Persistent Globe Flattening in Astronauts following Long-Duration Spaceflight

Abstract

Posterior globe flattening has been well-documented in astronauts both during and after long-duration space flight (LDSF) and has been observed as early as 10 days into a mission on the International Space Station. Globe flattening (GF) is thought to be caused by the disc centred anterior forces created by elevated volume and/or pressure within the optic nerve sheath (ONS). This might be the result of increased intracranial pressure, increased intraorbital ONS pressure from compartmentalisation or a combination of these mechanisms. We report posterior GF in three astronauts that has persisted for 7 years or more following their return from LDSFs suggesting that permanent scleral remodelling may have occurred.

Keywords: SANS; astronaut; hyperopic shift; international space station (ISS); long-duration space flight (LDSF); visual changes.

Figure 1.

Astronaut 1 pre-flight (1a; L-3 years) axial T2 (3 T magnetic resonance imaging) showing pre-existing pre-flight optic nerve sheath (ONS) distention and globe flattening. Figure 1b at R + 30 days demonstrates further post-flight globe flattening (OD>OS), disc swelling (OD) and ONS distention (OD>OS). Figure 1c shows persistent globe flattening and ONS distention, most apparent on the right, at R + 7 years

Figure 2.

Astronaut 3 pre-flight (2a) and post-flight (2b; R + 6 days) axial T2 (3 T magnetic resonance imaging) suggesting post-flight globe flattening OU. This astronaut had a previous short-duration space shuttle mission without baseline magnetic resonance imaging. Pre-flight and post-flight IOL master axial length measurements are consistent with bilateral globe flattening (Bottom)