Protective physical and biological characteristics of tear substitutes
| Molecule | Characteristics | Author, year (Ref.) |
|---|---|---|
| Physical protection | ||
| Cellulose derivates | Increase residence time and tear film volume. Good level of adhesion to epithelial cells, especially in high concentration. | Toda, 199670
Garrett, 200771 |
| Hydroxypropyl guar | Lubricates the interface between lids and bulbar surface reducing epithelial stress. | Rolando, 200972 |
| Medium/high- molecular-weight and chain length biopolymers (ie, sodium hyaluronate) | Non-Newtonian viscoelastic activity. Allow for a good viscosity when the eye is open that suddenly decreases during blinking, thus improving tear film thickness when the eyes are open and comfort during eye closure. | Iester, 200073
Aragona, 200274 Aragona, 200275 |
| High concentration polymers, complexed biopolimers, carbomer gels | Retain water in their structure so reducing the effect of lid friction and maintaining the volume of the tear film. | Garrett, 200771
Postorino, 201776 Cagini, 201777 Sullivan, 199778 |
| Membrane stabilisers | Ectoin and trehalose stabilise lipid layers cells by the interaction between hydrocomplexes and lipids, creating a protective and stabilising water shell. | Graf, 200886 |
| Biological protection | ||
| Sodium hyalunorate | Reduces squamous metaplasia improving goblet cells expression and epithelial cells morphology; improves cellular kinetics, binds to CD44, the specific receptor present in the cells. | Entwistle, 199681
Lerner, 199882 Gomes, 200483 Aragona, 200784 |
| Compatible solutes | Osmoprotection by antagonising cell dehydration protecting from denaturation of cellular proteins, preventing cellular shape changes and apoptosis (carnitin, eritritol, trehalose, glycerin, betaine, etc). | Baudouin, 201346
Aragona, 201485 |
| Vitamins, antioxidants, and fundamental ions | Influence metabolic activities of the cells improving cell viability | Macrì, 201587
Uchida, 201447 |
| Trehalose | Cell hydration maintainer; its presence confers desiccation resistance to bacterial and human cells; its remarkable effectiveness is due to the ability to replace some of the water in the cell, thereby stabilising and protecting the cellular membrane and proteins during the freezing process. Autophagy promotion: cleaning of immunostimulating DNA fragments lowering the risk of adaptive immune response. | Guo, 200079
Nakamura, 200880 Ohsumi, 201488 Sarkar, 200748 |