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The following is a summary of “Analysis of Spaceflight-Associated Biometric and Refractive Changes in Astronauts,” published in the April 2025 issue of American Journal of Ophthalmology by Svoronos et al. 

Researchers conducted a retrospective study to examine changes in ocular biometry and refraction in the largest cohort of astronauts who experienced long-duration spaceflight on the International Space Station (ISS).   

They collected preflight and postflight cycloplegic refraction and ocular biometry data from 56 eyes of 29 subjects. Changes in spherical equivalent (SE), axial length (AL), average corneal curvature (K), and anterior chamber depth (ACD) were calculated for each eye. The Fyodorov and Olsen-C formulas estimated the individual contributions of biometric parameters to total SE changes. A linear mixed-model approach analyzed relationships between refraction, biometric parameters, optic disc edema, and time spent on the ISS.  

The results showed that 27 of 56 (48.2%) eyes had a hyperopic shift, 8 of 56 (14.3%) had a myopic shift, and 21 of 56 (37.5%) exhibited no measurable change in SE. The average change was a mild hyperopic shift of +0.12 D (95% CI, +0.02 to +0.22 D), driven by a reduction in AL of -0.09 millimeters (mm) (95% CI, -0.14 to -0.04 mm), offset by an ACD decrease of -0.09 mm (95% CI, -0.12 to -0.06 mm). Variability in K contributed minimally to SE changes at the group level but showed significant individual differences. Statistical modeling identified baseline preflight refraction as the strongest predictor of refractive changes (P = 0.034), with myopic individuals exhibiting the greatest hyperopic shifts and no myopic shifts, while those with baseline hyperopia showed variable refractive changes.   

Investigators concluded that spaceflight was associated with decreases in AL with ACD and variable changes in K, generally leading to a mild hyperopic shift in SE, although individual myopic shifts occurred, and previously reported larger hyperopic shifts might have been due to more myopic baselines. 

Source: ajo.com/article/S0002-9394(25)00169-2/abstract