Spaceflight Associated Neuro-Ocular Syndrome (SANS): A Systematic Review and Future Directions

Abstract

Purpose

To present a systematic review of the current body of literature surrounding spaceflight associated neuro-ocular syndrome (SANS) and highlight priorities for future research.

Methods

Three major biomedical databases were searched with the following terms: ((neuro ocular) OR ((brain) AND (eye))) AND ((spaceflight) OR (astronaut) OR (microgravity)) AND (ENGLISH[Language]). Once duplicates were removed, 283 papers were left. Articles were excluded if they were not written in English or conference abstracts only. We avoided including review papers which did not provide any new information; however, two reviews on the pathophysiology of SANS were included for completeness. No limitations on date of publication were used. All included entries were then summarized for their contribution to knowledge about SANS.

Results

Four main themes among the publications emerged: papers defining the clinical entity of SANS, its pathophysiology, technology used to study SANS, and publications on possible prevention of SANS. The key clinical features of SANS include optic nerve head elevation, hyperopic shifts, globe flattening, choroidal folds, and increased cerebrospinal fluid (CSF) volume in optic nerve sheaths. Two main hypotheses are proposed for the pathophysiology of SANS. The first being elevated intracranial pressure and the second compartmentalization of CSF to the globe. These hypotheses are not mutually exclusive, and our understanding of the pathophysiology of SANS is still evolving. The use of optical coherence tomography (OCT) has greatly furthered our knowledge about SANS, and with the deployment of OCT to the International Space Station, we now have ability to collect intraflight data. No effective prevention for SANS has been found, although fortunately, even with persistent anatomic and physiologic neuro-ocular changes, any functional impact has been correctable with spectacles.

Conclusion

This is the first systematic review of SANS. Despite the limitations of studying a syndrome that can only occur in a small, discrete population, we present a thorough overview of the literature surrounding SANS and several key areas important for future research are identified.

Keywords:

• subarachnoid space
• cerebrospinal fluid
• idiopathic intracranial hypertension
• space flight
• optic nerve

Abbreviations

CPG, clinical practice guideline; CSF, cerebrospinal fluid; HDT, head down tilt; ICG, indocyanine green; ICP, intracranial pressure; IIH, idiopathic intracranial hypertension; IOP, intraocular pressure; LBNP, lower body negative pressure; LDSF, long-duration spaceflight; NASA, National Aeronautics and Space Administration; NIRFLI, near-infrared fluorescence lymphatic imaging; OCT, optical coherence tomography; SANS, spaceflight associated neuro-ocular syndrome; TRT, total retinal thickness; VIIP, vision impairment intracranial pressure.

Disclosure

Prem S Subramanian reports grants from Research to Prevent Blindness, Inc., during the conduct of the study; In addition, Dr Prem S Subramanian has a patent on novel therapeutics for lowering intracranial pressure pending. The authors report no other potential conflicts of interest in this work. This study was supported in part by an unrestricted grant from Research To Prevent Blindness, Inc. to the Department of Ophthalmology, University of Colorado School of Medicine.