What's in Contact Lens Cleaning Solutions and Eye Drops?
Updated: Dec 11, 2020
We already wrote about the different types of cleaning solutions and eye drops and their important role in a daily lens cleaning regimen. The market for cleaning solutions is huge, and there are many different brands and products. It can be quite overwhelming to understand the purpose of the various ingredients and what manufacturers put into their products. Which ingredients are for what? What is the science behind them? Disinfectants, wettings agents, protein removers, and preservatives are critical components of any lens care product.
Our general advice when it comes to picking the right solution: If you experience a problem with a bi-weekly or monthly replaceable contact lens such as dryness, itchiness, red eyes, or discomfort, the issue could stem from the cleaning solution you are using and the cleaning routine your applying. Moreover, if you have switched to a different lens care product, there could be an ingredient that your eyes don't like. And what's right for you, might not work for another patient. Our eyes are unique and the way they tolerate certain ingredients is different for every person. And personal taste put aside, it's a little bit like trying different shoes to find the perfect fit.
And one final note before we talk about all those ingredients: We always recommend patients to ask their eye doctors for daily-replaceable lenses instead of bi-weekly or monthly lenses. Although contact lens solutions got better over the years, you will not be able to avoid the additional risk of externally induced micro-organisms onto the lens surface when cleaning or storing your lenses.
Table of Contents
- Alexidine dihydrochloride
- Boric acid
- Edetate disodium (EDTA)
- Myristamidopropyl dimethylamine (e.g. ALDOX®)
- Polyhexanide and Polyaminopropyl biguanide
- Polyquaternium-1 (e.g. POLYQUAD®)
- Sodium citrate
- Hyaluronic acid (e.g. Hyaluronan)
- HydraGlyde (EOBO-41 - polyoxyethylene-poly-oxybutylene)
- Hydroxypropyl guar
- Hydroxypropyl methylcellulose
- Mineral Oil and Light Mineral Oil
- TETRONIC 1304, TETRONIC 904 and other Poloxamines
Lens & Eye Care Product Ingredients Explained
Disinfectants, Surfactants & Preservatives
Alexidine Dihydrochloride - another member of the biguanide class - is known for its ability to fight a broad variety of fungal and disease-causing microorganisms.
Boric acid is a very popular ingredient added to contact lens cleaning solutions in very low dosages. It is also called hydrogen borate, boracic acid, and orthoboric acid. It controls bacteria development and outside of cleaning solution and - when highly diluted - is sometimes used as an antiseptic eyewash. Boric acid also acts as a buffer supporting the cleaning solution to maintain a constant ph-value.
One study suggests, that boric acid used in multipurpose contact lens cleaning solutions should be chosen carefully to avoid ocular surface damage and promote microbial pathogens resulting in a higher chance to get an eye infection. However, in another study (conducted by Bausch & Lomb - the makers of Biotrue contact lens solution), the author claims that boric acid was well-tolerated on-eye following repeated administration in an in-vivo model.
Edetate disodium (EDTA)
Disodium edetate (EDTA) is another buffer widely used in contact lens cleaning solutions. EDTA stands for EthyleneDiamineTetraacetic Acid and is a chemical used for many medical applications. Variations of EDTA are produced as salts, such as disodium EDTA and calcium disodium EDTA which can be found as a buffering ingredient in many popular contact lens solutions. And, while used there in very low doses, EDTA - as a chemical - is not without controversy, as its degradation is slow and abiotic (e.g. through exposure to sunlight). In contact lens cleaning solutions its role is to prevent calcium-bound protein sticking to the surface of contact lenses and as such supports the disinfection process.
Myristamidopropyl dimethylamine (e.g. ALDOX®)
ALDOX® is another bacteria- and fungus-fighting ingredient and often combined with POLYQUAD®. Developed by Alcon and combined with POLYQUAD®, it creates an effective dual-disinfection system that can be found in many of Alcon's OPTI-FREE products.
Polyhexanide and Polyaminopropyl biguanide
Polyhexanide and Polyhexamethylene biguanide (PHMB)) are widely used disinfectants known for their broadspectrum antibacterial properties killing harmful bacteria, fungus and germs. One of the advantages is their effectiveness at a very low concentration combined with very low toxicity.
Polyquaternium-1 (e.g. POLYQUAD®)
Polyquaternium-1 0.001% is a detergent-type preservative developed by Alcon and trademarked as POLYQUAD®. It is preservative derived from the benzalkonium chloride of the quaternary ammonium class. Originally used as a disinfecting, biocidal ingredient in cleaning solutions, it can also be found in eye drop products such as re-wetting drops, and artificial tears.
Did you know that sodium citrate can be used at home to make cheese? It occurs naturally in citrus fruits and is more commonly known as citric acid. In contact lens cleaning solutions, sodium citrate is used as a buffering agent and added to loosen protein during the soaking period.
Sulfobetaines are surface-active substances that are used to loosen up protein deposits on the lens surface. While they support the protein removal process, you still (regardless of what you contact lens solution contains) need to rub and rinse your contact lenses at the end of a cleaning cycle and before inserting them into your eyes.
Wetting Agents & Lubricants
Dextran is a popular lubricant used in eye drops and many other medical applications such as vaccines, blood cell separation, organ preservation, protein stabilization, and many oral pharmaceuticals. Dextran's role in eye drops is linked to lubrication, tear replacement and to relieve dry or irritated eyes.
Hyaluronic acid (e.g. Hyaluronan)
HydraGlyde® Moisture Matrix [EOBO-41®- polyoxyethylene-poly-oxybutylene]
Hydroxypropyl guar is used as a thickener in many cosmetics and pharmaceutical products. It's a gellable ingredient in eye drops and eye gels and supports dry eye treatment.
Hydroxypropyl methylcellulose is also referred to as Hypromellose. Known as artificial tears, Hypromellose is often used in eye drops, eye gels, and other ophthalmic products.
Mineral Oil and Light Mineral Oil
Several eye drop manufacturers use mineral oil in their products. Mineral oil and its sibling light mineral oil are lubricant ingredients that are also called emollients - known as non-cosmetic moisturisers. In combination with other lubricants and disinfectants or preservatives (such as Polyquad or hyaluronan and polysorbate), it is used for temporary relief in the treatment of MDG (Meiboniam Glands Disease). The concentration usually is in the 1-2% range for light mineral oil and 4-5% for mineral oil. Eye drops containing mineral oil appear as a white, milky solution.
The National Library of Medicine published an article in 2015 about the 'Efficacy of the Mineral Oil and Hyaluronic Acid Mixture Eye Drops in Murine Dry Eye' investigating the effect on tear film tear volume and tear break-up time when combining mineral oil with hyaluronan. The in-vivo study showed a beneficial effect on the tear films and ocular surface for the mixture containing mineral oil and hyaluronan, suggesting that eye drops with mineral oil and hyaluronan benefit corneal irregularity, the staining score, and conjunctival goblet cell count.
Povidone mimics eye tears due to its lubricant viscosity. It is also known as polyvinylpyrrolidone (PVP). It's been used in many popular eye lubricants and rewetting drops. First synthesized in 1939, PVP was initially used as a substitute for blood plasma and later found its way into many pharmaceutical and cosmetical products and applications.
Many of us know sorbitol as a sugar substitute in many food items such as drinks, sweets, dairy products (e.g. yoghurt), and chewing gum. While sorbitol is not widely used in cleaning solutions, its role is known as a moisturizer binding H2O molecules to the lens surface.
TETRONIC 1304, TETRONIC 904 and other Poloxamines
Tetronic is a trademarked term owned by BASF and represents a group of poloxamine substances used to increase the wettability of contact lenses. These substances are also part of a surface layer that protect your contact lenses from accumulating protein particles. Tetronic 1304 and Tetronic 904 are the most common Tetronic substances used in contact lens cleaning solutions.
In general, poloxamines are a group of co-polymers, that loosen up lipids and other deposits caused by the environment (e.g. from particles in the air). Once loose, these particles can then be removed in the rubbing and rinsing process. Poloxamines also increase the level of moisture.
Buffer & Saline
Aminomethyl propanol (H2NC(CH3)2CH2OH) is an organic chemical compound that is colorless and liquid. It belongs to the broader class of Alkanolamines and - like other buffers - is a helpful buffer to keep your contact lens solution stable, so it doesn't change its ph-value.
Sodium borate - also known as Borax - is better known as a water softener, food additive, and laundry detergent. Its medicinal uses are primarily based on its anti-fungal properties. Sodium borate is added to contact lens solutions as a stabilizing buffering agent, keeping the solution pH-optimized between 6.6 and 7.8 pH.
Sodium chloride (Saline)
In simple words, sodium chloride is salt, similar to the salt we use every day in the preparation of meals. Dissolved in purified water, it creates an isotonic solution that is compatible with your tears. As such it is also a popular component of preservative-free artificial tears and rewetting drops. A short-term study by the Department of Neurosciences, Ophthalmology, and Genetics at the University of Genoa (Italy) showed that treatment with a preservative-free 0.9% sodium chloride ophthalmic solution reduced ocular surface discomfort and allowed patients to wear contact lenses longer without interfering with the tear film.
Sodium phosphate is another ingredient used in solutions and eye drops. And it is another ingredient that some studies suggest, should be avoided - especially in eye drops. While sodium phosphate is a great ingredient to maintain the pH-value of lens cleaning solutions and to prevent the decay of theirs ingredients, in eye drops it can cause permanent corneal opacity from frequent use by patients with a damaged cornea (e.g. after eye surgery or injury). As such, citrate buffers are considered to be better than phosphate buffers.
References and Citations
Boric Acid-based Multipurpose Contact Lens Care Solutions (MPSs) Cytotoxicity Effect on Human Corneal Epithelial Cells
by: Kissaou Tchedre, Masaki Imayasu, Yuichi Hori, H Cavanagh;
published in: Investigative Ophthalmology & Visual Science 2013;54(15):552
Nonclinical safety evaluation of boric acid and a novel borate-buffered contact lens multi-purpose solution, Biotrue multi-purpose solution
by: David M. Lehmann, Megan E. Cavet, Mary E. Richardson
published by: Bausch & Lomb Incorporated, 1400 North Goodman Street, Rochester, NY 14609, United States
Effects of a 0.9% sodium chloride ophthalmic solution on the ocular surface of symptomatic contact lens wearers
by: Barabino S, Rolando M, Camicione P, Chen W, Calabria G.
published by: Department of Neurosciences, Ophthalmology and Genetics, University of Genoa
Final Report on the Safety Assessment of Sodium Borate and Boric Acid
published by: Journal of the American College of Toxicology, Volume: 2 issue
Optimization of Concentration of Polyhexadine Hydrochloride in Multipurpose Solutions
by: A. Arora, A.Ali, M.T.Zzaman1, S.Chauhan, V.Handa
published by: Faculty of Pharmacy, Dept of Pharmaceutics, Hamdard Nagar, New Delhi India
Preservatives from the Eye Drops and the Ocular Surface
by: Mihaela Cristina Coroi, Simona Bungau, and Mirela Tit
published online: U.S. National Library of Medicine
Alexidine Dihydrochloride Has Broad-Spectrum Activities against Diverse Fungal Pathogens
by: Zeinab Mamouei, Abdullah Alqarihi, Shakti Singh, Shuying Xu, Michael K. Mansour, Ashraf S. Ibrahim, Priya Uppuluri
published by: American Society of Microbiology