This study aims to see if the amount of iron in tears is linked to how severe dry eye disease is. We hope this can lead to a new way to help diagnose and understand dry eye. This is an observational study. We will compare tear samples from people with dry eye to samples from people with healthy eyes. We will measure the iron content in the tears and see if it correlates with standard dry eye test results and symptom scores.

Inclusion Criteria:

• Aged between 18 and 70 years, inclusive.
• Willing and able to provide written informed consent.

Exclusion Criteria:

• History or clinical suspicion of significant systemic conditions: hematologic diseases, severe systemic infections, malignancies (treated or untreated), or chronic hepatic/renal insufficiency.
• Use of artificial tears or any topical eye drops within 2 hours prior to examination.
• Active ocular allergy, infection, or severe blepharitis within the past 1 month.
• Systemic or topical use of antibiotics, corticosteroids, NSAIDs, or immunosuppressants within the past 1 month.
• History of contact lens wear within the past 1 month.
• History of blood transfusion, ocular surgery, or significant ocular trauma within the past 6 months.
• Women who are pregnant, breastfeeding, or postmenopausal women undergoing hormone replacement therapy.
• Known hypersensitivity to fluorescein sodium.

Based on your study protocol, here is the description for the "Study Population Description" field:

This single-center, cross-sectional study will recruit participants from the patient population and staff/community at the Ophthalmology Department of Shanghai Changzheng Hospital. The Dry Eye Disease (DED) group will consist of consecutive patients presenting to the clinic who are diagnosed with DED according to the 2024 Chinese Expert Consensus criteria. The healthy control group will be recruited through hospital staff volunteers and community advertisements. All participants will be enrolled during the specified study period from the single site.