Tears contain over five hundred proteins and around seventy percent of these are also found in other tissue fluids. The tear film, apart from its traditional role on the ocular surface, also remains an untapped reservoir for many potential biomarkers for both systemic and ocular surface diseases. It has become increasingly feasible to assess the ocular surface as a potential reservoir for biomarkers, especially with the use of emerging technologies such as enzyme-linked immunosorbent assay (ELISA) testing Kits, anterior segment OCT, functional slit lamp biomicroscopy setup for conjunctival microcirculatory parameters, and corneal confocal microscopy.

Biomarkers provide an objective, measurable algorithm for evaluating the process of a disease. Some biomarkers aim to diagnose illnesses, which has a clear translation to clinical practice, but they can also help investigators to more accurately detect the disease and thereby also identify the risk factors and early signs of the disease at the preclinical stage. Detection of these early signs of illness could lead to early intervention and better health outcomes for patients. Other ocular surface biomarkers will allow pharmaceutical companies to accurately measure the effectiveness of treatments. The most desirable biomarkers will be easily and rapidly quantifiable and cost-effective. Ocular surface biomarkers fit this distinction in that its detection is minimally invasive and its potential transcends beyond eye care. As many potential biomarkers may exist on the ocular surface, it remains an ever available reservoir to research and discover biomarkers.

This Special Issue aims to gather papers that will address this emerging and exciting area in eye research. We welcome both original research and review articles that investigate ocular surface biomarkers for ocular and systemic diseases and hope to encourage collaboration with many physicians including neurologists and endocrinologists.

Potential topics include but are not limited to the following:

• Ocular surface biomarkers for dry eye disease
• Ocular surface biomarkers for ocular allergies
• Tear neuromediators as biomarkers for diabetes
• Tear proteins as biomarkers for systemic disease
• Conjunctival microcirculatory parameters as biomarkers for systemic disease
• Tear neuromediators as biomarkers for contact lens discomfort
• Tears proteins as biomarkers for dry eye disease
• Anterior segment OCT parameters as biomarkers for dry eye disease
• Tear neuropeptides in contact lens discomfort
• Tear cytokine profiles in meibomian gland dysfunction
• Detection of ocular surface genetic biomarkers, such as tear telomeres, in ocular surface disease
• Ocular surface inflammatory biomarkers for systemic disease
• Corneal confocal microscopy parameters as biomarkers for systemic disease
• Corneal confocal microscopy parameters as biomarkers for ocular disease