Spaceflight Associated Neuro-Ocular Syndrome as a Potential Variant of Venous Overload Choroidopathy
INTRODUCTION: Novel ocular findings have been identified in spaceflight. We discuss their potential association with Spaceflight Associated Neuro-ocular Syndrome (SANS) and integrate them in a framework that may help explain the pathophysiology. METHODS: We reviewed literature using the Medline/PubMed database starting in October 2020. Search terms included ocular circulation, hyperopia, serous chorioretinopathy, pigment epithelial detachment, choroidal folds, choroidal thickening, pachychoroid disease, optic disc edema, venous overload choroidopathy. No date exclusions were placed on the search. Articles were reviewed for relevance. Articles relevant to the pathophysiology of choroidal thickening and choroidal venous overload as it applies to SANS were included. RESULTS: Terrestrial venous overload choroidopathy is thought to be due to impediment to choroidal venous outflow, resulting in dilation of choroidal veins, increased choroidal thickness, pigment epithelial detachments, and serous detachment of the retina. Serous detachment of the retina, pigment epithelial detachments, choroidal folds, and thickening of the choroid were identified on in-flight optical coherence tomography testing. Postflight findings include these, as well as globe flattening. During spaceflight, there is a cephalad displacement of both blood and cerebrospinal fluid. This may lead to pathological consequences in the eye. Remodeling of the choroidal venous vortex system may result in continuance of pathophysiological findings after return to Earth, suggesting the best strategy is prevention. DISCUSSION: Microgravity induced venous overload of the choroid may play a role in SANS pathophysiology, and a venous overload choroidopathy may help explain several SANS features that remain unexplained by an etiology of elevated intracranial pressure. Mampre D, Spaide R, Mason S, Van Baalen M, Gibson CR, Mader TH, Wostyn P, Briggs J, Brown D, Lee AG, Patel N, Tarver W, Brunstetter T. Spaceflight-Associated Neuro-ocular Syndrome as a potential variant of venous overload choriodopathy. Aerosp Med Hum Perform. 2025; 96(6):496–508.
Lumbar puncture opening pressures measured in astronauts by days postflight.
Postflight axial T2 (3T magnetic resonance imaging) showing the flattening of the posterior aspect of the right globe (small arrows) and optic nerve head protrusion (central large arrow) consistent with the optic nerve photography and optical coherence tomography data. Note the marked distension of the optic nerve sheath, which is consistent with congestion seen at the level of the optic disc. Image and legend adapted from Mader et al.1
Factors that may contribute to flattening of the globe in SANS. A) Normal globe. The choroid naturally thins toward the optic nerve; the outer scleral fibers merge into the dural sheath surrounding the optic nerve. B) In SANS there is increased cerebral spinal fluid (CSF) in the optic nerve subarachnoid space (blue arrows) that dilates the optic nerve sheaths. This would be expected to create a vector of force (green arrows). There is also an increase in choroidal thickness. The combination of these factors could lead to flattening of the posterior portion of the globe.
Recession of the Bruch’s membrane opening (BMO) height in astronauts. A) Marking of the BMO (light circles) is shown on 1 radial section through the optic nerve head of an astronaut. The BMO center (dashed line) was used to determine the location for a reference plane at 2 mm (white line), from which the BMO height was quantified (vertical lines from the BMO markers). B) The BMO height is recessed in preflight optical coherence tomographic (OCT) scans compared with healthy controls. This difference increases after long-duration microgravity exposure. It should be noted that most astronauts included in this study had previous spaceflight experience. (Reprinted with permission from Patel et al.61)
Choroidal and retinal folding observed in an astronaut. A) Preflight scanning laser ophthalmoscopy image of the left eye (OS) and B) preflight cross-sectional optical coherence tomography (OCT) imaging showing lack of choroidal and retinal folding. C) In-flight scanning laser ophthalmoscopy image OS, and D) in-flight cross-sectional OCT imaging showing the presence of linear choroidal and retinal folding in an astronaut.
Development of serous chorioretinopathy in an astronaut. A) Preflight scanning laser ophthalmoscopy image of the right eye with mild, pre-existing retinal pigment epithelium (RPE) disturbance nasal to the fovea, and B) preflight cross-sectional optical coherence tomography (OCT) imaging showing mild chronic/stable retinal pigment epithelium detachment (PED) and absence of serous chorioretinopathy (SCR). C) Postflight scanning laser ophthalmoscopy image OD and D) postflight cross-sectional OCT imaging showing the presence of SCR in an astronaut which developed within 5 mo following return to Earth.
A) Preflight and B) in-flight optical coherence tomography demonstrating pigment epithelial detachment (PED) in an astronaut. Note a relatively thick choroid preflight, along with a subtle disruption of the retinal pigment epithelium at the line; these may have predisposed the crewmember to develop an in-flight PED.
In-flight optical coherence tomography demonstrating retinal cystoid space at the optic nerve head-retina junction (arrow).
Flow chart of proposed influence of venous overload on the pathophysiology of Spaceflight Associated Neuro-ocular Syndrome (SANS) as it relates to choroidal thickening.
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