquired quasi-coronal orbital magnetic resonance imaging using central, ~20° abduction, and ~30° adduction fixation targets in 41 healthy controls (77 orbits), 20 patients with POAG but IOP<21mmHg (40 orbits), and 25 esotropic (19±4D SEM) adults without POAG (49 orbits). ON path straightness and globe position were computed from area centroids.
Results: The ON was significantly (P<0.025) more sinuous than normal in central gaze and abduction for POAG but not ET, and straightened completely in all groups in adduction, indicating tethering. POAG uniquely, not ET or controls, demonstrated globe retraction due to adduction tethering of 0.75±0.10mm (P<10-7). In abduction, the globe translated temporally 0.43±0.04mm in ET, significantly less than normal (0.77±0.05mm, P<10-4), but not different from POAG (0.36±0.07mm, P=0.3).
Discussion: Similar to POAG without elevated IOP, ON tethering in adduction occurs in ET, but similar to controls, no globe retraction occurs during adduction in ET. ET patients may avoid the pathological ON and sheath stiffening proposed in POAG to inhibit ON elongation in adduction and transfer muscle reaction force to the peripapillary sclera to retract the globe.
Conclusion: While adduction tethering significantly retracts the globe in POAG with normal IOP, this potential cause of optic neuropathy is absent in ET without glaucoma.
References: 1. Demer, J. L., Clark, R. A., Suh, S. Y., Giaconi, J., Nouri-Mahdavi, K., Law, S. K., Bonelli, L., Coleman, A. L., and Caprioli, J. Magnetic resonance imaging of optic nerve traction during adduction in primary open angle glaucoma with normal intraocular pressure. Invest. Ophthalmol. Vis. Sci., 58: 4114-4125, 2017.
2. Shin, A., Yoo, L. Park, J., and Demer, J. L. Finite element biomechanics of optic nerve sheath traction in adduction. J. Biomech. Eng., 139: 2017. doi: 10.1115/1.4037562.
3. Suh, S. Y., Le, Alan, Shin, A., Park, J., and Demer, J. L. Progressive deformation of the optic nerve head and peripapillary structures by graded horizontal duction. Invest. Ophthalmol. Vis. Sci. 58:5015-5021, 2017.