Miller School Researchers Find Cause of Visual Changes in Astronauts during Long Spaceflights
A team of researchers at the University of Miami Miller School of Medicine has determined that certain visual changes in astronauts who have experienced long periods of weightlessness during space missions are due to changes in cerebrospinal fluid — not vascular fluid as previously believed.
The condition, known as vision impairment and intracranial pressure syndrome, or VIIP, occurs in about two-thirds of astronauts who have been deployed on the International Space Station for six months or longer. The most consistent signs associated with VIIP are ophthalmic anatomical changes, including flattening of the posterior sclera, known as globe flattening, and protrusion of the optic disk, or nerve protrusion.
VIIP-related ocular structural changes do not fully resolve following return to Earth from long-duration missions, and in several astronauts, the ophthalmic changes were still present several years after their return from the space station. As NASA plans continued long-term deployments aboard the space station, and eventual lengthy voyages such as manned flights to Mars, there is a strong interest in learning how VIIP might be prevented or minimized.
The researchers studied nine astronauts who had flown on the space shuttle, with an average mission length of 14.1 days, and seven astronauts who had flown on the space station, for an average mission length of 188 days. MRI data of the astronauts was used to quantify pre- to post-flight changes in orbital and ventricular cerebrospinal fluid volumes and in brain tissue volumes.
“Pre- to post-flight increases in globe flattening and optic nerve protrusion were significant only in the long-duration cohort. In fact, accumulated flattening and nerve protrusion in each of the long-duration crew members was larger than the largest change measured in the short-duration crew members,” said Noam Alperin, Ph.D., professor of radiology and biomedical engineering, and director of the Physiologic Imaging and Modeling Lab. “In addition, brain tissue volumes did not change or correlate with globe flattening and optic nerve protrusion. These findings are evidence for a primary role for cerebrospinal fluid and a lesser role for intracranial vascular cephalad fluid shift in the formation of VIIP.”
Other Miller School researchers participating in the study were Ahmet Bagci, Ph.D., senior research associate in radiology; Carlos J. Oliu, a medical student; Sang H. Lee, M.S., systems analyst in radiology; and Byron L. Lam, M.D., professor of ophthalmology. The team’s findings, with Alperin as first author, were published online by the journal Radiology on April 21.
The next step is for the investigators to apply their methodology to glaucoma research.
“The role of cerebrospinal fluid in glaucoma is not well understood,” said Alperin. “We believe our methodology will provide a quantitative assessment of the role of cerebrospinal fluid in the globe deformations around the optic nerve head present in glaucoma.”
The research was supported, in part, by a grant from NASA.