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Contact Lens Cleaning: Finding the Perfect Solutions

2 CPD in Australia | 0.25G in New Zealand | 1 February 2018

Simon Allen

All contact lens cleaning solutions are the same, right? Besides, I only prescribe 100 per cent daily disposables… If this is your approach to contact lens care, it’s time to think again.

LEARNING OUTCOMES

1. Understand that all contact lens care solutions are not the same
2. Know the key features of an ideal contact lens care solution
3. Understand how contact lens solutions work to clean, wet and disinfect contact lenses
4. Realise the importance of recommending a contact lens solution that offers patient comfort
5. Understand the reasons for applying scientific evidence when advising patients on contact lens solutions.

 

We’ve all had that moment…

Patient: “So which contact lens solution is the best for me?”
Optometrist: “Umm, the one I gave you the free sample kit for.” (ie the brand who’s rep tops up your trial kit stock).
Patient: “I’ve forgotten which one it was and I’ve run out. What should I get? Which one is best for my eyes?”
Optometrist: “Umm…” (I don’t know, they’re all the same aren’t they?).

Optometrists are recommending daily disposables more frequently1 than ever before due to their health, convenience and compliance benefits.2 However, frequent replacement lenses are still a AU$72 million market3 in Australia and New Zealand, and in fact, they constituted 40 per cent of all contact lens fits in 2016.1 Hence, a significant number of our patients still require contact lens cleaning solutions.

Thankfully, the days of disinfecting soft contact lenses by boiling them in salt and water are long behind us. There is now a multitude of convenient contact lens care options available for our patients.

But are they all the same?
It goes without saying that we need to ensure our patients keep their contact lenses clean and are compliant with their lens care. Having a contact lens cleaning solution that is effective in disinfection and deposit removal is incredibly important to reduce the chances of infection and inflammation.

We also know there is a high drop-out rate of contact lens wearers due to discomfort4 – the ‘leaky bucket’, as it’s often described. To reduce this level of drop out, it is imperative to ensure our patients’ contact
lens wearing experience is as comfortable and positive as possible.

So what would the perfect contact lens solution look like?

How To Find the Perfect Contact Lens Cleaning Solution

Dr. Debarun Dutta described the ideal contact lens care solution in his mivision article in 2016.5 He wrote that it should be;
1. Effective in disinfection, especially to those micro-organisms known to cause adverse events
2. Able to maintain surface wettability and enhance comfort
3. Able to resist deposits
4. Compatible with the ocular surface
5. Simple to use
6. Inexpensive
7. Able to be stored at room temperature and have a long shelf life.

So, we need to have something that kills micro-organisms but not us, removes deposits but does not damage the delicate ocular surface, is comfortable to put in the eye and makes contact lenses feel great, is easy to use, cheap and also, safe to use forever.

Easy right?

Ticking all these boxes is no mean feat. As a result, many contact lens care solutions are a complex mix of disinfectants, preservatives, wetting agents, cleaning agents, chelating agents, buffers and lubricants. Let’s look at how those ingredients come together to enable a modern contact lens care solution to meet the demands of our modern contact lens patients.

Disinfection and Efficacy

Many people believe there are only two categories of soft contact lens care solutions: those being multipurpose solutions and hydrogen peroxidebased solutions.

Wrong.
There are actually three categories of contact lens care solutions. If a lens care solution reaches the primary criteria of 99.9 per cent antimicrobial efficacy, it can be classified as a ‘Multipurpose Disinfecting Solution’
(MPDS).6,7

If a solution fails this primary criteria, it must meet a secondary standard of 90 per cent efficacy, and may only be described as a ‘Multipurpose Solution’ (MPS).6,7

We know that we need to provide our patients with a broad spectrum antimicrobial contact lens care solution to reduce the risk of microbial keratitis.8 MPDS’s have higher antimicrobial efficacy,6,7 which means they should be the first choice contact lens care solution category for our patients who want the convenience of a multipurpose product.

In a study by Kuzman and colleagues, Alcon’s Opti-Free formulation had the highest antimicrobial activity against all bacteria and fungi tested. He postulated that this is due to the fact that it’s dual disinfection system that combines Polyquad and Aldox gives antimicrobial coverage against bacteria, fungus and acanthamoeba.10 As a result, Alcon’s Opti-Free PureMoist is one of the only contact lens care solutions on the market awarded MPDS status.

It is also important to assess the efficacy of contact lens care solutions in realworld conditions. In 2008 the draft standard ‘Antimicrobial Efficacy Endpoint Methodology to Determine Compatibility of Contact Lens Solutions, Lens Cases and Hydrogel Lenses for Disinfection’ (AEEMC) was released with this in mind. Gabriel et al found that when AEEMC testing was performed on a range of contact lens care solutions combined with a range of commercially available disposable soft contact lenses, there was a biocide-specific reduction in efficacy. Overall, the combination of Polyquad and Aldox (Opti-Free Puremoist) demonstrated the best efficacy when compared with Polyquad and Alexidine, Polyquad and PHMB, and PHMB.11

For our non-compliant patients, it is safe to store contact lenses in Opti-Free PureMoist for 30 days12 and according to Wilcox, the combination of Polyquad and Aldox can result in significantly less bacteria in contact lens cases when compared to other contact lens care solutions.13

Biotrue also contains a ‘Dual Disinfection System’ with antimicrobial agents PHMB and polyquaternium-1. However, its manufacturers do not label it as an MPDS, instead assigning the lower grading of MPS.6,7,48

Hydrogen Peroxide-Based Solutions

Hydrogen peroxide solutions (HPS) continue to be regarded by many as the gold standard in contact lens care due to the fact that the 3 per cent H2O2 exhibits high levels of efficacy against a broad spectrum of pathogens including bacteria, fungi and acanthamoeba.14 It is also more effective than MPSs against biofilm in contact lens cases,15 and as it contains no preservatives, is ideal for patients who suffer from contact lens solution allergies. We also know that H2O2 solution users are far more compliant than MPS users.16

One example of a HPS, AOSEPT PLUS with HydraGlyde, can be used for both soft and hard lenses, making it suitable for ortho-k patients who want the convenience of a one-step system. In addition, it has an inbuilt neutralising disc in the case, which may reduce the risk of misuse when compared to some products that require the additional step of adding a neutralising tablet to the case.

One of the occasional complaints you may hear from patients is, “It stings my eyes sometimes when I put my lenses in after using HP solution”.

Residual peroxide can be an issue with HPSs and there are different schools of thought as to the concentrations at which we can actually sense or feel it. It is important to note that pure saline contains hydrogen peroxide at levels of 60ppm, however some studies suggest the threshold for discomfort is around 100ppm,17 while others suggest it is as little as 30ppm.18,19 Either way, the less residual peroxide, the better.

We know the ability of the platinum disc to neutralise can reduce as peroxide is cycled through the case due to the build-up of oils from the lenses and disc degradation.20 Hence these cases are approved for a maximum number of uses.

AOSEPT PLUS with HydraGlyde has effective neutralisation, down to between five and 60ppm, even after 100 cycles with the one lens case (the maximum recommended), both with and without lenses present.21
However, with other HPSs, the residual peroxide after the recommended four hours is 65ppm after only one cycle without lenses.22

To highlight the importance of residual peroxide, Bausch & Lomb is recalling EasySept Hydro+ from European markets after it was found that some products exceeded the residual peroxide level specified.23

Despite this, HPSs are still seen as the ‘gold standard’ in contact lens care and with adequate information and patient instruction, are an effective way to improve your patients’ compliance.16

Acanthameoba

Acanthamoeba appears to have become the topic du jour in optometry circles due to recent cases in the UK. However, it is important to note that it is extremely rare in Australia and there are estimated to be only one to five cases per million contact lens wearers per year.24 When we consider that the market penetration of contact lenses is less than 5 per cent,25 and hence that there are probably less than one million contact lens wearers in Australia, the low prevalence of this condition becomes clear. This may be because acanthamoeba is less commonly found in our drinking water when compared to the UK, where domestic water storage and heating systems potentially create a more acanthamoebafriendly environment.24

Regardless, it is important that our contact lens care systems are effective against this pathogen. Kern and colleagues in 2011 showed that the combination of  Polyquad and Aldox had effective kill rates against both acanthamoeba  trophozoites and cysts and was superior to some other antimicrobial combinations.26
HPSs have also been shown to be efficacious against acanthamoeba26 and, due to the higher levels of compliance associated with their use, potentially provide superior protection for our patients.

Comfort and Wettability

Ideally, a perfect contact lens care solution should also improve contact lens  wettability and comfort for the wearer. This has become even more important with the increased use of silicone hydrogel contact lenses. Whilst they have higher oxygen permeability than hydrogel lenses, they can also have reduced wettability and increased lipid deposition27 – two factors that are thought to contribute to reduced contact lens comfort.27

You may have heard the term ‘exposed silicone’ around contact lens discomfort. Essentially because we know silicone is inherently hydrophobic, it is wise to cover or hide the silicone so that it is not exposed at the surface of the contact lens. In aqueous environments, the hydrophobic sites are oriented away from the surface and the hydrophilic sites are oriented towards the surface (Figure 1). However, in air-exposed or dry environments, the siloxane bonds rotate so that the hydrophobic sites are exposed on the surface, the surface becomes hydrophobic and lipid deposition can increase.28,29 Hence, it is important to keep the surface of a silicone hydrogel contact lens wet to minimise the amount of exposed silicone.

Figure 1. Impact of environment on the surface properties of silicon hydrogel lenses. Adapted From 1. Epstein A, Stone R. Surface and polymer chemistry: the quest for comfort28 and 2. Tighe, B. A Decade of Silicone Hydrogel Development; Surface Properties, Mechanical Properties, and Ocular Compatibility.29

Most contact lens care solutions contain some form of wetting agent, but not all are designed to work specifically with silicone hydrogel lenses.

The wetting agent EOBO-41 (also known as Hydraglyde Moisture Matrix) consists of two ‘blocks’; a hydrophobic tail (BO) and hydrophilic head (EO) (Figure 2). The tail is designed specifically to bond to the hydrophobic surface of silicone hydrogel lenses,30 while the head is hydrophilic and bonds to water.

Figure 2. Molecular diagram of EOBO-41

Essentially the molecule acts as a mask to cover over any dry, hydrophobic areas on the surface of the lens and creates a layer of moisture for up to 16 hours,31 increases wettability and reduces tear-break up time.32
Sechyna et al found that the hydrophobicity of silicone hydrogel lenses was significantly reduced by exposure to EOBO-41, and that this may reduce lipid deposition.32

Similarly, Keelson et al found there was a significant reduction in Sessile Drop contact angles of water (a measure of wettability) across five different commercially available soft disposable contact lenses, and that hydrophobic lens surfaces were transformed into being hydrophilic.27

Another potential measure of contact lens comfort is lubricity. One study found that for a commercially available disposable soft contact lens, there was an 84 per cent reduction in the coefficient of friction after soaking in EOBO-41 solution.27

But you’re thinking, ‘so what’ right? A wetting agent is supposed to keep things wet isn’t it? What makes EOBO-41 so much better?

Well, it sticks.

A technique called X-ray photoelectron spectroscopy uses X-rays to probe the outermost few nanometers of a material surface, and an analysis can be made of the chemical elements. A study by Perry et al found that EOBO-41 was superior to Hyaluronic Acid (another wetting agent) at persisting at the lens surface after a solution rinse.34

Opti-Free PureMoist contains EOBO-41 and studies have shown that patients experienced nearly two hours of increased comfortable wear time, reduced end of day dryness and better end of day clear vision, even after 30 days of wear when they used this MPDS.35

But it’s not just multipurpose solutions that benefit from wetting agents. AOSEPT PLUS with HydraGlyde contains a version of the EOBO diblock copolymer called EOBO-21 or nEOBO. When compared with five other commercially available hydrogen peroxide contact lens care solutions, this solution provided superior wetting angles by the sessile drop technique.36

Deposits

We’ve all had that patient who overwears their contact lenses, is non-compliant with care and maintenance, and presents complaining of blurry vision and sore eyes. Usually they call up in a panic, are given an urgent appointment and come rushing in the door. The conversation usually goes something like this...

Patient: “My eyes are really scratchy and sore and my vision is really blurry, I’m worried I’ve got an infection.”
Optometrist: “OK, so have you taken your contact lenses out?”
Patient: “No. Do I have to?”
Optometrist: “When was the last time you changed your contact lenses?”
Patient: “Ummm, a few months?”

After some further discussion, you check visual acuity which is indeed down. Under the slit lamp, it’s entirely obvious what’s going on. The contact lenses are covered in lumpy deposits.

Good or Bad?

There has been some discussion recently about ‘good’ contact lens deposits vs. ‘bad’ contact lens deposits.37 Some of the proteins found in the tear film when in their natural state (ie. not denatured) may have a bateriocidal effect and be protective.38

However, it is well known that when proteins come into contact with a hydrophobic surface they are more likely to denature than when exposed to hydrophilic surfaces,38 and that denatured protein on the surface of a contact lens can be associated with palpebral lid changes.38

Hence, one of the best ways to limit the amount of denatured proteins on the surface of contact lenses – in particular silicone hydrogels – is to ensure that the lens remains fully wet, and a good wetting agent such as EOBO-41 outlined above is designed to achieve just that.

Deposit Removal

Whether deposits are good or bad, once denatured they need to be removed. As outlined by Dutta, the ideal contact lens solution should be able to resist or remove deposits.

So how do contact lens care solutions achieve this?

Most contact lens care solutions contain a chelating agent and a surfactant (or  surface active agent) which helps remove deposits by lowering the surface tension between the deposits and the lens surface, allowing the deposit to be easily washed off.39

Surfactants can also act as wetting agents, but their ability to bind to the lens surface varies considerably as discussed above with EOBO-41, which was designed specifically for silicone hydrogel lenses.32

AOSEPT PLUS with HydraGlyde is one of the only HPSs to contain a surfactant and so does not need the addition of a weekly protein removal tablet that some other HPSs require.

Opti-Free PureMoist contains both the wetting agent EOBO-41 and the surfactant Tetronic 1304, and has been shown to be the most effective at removing lipid deposits from a variety of contact lens materials when compared to other commercially available multipurpose contact lens care solutions40 (Figure 3).

Figure 3. Subbaraman et al, in vitro efficiency of contact lens care solutions in removing deposits from silicon hydrogel lenses. ARVO 201340

It is also important to remember that because different contact lens materials will tend to attract more deposits than others, we should avoid recommending a contact lens material that deposits easily with a contact lens care solution that is less effective at removing deposits.

Biocompatibility

Having a fantastic contact lens care solution that cleans, wets and disinfects your lenses is worth nothing if it is not compatible with the eye’s delicate anatomy. If it stings, our patients aren’t going to use it.

pH

To maximise comfort on insertion, manufacturers use buffers to match the pH of their solution to the pH range of healthy tears. Most contact lens solutions fall into this range.41,42

Solution-Induced Corneal Staining

While there is some debate about the relationship between solution-induced corneal staining (SICS) and contact lens discomfort, there is evidence that those with SICS show higher levels of discomfort.43 Regardless, it is important to avoid SICS as they have been shown to be associated with an increased risk of lowgrade inflammatory events.44

A contact lens material’s ability to absorb and release certain components of contact lens care solutions is thought to be associated with SICS.43 Different antimicrobial agents have different molecular weights, and different contact lenses  and contact lens cases have different ‘pore’ sizes. This may influence the amount of uptake of the agent into the case or into the lens itself. For example alexidine and PHMB have a smaller molecular weight compared to Polyquad and so can be more easily absorbed into the contact lens and contact lens case, resulting in reduced biocidal efficacy.45

The different molecular weights of some common anti-microbial agents are shown in Figure 4. This difference in absorption may be associated with an increase in SICS. Andrasko and colleagues in 2008 measured corneal staining across many different commercially available contact lens care solutions and many different soft disposable contact lenses.47 The results are best illustrated in Figure 5.

 

Figure 4. Adapted from Approximate Contact Lens Solution Preservative Molecular Weights. Adapted from Aktins, Contact Lens Care Part Two. Contact Lens Monthly 04/02/201146

 

Figure 5. Adapted from Subbaraman et al, in vitro efficiency of contact lens care solutions in removing deposits from silicon hydrogel lenses. ARVO 201340

What is obvious is that different antimicrobial agents may have starkly different effects on the cornea and we should be mindful of this when recommending a contact lens care solution for our patients.

Shelf Life

The final recommendation of Dutta’s perfect contact lens solution is that it should have a long shelf life. Opti-Free PureMoist has an expiry date of six months after opening, compared to 90 days for most other available contact lens care solutions.48

Summary

Just like we do with the contact lenses we prescribe, it is important that we as optometrists take the same level of interest and care with the contact lens care solutions we recommend to our patients. Contact lens care solutions are not all the same; some have higher anti-microbial efficacy and are better at removing deposits. We should look at the scientific data, particularly in real-world conditions so that we truly can recommend the best contact lens care solutions for our patients based on their particular needs, lifestyle, contact lens modality and ocular health requirements


       Simon Allen graduated from UNSW with a Bachelor of Optometry (Hons) in 2003. He has worked in both Australia and the UK, most recently in a practice where he gained broad experience with unusual and complicated refractive cases, including contact lenses. He is a member of Alcon’s Professional Affairs team.  
This education article was sponsored by Alcon.
NP4#: A21711740765

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48. Opti-Free PureMoist Package Insert
49. Biotrue Package Insert