Magnetic resonance imaging quantification of ophthalmic changes due to spaceflight
Sater SH, Rohr JJ, Sass AM, Stenger MB, Macias BR, Ebert D, Sargsyan AE, Marshall Goebel K, Hargens A, Dulchavsky SA, Ploutz-Synder RJ, and Martin BA. Magnetic resonance imaging quantification of ophthalmic changes due to spaceflight. Fluids and Barriers of the CNS 2019; 16.
Fluids and Barriers of the CNS
Introduction: Approximately 37% of long-duration spaceflight astronauts develop signs/symptoms of the spaceflight associated neuroocular syndrome (SANS), including optic disc edema, chorioretinal folds, ocular globe flattening and hyperopic shifts. Quantification of ophthalmic changes that occur during spaceflight may provide clues into the mechanisms responsible for SANS. Automated and manual methods were developed to quantify optic nerve (ON), optic nerve sheath (ONS), and optic globe geometry to better understand how microgravity may impact these structures. Methods: Magnetic resonance (MR) images were collected from astronauts before and after long-duration spaceflight. 3D ON and ONS geometries were analyzed using threshold-based segmentation to compute cross-sectional area. Threshold segmentation was applied to the optic globe after radially re-slicing MRI sequences. Resulting pre- and post-flight point clouds were aligned using an iterative closest point algorithm. Posterior ocular globe flattening was assessed in terms of volume deformation at a radius of 4 mm around the ONH. Results: No significant changes were observed in ON and ONS geometries after long-duration spaceflight, however some astronauts did exhibit significant flattening of the posterior ocular globe. The average and standard deviation of the posterior globe volume deformation was - 8.3 ± 9.1 mm3 (p = 0.0001, N = 20 eyes). Notably, the subject with the greatest degree of posterior ocular globe volume deformation (39.2 mm3) was clinically diagnosed grade 1 optic disc edema via fundus imaging. The role of intracranial pressure changes in astronauts presenting with ocular globe deformation in astronauts is unknown.