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NASA looks at visual impairment intracranial pressure risk in astronauts
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CORONADO, Calif. — NASA is looking at causes of ocular changes in U.S. astronauts before, during and after 6-month space flights on board the International Space Station.
Ocular findings have developed in 22 of 31 astronauts so far, either during or after a 6-month flight, Christian Otto, MD, said at the annual meeting of the American Glaucoma Society. Those findings include hyperopic shift, choroidal folds, optic nerve sheath distention, optic nerve kinking, globe flattening, disc edema and cotton wool spots. In five of six subjects who underwent post-flight lumbar puncture, cerebrospinal fluid opening pressure was elevated by almost 21 cm H2O to 28.5 cm H2O.
Christian Otto
“We think that the loss of hydrostatic drainage and possibly cerebral venous congestion may be playing a role in elevated intracranial pressure,” Otto said, with a cephalic fluid shift occurring at zero gravity.
“Approximately 2 liters of fluid from the lower limb moves into the thorax towards the head, and we see an equilibration of pressures across the body, not just arterial but also venous,” Otto said. “So we think this fluid redistribution results in this ocular pathology resembling terrestrial idiopathic intracranial hypertension, characterized by high intracranial pressure.”
Otto delivered interim results of an occupational exposure study, in which six of 13 subjects had completed 6 months of flight plus post-flight follow-up. In all six astronauts, the optic nerve sheath diameter increased in-flight and returned toward baseline post-flight. One astronaut had papilledema in one eye and was deemed to be a visual impairment intracranial pressure (VIIP) case; the other five were “non-cases.”
“We have a high suspicion that the translaminar pressure gradient may be playing a role and may be causal in the development of papilledema,” Otto said. “Unlike glaucoma, we think the cerebrospinal fluid pressure is elevated in relation to the IOP.”
IOP, measured by applanation tonometry, did not appear to change across flight phases in the non-cases, whereas in the VIIP case, IOP in the affected eye appeared to be lower than that in controls, Otto said. The VIIP case also demonstrated greater retinal nerve fiber layer increase in the affected eye than did the non-cases, as measured in-flight with the Heidelberg Spectralis OCT, although increased RNFL was demonstrated in all astronauts. – by Patricia Nale, ELS
Disclosure: Otto reports no relevant financial disclosures.