Tear film viscosity (TFV)

Tear film viscosity refers to the physical property describing the resistance of the tear fluid to flow. It is not a molecule, receptor, enzyme, or protein but rather a measurable characteristic of the entire tear film—a complex mixture composed mainly of water, proteins (such as mucins and lysozyme), lipids, and electrolytes. The optimal viscosity is crucial for ocular health; low viscosity during blinking prevents damage to epithelial surfaces by allowing easy shear movement, while higher viscosity when the eye is open helps maintain a stable tear layer and resists drainage or break-up[1][3]. Abnormalities in tear film viscosity are associated with dry eye diseases such as Sjögren syndrome; lower TFV indices have been shown to distinguish between different types of dry eye disease[5]. Artificial tears are formulated with varying viscosities to supplement natural tears in patients with deficient or abnormal tear films. However, excessively viscous artificial tears may cause visual disturbances or discomfort—especially for contact lens users—highlighting the need for balanced rheological properties in therapeutic products[7]. **Note:** "Tear film viscosity" is not itself a molecular target but rather a biophysical property resulting from interactions among multiple molecular components within the tear film. Therefore, it should not be classified as a canonical drug target such as an enzyme or receptor.

Increase or modulate tear film viscosity to improve lubrication and reduce evaporation[3][5]