Is there anything natural about dry eye drops? Are any of the ingredients in dry eye drops actually natural?
That is a very tricky question and will require Dry Eye Zone taking a very detailed look into the ingredients commonly listed on the labels of dry eye drops. Also, for the purposes of this blog we need to attempt to define what is meant by ‘natural’. We will assume ‘natural’ to mean similar to natural tear components, rather than ‘harvested’ from a natural source. It is unlikely that anything that is used in a dry eye drop has not been altered by purification or made synthetically for safety. Also, an eye drop might be using something that is considered natural, such as glycerin or sodium hyaluronate but these are not naturally part of our tears.
Let’s start with the natural components of our tears and see what is being used to create a similar effect in the eye with a dry eye drop.
Lipids protect and lubricate
The outer layer of our tears are made up of a smooth oily layer of lipids produced by the meibomian glands, which helps reduce the rate of evaporation of moisture from the tears. This lipid layer is very complex chemically and few eye drops actually contain lipids. When they do contain oil its role is often that of a viscosity agent to thicken the solution for longer retention and greater stability. Look out for ingredients such as castor oil, flaxseed oil and mineral oil. These are all available via natural sources but do not occur naturally in the eye!
Essential moistureThe central, and thickest layer of the tear film is the aqueous layer. This is made up of water (I think we will all agree that is natural) but will of course needs to be purified and sterilised before it can be used. Within the aqueous layer are different salts, you can recognise these on the label as they end with a ‘chloride’. Sodium chloride (salt) is a natural and essential ingredient that helps the eye drop get the solution electrolyte balance right. Other commonly used and natural tear salts are potassium, magnesium or calcium chloride.
Artificial tears often use chemicals called demulcents to help hold extra moisture as these bind with large numbers of water molecules. They also spread across the surface of the eye to help lubricate and protect. Although not strictly natural they are mimicking the natural role of tears and some like sodium hyaluronate (sodium salt of hyaluronic acid) are naturally occurring. Sodium hyaluronate is found extensively in the body so it certainly is natural but the type used in eye drops will be manufactured rather than come from a living source. Other examples include glycerin, hydroxymethylcellulose (Hypromellose), carboxymethylcellulose and propylene glycol.
Tears are so much more than just water
Because tears are made up of so many different ingredients attempts are made to create a solution which reflects this viscosity or thickness. This is achieved by adding larger viscosity enhancing molecules such as sodium hyaluronate, hydroxypropyl methylcellulose (HPMC), carbomer or hydroxylpropyl-guar (HP-guar, Guar gum). Some dry eye drops are deliberately formulated to be far thicker than natural tears in order to help retention times and soothe particularly severe dry eyes. As dry eye drops become thicker there is a tendency for them to also be more likely to cause blurring. This is why, when very viscous, they are sometimes recommended for night-time use.
Holding it all in place
The inner layer of the natural tear film sits against the surface of the eye and is known as the mucin layer. This actually produces some of the other tear components as well as playing a role in ‘holding’ the tear film on the eye. Ingredients which have a muco-mimetic role include tamarind seed polysaccharide and have been shown to help the eye drop stay in the eye for longer and improve the condition of the surface of the eye.
There are also dry eye drop ingredients which help hold all the components together and stop them separating from each other. These are known as emulsifiers and work to keep things blended – like mixing oil and water. Some lipid containing dry eye drops will ask you to give them a shake before use to help the blending process.
Some molecules miraculously perform more than one function in the eye drop. Sodium hyaluronate or hyaluronic acid (HA) is a great example of this, it holds moisture, thickens and soothes all in one. And when combined with certain other polymers such as tamarind seed polysaccharide, has been found to perform even better!
Some natural tear components which scientists are still trying to mimic
Our natural tears are beautifully engineered and some elements are not found in any dry eye drops at all. Things like proteins (lysozymes), lactoferrin or enzymes fulfil essential roles as antimicrobials in our tear film in order to help maintain our ocular health. Maybe looking for ways to mimic these components is an area of future development for scientists. It might also surprise you that hormones, such as adrenaline or noradrenaline, are also present in our emotional tears. Some of the components mentioned here also serve as biomarkers as an indicator of overall health.
What might you find in eye drops which definitely is not natural?
The most obvious things are preservatives, although not natural they are really important to prevent pesky bacteria growing in the solution and then being transferred to the eye. This tends to be the case with older generation eye drops. The problem with preservatives for dry eye sufferers is that some of them, like benzalkonium chloride (BAK), actually cause irritation to the eye if used frequently. Newer generations preservatives like polyquaternium, sodium chlorite and polixetonium are gentler on the eye. However, most eye care professionals would advise you to look for preservative free variations where available.
The latter has been made possible thanks to specially designed bottles with a one-way valve or filter to allow the solution out but stopping microbes entering. Another approach is to use smaller single-use or daily-dose vials which contain enough solution for a single dose, or in the case of daily-dose vials with re-closable caps, for up to 12-hours ,and then need to be thrown away.
Sometimes it can be surprising to see certain ingredients on the label such as hydrochloric acid or the powerful alkali sodium hydroxide. These are often present in tiny amounts to help adjust the pH of the eye drop to that of the natural ocular environment – this is typically about pH 7.3 which is neutral . This means when the eye drop hits the eye there is less chance of any temporary stinging. These pH controllers are collectively known as buffers. Once again these molecules occur naturally - but are a natural component of our tear.
There are often other added extras such as certain vitamins and minerals. Although these may be linked to ocular health it is unlikely they will help your immediate need for dry eye symptom relief.
We hope this brief tour around the label of a dry eye drop has been helpful. Overall, Dry Eye Zone would say do not worry too much about ‘natural’ ingredients because they almost certainly will not be – but they will do a good job at helping keep your dry eyes moist and comfortable. If you want to know which eye drop is best for you then you should ask your eye care professional.
You can find more information about the causes of dry eye and its management at Dry Eye Zone.
And don’t forget to visit Dry Eye Zone and subscribe to the regular free information updates.
If you are experiencing dry eye symptoms then you should ask the advice of your eye care professional. Why not book your next eye examination with an independent optician today.
Sources:
Chang AY, Purt B. Biochemistry, Tear Film. [Updated 2023 Jun 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK572136/#
Stapleton F., Alves M., Bunya V.Y., Jalbert I., Lekhanont K., Malet F., Na K.-S., Schaumberg D., Uchino M., Vehof J., et al. TFOS DEWS II Epidemiology Report. Ocul. Surf. 2017;15:334–365. doi: 10.1016/j.jtos.2017.05.003.
Labetoulle M, Benitez-Del-Castillo JM, Barabino S, Herrero Vanrell R, Daull P, Garrigue JS, Rolando M. Artificial Tears: Biological Role of Their Ingredients in the Management of Dry Eye Disease. Int J Mol Sci. 2022 Feb 23;23(5):2434. doi: 10.3390/ijms23052434. PMID: 35269576; PMCID: PMC8910031.
Barabino S., Benitez-Del-Castillo J.M., Fuchsluger T., Labetoulle M., Malachkova N., Meloni M., Utheim T.P., Rolando M. Dry eye disease treatment: The role of tear substitutes, their future, and an updated classification. Eur. Rev. Med. Pharmacol. Sci. 2020;24:8642–8652. doi: 10.26355/eurrev_202009_22801.
Raposo AC, Portela RD, Aldrovani M, Barral TD, Cury D, Oriá AP. Comparative Analysis of Tear Composition in Humans, Domestic Mammals, Reptiles, and Birds. Front Vet Sci. 2020 May 22;7:283. doi: 10.3389/fvets.2020.00283. PMID: 32528986; PMCID: PMC7256680.
Kopacz, D., Niezgoda, Ł., Fudalej, E., Nowak, A. & Maciejewicz, P. (2021). Tear Film – Physiology and Disturbances in Various Diseases and Disorders. Ocular Surface Diseases - Some Current Date on Tear Film Problem and Keratoconic Diagnosis. doi: 10.5772/intechopen.94142
Comments