Chorioretinal folds in astronauts: risk of chorioretinal fold-related maculopathy and terrestrial staging of disease

Introduction

Chorioretinal folds-related maculopathy, commonly referred to as chorioretinal folds (CRFs), is characterized by the presence of wrinkles that impact various layers of the eye, namely the choroid, Bruch’s membrane, retinal pigment epithelium (RPE), and the neurosensory retina that sits above them [1]. Those wrinkles are primarily detected in the posterior pole of the eye and are characterized by the presence of alternating light and dark lines on fluorescein angiography [1]. Chorioretinal folds exhibit a wide range of causes and are frequently associated with different ocular and orbital conditions [2]. These conditions include acquired hyperopia, posterior scleritis, orbital tumours, choroidal nevi, thyroid eye disease, or idiopathic chorioretinal folds [2].

The development of chorioretinal folds has been associated with changes in the anatomical positioning of the sclera and the retina, resulting in the compression of structures within the eye [2]. Several potential mechanisms have been suggested, such as choroidal congestion, alterations in the structure of Bruch’s membrane and the retinal pigment epithelium, and stress-strain interactions between the choroid and sclera [2]. Advancements in retinal imaging technologies have played a significant role in enhancing the identification and assessment of chorioretinal folds [1].

Ferguson et al. [3]. recently conducted a cohort study which included 36 astronauts and found that 6 (17%) developed chorioretinal folds (CRF). We applaud the authors for their novel findings and reporting quantitative metrics for the development of CRF as CRF progression in astronauts is a concern for long-duration spaceflight (LDSF). Spaceflight-associated neuro-ocular syndrome (SANS) is a condition unique to spaceflight with no terrestrial equivalent [4, 5]. The main findings in SANS include optic disc edema, chorioretinal folds, posterior globe flattening, and hyperopic refractive shift [6].

Although no cases of permanent visual loss have been described to date from SANS, the condition remains a potential barrier to future crewed LDSF missions. Olsen et al. [2]. described CRF-related maculopathy as a potential complication following chronic CRFs that may be accompanied by central vision deterioration. The study characterized CRF-related maculopathies into 3 stages: (Stage 1) alternating bands of hyper/hypo-fluorescence; (Stage 2) areas of staining that correspond to early breakdown of retinal pigmental epithelium (RPE); and (Stage 3) occult choroidal neovascularization (CNV) like findings on fundus fluorescein angiography (FFA) [2]. Thus, Stage 3 CRF-related maculopathy has the potential to cause significant central vision deterioration and thus is an additional long-term hazard from SANS.

Olsen et al. [2]. utilized FFA to stage CRF-related maculopathies. However, FFA is not currently available onboard the International Space Station (ISS). Fortunately, optical coherence tomography angiography (OCTA) was recently added in 2018 to the available ocular imaging modalities on ISS [7]. OCTA is both a rapid and non-invasive imaging modality of the deep and superficial retinal vasculature layers [8]. This useful imaging modality may be helpful in characterizing CRFs as it has been utilized terrestrially [9]. OCTA may be useful for tracking CRF and the potential risks posed by chronic CRF-related maculopathy in SANS during future LDSF including the proposed crewed mission to Mars.

Author contributions

MM—writing, editing, JO—writing, editing, idea synthesis, EW—writing, editing, idea synthesis, AGL—editing.

Competing interests

The authors declare no competing interests.