The new TFOS DEWS II report provides the latest understanding of dry eye disease (Click here to know more about TFOS DEWS II, the most authoritative literature review worldwide on dry eye disease). How are eye doctors treating dry eye? It turns out, artificial tears are still the first line of treatment. Go to any drug store, and you will find dozens of different bottles of artificial tears. What are in them, what are the differences, and how can you pick out one that is good for you? Let’s take a look. Much of this article is based on information from “TFOS DEWS II Management and Therapy Report”.
There are two major types of artificial tears, one that supplements the aqueous, or water part of the tear, and the other that supplements the lipid part of the tear. We know from my previous post (link here) that majority of dry eye is actually caused by Meibomian gland dysfunction (MGD) which results in lipid deficit and rapid evaporation of the tear. Therefore some of the newer artificial tears contain lipid.
To provide lubrication, viscosity enhancing agents are used. These are often referred to as the ‘active ingredient’ in the artificial tears. They include carbomer 940 (polyacrylic acid), carboxymethyl cellulose (CMC), dextran, hyaluronic acid (HA), HP-guar, hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and polyethylene glycol. You don’t have to memorize these names at all. I have listed them here in case you want to read the ingredient list on a product and wonder what that weird name means. What matters is that they prolong the time the artificial tear stays on your eye, and that most of these viscosity agents work similarly well.
Some examples: Carboxymethycellulose is used in Refresh and TheraTears; Hydroxypropyl Cellulose is used in Genteal; Hydroxypropyl Guar is used in Systane; and Sodium hyaluronate is used in Blink.
These are emulsions where small lipid droplets are suspended in the water base. For example, Systane Balance contains a polar phospholipid, DMPG (dimyristoylphosphatidylglycerol), in addition to Propylene Glycol which is a lubricant; and Retaine MGD contains mineral Oil 0.5% as a lipid.
These are thick tears that will stay on the eye for longer, but will cause blurry vision while they stay on the eye, so mostly used at night or before bedtime. They contain high concentration of the viscosity agent, and/or mineral oil. Examples include Genteal Night time gel, Refresh PM and Refresh Lacrilube. These are good choices to use especially if you suffer from dry eyes in the morning or when waking up.
Preservatives are essential these days to prolong the shelf-life of food, cosmetics, medication, as well as artificial tears. For a ½ oz (15 ml) drop bottle, it will take about a month to finish if you put 4 drops in each eye daily. Of course you will try to avoid touching the tip with finger or eye or anything except for air, and replacing the lid immediately after each use. Still, as soon as you open that sterile bottle, bacteria or fungus free-floating in the air will inevitably get in, let alone the accidental touching of hand, eyelids or other objects. In addition, many people use artificial tears in an as needed manner, this will make each bottle last longer, increasing risk of contamination. A good practice I would recommend is that once you open a bottle, label it with date of opening, and discard after 3 months even if it’s not finished.
So, preservatives allow us to store artificial tears for longer. However, they are known to cause adverse effects on the surface of the eye. The most commonly used preservative in eye drops is called benzalkonium chloride (BAK). “BAK can induce corneal and conjunctival epithelial cell death, damage the corneal nerves, delay corneal wound healing, interfere with tear film stability and cause loss of goblet cells”. To prevent these adverse actions, you should not use preserved artificial tears more than 6 times a day.
Of course, the far better alternative is to use preservative-free (PF) artificial tears. You will know if an artificial tear is PF when you see it is individually packaged in small vials. Once you open one vial, it is good for 24 hours and you should discard it after that. Examples of PF artificial tears include Refresh Celluvisc, TheraTears Liquid Gel, and Retaine MGD.
The problem with these is that they are expensive. A number of new products are now available that use one-way valve dispensers which avoid contamination and allow multiple-use of a PF bottle. I am awaiting for artificial tears to be packaged this way, and hopefully it will be cheaper than the PF tears individually packed. If you know of such a product, let me know by leaving a comment.
Another alternative to the BAK issue is to develop alternative “softer preservatives” which are less harmful to the eye. These are used in eye drops such as glaucoma medications and not just limited to artificial tears. These include oxidative preservatives (sodium chlorite; Purite® and OcuPure™ and sodium perborate; GenAqua™), polyquaternium-1 (Polyquad®) and Sof-Zia™. They cause less adverse reactions on the eye, but still, PF is better, especially if you are using the eye drops multiple times for long-term.
Some OTC eye drops provide a quick redness relief, such as Visine, ClearEye, Rohto. While they do contain lubricants for dry eye, the redness relief ingredients, which include Tetrahydrozoline or Naphazoline, should not be used long-term. These redness relief ingredients are vasoconstrictors that restrict tiny blood vessels in the eye, making the redness disappear; when used long-term, can actually cause rebound redness, making red eyes worse.
With chronic dry eye, the irritation on the surface of the eye can lead to dilation of the tiny vessels in the conjunctiva, which is the white part of the eye. Therefore the root cause of redness in this case is dry eye itself. Regular use of artificial tears helps to restore normal ocular surface environment, this will get rid of the redness. Forcing the blood vessels to constrict with medication without treating dry eye itself, such as using a vasoconstrictor, will make redness worse if you stop the medication.
In practice, we routinely recommend lubricating artificial tears, but suggest patients to use redness relief only in temporary or emergent situations, such as going to a party in a few hours. In the long term, please control your dry eye, the cause of redness in many cases.
I have given a brief guide to the various artificial tears available over-the-counter. There are artificial tears that are primarily lubricating via supplementing the water part of the tear, there are also ones that supplement the lipid part. Some are more viscous than others, and the gels and ointments are so thick that they will blur vision for hours, so they are best used before bedtime. Most artificial tears in regular eye drop bottles contain preservatives, which are harmful for the surface of the eye when used in long-term. I would like all patients to use PF artificial tears if possible, but cost is a significant impeding factor. Finally, watch out for quick redness relief, and do not rely on these long-term, as you will find redness coming back worse once you stop using them. In reality, you may find one particular eye drop to be soothing to you while others are not so great. Don’t be afraid to try a few ones and find the best for you.
About the Author ...
Juan Ding, OD, PhD. has written an assortment of articles about eye health so that patients may better understand their diagnosis, treatments and management of their conditions.
Dr. Ding is interested in promoting patient awareness and education of eye conditions and diseases. Dr. Ding is a member of TFOS.
Dr. Ding works at UMass Memorial Medical Center in Worcester, Massachusetts (US) as an attending optometrist and an assistant professor of UMass Medical School. Dr. Ding specializes in comprehensive eye exams for adults and children, diabetic eye exams, refraction, contact lens fitting, and binocular visual dysfunctions.
Please visit Dr. Ding’s website for additional articles about eye care: https://bostoneyeblink.com/
