Anders Wåhlin1, Petter Holmlund2, Abigail M Fellows3, Jan Malm4, Jay C Buckey3, Anders Eklund5. 1. Department of Radiation Sciences, Umeå University, Umeå, Sweden; Umeå Center for Functional Brain Imaging, Umeå University, Umeå, Sweden. 2. Department of Radiation Sciences, Umeå University, Umeå, Sweden. 3. Geisel School of Medicine at Dartmouth, Lebanon, New Hampshire. 4. Department of Clinical Science, Umeå University, Umeå, Sweden. 5. Department of Radiation Sciences, Umeå University, Umeå, Sweden; Umeå Center for Functional Brain Imaging, Umeå University, Umeå, Sweden. Electronic address: anders.eklund@umu.se.
Abstract
PURPOSE: The spaceflight-associated neuro-ocular syndrome (SANS) affects astronauts on missions to the International Space Station (ISS). The SANS has blurred vision and ocular changes as typical features. The objective of this study was to investigate if microgravity can create deformations or movements of the eye or optic nerve, and if such changes could be linked to SANS. DESIGN: Cohort study. PARTICIPANTS: Twenty-two astronauts (age 48 ± 4 years). METHODS: The intervention consisted of time in microgravity at the ISS. We co-registered pre- and postspaceflight magnetic resonance imaging (MRI) scans and generated centerline representations of the optic nerve. The coordinates for the optic nerve head (ONH) and optic chiasm (OC) ends of the optic nerve were recorded along with the entire centerline path. MAIN OUTCOME MEASURES: Optic nerve length, ONH movement, and OC movement after time in microgravity. RESULTS: Optic nerve length increased (0.80 ± 0.74 mm, P < 0.001), primarily reflecting forward ONH displacement (0.63 ± 0.53 mm, P < 0.001). The forward displacement was positively related to mission duration, preflight body weight, and clinical manifestations of SANS. We also detected upward displacement of the OC (0.39 ± 0.50 mm, P = 0.002), indicative of brain movement, but this observation could not be linked to SANS. CONCLUSIONS: The spaceflight-induced optic nerve lengthening and anterior movement of the ONH support that SANS is caused by an altered pressure difference between the brain and the eye, leading to a forward push on the posterior of the eye. Body weight is a potential contributing risk factor. Direct assessment of intracranial pressure in space is required to verify the implicated mechanism behind the ocular findings in SANS.
PURPOSE: The spaceflight-associated neuro-ocular syndrome (SANS) affects astronauts on missions to the International Space Station (ISS). The SANS has blurred vision and ocular changes as typical features. The objective of this study was to investigate if microgravity can create deformations or movements of the eye or optic nerve, and if such changes could be linked to SANS. DESIGN: Cohort study. PARTICIPANTS: Twenty-two astronauts (age 48 ± 4 years). METHODS: The intervention consisted of time in microgravity at the ISS. We co-registered pre- and postspaceflight magnetic resonance imaging (MRI) scans and generated centerline representations of the optic nerve. The coordinates for the optic nerve head (ONH) and optic chiasm (OC) ends of the optic nerve were recorded along with the entire centerline path. MAIN OUTCOME MEASURES: Optic nerve length, ONH movement, and OC movement after time in microgravity. RESULTS: Optic nerve length increased (0.80 ± 0.74 mm, P < 0.001), primarily reflecting forward ONH displacement (0.63 ± 0.53 mm, P < 0.001). The forward displacement was positively related to mission duration, preflight body weight, and clinical manifestations of SANS. We also detected upward displacement of the OC (0.39 ± 0.50 mm, P = 0.002), indicative of brain movement, but this observation could not be linked to SANS. CONCLUSIONS: The spaceflight-induced optic nerve lengthening and anterior movement of the ONH support that SANS is caused by an altered pressure difference between the brain and the eye, leading to a forward push on the posterior of the eye. Body weight is a potential contributing risk factor. Direct assessment of intracranial pressure in space is required to verify the implicated mechanism behind the ocular findings in SANS.
Authors: Stuart H Sater; Austin M Sass; Akari Seiner; Gabryel Conley Natividad; Dev Shrestha; Audrey Q Fu; John N Oshinski; C Ross Ethier; Bryn A Martin Journal: J R Soc Interface Date: 2021-04-28 Impact factor: 4.293
Authors: Petter Holmlund; Karen-Helene Støverud; Anders Wåhlin; Urban Wiklund; Jan Malm; Gauti Jóhannesson; Anders Eklund Journal: Invest Ophthalmol Vis Sci Date: 2021-04-01 Impact factor: 4.799
Authors: M P Van Akin; O M Lantz; A M Fellows; Christine Toutain-Kidd; Michael Zegans; J C Buckey; A P Anderson Journal: Front Physiol Date: 2022-08-31 Impact factor: 4.755