Identification of Factors Associated With the Development of Optic Disc Edema During Spaceflight

Abstract

ImportanceApproximately 70% of crew members who complete long-duration missions to the International Space Station develop signs of optic disc edema, a hallmark finding of spaceflight-associated neuro-ocular syndrome. The onset and magnitude of edema differ across individuals, and the reason for this variability remains unknown. Identifying risk factors for spaceflight-induced disc edema is important because this condition may become more severe during extended-duration missions to the moon and Mars and could be associated with irreversible vision loss.ObjectiveTo assess whether preflight indicators of crowded optic nerve head morphology, other ocular measures (such as choroid thickness and axial length), body weight, body mass index, sex, age, and previous flight experience are associated with optic disc edema development.Design, Setting, and ParticipantsThis cohort study analyzed ocular, body weight, and demographic data collected from 31 US and international crew members before, during, and after spaceflight at the NASA Johnson Space Center and International Space Station. Ocular factors assessed included preflight and in-flight peripapillary total retinal thickness, minimum rim width, optic cup volume, mean cup depth, mean cup width, cup-disc ratio, Bruch membrane opening area, retinal nerve fiber layer thickness, choroid thickness, axial length, and refractive error. In addition, body weight, body mass index, sex, age, and previous spaceflight experience were assessed for associations with optic disc edema development. The data were analyzed from August 2021 to June 2022.ExposureApproximately 6 to 12 months of spaceflight.Main Outcomes and MeasuresIn-flight increases in peripapillary total retinal thickness. Linear mixed models were used to assess for associations between a wide range of risk factors and in-flight increases in peripapillary total retinal thickness, which is a sensitive objective measure for detecting optic disc edema.ResultsThis study included 31 International Space Station crew members with a mean (SD) age of 46.9 (6.0) years (25 men [80.6%]). During spaceflight, mean (SE) peripapillary total retinal thickness increased from 392.0 (5.8) μm to 430.2 (9.6) μm (P < .001), and greater individual changes were associated with smaller preflight cup volume (slope [SE], −62.8 [18.9]; P = .002), shallower preflight cup depth (slope [SE], −0.11 [0.03]; P < .001), and narrower preflight cup width (slope [SE], −0.03 [0.01]; P = .03). No associations were observed between changes in peripapillary total retinal thickness and any other variable evaluated.Conclusions and RelevanceFindings of this cohort study suggest that smaller optic cup morphology may be associated with optic disc edema development during spaceflight. Crew members with this cup profile may benefit from enhanced ophthalmic monitoring during spaceflight and use of countermeasures against spaceflight-associated neuro-ocular syndrome.

Possible Mitigating Factors in Optic Disc Edema During Spaceflight

“…Pardon and colleagues have presented data in this issue of JAMA Ophthalmology that may provide some insight into understanding SANS and factors associated with optic disc edema. They assessed risk factors that might be associated with in-flight changes in peripapillary total retinal thickness.…”

“…As Pardon and colleagues reported, optic disc edema, as assessed by change in total retinal thickness, was associated with smaller preflight cup volume ( P = .002), narrower preflight cup width ( P = .03), or shallower preflight cup depth ( P < .001), suggesting that the variables associated with crowded optic nerve head are associated with an increased risk of developing spaceflight-related optic disc edema. Additionally, no associations were identified between development of optic disc edema, as assessed by change in total retinal thickness, and preflight measures of cup-disc ratio or Bruch membrane opening area .…”

“…1 However, they did demonstrate a small increase in in-flight Bruch membrane opening area compared with preflight measures. 1 It is possible that partial optic nerve edema increased the observed Bruch membrane opening area. Alternatively, mechanical factors, such as an uplifting of the central nervous system structures, including the optic chiasm, could result in posterior optic nerve pulling and an increase in observed Bruch membrane opening area.…”

“…Third International Visual Field Symposium Tokyo, May 3-6, 1978 The ocular findings in spaceflight, including posterior globe flattening, hyperopic shift, choroidal folds, and optic disc edema, are currently referred to as spaceflight-associated neuro -oc ular syndrome (SANS). 1 Because optic disc edema has been reported to be as frequent as 70% in spaceflight crew members, a better understanding of potential risk factors and the underlying processes is important.…”

“…They assessed risk factors that might be associated with in-flight changes in peripapillary total retinal thickness. These included factors are associated with the optic disc and cup, along with multiple other potential ocular and demographic factors . After approximately 150 days of spaceflight, there was a correlation of change in optical coherence tomography–measured retinal thickening at the optic nerve head with preflight optic cup size (width, depth, and volume), similar to the crowded optic nerve head findings seen clinically in persons with nonarteritic anterior ischemic optic neuropathy or persons with idiopathic intracranial hypertension.…”