Tear hyperosmolarity is one of the primary causes of chronic dry eye disease. It is considered as the core mechanisms in the development of dry eye. Dry eye disease is defined by the Definition and Classification Subcommittee of the 2007 International Dry Eye Workshop as a disease related to the tears and ocular surface which results in the indications of discomfort, ocular disturbance, and tear film instability with probable damage to the visual surface. It is linked with increased osmolarity of the tear film and inflammation of the ocular surface.
Dry eye is a common condition that affects millions of people. It is characterized by symptoms of ocular discomfort, dryness, irritation, and visual disturbance. Tear hyperosmolarity occurs as a result of water evaporation from the exposed ocular surface. It is common in people with low aqueous tear flow or excessive evaporation, or a combination of both events. Hyperosmolarity stimulates a flow of inflammatory events in the epithelial surface cells that involves MAP kinases and NFkB indicating pathways and the generation of inflammatory cytokines (IL-1α; -1β; TNF-α) and MMPs (MMP9).
Tear hyperosmolarity is mainly the hidden factor in the development of the disease. In simple it can be called the saltiness of the tears. Tearlab.com stresses that osmolarity in tears increases the risk of damage to the ocular surface cells resulting in added chances of developing dry eye disease.
It is proved that these inflammatory measures lead to death of surface epithelial cells, including goblet cells. The loss of the goblet cells is directly related to the effects of chronic inflammation.
The normal tear production is controlled by the lacrimal functional unit. The tear film consists of three major elements namely, lipid, aqueous, and mucin, secreted by the lacrimal unit under various biological mechanisms that help the tear production procedure to run on the ocular surface properly in an organized manner.
The reduction in the normal tear producing capacity of the lacrimal functional unit leads to tear hyperosmolarity.
The increased rate of the evaporation level and reduced tear flow results in tear hyperosmolarity. The epithelium tissue on the surface of the eyes gets harmed due to various factors. It also leads to volatility of tear film and death of the cells. The recurring episodes of volatility of tear film leads to further hyperosmolarity, worsening the damage of the ocular surface leading to severe chronic dry eye condition.
Prevention measures for tear hyperosmolarity include osmoprotectants which are small organic molecules. These organic molecules are usually used in cell types to restore cell volume and alleviate protein function. Osmoprotectants is useful in protecting ocular cells from destruction due to hyperosmolarity.