Abstract
Purpose :
Approximately 70% of long-duration crewmembers develop signs of optic disc edema (ODE), a finding of spaceflight-associated neuro-ocular syndrome (SANS). The severity of ODE differs across individuals subjected to similar environmental factors on the International Space Station (ISS). Understanding the sources of this variability is of high priority because the incidence and severity of ODE may increase as mission durations are extended, potentially causing irreversible vision loss. We therefore tested the hypothesis that having crowded optic nerve head (ONH) morphology prior to flight confers a predisposition to spaceflight-induced ODE development.
Methods :
Radial and circular OCT scans centered on the ONH were collected preflight and on flight day ~150 from both eyes of 31 crewmembers completing missions on the ISS. ODE was quantified as the change in total retinal thickness (TRT) from the annular region extending 250 µm from Bruch’s membrane opening (BMO). ONH metrics included minimum rim width (MRW), cup volume, and cup-to-disc ratio. For each radial B-scan (≥24 per scan), the optic cup was defined as the region bounded by the internal limiting membrane and a cup reference line that was 200 µm anterior to a disc reference line connecting the BMO points. Circumpapillary retinal nerve fiber layer (RNFL) thickness and choroid thickness were also measured. Associations between the preflight variables and inflight changes in TRT were assessed using a linear mixed-effects model.
Results :
Mild ODE was observed across the cohort during spaceflight, as evidenced by a mean (SE) increase in TRT of 38.3 (6.4) µm from baseline (392.0 (5.8) µm, P < 0.001). A greater increase in TRT during spaceflight was associated with shallower preflight optic cup depth (slope = -0.11 ± 0.03, P < 0.001) and smaller preflight optic cup volume (slope = -62.8 ± 18.9, P = 0.002). TRT changes were not associated with preflight cup-to-disc ratio (P = 0.31), MRW (P = 0.14), RNFL thickness (P = 0.81), or choroid thickness (P = 0.38).
Conclusions :
Crowded ONH morphology represents a possible risk factor for the development of spaceflight-induced ODE. However, variables outside of the optic cup (MRW, RNFL, choroid thickness) do not have an association with ODE. Crewmembers with small and/or shallow optic cups may benefit from additional ophthalmic monitoring during spaceflight and use of countermeasures against SANS.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.