Featured image: Astronaut Steve Bowen wearing DTL electrodes while performing an electroretinography (ERG) test in microgravity on the International Space Station. Courtesy of NASA.
The study of Spaceflight Associated Neuro-Ocular Syndrome (SANS) represents a new frontier in space medicine. As humanity sets its sights on long-duration space missions, understanding and mitigating the health risks associated with microgravity gains relevance. SANS poses a direct threat to astronauts’ vision and therefore, overall mission success. While the investigation of SANS will most directly affect astronauts, the knowledge gained may enhance our understanding of human vision on Earth.
SANS is currently classified as a syndrome that involves optic disc edema, hyperopic shifts, globe flattening, choroidal / retinal folding, and cotton wool spots. These symptoms seem to be directly linked to the microgravity conditions on the International Space Station (ISS). In fact, one in three astronauts who stay in microgravity for longer than 3-months will present with one or more of these ocular findings.
In the microgravity environment of space, astronauts float without the ability to stand or sit upright as they would on Earth. Without Earth’s gravitational pull, bodily fluids cannot drain in the same way, leading to a redistribution of these fluids within the body. This phenomenon forms the basis of the leading explanation for the development of SANS, known as the Fluid Shift Hypothesis.
To advance the study of SANS, NASA has decided to involve electrophysiology to expand its ocular testing methods. On August 10th, 2021, NASA launched a Diagnosys E3 system, equipped with Envoy and ColorBurst, to the ISS where it joined existing ophthalmic equipment including OCT (optical coherence tomography), fundus photography, and ultrasound.
To further enhance the study of vision in microgravity, pattern electroretinography (PERG) and photopic negative response (PhNR) tests will now be included as routine eye exams for astronauts. These tests are capable of detecting subtle changes in optic nerve function. They are effective for detecting early signs of glaucoma and serve as indicators for optic neuropathy and optic neuritis and will now be used to uncover further insights into the mechanisms of SANS.
On August 10, 2021, the Diagnosys E3 system was launched alongside an array of scientific equipment, spacewalk gear, and even fresh produce, including kiwis and tomatoes. This cargo shipment, weighing a record-breaking 8,210 pounds, included 2,346 pounds dedicated to scientific investigations. We’re proud to note that the E3 system represented approximately 0.3% of the total payload. The shipment traveled aboard a spacecraft named after NASA astronaut S.S. Ellison Onizuka, the first Asian-American astronaut selected by NASA in 1978. Onizuka flew his first mission aboard the Space Shuttle Discovery and tragically lost his life, along with his crew, in the Challenger disaster. Before his passing, he left us with these inspiring words: “Your vision is not limited by what your eyes can see, but what your mind can imagine.”