Choroidal Thickness Increases During Parasympathetic Dominance After Immersion of the Foot in Warm Water

Abstract

Purpose: This study aimed to assess the course of changes in choroidal morphology after immersion of the foot in warm water at 40°C using enhanced depth imaging optical coherence tomography (EDI-OCT).

Methods: Forty-three right eyes of 43 healthy participants were included. Changes in choroidal morphology were determined using EDI-OCT to evaluate subfoveal choroidal thickness (SCT). Systolic, diastolic, and mean blood pressures (SBP, DBP, and MBP, respectively) were also measured to determine systemic circulatory dynamics at baseline, immediately after immersion (0 min), and 10, 20, and 30 min after immersion.

Results: Immediately after immersion, SBP, DBP, and MBP were significantly declined versus baseline. In contrast, the SCT was significantly increased after warm water immersion. However, all these parameters did not change significantly compared to the baseline within 30 min.

Conclusion: In the normal eye, parasympathetic nerve activity induced by warming stimuli increases choroidal morphology in response to a decrease in systemic circulatory activity, which normalizes within 30 min. The findings of this study may provide basic data for the prevention and treatment of various choroidal diseases in which sympathetic hyperactivity is involved in the pathogenesis.

Keywords: choroidal morphology; enhanced depth imaging optical coherence tomography; parasympathetic activity; subfoveal choroidal thickness; systemic circulation.

Figure 1. Enhanced depth imaging optical coherence tomography images at baseline (a), immediately after the immersion (b), and at 10 min (c), 20 min (d), and 30 min (e) later in a participant (case 6).

SCT was 339 μm at baseline (a), 348 μm at 0 min (b), 341 μm at 10 min (c), 339 μm at 20 min (d), and 341 μm at 30 min (e), respectively. SCT was thickest after warm water immersion. SCT: subfoveal choroidal thickness