This study will examine how hydration status (drinking a large amount of water or avoiding water for a short period of time) affects the eye. Healthy adult volunteers will participate in two sessions: one after mild dehydration (no water for 12 hours) and one after drinking 2 liters of water within 4 hours. At each session, detailed eye measurements will be taken, including scans of the retina and optic nerve using optical coherence tomography (OCT), corneal imaging with Pentacam, and eye length measurements with an optical biometer. The results from the two conditions will be compared within the same participants.

The main goal is to determine whether hydration influences the thickness of the retina (macula). Secondary goals include assessing changes in the optic nerve, cornea, and other biometric eye parameters. The study involves only non-invasive tests and minimal risk. Findings may help improve understanding of how hydration affects the eye and may be important for clinical practice, such as planning cataract or refractive surgery.

Inclusion Criteria:

• Healthy adult volunteers aged 18 to 65 years
• Normal ophthalmological findings
• Best corrected visual acuity (BCVA) ≥ 1.0 (decimal)
• Willingness to participate and provide written informed consent

Exclusion Criteria:

• Known ocular diseases (e.g., glaucoma, keratoconus, retinal pathology)
• History of ocular surgery
• Systemic diseases affecting hydration status (e.g., diabetes mellitus, kidney disease)
• Any condition that, in the investigator's opinion, could interfere with study participation or data quality
• Refusal to participate