Currently, tear supplements are available as solutions, ointments and gels. They can be used as often as necessary to keep the corneal surface and conjunctiva wet. Preferably, the topical application of a well-formulated tear supplement and lubricating agent should provide relief for both aqueous- and mucin-deficient dry eye. Moreover, functions associated with the lipid layer of the precorneal tear film should not be altered by the tear supplement.
There are several objectives that tear supplements aim to fulfil in the treatment of dry eye.
Objectives of tear supplements
Ideally, tear supplements should fulfil the physico-chemical role of a normal tear film. In addition, they should not disturb corneal metabolism nor be toxic to the eye, even with frequent use. It should also have a refractive index similar to that of the cornea to see correctly. This involves consideration of certain characteristics in the formulation if tear supplements are to resemble physiological tears. These include electrolyte concentration, viscosity, mucomimetic properties, pH, osmolarity and the absence of preservatives.
Your can read more about this subject here: http://vismed.trbchemedica.co.uk/business-professionals/vismed-eye-drops/the-ideal-tear-supplement