In Reply In the letter by Mader et al, the idiopathic intracranial hypertension mechanism–like theory and possible ball-valve effect are focused on to explain optic nerve sheath (ONS) diameter expansion and globe flattening in spaceflight-associated neuro-ocular syndrome (SANS). In this commentary, we reply to their opinion and argue that brain upward shift is the major origin for SANS.
The diagnostic criteria of idiopathic intracranial hypertension include papilledema and increased cerebrospinal fluid pressure (>18 mm Hg) measured using lumbar puncture, and its typical symptoms include daily headache, diplopia, transient visual obscurations, pulse-synchronous tinnitus, and photophobia.1 In SANS, however, there is no complaint of these symptoms, suggesting that the origins of idiopathic intracranial hypertension and SANS are less likely to be shared.2
Shinojima A, Kakeya I, Tada S. Brain Upward Shift and Spaceflight-Associated Neuro-Ocular Syndrome—Reply. JAMA Ophthalmol. 2019;137(5):586–587. doi:10.1001/jamaophthalmol.2019.0223
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