Using osmolarity to diagnose dry eye: a compartmental hypothesis and review of our assumptions

Ophthalmic drug delivery faces major limitations due to poor absorption across the corneal membrane. This process is primarily driven by diffusion and is influenced by two main factors: the physicochemical properties of the drug and tear drainage. Most ophthalmic drugs, such as pilocarpine, epinephrine, atropine, and local anesthetics, are weak bases. They are typically formulated at an acidic pH to enhance chemical stability. However, this leads to high ionization, reducing their ability to...

The human eye has a specialized microbiota that reflects its unique anatomical and immunological environment. This low-biomass microbial community predominantly colonizes the conjunctiva and eyelid margins, playing a vital role in ocular surface homeostasis and defense. Despite its proximity to the richly colonized facial skin, the ocular surface maintains a distinct microbial profile due to continuous mechanical and biochemical defense mechanisms.The conjunctival surface hosts fewer microbial...

Osmosis is the movement of free water molecules through a semipermeable membrane.  The water's concentration gradient across the membrane is inversely proportional to the solutes' concentration. Whereas diffusion transports material across membranes and within cells, osmosis transports only water across a membrane, and the membrane limits the diffusion of solutes in the water. Osmosis is a special case of diffusion.
Water, like other substances, moves from a high concentration of free water...

Approximately 60% to 95% of the weight of living organisms is attributed to water. Therefore, maintaining appropriate water balance within cells is of paramount importance. Osmosis is the movement of water across a semipermeable membrane, such as a cell’s plasma membrane. In living organisms, water plays a crucial role as a solvent—a molecule that dissolves other molecules.Diffusion Versus OsmosisBoth diffusion and osmosis are types of passive transport—cellular transport that does not require...

A number of natural and synthetic materials exhibit selective permeation, meaning that only molecules or ions of a certain size, shape, polarity, charge, and so forth, are capable of passing through (permeating) the material. Biological cell membranes provide elegant examples of selective permeation in nature, while dialysis tubing used to remove metabolic wastes from blood is a more simplistic technological example. Regardless of how they may be fabricated, these materials are generally...

Glaucoma is an eye condition characterized by increased intraocular pressure that damages the retina and optic nerve, leading to irreversible blindness if left untreated. The human eye has various components, including the cornea, iris, pupil, lens, and optic nerve. Aqueous humor is secreted by the epithelium of the ciliary body in the posterior chamber and flows through the trabecular meshwork and canal of Schlemm, maintaining normal intraocular pressure. The trabecular meshwork and the canal...