Abstract
Spaceflight acutely but transiently elevates intraocular pressure (IOP), often attributed to cephalad fluid shift and choroidal expansion. We propose that anterior segment mechanics, including lens–iris diaphragm position and conventional outflow loading, may contribute to early IOP changes. Comparing phakic and pseudophakic eyes, paired with anterior segment OCT and complementary imaging aboard the International Space Station, could define mechanisms and inform astronaut screening and ocular risk mitigation.
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References
Draeger, J., Wirt, H. & Schwartz, R. “TOMEX”, Messung des Augeninnendrucks unter μG-bedingungen. Naturwissenschaften 73, 450–452 (1986).
Draeger, J., Schwartz, R., Groenhoff, S. & Stern, C. Self-tonometry under microgravity conditions. Clin. Investig. 71, 700–703 (1993).
Cook, J. A. et al. Systematic review of the agreement of tonometers with Goldmann applanation tonometry. Ophthalmology 119, 1552–1557 (2012).
Linder, B. J. & Trick, G. L. Simulation of spaceflight with whole-body head-down tilt: influence on intraocular pressure and retinocortical processing. Aviat. Space Environ. Med. 58, A139–A142 (1987).
Mader, T. H., Taylor, G. R., Hunter, N., Caputo, M. & Meehan, R. T. Intraocular pressure, retinal vascular, and visual acuity changes during 48 h of 10 degrees head-down tilt. Aviat. Space Environ. Med. 61, 810–813 (1990).
Mader, T. H. et al. Intraocular pressure and retinal vascular changes during transient exposure to microgravity. Am. J. Ophthalmol. 115, 347–350 (1993).
Berdahl, J. P. Cataract surgery to lower intraocular pressure. Middle East Afr. J. Ophthalmol. 16, 119–122 (2009).
Schachar, R. A. Gravity does not affect lens position during accommodation. Invest. Ophthalmol. Vis. Sci. 57, 4566–4567 (2016).
Lister, L. J., Suheimat, M., Verkicharla, P. K., Mallen, E. A. H. & Atchison, D. A. Influence of gravity on ocular lens position. Investig. Ophthalmol. Vis. Sci. 57, 1885–1891 (2016).
Helmholtz, H. Ueber die accommodation des auges. Arch. Ophthalmol. 1, 1–74 (1855).
Wang, F. et al. Differences between angle configurations in different body positions by ultrasound biomicroscopy in patients with cortical age-related cataract. Clin. Interv. Aging 18, 799–808 (2023).
Mader, T. H. Intraocular pressure in microgravity. J. Clin. Pharmacol. 31, 947–950 (1991).
Smith, T. J. & Lewis, J. Effect of inverted body position on intraocular pressure. Am. J. Ophthalmol. 99, 617–618 (1985).
Mader, T. H. et al. Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed in astronauts after long-duration space flight. Ophthalmology 118, 2058–2069 (2011).
Macias, B. R. et al. Association of long-duration spaceflight with anterior and posterior ocular structure changes in astronauts and their recovery. JAMA Ophthalmol. 138, 553–559 (2020).
Yücel, Y. H., Johnston, M. G., Ly, T. et al. Identification of lymphatics in the ciliary body of the human eye: a novel “uveolymphatic” outflow pathway. Exp. Eye Res. 89, 810–819 (2009).
Yücel, Y. H., Cardinell, K., Khattak, S. et al. Active lymphatic drainage from the eye measured by noninvasive photoacoustic imaging of near-infrared nanoparticles. Investig. Ophthalmol. Vis. Sci. 59, 2699–2707 (2018).
Kim, M., Johnston, M. G., Gupta, N., Moore, S. & Yücel, Y. H. A model to measure lymphatic drainage from the eye. Exp. Eye Res. 93, 586–591 (2011).
Marshall-Goebel, K. et al. Assessment of jugular venous blood flow stasis and thrombosis during spaceflight. JAMA Netw. Open 2, e1915011 (2019).
Rasmussen, J. C. et al. Assessing lymphatic route of CSF outflow and peripheral lymphatic contractile activity during head-down tilt using near-infrared fluorescence imaging. Physiol. Rep. 8, e14375 (2020).
Stern, C. et al. Eye-brain axis in microgravity and its implications for spaceflight associated neuro-ocular syndrome. npj Microgravity 9, 56 (2023).
Johnstone, M., Xin, C., Martin, E. & Wang, R. K. Trabecular meshwork movement controls distal valves and chambers: new glaucoma medical and surgical targets. J. Clin. Med. 12, 6599 (2023).
Aspelund, A. et al. The Schlemm’s canal is a VEGF-C/VEGFR-3–responsive lymphatic-like vessel. J. Clin. Investig. 124, 3975–3986 (2014).
Park, D.-Y., Lee, J., Park, I. et al. Lymphatic regulator PROX1 determines Schlemm’s canal integrity and identity. J. Clin. Investig. 124, 3960–3974 (2014).
Memarzadeh, F., Tang, M., Li, Y., Chopra, V., Francis, B. A. & Huang, D. Optical coherence tomography assessment of angle anatomy changes after cataract surgery. Am. J. Ophthalmol. 144, 464–465 (2007).
Azuara-Blanco, A. et al. Effectiveness of early lens extraction for the treatment of primary angle-closure glaucoma (EAGLE): a randomised controlled trial. Lancet 388, 1389–1397 (2016).
Anderson, A. P. et al. Acute effects of changes to the gravitational vector on the eye. J. Appl. Physiol. 120, 939–946 (2016).
Mader, T. H. et al. Stability of vision during space flight in an astronaut with bilateral intraocular lenses. Am. J. Ophthalmol. 127, 342–343 (1999).
Mader, T. H. et al. Intraocular lens use in an astronaut during long duration spaceflight. Aerosp. Med. Hum. Perform. 89, 63–65 (2018).
Chung, K.-Y. et al. Diurnal pattern of intraocular pressure is affected by microgravity when measured in space with the pressure phosphene tonometer (PPT). J. Glaucoma 20, 488–491 (2011).
Huang, A. S., Stenger, M. B. & Macias, B. R. Gravitational influence on intraocular pressure: implications for spaceflight and disease. J. Glaucoma 28, 756–764 (2019).
Sandhu, B. S. et al. The case for anterior segment optical coherence tomography (AS-OCT) for the International Space Station and future planetary spaceflight: clinical relevance and technical implementation. Life Sci. Space Res. 46, 74–85 (2025).
Asam, J. S., Polzer, M., Tafreshi, A., Hirnschall, N. & Findl, O. Anterior segment OCT. in High Resolution Imaging in Microscopy and Ophthalmology: New Frontiers in Biomedical Optics (ed. Bille, J. F.) (Springer, 2019).
Xu, B. Y., Mai, D. D., Penteado, R. C., Saunders, L. & Weinreb, R. N. Reproducibility and agreement of anterior segment parameter measurements obtained using the CASIA2 and Spectralis OCT2 optical coherence tomography devices. J. Glaucoma 26, 974–979 (2017).
Ritch, R. & Liebmann, J. M. Role of ultrasound biomicroscopy in the differentiation of block glaucomas. Curr. Opin. Ophthalmol. 9, 39–45 (1998).
Pavlin, C. J., Rutnin, S. S., Devenyi, R., Wand, M. & Foster, F. S. Supraciliary effusions and ciliary body thickening after scleral buckling procedures. Ophthalmology 104, 433–438 (1997).
Liebmann, J. M., Weinreb, R. N. & Ritch, R. Angle-closure glaucoma associated with occult annular ciliary body detachment. Arch. Ophthalmol. 116, 731–735 (1998).
Chiao, L. et al. Ocular examination for trauma: clinical ultrasound aboard the International Space Station. J. Trauma 58, 885–889 (2005).
Meer, E. et al. Ocular conditions and injuries, detection and management in spaceflight. npj Microgravity 9, 37 (2023).
Ishikawa, H. & Schuman, J. S. Anterior segment imaging: ultrasound biomicroscopy. Ophthalmol. Clin. North Am. 17, 7–20 (2004).
Willekens, K. et al. Review on dynamic contour tonometry and ocular pulse amplitude. Ophthalmic Res. 55, 91–98 (2015).
Kaufmann, C., Bachmann, L. M., Robert, Y. C. & Thiel, M. A. Ocular pulse amplitude in healthy subjects as measured by dynamic contour tonometry. Arch. Ophthalmol. 124, 1104–1108 (2006).
Masis Solano, M. M., Dumas, R., Lesk, M. R. & Costantino, S. Ocular biomechanical responses to long-duration spaceflight. IEEE Open J. Eng. Med. Biol. 6, 127–132 (2024).
Norsk, P., Asmar, A., Damgaard, M. & Christensen, N. J. Fluid shifts, vasodilatation and ambulatory blood pressure reduction during long duration spaceflight. J. Physiol. 593, 573–584 (2015).
Luce, D. A. Determining in vivo biomechanical properties of the cornea with an ocular response analyzer. J. Cataract Refract. Surg. 31, 156–162 (2005).
Lopes, B. T. et al. Review of in-vivo characterisation of corneal biomechanics. Med. Nov. Technol. Dev. 11, 100073 (2021).
Piñero, D. P. & Alcón, N. In vivo characterization of corneal biomechanics. J. Cataract Refract. Surg. 40, 870–887 (2014).
Touboul, D. et al. Correlations between corneal hysteresis, intraocular pressure, and corneal central pachymetry. J. Cataract Refract. Surg. 34, 616–622 (2008).
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A.W. led the conceptual development of the paper, produced Figs. 1 and 3, and was a primary contributor to the writing and editing. J.O. proposed the initial research question and contributed to editing. B.S. contributed to writing and editing involving imaging technology. R.S., A.B., A.L., J.B., R.G., and T.M. contributed through editorial suggestions and revisions during later stages of the manuscript preparation. All authors reviewed and approved the final version of the manuscript.
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Weaver, A., Ong, J., Sandhur, B.S. et al. Anterior segment biomechanics and intraocular pressure in microgravity: implications for future spaceflight studies. npj Microgravity (2026). https://doi.org/10.1038/s41526-026-00592-2
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DOI: https://doi.org/10.1038/s41526-026-00592-2
