In this study, the investigators aim to determine the effects of age, sex, history of ocular surgery and contact lens use, and ocular surface and meibomian gland parameters on the lipid layer thickness (LLT) in normal subjects and patients with dry eye syndrome. Patients with dry eye syndrome and subjects with a healthy ocular surface will be enrolled. All participant will underwent LLT measurement with a LipiView interferometer, tear meniscus height measurement using optical coherence tomography, tear film break-up time (TBUT) determination, corneal and conjunctival staining, Schirmer's test, examination of the lid margins and meibomian glands, and assessment using the Ocular Surface Disease Index(OSDI) questionnaire.

Inclusion Criteria:

1. age over 19 years old, Patients with dry eye syndrome and normal subjects

Exclusion Criteria:

1. patients less than 18 years of age and patients with histories of ocular surgery within 3 months; ocular injury; and ocular diseases such as ocular infection, allergy, and autoimmune disease; and patients with the use of a punctal plug or topical ocular medications other than artificial tears.
2. Patients who used artificial tears were instructed not to apply them for at least 12 hours 99 before the examinations

age over 19 years old, Patients with dry eye syndrome and normal subjects

no plan to share IPD