Vision Impairment and Intracranial Pressure (VIIP) project examined the effect of long-term exposure to microgravity on the structure of the eye along with change in distance and near vision of crewmembers before and after they returned to Earth.Principal Investigator(s)
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration:
Information PendingPrevious ISS Missions
VIIP is a unique investigation which has not been performed for ISS crewmembers.
Complete eye examinations before and after long-duration space flight were completed for participating crewmembers using clinical opthalmic procedures such as manifest (no dilating agent) and/or cycloplegic (pupils are dilated with a chemical) refraction tests to determine refractive error, fundus (rear portion of the eye) photography to capture detailed images of retina along with associated blood vessels and nerves, noninvasive optical coherence tomography (OCT) imaging technology to capture high resolution retinal structures where the layers and thickness can be measured, direct imaging of the eye and optic nerver (ON) by magnetic resonance imaging (MRI) to determine eye globe geometry and axonal sheath thickness, lumbar punctures (LP) to measure the pressure of cerebrospinal fluid (CSF) in the space surrounding the spinal cord as a correlation to the intracranial and intraorbital pressure of the eye, visual acuity testing to document ability to focus images at a certain distance.
Also, approximately 300 astronauts were queried with vision questionaires to document changes during space missions.
Possible countermeasures may be developed to mitigate space-induced ocular impairments.Earth Applications
Before and after long-duration space opthalmic examinations of 7 crewmembers including cycloplegic and/or manifest refraction and fundus photography. Six underwent postmission retina optical coherence tomography (OCT) and magnetic resonance imaging (MRI). 4 had lumbar punctures (LP). Approximately 300 astronauts were queried regarding visual changes during space missions.Operational Protocols
All activities were conducted preflight and postflight.
Since 1989, as part of the postflight eye examination, astronauts were queried as to whether they perceived a subjective improvement or degradation in distant or near vision (none, mild, moderate, or severe) during their short- and long-duration missions. Prompted by persistent reports of vision changes, NASA began a stepwise operational process to determine the cause(s). Several ophthalmic procedures were initiated on astronauts, including dilated fundus (the rear portion of the eye) examinations with binocular ophthalmoscopy, cycloplegic refraction, optical coherence tomography (OCT), magnetic resonance imaging (MRI) of orbits, and fundus photography for before and after space missions.
300 astronauts completed postflight questionnaires regarding in-flight vision changes and survey results showed approximately 29% and 60% of astronauts on short and long-duration missions, respectively, experienced a degradation in distant and near visual acuity, and some of these vision changes remain unresolved years after flight. Clinical data were collected for 7 astronauts who underwent complete visual and structural eye examinations before and after completing 6-month missions on board the ISS. The battery of ophthalmic tests revealed, with varying degrees, distinct changes in the eye including optic disc edema, nerve fiber layer thickening, choroidal folds (buckling of the eye’s vascular membrane), posterior globe flattening, cotton wool spots (tiny white areas in the retina caused by damage to nerve fibers), and decreased near vision accompanied by hyperopic shift (more farsighted) after prolonged exposure to microgravity. Considering these findings, investigators forward a hypothesis that the observed changes in the internal structures of the eye and the optic nerve is due to venous congestion in the brain and/or eye, brought about by the prolonged increase in intracranial pressure (ICP) from fluid shifting toward the head and upper body as a response to weightlessness (Mader et al. 2012).
In a follow-on study, twenty-seven astronauts underwent thin-section, three-dimensional, eye orbital, and conventional MRI brain scans. Eight astronauts underwent repeat imaging after an ad-ditional mission in space. All astronauts had previous exposure to microgravity. Image analysis of the optic nerve sheath, optic disc, posterior globe, and pituitary gland was performed and compared for association with intracranial evidence of excessive fluid buildup inside the skull, cells, tissues, or body cavities, venous blood clotting in the brain and/or mass lesion.
These post-mission MRI exams revealed various combinations of optic nerve sheath swelling, posterior globe flattening, optic disc protrusion, increased optic nerve diameter (OND), and moderate or greater concavity of the pituitary gland with posterior stalk displacement, which are hypothesized to be related to increase intracranial pressure (hypertension) due possibly to fluid shifts to the head in the absence of gravity. Posterior globe flattening was seen in seven of the 27 astronauts (26%), optic nerve protrusion in four (15%), and moderate concavity of the pituitary dome with posterior stalk deviation in three (11%) without additional intracranial abnormalities. A tissue change in a central area of altered optic nerve sheath (ONS) was identifiable in 26 of the 27 astronauts (96%) and increased in diameter in association with kinking of the ONS. Posterior globe flattening was identified in some as-tronauts 100 days after flight indicating that with long-standing compression of the eyes, this condition may not return to normal. Posterior globe flattening was associated with increased optic nerve sheath diameter (ONSD), thus elevated CSF pressure around the optic nerve may be a contributing factor. This was identified in a subset of astronauts with confirmed intracranial hypertension or borderline high Cerebral Spinal Fluid (CSF) pressure. Optic disc protrusion was only found with longer cumulative mission duration, indicating that clinical severity is associated with increasing microgravity exposure.
Visual acuity degradation in astro¬nauts exposed to microgravity is a newly recognized phenomenon. Although the exact mechanism is yet to be fully determined, many MRI findings suggest that intracranial hypertension is an important component. However, a large proportion of astronauts do not show these ocular effects suggesting there could be variable biologic response to the space flight environment and warrants a search for existing risk factors. Standardization of qualitative and quantitative imaging criteria will further help in the identification of asymptomatic changes and allow for the use of countermeasures to mitigate potential long-term vision damage. Future studies involving advance tissue imaging techniques would improve our understanding of the cause-versus-effect relationship of ICP after exposure to microgravity (Kramer et al. 2012).
Kramer LA, Sargsyan AE, Hasan KM, Polk JD, Hamilton DR. Orbital and Intracranial Effects of Microgravity: Findings at 3-T MR Imaging. Radiology. 2012; 263: 819-827. DOI: 10.1148/radiol.12111986.
Chylack Jr LT, Peterson LE, Feiveson AH, Cucinotta FA, Tung WH, Wear , Marak LJ, Hardy DS, Chappell LJ. NASCA Report 2: Longitudinal Study of Relationship of Exposure to Space Radiation and Risk of Lens Opacity. Radiation Research. 2012; 178(1): 25-32. DOI: 10.1667/RR2876.1.
Sargsyan AE, Gibson CR, Mader TH, Pass AF, Kramer LA, Hamilton DR, Lee AG, Fogarty J, Tarver WJ, Dervay JP, Phillips JL, Tran D, Lipsky W, Choi J, Stern C, Kuyumjian R, Polk JD. Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight. Opthalmology. 2011; 118(10): 2058-2069. DOI: 10.1016/j.ophtha.2011.06.021. PMID: 21849212.