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Development of Ophthalmic Formulations
Published in Sandeep Nema, John D. Ludwig, Parenteral Medications, 2019
Paramita Sarkar, Martin Coffey, Mohannad Shawer
The tear fluid osmolality normally ranges from about 300 to 320 mOsm/kg [3,12], and most of the osmolality in the tear fluid can be attributed to the salt content of the lacrimal fluid, which is primarily sodium chloride, sodium bicarbonate, potassium chloride, calcium chloride, and magnesium chloride [3]. Normally, there is about five times more sodium than potassium in the tear fluid, and the levels of calcium and magnesium are less than 1/200th of the sodium levels [3]. Higher-than-normal osmolality in the tear fluid is often seen in patients with dry eye syndrome. Abnormally high evaporation of tear fluid increases the salt levels and results in higher osmolality. As a result, many products for the treatment of dry eye are often formulated with lower-than-normal osmolality.
Biomimetic materials based on zwitterionic polymers toward human-friendly medical devices
Published in Science and Technology of Advanced Materials, 2022
Focusing on the structure of the biological corneal surface, the corneal cell surface is covered with bound mucin [230]. Figure 13(a) shows an electron micrograph of the tear film contacting the surface of the conjunctival epithelium. Epithelial cells have a rough endoplasmic reticulum, are synthetically active, and contain small secretory vesicles in the apical cytoplasm. The cell membrane has raised folds, called microplicas, which form regular undulations in the cross-section. These cells express and produce a thick glycocalyx along with membrane-bound mucins, which are important components of the epithelial-lacrimal interface. Figure 13(b) shows a schematic representation of biomolecules at the corneal surface. Free mucin is also present at relatively high concentrations in the tear fluid. These compounds inhibit the evaporation of water from the corneal tissue and prevent dry eye syndrome. If the function of these hydrophilic molecules in a small portion of the surface can be applied to silicone-based contact lens materials, it is thought that both surface properties and oxygen permeability can be solved simultaneously. Although still in the basic stage, research is underway to coat the surface of contact lenses with biomolecules such as mucin and hyaluronic acid to increase lubricity and improve the wearing experience [231,232].s