Contact Lens Wetting Agents
Soft contact lenses are remarkable tiny medical devices that make our lives so much more convenient. And the development of new technologies has resulted in many lens innovations, most recently auto-dimming lenses and lenses with the ability to let oxygen pass through at a very high rate. Manufacturers are investing heavily to make the wearing of contact lenses a more pleasant experience with better vision, more and longer-lasting comfort and easier handling.
One of the components used in modern soft contact lens technologies are wetting agents. As the name already suggests, these are tiny helpers in the form of water-binding molecules that increase the wettability of a contact lens, decrease friction, increase the moisture level and act as a lubricant with the goal to have a positive impact on wearing comfort and tolerance. They can be either found in the lens material and/or in the packaging buffering solution. Besides, there are contact lens multi-purpose cleaning solutions that contain wetting agents that interact with the lens and increase the moisture level, so the moisture can be slowly released when the lens has been inserted. There are a few different types of wetting agents, known by their cryptical-sounding chemical name and often recognized by a 3-letter acronym.
Some manufacturers try to avoid using wetting agents in the design of some of their lenses and the argument of 'yet another chemical in my eye' and 'possible allergic reaction' comes to mind. By the way, similar is true for the visibility tint - a chemical added to colorize the lens for easier handling.
You, the patient, need to decide what is right for you. Wetting agents are helpers to improve the overall experience and comfort. How well your eyes tolerate a lens is a sum of many factors such as material, fitting parameters, oxygen and moisture levels, lens edge design and your lifestyle.
PVP - Polyvinylpyrrolidone
PVP has been used for a long time and is one of the most common wetting agents. Also called polyvidone or povidone, PVP is a water-soluble polymer made from the monomer N-vinylpyrrolidone. Its chemical formula is (C6H9NO). PVP was first synthizied in 1939 and with its excellent wetting properties, it easily forms films and makes it a great coating additive.
PEG - Polyethylene glycol
PEG is another popular wetting agent and known for many medical uses including the pre-surgery preparing of bowels and intestines. Due to its hydrophilic nature, this flexible, water-soluble polymer is used to support contact lenses in reducing protein-based debris, a factor that can lead to itchiness and discomfort.
PEOX - Poly-2-ethyl-2-oxazoline
The lesser-known PEOX is an alternative to PEG with higher stability compared to PEG; it is considered to be non-toxic and non-immunogenic and having a highly tuneable structure, makes it a substitute for PVA (Polyvinyl alcohol). It has also shown potential antimicrobial properties as mentioned in this publication found on research gate.
HPMC - Hydroxypropyl Methylcellulose (Hypromellose)
HPMC is often used in eye drops or added to the packaging solution. It is considered a semi-synthetic substitute for our tear film, explaining its use in many popular wetting drops.
When applied, HPMC acts to expand and absorb water, thereby increasing the thickness of the tear film and - in theory - contributing to reduced eye irritation, particularly in dry environments such as dry climates, home, or office environments.
PVA - Polyvinyl alcohol
PVA can be found in many contact lenses and is non-toxic, has no odor and easily creates a film. Polyvinyl alcohol reduces the surface tension of the tears and has similar properties when compared to our natural mucin. PVA lubricates the eye and increases tear film stability.
So it is no surprise that it found its way into contact lenses and eye drops. There is a lot of research that has been done on PVA-based hydrogel contact lenses - research that dates back to the early '90s. Focus Dailies (the predecessor of Dailies AquaComfort Plus) were one of the first daily lenses that contained PVA as a moisturizing agent designed for continuous release throughout the day.
PC - Phosphatidylcholine
PC is an interesting chemical, better known when commonly referred to as lecithin; it is naturally present in our tear film. Phosphatidylcholine is studied extensively as research has shown its positive contributions in the fight against brain-related diseases and disorders, blood circulation problems, eczema, gallbladder disease, high cholesterol, hepatitis, and premenstrual syndrome. PC is used in Delefilcon A, the base material of Alcon's Dailies Total1.
PO - Poloxamer
Poloxamers were invented and patented in the '70s and are copolymeric substances used to increase the absorption of water by hydrophobic substances. Poloxamer forms a water-loving contact lens surface to reduce lens-lid interference and a smoother gliding of the eye lid over the lens. Poloxamer also supports the removal of lipid films on contact lenses and therefore is used in contact lens packaging solutions and in multi-purpose cleaning solutions. Poloxamer 407 has also shown the capability of inhibiting bacterial adherence onto contact lens surfaces.
Poloxamer 407 as a bacterial adhesive for hydrogel contact lenses
by Portolés M1, Refojo MF, Leong FL.
Schepens Eye Research Institute, Department of Ophthalmology