The major cause of the pathological process in dry eye disease is the breakdown of the tear film which induces an over-stimulation of the corneal nerve receptors and a localized boost in osmolarity; phenomena that seem to be the beginning of the process leading to inflammation and symptoms typical of the disease. One of the main characteristics of lacrimal dysfunction is the variability of symptoms and the anatomical conditions over the year and throughout the day. At the same time, alimentary variations can lead to secretion of different lipids with different consequences and they may promote bacterial growth in the Meibomian glands, with different lipases characteristics, or changes in the anti-evaporative efficacy of the lipid film or they may increase inflammation. Emotional conditions, hormonal and environmental modifications also affect lacrimal secretion rate on behalf of lacrimal and accessory glands. Furthermore, if not promptly corrected, factors sustaining the disease tend to evolve, stimulating inflammatory and metaplastic processes. Therefore, an effective therapy for dry eye disease cannot be obtained only by restoring the tear volume but it will have to affect all the mechanisms involved in the pathogenesis of the damage. Most publications suggest that also oxidative stress is involved in the extension of cellular damage in conjunctivochalasis, dry eye disease and UV radiation damage, thus protection against oxidative damage is fundamental to prevent excessive water evaporation from the tear film, the main pathogenetic mechanism in the development of dry eye disease. The new tear substitutes contain an increased percentage of substances with different structural and functional characteristics which are able to correct, simultaneously, the various critical factors of the tear film and the corneo-conjunctival epithelium. The most recent preparations, such as the combination of xanthan gum, hyaluronic acid and osmoprotectors in hypotonic solution (Synfo, SIFI spa, Catania, Italy) thanks to the synergic activity of each component, provide an adequate volume of water, improving the stability of the tear film and ensuring good hydration of the epithelium. The hypotonic tear substitute containing xanthan gum and hyaluronic acid allows to stabilize the tear film, reducing inflammatory risk, to reduce the discomfort and protect directly (physically) and indirectly (biological) ocular surface epithelium and promote its repair. This new tear substitute exerts its protective action through the combination of two different molecules capable of combining into a mixture of linear and branched polymers. Both polymers show the ability to stimulate re-epithelization and guarantee physical and biological protection of the epithelium in a synergic way, thanks to the mucomimetic activity, the antioxidant properties and the promotion of cellular vitality and motility.
