We read with great interest the article by Fukui A et al. concerning the “Changes in Choroidal Thickness (ChT) and Structure in Preeclampsia with Serous Retinal Detachment”

Background: Caffeine, the most widely consumed dietary bioactive compound worldwide, exerts acute vasoactive effects on several vascular beds, but its impact on the internal composition of the choroid remains unclear. We evaluated the acute effects of a single oral dose of caffeine on choroidal structure and vascularity, retinal superficial capillary plexus (SCP) microcirculation, optic nerve head (ONH) perfusion, and intraocular pressure (IOP) in healthy young adults. Methods: In this prospective, single-arm observational study without a control group, 46 healthy adults were examined at baseline and 30 and 60 min after ingesting 200 mg of caffeine. Subfoveal choroidal thickness (SCT), total, luminal and stromal choroidal areas, and the choroidal vascularity index (CVI) were derived from EDI-OCT with Niblack binarization. SCP vessel density and perfusion, ONH perfusion and flow index, and IOP were also recorded. Data were analyzed using repeated-measures ANOVA. Results: SCT decreased progressively from 356.0 ± 84.2 µm to 325.9 ± 81.0 µm at 60 min (p < 0.001; η²p = 0.61). Luminal and stromal areas declined in parallel (r = 0.919, p < 0.001), with only a minimal change in CVI (p = 0.003). IOP decreased modestly (p = 0.009), whereas SCP and ONH parameters showed no significant changes. The response was independent of sex and axial length. Conclusions: A single dose of caffeine was associated with acute, progressive choroidal thinning, paralleled by a near-proportional constriction of the luminal and stromal compartments, with no significant short-term change detected in the retinal and optic nerve head circulations, consistent with an adenosine-mediated vasoconstrictive mechanism.