Persistent Asymmetric Optic Disc Swelling After Long-Duration Space Flight: Implications for Pathogenesis

Abstract

The persistent asymmetric findings noted above, coupled with the lumbar puncture opening pressures, suggest that prolonged microgravity exposure may have produced asymmetric pressure changes within the perioptic subarachnoid space.

Astronaut ophthalmic syndrome

“…A second possible mechanism for the etiology of ophthalmic changes is that the disc edema, ONS distention, globe flattening, and resultant visual changes were caused by an elevation in ONS CSF pressures as a result of a microgravity‐induced compartmentalization of orbital subarachnoid space (SAS) with or without increased ICP (1, 4, 7, 9, 10). Perhaps asymmetric anatomy in the tightly confined, densely septated anatomic connection between the intracranial and orbital SAS, in conjunction with microgravity‐induced venous and lymphatic stasis, caused a localized decrease in CSF absorption within the SAS of the optic nerve and a rise in local pressure (4, 9). In addition, variable ONS anatomy might lead to asymmetric CSF flow down the ONS cul‐de‐sac in a 1‐way, ball valve–like fashion, adding to the elevation of SAS pressure in the orbital optic nerve (7).…”

The “Ocular Glymphatic System”: An Important Missing Piece in the Puzzle of Optic Disc Edema in Astronauts?

“…These ophthalmic findings after long-duration space flight were initially referred to as the visual impairment and intracranial pressure (VIIP) syndrome, 2 and a leading hypothesis is that VIIP is caused by elevated intracranial pressure (ICP) resulting from microgravity-induced cephalad fluid shifts leading to venous stasis in the head and neck. 3,4 This stasis could cause impairment of CSF drainage into the venous system and cerebral venous congestion, both of which could lead to a rise in ICP. 4 The resulting elevated ICP could lead to optic nerve sheath distention, globe flattening, and stasis of axoplasmic flow with optic disc swelling.…”

“…4 The resulting elevated ICP could lead to optic nerve sheath distention, globe flattening, and stasis of axoplasmic flow with optic disc swelling. 4 We believe that the existence of an ocular glymphatic system offers an attractive additional explanation for how microgravity may cause optic disc edema in astronauts.…”

Ergonomic Challenges for Astronauts during Space Travel and the Need for Space Medicine

“…It has been known for many years that astronauts who undergo prolonged space flight may be affected by visual disturbances [12][13][14][15]. These changes in vision may persist for years post flight and be more prevalent in male astronauts [3].…”

“…The planet is rocky, has a magnetic field and an axial tilt which may provide seasonal variations in climatic conditions. Now in 2017, as we comprehend taking our first steps towards space travel within the solar system which are designed to lead to lunar or planetary colonization within the next [10][11][12][13][14][15][16][17][18][19][20] years, what will we need to know and to develop which will allow such a crew to be safely maintained for these first steps and which may ultimately provide a foundation to permit travel to and permanent colonization of a new world?…”