Artificial Tear Drops
A quick and simple option for managing dry eye symptoms are lubricating eye drops (artificial tears). The eye drops replace and supplement a tear film that is not being produced properly.
There are many different formulations of artificial tears, and while all options are good, the best choice of drop will differ from person to person.
The primary use for artificial tears is short term relief of symptoms. If nothing else, they provide comfort and short term hydration. As artificial tear technologies advance, some of the more modern formulations in newer drops include ingredients to stabilize the tear film layers and break the cycle of Dry Eye.
Lubricating eye drops are considered to be a short term management option, requiring ongoing use to maintain long lasting comfort.
The aim of using artificial tears is to:
- Improve patient comfort. They top up the tear volume to replenish our supply of tears to keep the eye protected and hydrated so it can get oxygen.
- Promote tear retention. We want artificial tears to sit comfortably within the normal tear film and help keep natural tears around. Artificial tears create a scaffold for normal tears to stick to, to try and create stability.
- Preserve the smooth refracting surface. Dry eyes don’t see well. A drop goes a long way to maintaining good vision by smoothing out the optical surface.
The truth is that all moisturizing eye drops pass steps 1, 2 and 3. And the science is confusing as to which drops are better than others.
Traditionally, the aim of the game was to find an eyedrop that lasts the longest on the eye’s surface, reducing the need for such frequent use. The easiest way to keep a drop on your eye longer is make it thicker, more sticky, more viscous! But when you have a very thick sticky eye drop, it makes your vision smeary, filmy and blurry as you can’t see through it.
Scientists then looked into the next option which was to add in active ingredients to allow the drop to stay in the eye longer.
Nowadays, science is catching up as we learn more about dry eye. Newer generations of dry eye drops include ingredients that help to break the nasty dry eye cycle, instead of just providing relief until the drops wear off again.
What’s in dry eye drops?
Remembering our tear film structure is made up of three main layers: glue, water and oil.
Dry eye tends to start when there are problems producing these three layers, or keeping the balance correct. This is where artificial tears come in.
Artificial tears need an active ingredient that binds the whole thing together. Moisturising eye drops use a hydrogel polymer or viscoelastic agent. Often these ingredients supplement the aqueous layer and often the mucin layer too.
From there extra bits are added like
- Thickeners to increase the viscosity or stickiness to keep them on the eye for longer
- Oils to help with the oily layer of the tears and stop the drop from evaporating off the surface
- Nutrients and electrolytes to help balance tear film layers and break the dry eye cycle
- Preservatives to prevent bacteria entering the bottle after opening.
Polymers (hydrogels)
The main ingredient of most artificial tears are hydrogel polymers. Polymers are found everywhere! Glucose, the sugar we eat are polymers, cellulose or plant sugars are polymers. Polyethylene in plastic bags is a polymer. Nylon and polyesters are synthetic polymers. Contact lenses are hydrogel polymers.
Hydrogel polymers have a high affinity for water, so they attract and stick to water in the tears. Hydrogel polymers in artificial tear eye drops basically create a scaffold on the eye for water to stick to. This allows our natural tears to stay in the eye for longer.
Hydroxypropyl methylcellulose (HPMC) and Carboxymethyl cellulose (carmellose) are two examples of hydrogel polymers used in dry eye drops. Both are made from Methylcellulose which is derived from cellulose plant sugars. HPMC has been shown to stick to the cornea like the mucin layer, so makes a good replacement if there is an absence of natural mucin production.
Carmellose is traditionally the most common polymer and used in many of the older style eyedrops that have been on the market for many years. The negative to cellulose based eyedrops is they require a high viscosity (goopyness) to prevent them running away or drying up. If the drop is too viscous, it will cause vision to blur when instilled. If the drop is not viscous enough, drops will need to be instilled very frequently to provide adequate relief.
Viscoelastic agents:
Sodium hyaluronate (SH) is a natural polymer with viscoelastic properties. It is found naturally in connective tissue like cartilage. The cartilage in our ears is what makes them sturdy as we don’t have bones in our ears. Science supports Sodium hyaluronate for healing dehydrated corneal tissue, which is a fantastic property for damaged dry eyes. Because it heals dehydrated tissue, it is capable of repairing damaged cells and assists in breaking the cycle of dry eye. Sodium hyaluronate itself attracts water, so it also helps retain natural tears.
During blinks, sodium hyaluronate forms an elastic matrix that spreads easily over the cornea, making it last longer on the eye as it is difficult to blink away. It has water trapping ability and mucoadhesive properties to delay evaporation and help tears stick to the eye.
An example of eyedrops containing Sodium Hyaluronate are Hylo fresh and its extra strength sibling Hylo Forte. Hylo Forte has double the concentration of Sodium Hyaluronate than Hylo Fresh, is thicker so lasts longer, but can blur vision on occasion. Don’t be fooled into thinking everything that looks like a bottle has preservatives to stop the bottle from going off. As much as this looks like a normal bottle, it is actually an airless canister with a 2 way valve at the top to enable multiple sterile doses of solution. 300 sterile drops per canister! The valves stop microorganisms from entering the interior of the bottle. As none of the natural bacteria that lives on our skin and eyelashes can make it back inside the bottle so it doesn’t need to be preserved.
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Some eyedrops mix carmellose and Sodium hyaluronate and according to science, this combination is superior to the individual ingredients with great retention, so the drops last a longer time on the eye. When mixed together, the two ingredients form a structure that alters and strengthens with blinking making it more difficult to blink away.
Optive Fusion is an example of an artificial tear eye drop containing both carmellose and Sodium hyaluronate. It is preservative free and great for healing damaged corneas and sensitive eyes.
Hydroxypropyl guar (HP-Guar) is another compound and is commonly added as a thickening agent in some of the foods we eat, for example salad dressing. Its structure is similar to the glue layer of the tears so it helps lock our own tears to the eye, making it long lasting. The science rates HP-Guar well as it improves the glue production in tears, makes our own natural tears stickier, and contributes to breaking the cycle long after the drop has worn off. Like the combination of carmellose and Sodium hyaluronate, HP-Guar lasts longer on a blinking eye than a non blinking eye which is great for humans as we blink 18,000 times a day. HP-Guar is a liquid at the pH of 7, but forms a gel when exposed to the pH of the tear film to protect and repair the ocular surface.
Examples of eyedrops containing HP-Guar are Systane Ultra, Systane Balance and Systane Complete.
Other active ingredients added to thicken artificial tear eye drops are gelatin (like we use in cakes), Glycerin (like we use in face cream), Polyethylene glycol, Poloxamer and Polysorbate.
Mineral oils
The addition of mineral oils in an eye drop formulation helps replace the oily layer of the tears. The function of the oily layer is to prevent the tears from evaporating off the surface of the eye. Think of it like a cup of water out in the wind; that water is going to evaporate, but if that same water had a thin layer of olive oil on top, it would take a lot longer to evaporate. Often you only need a small amount of these mineral oils to spread across the whole surface of the eye with ease.
Examples of eyedrops with mineral oils is NovaTears, Systane Balance, Systane Complete. Optrex Actimist is a liposomal spray that contains mineral oils.
Optrex Actimist Spray in alternative to an eyedrop, as it’s a spray instead. It is designed to spray onto a closed eye as if you spray it onto an open eye, too much of the oil mist hits the ocular surface. The idea is the fine liposomal spray creates a mist that rolls down your eyelid and eyelashes throughout the day, and adds extra oil to your tear film as you blink. It’s particularly appealing if you struggle with using eyedrops. Its downside is it’s just oil, so it often needs to be layered with other drops for the true benefit, so we recommend it as a stand alone product if you have mild dry eyes.
(photo and product to be added to online store)
Nutrients
Nutrients and electrolytes are a relatively new addition to dry eyedrops, and the aim is to balance the tear ingredients with the intent to help break the dry eye cycle. Like powerade after a marathon, nutrients and electrolytes help the eye recover faster so it returns to producing good quality tears naturally again. Nutrients are necessary for corneal health and metabolism. The most important nutrient in artificial tear eyedrops is water.
Other nutrients include dextrose, sodium lactate, sodium citrate, and vitamins A, B₁₂ and C.
Vitamin A increases the mucous production of goblet cells which makes the glue layer at the bottom of our tear film. Agents that help maintain tonicity and pH similar to the normal tear film include Sodium chloride, Potassium Chloride, Boric acid and various other ions.
The addition of bicarbonate ions aids healing to repair damaged cells. Bion Tears are non preserved eye drops for dry eyes containing bicarbonate.
Manuka Honey
Manuka honey is known for its antibacterial and anti-inflammatory properties, and it is fantastic for the long term treatment of blepharitis and eyelid inflammation in dry eye sufferers. Patients with tear deficiency and meibomian gland dysfunction (MGD) have more natural bacteria than usual and it is believed this overgrowth contributes to tear film instability and ocular surface damage.
Research has looked at possible reasons dry eye sufferers have an overgrowth of natural bacteria in and around their eyes. There are antibacterial proteins in the tear film, but when your tear layer is thin and fragile in dry eyes, you have less antibacterial proteins floating around to protect the eye from opportunistic germs. Also, when the oil glands aren’t flowing and pumping out a smooth clear liquid oil, they get clogged and the oil in the glands turns buttery. This stagnant environment is perfect for germs to breed.
The advantages of adding antibacterial manuka honey to moisturising eye drops for chronic dry eye patients is to reduce the risk of bacterial conjunctivitis and eye infections. Manuka honey also breaks down the waste produced by the bacteria, which is toxic to the corneal surface. Bacterial exotoxins, or waste products causes tear film instability and exacerbates dry eye disease.
Antibacterial honey’s also activate the immune response to infection, which is our bodies natural way of fighting off illness. Optimel eyedrops contains Manuka honey but its downside is it can sting a little when first instilled.
Preservatives
A baker puts preservatives in bread to increase its shelf life and to stop it from going mouldy.
Preservatives kill or inhibit growth of microorganisms. Preservatives in eyedrops allow you to keep the bottle for a few months after opening so you get better value for money.
However, preservatives are chemicals which have the ability to damage the cornea and upset our natural tear ingredients. The wrong preservatives can be toxic to the corneal surface, upset the stability of the tears, cause inflammation, and contribute to the dry eye cycle. Some people even have allergic reactions to the preservatives in some eye drops.
Some preservatives are considerably better than others but where possible, we recommend a non preserved drop. Going preservative free does mean a short shelf life, or individual vials, or a fancy bottle that stops germs from getting inside though.
Eye Ointments:
Thick oily ointments work in the same way mineral oils do, to help replace the oily layer of the tears to stop tear drops evaporating away, but they’re incredibly thick. They literally lock tears in, stop any moisture getting out, and stop any friction from a blinking eyelid. However, because they are so goopy and thick they make your vision very blurry so they are best for overnight use or severe cases of dry eye. We liken them to Vasoline or lip balm and are basically a liquid bandaid to lock in moisture.
Eye Ointments are designed to melt at the temperature of the ocular tissue and disperse with tears.
Examples of good ointments available are Polyvisc, Vitapos. Vitapos has the addition of Vitamin A to restore tear stickiness and help with the production of your own tear glue. Vitapos should be used with caution by anyone with a peanut allergy.
