Incidence and Progression of Chorioretinal Folds During Long-Duration Spaceflight

Abstract

ImportanceThe primary contributing factor for development of chorioretinal folds during spaceflight is unknown. Characterizing fold types that develop and tracking their progression may provide insight into the pathophysiology of spaceflight-associated neuro-ocular syndrome and elucidate the risk of fold progression for future exploration-class missions exceeding 12 months in duration.ObjectiveTo determine the incidence and presentation of chorioretinal folds in long-duration International Space Station crew members and objectively quantify the progression of choroidal folds during spaceflight.Design, Setting, and ParticipantsIn this retrospective cohort study, optical coherence tomography scans of the optic nerve head and macula of crew members completing long-duration spaceflight missions were obtained on Earth prior to spaceflight and during flight. A panel of experts examined the scans for the qualitative presence of chorioretinal folds. Peripapillary total retinal thickness was calculated to identify eyes with optic disc edema, and choroidal folds were quantified based on surface roughness within macular and peripapillary regions of interest.Interventions or ExposuresSpaceflight missions ranging 6 to 12 months.Main Outcomes and MeasuresIncidence of peripapillary wrinkles, retinal folds, and choroidal folds; peripapillary total retinal thickness; and Bruch membrane surface roughness.ResultsA total of 36 crew members were analyzed (mean [SD] age, 46 [6] years; 7 [19%] female). Chorioretinal folds were observed in 12 of 72 eyes (17%; 6 crew members). In eyes with early signs of disc edema, 10 of 42 (24%) had choroidal folds, 4 of 42 (10%) had inner retinal folds, and 2 of 42 (5%) had peripapillary wrinkles. Choroidal folds were observed in all eyes with retinal folds and peripapillary wrinkles. Macular choroidal folds developed in 7 of 12 eyes (4 of 6 crew members) with folds and progressed with mission duration; these folds extended into the fovea in 6 eyes. Circumpapillary choroidal folds developed predominantly superior, nasal, and inferior to the optic nerve head and increased in prevalence and severity with mission duration.Conclusions and RelevanceChoroidal folds were the most common fold type to develop during spaceflight; this differs from reports in idiopathic intracranial hypertension, suggesting differences in the mechanisms underlying fold formation. Quantitative measures demonstrate the development and progression of choroidal folds during weightlessness, and these metrics may help to assess the efficacy of spaceflight-associated neuro-ocular syndrome countermeasures.

Spaceflight-Associated Neuro-Ocular Syndrome and Increased Intracranial Pressure—Are We Closer to Understanding the Relationship?

“…6 Again, this globe flattening was identified in the peripapillary region and did not extend to the macula, making it difficult to implicate presumed peripapillary forces in the development of the choroidal folds noted by Ferguson and colleagues. 1 Neither of the HDT studies nor the work here suggested that direct choroidal venous engorgement was causative. One possible explanation that may be related to observations of sequestration of cerebrospinal fluid within the optic nerve sheath being part of SANS 7 is that there is increased orbital compartment pressure from impaired venous return.…”

“…A recently published study using magnetic resonance imaging to assess globe deformation in participants exposed to HDT showed that posterior globe flattening was a frequent occurrence and could persist or even progress in the days following cessation of HDT . Again, this globe flattening was identified in the peripapillary region and did not extend to the macula, making it difficult to implicate presumed peripapillary forces in the development of the choroidal folds noted by Ferguson and colleagues . Neither of the HDT studies nor the work here suggested that direct choroidal venous engorgement was causative.…”

“…In this issue, Ferguson and coauthors 1 assess the incidence and location of choroidal and retinal folds in astronauts after long-duration spaceflight (LDSF) and contrast them with findings in patients with elevated intracranial pressure (ICP) from idiopathic intracranial hypertension (IIH). They found that the majority of their astronaut cohort had optical coherence tomography evidence for optic disc edema as measured by total retinal thickness changes and that only 1 in 6 eyes (17%) had choroidal folds.…”

“…We still do not know if ICP is elevated in microgravity, although there are pending efforts that may answer this question. The work presented here gives further evidence that neither ICP nor venous outflow changes are sufficient to explain key findings in SANS such as choroidal folds beyond the optic disc area, and further studies are needed to identify the forces acting on the globe and orbit in microgravity. Additionally, it is reassuring that choroidal folds are seen in only a minority of LDSF astronauts and that vision loss has not been observed in association with either these folds or the much more prevalent optic disc edema.…”

Insights into spaceflight-associated neuro-ocular syndrome with review of intraocular and orbital findings

“…As reported per these articles, the incidence of developing visible optic disc edema during long-duration spaceflight (LDSF) ranges from 5–29% [11 ▪▪ ,16 ▪ ,17–19,20 ▪▪ ,21–24,25 ▪ ,26,27,28 ▪ ,29,30 ▪▪ ]. In the articles that graded the visible disc edema, nearly all cases were considered Frisén grade 1 [6,7,21–23,26,29,30 ▪▪ ]. Frisén grade 1corresponds to blurring of the optic disc margin that spares the temporal quadrant [15].…”