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ROHTO Dry Eye Relief (Figure 1) is a new alternative for the management of dry eyes, manufactured by The Mentholatum Company. This article provides a brief introduction to the patented technology used in ROHTO Dry Eye Relief, in order to assist practitioners in considering its use with their dry eye sufferers.
Dry eye is on the increase
Eye care practitioners are dealing with an increasing number of patients complaining of symptoms associated with ocular dryness. The prevalence of dry eye varies depending on which report you read and these variations can largely be accounted for by differences in study design and protocols. However, the literature suggests ranges from 15-33 per cent in the over-65s and suggests that between 17 and 30 per cent of people will experience dry eye syndrome at some point during their life.
Dry eye
Dry eye disease has two fundamental causes - a reduction in either the quantity or quality of the tear film, or both. A contemporary definition of dry eye disease was developed by the International Dry Eye WorkShop group (DEWS) to reflect current understanding of the disease. The definition has been improved upon since the previous definition reported by Lemp, in the light of new knowledge about the roles of tear hyperosmolarity and ocular surface inflammation in dry eye, and the effects of dry eye on visual function. After many years of discussion the committee approved the following definition.
'Dry eye is a multifactorial disease of the tears and ocular surface that results in symptoms of discomfort visual disturbance and tear film instability with potential damage to the ocular surface. It is accompanied by increased osmolarity of the tear film and inflammation of the ocular surface.'
The ideal artificial tear solution
The ideal tear supplement can be said to require the following key features:
- Provide immediate relief
- Gives prolonged residency in the tear film, for longer lasting relief
- Is non-toxic to the ocular surface
- Is simple to instil
- Does not blur vision following instillation.
The ideal delivery system for such a solution can be said to have the following key features:
- Easy/simple to use/instil
- Small droplet size to avoid blurring/washing away the tear film
- Helps maintain solution sterility between usage (with or without preservatives)
- Affordable.
Artificial tear formulations
Numerous formulations have been introduced over the years. They can be broadly been classified in three groups.
Aqueous artificial tears
For many years synthetic polymers and cellulose derivatives and have been used as the 'standard' therapy in preparations often referred to as 'artificial tears'. An example of such a solution is hypromellose - still widely used today largely due to the fact that it is inexpensive and can be supplied on an NHS prescription.
Ocular lubricants
An alternative to traditional teardrops, these are high viscosity ointments similar in formulation to E45 cream, designed to help reduce friction between the ocular surfaces. They are limited to night-time use due to the significant blurring following instillation.
Viscoelastics
Viscoelastics encompass a growing range of agents that are primarily gel polymers demonstrating thixotropic properties. In the case of eye drop preparations this means that when stationary between blinks they demonstrate high viscosity and while in motion during blinking their viscosity reduces to a level similar to water. Figure 2 shows how this non-Newtonian (rheologic) behaviour simulates the function of the tear glycoprotein as a force is applied. Currently, the two most widely adopted viscoelastic polymers are carbomer gels and hyaluronic acid.
ROHTO Dry Eye Relief
ROHTO Dry Eye Relief is a hypotonic solution that contains a new bi-polymer developed from the combination of the currently popular and naturally occurring polysaccharide, hyaluronic acid (HA), with a new polysaccharide derived from the seed of the tamarind tree. The hypotonicity of ROHTO Dry Eye Relief is designed to counteract any tear film hypertonicity and quickly restore its osmotic balance. The solution is available in multi-dose and, what the company describes as, a 'daily-dose vial'. The latter has a clever replaceable cap (Figure 3) with data supporting the safety of its reuse within the same day.
The simple idea for the research and development of ROHTO Dry Eye Relief was to combine HA and tamarind seed polysaccharide (TSP) but it soon became clear that this concept had more to it than the researchers envisaged. The development team actually found that the interaction between HA and TSP was complementary and the resultant bi-polymer was patented as HydraMed.
HydraMed
The cooperative nature of HA and TSP involves HA acetyl groups and the TSP internal glucose (Glc) and galatose (Gal) units as seen in Figure 4.
Hyaluronic acid
HA is a naturally occurring linear structured polysaccharide that is found in the aqueous and vitreous humour and the synovial fluid of joints. It is finding increasing favour in dry eye preparations in differing concentrations. It is a viscoelastic, biological polymer that displays rheological, non-Newtonian behaviour. In this case HA mimics the natural tear film in becoming more elastic during the blink, increasing spreading and improving aqueous lubrication of the anterior ocular surface epithelial tissues.
HA is extremely effective at binding water and can attract up to 3,000 times its own weight. It has been shown to have a protective effect on the corneal epithelium, improving barrier function and wound healing. Its efficacy in keratoconjunctivitis sicca, as well as its ability to significantly lengthen tear break-up time, has been demonstrated in numerous studies. As in ROHTO Dry Eye Relief, a hypotonic formulation has been shown to maximise its effectiveness.
Tamarind seed polysaccharide (TSP)
TSP is a natural, water-soluble, branched-chain polysaccharide. It is sourced from the nut of the tamarind tree widely found across Asia. TSP has been found to have numerous properties that make it ideal for use as a tear film supplement. Figure 5 shows the structure of TSP, which is similar to that of natural mucins and, in particular MUC1 consequently TSP demonstrates muco-mimetic and muco-adhesive properties.
TSP consists of a cellulose-like backbone (repeating glucose units) with xylose and galactoxylose substituents, providing a branched chain structure. The polymer displays rheological, non-Newtonian behaviour and so, like HA, it increases spreading and improves aqueous lubrication.
The bi-polymer of HA and TSP has a higher capacity to encompass water when compared to each individual polymer. This characteristic is crucial to HydraMed's properties of bio-adhesion, biocompatibility and moisturising capacity.
Preservative efficacy
Some practitioners may be surprised to see that the multi-dose bottle is preserved with benzalkonium chloride (BAK). BAK is generally considered to be the most efficacious preservative available to formulators and by modifying the BAK molecule to work in ROHTO Dry Eye Relief's unique formulation, the manufacturer has ensured the solutions conformity to the 'gold standard' measure of preservation in sterile products - the European Pharmacopoeia Preservative Efficacy Test.
As with contact lens care products the balance of efficacy versus toxicity needs to be carefully considered. During use a bottle will 'suck-back' air into itself and this, combined with the potential for touching the surrounding eye, leaving the cap off and the likelihood that the bottle will be used beyond its expiry date, means that utilising powerful preservatives in sterile eye products is of paramount importance in protecting the patient from ocular infection.
Discussion
The technology behind dry eye preparations is improving. Products, such as ROHTO Dry Eye Relief, theoretically enable the practitioner to target a particular underlying cause of the dry eye with a specific eye drop formulation.
In recent years there have been a plethora of new dry eye drop introductions using a wide range of different approaches to alleviating the symptoms and signs of dry eye. Interestingly, one of the drivers for the large influx of new innovative drop formulations is the increased registration of dry eye solutions with the Medicines & Healthcare Products Regulatory Agency (MHRA) as medical devices as opposed to ophthalmic drugs, enabling the products to be brought to market more quickly and licensed with a CE mark.
Most of the traditional preparations are licensed as drugs by the Medicines Control Agency (now part of the MHRA). This has led to a somewhat counter intuitive situation, in that the licensed drugs are now relatively old technology, often providing an inferior level of performance compared to their counterparts registered as medical devices.
Conclusion
Practitioners' advice on dry eye management as well as the appropriate selection and use of drops, should not be underestimated. Consequently the author recommends practitioners take a look at new products such as ROHTO Dry Eye Relief to ensure that they are familiar with their formulations and mode of action. The considered and careful selection of such a solution has the ability to improve the comfort and quality of life of dry eye sufferers. ?
? Nick Atkins is a contact lens optician, past-president of the BCLA and director of PTR Consultants