Eye drops are expensive so don’t waste time and money with the wrong ones
For most people eye drops or ‘artificial tears’ are a first line defence against the often-debilitating symptoms of dry eye disease which include sore, aching, tired, watery or red eyes. Because dry eye is a chronic and progressive condition it is also associated with anxiety and depression. Getting an effective eye drop first time really makes a difference - a global group of dry eye experts got together as part of the ‘Dry Eye Workshop’ or DEWS committee to look at all aspects of dry eye, including what to look for in an eye drop. Dry Eye Zone took their advice when looking for a best-in-class eye drop and want to share this expert guidance with you.
The role of eye drops
It is important to state straight away that there is more than one type of dry eye and it is often a surprise to people that dry eye drops might not be the best therapy for your particular condition. To ascertain what type of dry eye you have you will need to visit your eye care professional.
However, generally dry eye drops are recommended to those who are affected by ADDE or aqueous deficient dry eye. This means that you are not producing enough of the watery or ‘aqueous’ component of your tear-film. Your tear film is a complex structure and a reduction in quality of any of its three layers will cause problems. There are eye drops available which target other layers of the tear film such as the oily lipid layer but these would be used in conjunction with other types of therapy.
By using a hydrating and lubricating eye drop you will be effectively replenishing that aqueous layer and bringing relief to those annoying symptoms. But with so many to choose from you need to know what to look for as they are far more than just water, they are liquid engineering!
Preservatives have a very important role in keeping many products, including eye drops, safe for us to use or consume by helping prevent the growth of potentially harmful bacteria.
However, the surface of a dry eye suffers eye can be even more delicate than usual. This means harsh chemicals, which include many preservatives, could make matters worse and should be avoided.
To achieve this and keep the solution safe for use special bottling technology is used. Look out for bottles with special filters to stop contamination or single use containers which provide small daily doses to avoid the need for a preservative.
As a dry eye sufferer you should select a preservative free eye drop where ever possible.
Water loving lubricants
All dry eye drops will have an aqueous base, which makes up the single largest component of the preparation, its’ role is to replenish the moisture loss from the natural tear film. Clever formulating will include lubricating humectants to enhance this hydration. A humectant is a substance which literally holds-on to water and helps reduce loss. Some of these can hold many times their own molecular weight in water and when combined to create larger co-polymers hold even more. One of the newer and most highly regarded molecules is sodium hyaluronate or hyaluronic acid (HA). It has long been a favourite of premium cosmetics and is now being widely used in dry eye drops.
Not too salty
When your eyes do lose moisture the naturally occurring electrolytes and proteins in your tears become more concentrated. This means your tears get saltier and with this an inflammatory response is triggered. Histamine is released which explains why some people experience itchiness as one of their dry eye symptoms. To stop this the salt concentration needs to be rebalanced, this can potentially be corrected by using an eye drop with a low salt concentration, this is measured using osmolarity. There have been studies done to indicate that there are benefits in selecting an eye drop with these properties. They are often labelled as ‘hypotonic’ or ‘osmoprotectors’.
Get the pH right
pH is the measure of how acidic or alkaline a solution is, normal human tears have a pH range of 6.5-7.6 which makes them fairly neutral. If the solution you add to your eye is not a pH match to your eyes natural environment then you will feel some stinging. To help adjust the pH of the eye drop to accommodate this natural range ingredients called buffers are added to help ‘hold’ the pH within the acceptable range. This is designed to make the solution more comfortable in the eye and help reduce the possibility of stinging. The concentration of the buffer used is critical to a successful formulation. Dry Eye Zone would recommend you select a pH balanced eye drop for additional comfort.
Viscosity is important too
The viscosity or ‘thickness’ of an eye drop will have an impact on the retention time in the eye. It is generally understood that more viscous solutions stay in the eye for longer, and therefore potentially give longer lasting relief. The DEWS team reviewed a range of viscosity enhancers in their report including carbomer 940, carboxymethyl cellulose (CMC), dextran, hyaluronic acid (HA), HP-guar, hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP) and polyethylene glycol. All of which will thicken a solution.
The benefit of enhanced viscosity has to be balanced against the increased likelihood of visual blurring which tends to occur with a thicker solution. In fact, very thick preparations, such as ointments, are reserved for night-time use.
Viscosity without the blur
Interestingly, according to the DEWS experts, some ingredients, like HA, exhibit non-Newtonian properties which means the viscosity varies depending on the pressure being applied. When you blink the shearing force of your eye lid causes the viscosity of the HA to reduce allowing it to spread across the eyes surface. Then when the eye is open and there is less shearing and the viscosity increases. It is thought by many scientists that this will provide improved retention with less blurring.
Hanging in there – improving retention for longer lasting relief
As we learn more about the ingenious engineering of our tear film new innovations in the way artificial tears are formulated emerge. Knowledge of the mucin layer’s structure and function has got developers thinking about the use of ingredients which will mimic this action. The use of muco-mimetics, such as HA or Tamarind Seed Polysaccharide (TSP) could make the difference, by bringing giving longer retention-times, and can be found in some more advanced formulations
You are not alone
Dry Eye Disease is on the increase, a recent study by researchers at Aston University stated that almost one-third of the UK population is experiencing dry eye. With such large numbers dry eye disease is becoming a significant global problem – even recognised by the WHO. In their Vision Report they called for dry eye not be overlooked as it is among the main reasons for people seeking eye health services. Dry Eye Zone hopes that this information will help guide you towards an effective dry eye drop, but if in any doubt speak to your eye care professional who will give you further advice.
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.
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