Table 3

Protective physical and biological characteristics of tear substitutes

MoleculeCharacteristicsAuthor, year (Ref.)
Physical protection
Cellulose derivatesIncrease residence time and tear film volume. Good level of adhesion to epithelial cells, especially in high concentration.Toda, 199670
Garrett, 200771
Hydroxypropyl guarLubricates 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 gelsRetain 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 stabilisersEctoin 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 hyalunorateReduces 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 solutesOsmoprotection 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 ionsInfluence metabolic activities of the cells improving cell viabilityMacrì, 201587
Uchida, 201447
TrehaloseCell 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