Glossary of Eye Drop Ingredients
Buffers
A buffer is a molecule that maintains pH at a specific level.
Buffers may be shown as two separate ingredients under Inactive Ingredients, because one ingredient prevents the pH from increasing and the other prevents it from decreasing. The concentrations of both ingredients will shift up and down in opposite directions, to keep the pH stable.
A buffer with the word “acid” in its name is designed to prevent the pH from increasing (becoming less acidic):
Anhydrous citric acid
Ascorbic acid
Boric acid
A buffer with the word “sodium” in its name is designed to prevent the pH from decreasing (becoming more acidic):
Edetate di-sodium (EDTA)
Sodium borate
Sodium citrate
Sodium lactate
Sodium phosphate
Some buffers are found naturally in food: citric acid (orange juice), ascorbic acid (vitamin C), and sodium lactate (milk).
Examples of two-ingredient buffer systems include boric acid plus sodium borate, or citric acid plus sodium citrate.
Homeopathic Ingredients
The central principle behind homeopathy is that the more times the active ingredient is diluted in a liquid, the more powerful the resulting liquid. The ingredients are described as working on a ‘vibrational’ or ‘energetic’ level.
Homeopathic ingredient strengths are given in units of X or C, and the higher the number the more dilute the ingredient (indicating greater activity according to homeopathic principles).
Because these products start from raw materials (plant, animal and mineral) that are crushed and then diluted, there is no guarantee as to the consistency of any one active ingredient in a particular eye drop.
Homeopathic eye drops may be marketed as preservative free. They are commonly packaged in standard multi-dose eye drop bottles, which makes them susceptible to bacterial contamination during use. Most of these products are labelled as “discard after 30 days,” but this does not prevent significant contamination from occurring during this time. Consumers are often reluctant to throw out a ‘mostly full’ bottle of eye drops after 30 days.
Some homeopathic eye drops are preserved with silver. Silver is never discussed in the modern literature on eye drop preservatives. Silver’s principal ophthalmic use was as a preventive treatment for eye infection in newborns (as silver nitrate), but this use was stopped many years ago due to toxicity and lack of effect.
Lubricants
The lubricant is the ingredient that is intended to give you dry eye symptom relief. The FDA allows an eye drop to have more than one lubricant listed as an Active Ingredient. Despite this, manufacturers may sometimes place a second or third lubricant in the Inactive Ingredient category. This may be a simple ‘paperwork’ decision, or it may be a desire to conceal the concentration of certain lubricants from their competitors. For OTC products, only Active Ingredients require a concentration (strength) to be specified.
Recently, manufacturers have been adding lubricants which are not recognized by the FDA as allowed ophthalmic lubricants, by placing them in the Inactive Ingredients category. Often these lubricants are already on the market in the UK, the EU, Canada, or Australia. Hyaluronic acid falls into this category. Hyaluronic acid has been used for decades in drugs utilized during cataract surgery and is safe for use on the surface of the eye as long as it is adequately pure. It is typically derived from rooster combs.
Some patients may be particularly interested in a certain lubricant or combination of lubricants. Patients should always confirm that an eye drop that interests them is listed with the Food & Drug Administration. Even if it contains lubricants under Inactive Ingredients that are not officially recognized lubricants, the drug has still been properly registered with the FDA as required by law.
Registration with the FDA is not a guarantee that the eye drop was properly manufactured under sterile conditions. However, not being registered with the FDA is a sign that the manufacturer is deliberately flouting US laws designed for patient protection.
Miscellaneous Ingredients
Amino acids (glycine, taurine, others)
Modified amino acids (N-acetyl carnitine, others)
Vitamins (vitamin A, vitamin C, biotin, pyridoxine, others)
These ingredients are often found in eye drops that make medical claims such as shrinking cataracts or preventing macular degeneration. These are unproven claims that have no scientific basis (for example, most of these ingredients are unlikely to penetrate into the eye in sufficient concentration to have any effect). OTC eye drops that make medical claims should be avoided.
Ingredients that may seem “nutritional” and therefore harmless may still create problems if they affect the pH of the eye drops. For example, vitamin C is ascorbic acid, and ascorbic acid is used as a buffer to prevent the eye drop from drifting too alkaline (the opposite of acidic). If the vitamin C is added by a manufacturer who is not paying attention to establishing and maintaining a proper pH, it could make the eye drop too acidic. Many amino acids affect the pH of liquids.
The body uses vitamins and amino acids as building blocks. This means they must be taken up by cells and put to use. Applying these ingredients to your eye via an eye drop may be completely ineffective if there is no uptake into cells. For example, there is a severe form of dry eye disease caused by vitamin A depletion. It is not treated through the use of vitamin A eye drops or eye ointments, but rather through high dose oral or intramuscular vitamin A supplementation.
Oils
Castor oil
Comment: castor oil is an inactive ingredient in the eye drop Restasis. The vehicle for Restasis (everything but the active ingredient cyclosporine) was found to be very effective in mild to moderate dry eye disease, so much so that Restasis was not originally approved because there was no evidence that the cyclosporine had any additional effect. It is possible that castor oil provided some of the benefit seen with the vehicle.
Other oils (sesame oil, others) have no proven benefit. All oils used in eye drops should be pharmaceutical grade. It is impossible to be confident that pharmaceutical grade oil is being used, unless the product is manufactured by a multi-national company with a long-established reputation and something to lose.
pH Adjusters
Correctly formulated artificial tears will have a pH close to neutral, around 7 to 7.4.
Hydrochloric acid and sodium hydroxide are used to achieve the correct pH. Depending on the exact pH of a particular lot of eye drops, the manufacturer may need to add either hydrochloric acid or sodium hydroxide to correct the pH.
These are not harsh chemicals. Your body produces abundant hydrochloric acid in your stomach to digest food. Sodium hydroxide in low concentration is naturally present in drinking water.
Preservatives
Alcohol 0.1%
Comment: a very old preservative, typically found in OTC products that have been on the market for many years such as redness relievers. Never discussed in modern literature on ophthalmic preservatives. Should be avoided.
Benzyl alcohol
Comment: a very old preservative from the 1950s if not earlier. Not found in products on the US market. Never discussed in modern literature on ophthalmic preservatives. Should be avoided.
Benzalkonium chloride
Comment: the most common preservative. Causes toxicity with long-term daily use.
Chlorobutanol
Comment: an older preservative, typically found in OTC products that have been on the market for many years such as redness relievers. Almost as toxic as benzalkonium chloride.
EDTA (ethylenediaminetetraacetic acid)
Comment: classified as both a buffer and a preservative, possibly depending on the concentration (stronger concentration as a preservative). Rarely if ever found as the only preservative. Some people are allergic to it.
Polyaminyl biguanide
Comment: primarily used in contact lens all-in-one solutions. Effective against acanthamoeba. Should be avoided in artificial tears.
Polyquaternium-1 (Polyquad)
Comment: falls into the same chemical class as benzalkonium chloride, but has different characteristics that make it less toxic.
Sodium chlorite (OcuPure)
[note: sodium chlorite with a ‘t’ not sodium chloride]
Comment: confusingly, the only ingredient typically stated is sodium chlorite while simultaneously OcuPure is described as a stabilized oxychloro complex (see below). Sodium chlorite by itself is not stable, and a single molecule is not considered to be a complex. This lack of clarity may be deliberate on the part of the manufacturer.
Sodium perborate (GenAqua, Dequest)
Comment: a newer preservative, classified as an ‘oxidative’ preservative. Effective against bacteria, viruses and fungus. Once in contact with the surface of the eye, rapidly broken down by the enzyme catalase to oxygen and water. Felt to be less toxic than benzalkonium chloride.
Stabilized oxychloro complex (SOC) (Purite)
Individual components = sodium chlorite + sodium chlorate + chlorine dioxide
Comment: a newer preservative, classified as an ‘oxidative’ preservative. When exposed to light, rapidly breaks down into water, oxygen, and sodium and chlorine free radicals. Felt to be less toxic than benzalkonium chloride.
Multiple preservatives are not indicated.
Avoid eye drops (mostly redness relievers) that have more than one preservative listed under Inactive Ingredients. If EDTA is combined with a preservative, the EDTA is more likely acting as a buffer (low concentration) and there is no need to avoid it.
Salts
Salts in eye drops are composed of two atoms, one of which is a chlorine atom. Salts in eye drops all end in “chloride.”
Sodium chloride (added to water to make normal saline)
Calcium chloride
Magnesium chloride
Potassium chloride
Salts are normal constituents of natural human tears.
Salts do not contribute directly to the lubricating effect of the eye drop.
Thickeners & Emulsifiers
Thickness is technically referred to as viscosity. Depending on the natural viscosity of the lubricant itself, a manufacturer may add a thickening agent to increase the length of the time the drop stays on the eye, and also to help it spread better.
An emulsifier is an ingredient that keeps a mixture of various ingredients blended together. Oil and water naturally separate. If you added an emulsifier to an oil / water mixture, it would stay blended without shaking.
Many ingredients act as both thickeners and emulsifiers. The original ingredient is often extracted from a plant source and then processed (anywhere from slightly to significantly). Examples include dextrose, sorbitol, guar gum, hydroxypropyl guar (chemically derived from guar gum), and sorbitan tristearate (derived from sorbitol).
