To the Editor:
We thank Masalkhi et al. for their letter [1]. Spaceflight Associated Neuro-Ocular Syndrome (SANS) findings include optic disc edema (ODE), globe flattening, choroidal folds, and hyperopic shift in astronauts during and after long-duration spaceflight [2]. These findings can be acquired with ophthalmic examination instruments, such as ultrasound, optical coherence tomography (OCT), computer optometry, etc.
Typical ODE is shown on ultrasound as heterogeneous hypoechoic bulges with varying degrees of spherical wall echo in the optic disc area, and the degree of the ODE can be quantitatively measured by ultrasound. However, we believe that ultrasound imaging of the retrobulbar optic nerve may not be suitable for monitoring this syndrome. In the case of optic disc swelling, the blood flow parameters of vessels may be affected to varying degrees, so we suggest considering the use of CDFI to monitor changes in retrobulbar blood flow in astronauts before and after entering the International Space Station (ISS). Additionally, the application of transcranial CDFI to monitor changes in cerebral blood flow can provide evidence for the mechanism of SANS.
Masalkhi et al.‘s study primarily used OCT to discover changes in the fundus, such as ODE and choroidal folds. With the emergence of OCT angiography (OCTA) for blood flow imaging, we also recommend using OCTA to compare and analyse differences in optic disc vascular distribution and blood flow density before and after astronauts entering the ISS. Perhaps this will also be helpful in the study of the mechanism of SNAS. Furthermore, whether optic disc swelling will cause corresponding changes in the field of vision (VF) can also be one of the indicators for observing this syndrome. Other abnormalities, such as changes in hyperopia, axis shortening, and cotton wool spots in the fundus, can be obtained through computerized refraction, optical biometry, and colour fundus photography, and the results can be analysed comprehensively.
In addition to ultrasound, these ophthalmic examinations have the advantages of being convenient, fast, repeatable, and easy to obtain, compared to large-scale examinations such as MRI and CT, and can be used as first-time and follow-up tools for SANS. SANS includes various modalities of ophthalmic ultrasound, OCT, fundus photography, refraction, and other data, providing a diverse reference dataset for AI technology to automatically identify pathological features. Multimodal image fusion technology is gradually being applied to research on image fusion reconstruction in different modalities in medical imaging, which also expands the possibility for artificial intelligence recognition research in small-sample medical images.
Author contributions
LF and MS were involved in the conception and conduct, LF, HQ and MS were drafted this manuscript, and YZ, WW and MS were involved in review the manuscript. All authors read and approved the final version.
Funding
This study was funded by Scientifc Research Funding for Education Department of Liaoning Province (Grant No. ZD2020002).
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Masalkhi M, Ong J, Waisberg E, Lee AG. Deep learning in Ophthalmic and Orbital Ultrasound for Spaceflight Associated Neuro-ocular Syndrome (SANS). Eye. 2023. In press [DOI] [PMC free article] [PubMed]
- 2.Ong J, Waisberg E, Masalkhi M, Kamran SA, Lowry K, Sarker P, et al. Artificial intelligence frameworks to detect and investigate the pathophysiology of Spaceflight Associated Neuro-Ocular Syndrome (SANS) Brain Sci. 2023;13:1148. doi: 10.3390/brainsci13081148. [DOI] [PMC free article] [PubMed] [Google Scholar]