Effects of dehydration and hyperhydration on macular and peripapillary retinal thickness assessed by OCT.

PURPOSE: To determine whether short-term dehydration and hyperhydration affect OCT-derived retinal thickness in healthy young adults in a randomized cross-over design. METHODS: Sixty volunteers aged 18-35 years completed two morning sessions ≥7 days apart: 12-h fluid restriction, representing relative dehydration, and water loading, defined as ≥2 L within 4 h. Spectral-domain OCT (Zeiss Cirrus HD-OCT 7000) was performed by a masked examiner. Primary outcomes were central subfield thickness (CST) and mean peripapillary retinal nerve fiber layer (RNFL) thickness; secondary outcomes were cube average thickness (CAT) and ganglion cell-inner plexiform layer (GCL-IPL) thickness. Hydration was documented using a self-reported thirst scale and recorded water intake. Within-subject comparisons used the Wilcoxon signed-rank test. RESULTS: Median age was 28.5 years and 65% of participants were female. Thirst was higher during dehydration than hyperhydration (P < 0.001). After review of OCT outputs and exclusion of outlying paired observations for GCL-IPL and CAT, the direction and statistical interpretation of the findings remained unchanged. CAT was slightly lower during dehydration in both eyes. CST was lower during dehydration in the left eye, with a similar non-significant trend in the right eye. RNFL thickness did not differ between hydration states in either eye. GCL-IPL thickness showed only a small right-eye difference and no significant difference in the left eye. CONCLUSIONS: Acute fluid restriction was associated with small reductions in macular OCT thickness measures, whereas RNFL thickness remained stable. The magnitude of these changes was modest and close to expected OCT test-retest variability, suggesting limited clinical relevance for routine individual interpretation but potential relevance for highly standardized research or longitudinal imaging settings.