Space flight and intraocular pressure
During and after prolonged space flight, about half of flyers experience hyperopic shift
Astronaut Michael Barrett MD discusses persistent hyperopic shift, globe flattening and choroidal folds he experienced from an extended flight on the International Space Station with Andrew Lee MD of Houston Methodist Hospital and Weill Cornell Medical College
During and after prolonged space flight, about half of flyers experience hyperopic shift, and a majority of those studied show optic disc oedema, globe flattening, choroidal folds and sometimes cotton wool spots, and these effects often persist after return to normal gravity. The findings appear to correlate with elevated cerebrospinal fluid (CSF) pressure, which apparently compresses the globe and optic nerve, Andrew G Lee MD told the American Academy of Ophthalmology 2017 annual meeting in New Orleans, USA.
Understanding the mechanisms involved is crucial to enable years-long flights to Mars, and could shed light on terrestrial vision problems such as idiopathic intracranial hypertension and postoperative vison loss in spine surgery. However, determining the relationship between CSF pressure and intraocular pressure (IOP) is challenging, added Dr Lee, who holds ophthalmology, neurology and neurosurgery appointments at Houston Methodist Hospital, Weill Cornell Medical College, UTMB Galveston and UT MD Anderson Cancer Center.
Differences between CSF and IOP transmitted across the lamina cribrosa also appear to be involved with glaucoma progression, and this has been known for more than 100 years, noted David Fleischman MD, FACS of the University of North Carolina at Chapel Hill. However, mounting evidence suggests orbital CSF pressure often may be higher than intracranial or lumbar pressure due to the valve-like action of the narrowing of the optic canal as it exits the cranial cavity. Therefore, translaminar pressure difference is related to IOP and local orbital CSF pressure rather than intracranial or lumbar CSF pressure, he said. As yet there is no way to determine orbital CSF pressure, making it a fertile area for further research.