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Evaluation of Optic Disc Edema in Long-Duration Spaceflight Crewmembers Using Retinal Photography
William E Valencia1, Sara S Mason, Tyson J Brunstetter
1The University of Texas Medical Branch at Galveston (WV), Galveston, Texas; MEI Technologies Inc (SM), Houston, Texas; NASA Johnson Space Center (TB, WT, MVB), Houston, Texas; KBR (AS), Houston, Texas; The University of Texas Health Science Center at Houston School of Public Health (CS), Houston, Texas; Coastal Eye Associates (CG), Webster, Texas; Department of Ophthalmology (AL), Houston Methodist Hospital, Houston, Texas; Gagarin Research and Test Cosmonaut Training Center (SD, VM), Star City, Russian Federation; Canadian Space Agency (PH), Chapman Space Centre, Longueuil, Canada; Institute of Biomedical Problems (IM), Russian Academy of Science, Moscow, Russian Federation; German Aerospace Center (CS), Cologne, Germany; Department of Ophthalmology (AT-S), Keio University School of Medicine, Shinjuku-ku, Tokyo, Japan; and School of Medicine and Dentistry (SF), Flaum Eye Institute, University of Rochester, Rochester, New York.
Background:
Long-duration spaceflight crewmembers are at risk for spaceflight-associated neuro-ocular syndrome (SANS). One of the earliest manifestations of SANS is optic disc edema (ODE), which could be missed using the subjective Frisén scale. The primary objective of this study is to determine the inter-rater and intrarater reliability of Frisén grade for SANS-induced ODE among a trained observer cohort. The secondary objective is to propose a standardized evaluation process for SANS-induced ODE across International Space Station Partner Agencies.
Methods:
Retrospective, double-blinded diagnostic study. Preflight and postflight fundus photographs were presented to subject matter experts who identified and graded ODE. Pairs of images were also compared side-by-side for disc ranking. Grader concordance was assessed for Frisén grading and disc ranking.
Results:
Expert graders identified Grade 1 ODE in 17.35% of images from 62 crewmembers (9 female, mean [SD] age, 47.81 [5.19] years). Grades 2 and 3 were identified less than 2% of the time. Concordance in Frisén grades among pairs of graders was 70.99%. Graders identified a difference in preflight and postflight fundus photographs 17.21% of the time when using disc ranking. Pairs of graders had complete concordance in disc ranking 79.79% of the time. Perfect intrarater agreement between Frisén grade and disc ranking occurred 77.7% of the time.
Conclusions:
These findings demonstrate intergrader and intragrader variability when using the Frisén scale to identify SANS-induced ODE, which is typically milder in presentation than terrestrial cases of idiopathic intracranial hypertension. It is possible to miss early ODE on fundoscopy alone, making it insufficient as a sole criterion for the diagnosis of SANS. A more sensitive and objective method of surveillance is necessary to monitor international crewmembers for ODE, perhaps using a multimodal approach that includes technology such as optical coherence tomography.
