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Eye Tech in the Age of High Tech

2 CPD in Australia | 0.75G in New Zealand | 27 July 2017

This course is temporarily unavailable as it is being re-registered for CPD points for 2018  It will be available in 2018.

By David Stephensen

Likening the process of effective contact lens correction to an efficient information technology system can create a useful analogy against which you can assess your clinical options.

The process of delivering a satisfying and functional pair of contact lenses to our patients is not as straightforward as it may seem on the surface. Each time we sit down with a patient to discuss and prescribe contact lenses, there are many variables that must be considered. The system of rationalising these variables is a complex one, despite the day-to-day nature of this process in clinical practice. Complex undertakings are best achieved by employing an organised system as a positive outcome relies on the practitioner recognising the contribution of all of the components of the complex system.1

With the improvements in contact lens availability and newer, more complex polymer architectures available, it is a good idea for practitioners to review their clinical decision systems from time to time. There are various tools available to assist in the process of analysing the complex systems involved in clinical decision making. An accessible technique to evaluate optimisation strategies for complex systems in a heuristic manner is the use of analogy to look at other examples of successful complex systems, and look for parallels to build a mental picture of how the individual elements of the system may fit together.2

In terms of soft contact lens correction, a useful analogy is that of information technology systems. That’s because both systems are aimed at improving the wellbeing and capacity of the end user. Information technology systems are the sum of their components – hardware, operating system, and software or apps. Individually each of these parts is not functional, but the successful interaction of these components creates amazing opportunities and productivity. Together they constitute a functional ecosystem.3

In our modern life, these information technology ecosystems have become familiar to us in terms of examples such as the Apple iOS operating system, iPhone hardware and the App Store. A similar example of an ecosystem is the Google Android operating system, although the ecosystem based around Android is more fragmented as the hardware is developed by third parties.3 By bringing a cohesion to the total ecosystem, Apple is able to engender a strong brand loyalty and a consistent desire on behalf of its customers to upgrade as new devices arrive to the market.4

The ecosystem behind contact lenses can be defined using this information technology analogy. Additionally, the positive examples from successful information technology systems can be used to build a path to better clinical outcomes for patients. This in turn can help optometrists define a strategy for optimising the vision correction system over the patient’s wearing lifetime.

The Hardware

Each contact lens wearer comes into the ecosystem carrying the hardware required for vision correction: they bring their eyes and neurological visual apparatus. The role of the optometrist is to assess the eyes for refractive error and classify the type of ametropia. The forms of ametropia most applicable to soft contact lens correction are myopia, hypermetropia, astigmatism and presbyopia.5 The optometrist also has a role in defining any hardware equipment faults that may be present in the eyes. These hardware faults are represented clinically by pathological issues. Examples may be the presence of a blepharitis, allergic conjunctivitis or keratoconjunctivitis sicca.6

The optometrist’s role in managing hardware faults is to aim to restore the hardware to a point at which it is possible to install the operating system in the form of the soft contact lens itself. Each operating system has specific hardware requirements, and if these hardware requirements cannot be met, then the operating system cannot be installed.7

The Operating System

The operating system is the most significant part of the clinical decision-making process for an optometrist in terms of prescribing an appropriate soft contact lens. Unlike computer technology, there is a multitude of contact lens brands, materials and designs that may be installed as the operating system.8 Various factors must be considered in the process of deciding on the appropriate contact lens to install on the patient’s eye.

The first consideration in selecting a contact lens operating system is to ensure that the contact lens chosen does not cause any problems for the underlying hardware in terms of creating pathology. One of the most obvious issues that is present for all contact lenses is the provision of oxygen to the cornea in order to maintain normal physiological function.9

Traditional hydrogel contact lenses have, in general, failed to keep pace with the oxygen needs of the cornea without compromising their mechanical integrity. Hydrogel contact lenses require an increased water content to improve oxygen transmission. With the increased water content, there are issues of poor durability of hydrogel contact lenses, which decreases their utility. In recent years there have been some novel advances in hydrogel contact lens material design, with the release of a hypergel polymer from Bausch and Lomb. By creating a hydrogel copolymer system containing 2-hydroxycyclohexyl methacrylate (TBE), the Biotrue ONEday hypergel material from Bausch and Lomb is able to provide an oxygen flux of 93 per cent,10 while maintaining a structural integrity similar to more robust hydrogel polymers such as HEMA.10,11

The addition of silicone in the form of polymers such as tris methacrylate in the 1990s significantly improved the oxygen flux through soft contact lenses. These early silicone hydrogels were able to provide as much as six times the oxygen of first generation hydrogels such as the Bausch and Lomb Soflens that was released in the early 1970s. However, the initial silicone hydrogels were not without issue as the silicone content reduced surface wettability significantly, requiring surface modifications such as plasma treatments. The early silicone hydrogels had a low water content and this created issues in terms of rigidity, sometimes affecting the fit of the contact lens on the eye.12

Imagine if it were possible to manufacture a contact lens out of multiple polymers within the one contiguous matrix. This would be analogous to being able to combine the best features of the Apple macOS operating system with the best features in Microsoft Windows 10. In this scenario, we would select each of the polymers to provide one of the various functional roles that are required by contact lenses during wear.

Broadly speaking we can define these properties as:13

  • providing a stable and accurate optical surface to provide vision correction for the patients’ ametropia;
  • providing a constant physical shape to avoid variations in physical fit on the surface of the eye, as well as alterations in lens form that would degrade the optical image quality;
  • providing an outer surface that remains clear of debris and foreign contamination both to decrease the likelihood of an adverse physiological response from the cornea and to allow for a smooth interface with the external tear layer overlying the contact lens;
  • providing a high affinity for water molecules to avoid dehydration of the contact lens during the period of wear as well as avoid corneal epithelial desiccation as a result of water gradients between the cornea and contact lens;
  • providing a material with sound mechanical structure that can resist handling as well as providing a low enough modulus that it may be worn with comfort on the eye; and
  • providing sufficient oxygen to the cornea to maintain corneal homeostasis during contact lens wear.

Newer silicone hydrogel materials such as the Bausch and Lomb Ultra material contain structured copolymer arrangements that represent these combined properties of different operating systems. In the context of the Ultra material, this combination of silicone hydrogel and hydrogel polymers is referred to as the MoistureSeal Technology system.14 The goal of the MoistureSeal Technology is to create both a polymer and a manufacturing system that produces an end copolymer system with stable and predictable bulk material properties. The MoistureSeal Technology that gives rise to the samfilcon A polymer creates a copolymer of silicone hydrogel materials and polyvinylpyrrolidone to take advantage of the unique individual properties of these materials and build upon them to create a superior wearing experience.

The silicone phase of samfilcon A is produced by creating an initial polymerisation phase that creates covalent bonds between siloxane chains of different molecular lengths. Different molecular lengths of siloxane are used to take advantage of their individual properties. Some will improve oxygen transmission, whilst others will improve the rigidity of the final material to make it easier to handle and potentially more comfortable on the eye of the wearer. The siloxane polymer creates a scaffold matrix or skeleton, and this polymerisation process is completed after approximately five minutes.

At this point in the series of chemical reactions the N-vinylpyrrolidone (NVP) monomer begins to react with itself to form the high molecular weight polyvinylpyrrolidone (PVP) in situ throughout the matrix, peaking at eight minutes into the process.15 The delayed commencement of the polymerisation of the PVP means that it forms around the scaffold matrix, thus forming the outermost presenting face of the contact lens material. The progress of this dual phase reaction can be tracked using thermography that illustrates this through the use of differential scanning calorimetry. The first peak observed in the thermogram after the first two minutes of lens curing reflects reaction of the siloxane components, while the second peak after eight minutes of lens curing reflects the polymerisation of NVP to PVP.16

The end result is an operating system that provides an increased water content and increased wettability – both at the core of the contact lens and on the surface. The ability to propagate the PVP through the core of the contact lens means that in total, the MoistureSeal technology of samfilcon A retains the PVP throughout the matrix of the contact lens, both at the surface and in the core of the contact lens.15

The availability of PVP at the surface of the Bausch + Lomb Ultra contact lens creates a very wettable contact lens, with a low co-efficient of friction at both the commencement of wear and after wear on the eye. The low co-efficient of friction created by the MoistureSeal technology reduces any retardation to the blink mechanism, assisting with enhancing wearer comfort.15

Today’s modern world contains many more visual challenges for patients due to the omniprescence of screen-based technology. From mobile phones to tablets to personal computers, the number of devices that contact lens wearers use in their day has been steadily increasing. Concurrently, there has been a trend towards patients dropping out or considering dropping out of contact lens wear due to discomfort.14 We know from clinical studies that the use of screen-based devices increases the inter-blink interval, and that this can have adverse implications for the stability of the tear film in the inter-blink interval.17

One of the more important modern requirements of contact lens polymers as an operating system is the maintenance of patients’ tear film. Evaporation of the tear film over the surface of the contact lens will degrade the wearer’s vision, and this results in sub-optimal visual performance. This issue is exacerbated further by the patient’s wearing environment and daily activities. An ideal contact lens polymer operating system would facilitate visual clarity by resisting blur induced by tear evaporation. Potentially, a well-designed polymer may be able to provide such a stable pre-lens tear environment that visual clarity is maintained at a level beyond that of the naked eye.

Comparative studies of a model of pre-lens tear film (PLTF) on an optical bench setup can demonstrate the relative abilities of different contact lens polymer operating systems to maintain PLTF stability and consequently promote more consistent visual acuity. By mounting contact lenses on a PMMA carrier, and taking photographic images through the contact lenses at 10 second intervals of a visual acuity test image, the effect of evaporation blur can be assessed. In a comparative test of the Bausch and Lomb Ultra MoistureSeal technology against the Johnson and Johnson Acuvue Oasys, Alcon AirOptix Aqua and CooperVision Biofinity contact lenses, the Bausch and Lomb Ultra MoistureSeal technology demonstrated a superior level of visual acuity performance, as well as consistent visual acuity performance up to a test period of 30 seconds.18 This makes the Bausch and Lomb MoistureSeal technology not only ideal for tasks involving screen-based equipment, but also the contact lens of choice for staring competitions.

The Software… or Soft Wear

Once the hardware of the patient’s eye and the operating system of the chosen contact lens polymer platform have been brought together, there remains one final consideration. The optometrist must consider the appropriate optical design required to correct the patient’s ametropia. The chosen contact lens optical design represents the software application, or app in modern parlance, that would run under the operating system on the hardware in the information technology analogy.

On the surface, it may seem that the choice of contact lens software is elementary in that it should match the patient’s particular ametropia in both form and magnitude. However, as contact lens polymers have become more dimensionally stable, there has been an improved ability to correct vision beyond the standard dioptric correction of defocus. Of the different aberrations, one of the most relevant to correct is that of spherical aberration as this is an inherent feature of many optical systems, including the human eye.19

The Bausch and Lomb Ultra contact lens is designed with a philosophy of reducing the spherical aberration of the corrected eye to a lower degree of manifest spherical aberration than the eye alone would present. Additionally the degree of spherical aberration that the Bausch and Lomb Ultra contact lens exhibits in bench testing is lower than other comparable products such as the Johnson and Johnson Acuvue Oasys, CooperVision Biofinity and the Alcon Air Optix Aqua contact lenses.19 Coupled with the absence of evaporation blur, and the Bausch and Lomb Ultra  MoistureSeal provides the contact lens wearer with more consistent and less aberrated vision.18,19

Moving beyond the single focus form of contact lenses, there is a need for a more complex optical form to compensate for the diminished accommodation found in presbyopia. An ideal presbyopia correcting multifocal lens would provide clear, consistent vision at distance, intermediate and near working distances. The ideal presbyopia correcting multifocal contact lens would provide consistent optical power profiles from the centre of the contact lens to the periphery, independent of the degree of ametropia being corrected. The ideal presbyopia correcting multifocal contact lens would provide stable optical zones, with an ability for the wearer to make rapid transitions between these different zones of focus.20 While this is easy to define in words, it is a more complex task to achieve in a manufacturing and clinical sense.

With the Bausch and Lomb Ultra for Presbyopia, the MoistureSeal polymer technology has facilitated the development of a range of contact lens powers in two near addition ranges with these optically stable, predictable powers. The design of the Ultra for Presbyopia contact lens was based on a novel methodology using a computerised model utilising the anatomical and biometric data from 180 eyes. Variables such as pupil size, corneal curvature and higher order aberrations were used to predict visual acuity outcomes for each eye. This means that the design of the Bausch and Lomb Ultra for Presbyopia could be optimised to suit a wide range of eyes, rather than providing a standardised design that does not account for individual variability.20 Using wavefront modelling it can be demonstrated that the Bausch and Lomb Ultra for Presbyopia with MoistureSeal maintains a consistency of predicted power compared to the package label of 0.101D in the near portion and 0.078D in the distance portion of the contact lens across the power range available. This means that if a patient has significant anisometropia, the progressive shift in power across the surface of each contact lens will remain consistent despite the difference in dioptric power between the eyes. As a result, the patient can make the most of the rapid transitions in focus between the three working ranges of distance, intermediate and near.20,21

The Entire System: Hardware, Operating System and Software

Breaking the contact lens wearing experience into layered components may be useful in creating a thought structure that optometrists can follow in choosing a contact lens for their patients. By considering the patient’s eye to be the hardware, and ensuring that there are no faults present, by selecting the appropriate operating system in terms of selecting a polymer or co-polymer that will perform consistently and with comfort, and by selecting a software platform that provides the best in class optical performance, the complex decision of contact lens selection can be rationalised to both the optometrist’s and patient’s advantage.

The final information technology analogy that the contact lens practitioner can take advantage of is that of the upgrade. By understanding the nuances of the polymer and optical technologies available in platforms such as the Bausch and Lomb Ultra MoistureSeal system, patients can be offered easy upgrade pathways to more advanced contact lens products that may help them to be more satisfied wearers and avoid patients becoming contact lens dropouts.

The Art of Communication

The importance of carefully selecting which of your patients is suited to wearing contact lenses goes without saying. As does the need to equip yourself with the knowledge and skills to select and fit the most appropriate contact lenses for them. Having trial lenses to hand is also essential.

Selecting the best lens to meet your client’s needs comes down to the results from your clinical examination and a thorough discussion about their lifestyle, vision needs etc. Once you’re convinced of the most appropriate lens options for your patient, it is vital that you discuss them with the patient, providing full information so that they can take an active, empowered role in the decision making process.

A positive, proactive attitude will give you a much greater chance of successfully fitting your patients, regardless of the type of contact lens required. If you are hesitant or negative about the options, you may find your patient doesn’t feel confident about trying your recommendation right from the start.

Clear and consistent information about contact lens hygiene – delivered both verbally and with appropriate literature – will help to ensure their experience with contact lenses is positive and will reduce the chance of drop out. This is important for all contact lens wearers – even those with the most experience will need to be reminded, from time to time to reduce the risk of ambivalence.

Finally, be sure to ask your patient whether they have any additional questions about contact lens wear as they leave your consult room. This will reassure them of your interest in their eye health and your ongoing support as their eye health practitioner.



 

David Stephensen B.App.Sc(Hons)(Optom) B.Bus Graduate, Certificate in Ocular Therapeutics, CASA CO conducts a specialty contact lens practice with his primary practice located in the southside Brisbane suburb of Moorooka. Dr. Stephensen is a Fellow of the Cornea and Contact Lens Society of Australia and is now a Honorary Vice President of the Cornea and Contact Lens Society and the Chair of the Case Report Section for the Fellowship programme. He has interests in anterior segment eye conditions, toric intraocular lenses, contact lens correction for presbyopia, orthokeratology and in contact lens correction of abnormal corneas – particularly pellucid marginal degeneration, post graft, and keratoconus.

 
 

References
1.  Bodenschatz E. Complex Systems.; 2009. www.mpg.de/36885/cpt08_ComplexSystems-basetext.pdf. Accessed May 28, 2017.
2.  Gavetti G, Rivkin JW. How Strategists Really Think. Harv Bus Rev. 2005;83(4):54-63. doi:Article.
3.  Maréchal N. What do we mean by mobile ecosystems? Ranking Digital Rights. rankingdigitalrights.org/2016/09/15/what-are-mobile-ecosystems/. Published 2016. Accessed May 28, 2017.
4.  Kelly G. The Majority of iPhone Users Admit to “Blind Loyalty” - Why This Is A Problem For Apple. Forbes. www.forbes.com/sites/gordonkelly/2014/03/21/the-majority-of-iphone-users-admit-to-blind-loyalty-why-this-a-problem-for-apple/#3f75f22130f6. Published 2014. Accessed May 28, 2017.
5.  Ford M, Stone J, Rabbetts R. Optics and Lens Design. In: Phillips A, Speedwell L, eds. Contact Lenses. 5th ed. Edinburgh: Butterworth Heinemann Elselvier; 2007:129-158.
6.  Stone J, Terry R. Assessment of patient suitability for contact lenses. In: Phillips A, Speedwell L, eds. Contact Lenses. 5th ed. Edinburgh: Butterworth Heinemann Elselvier; 2007:173-188.
7.  Windows 10 System Requirements Specifications | Microsoft. www.microsoft.com/en-au/windows/windows-10-specifications. Accessed May 28, 2017.
8.  White P. Contact Lenses & Solution Summary. Contact lens Spectr. 2016;(Supplement July):1-36. www.clspectrum.com/class.
9.  Sweeney D, Stretton S, Fonn D, Swarbrick H, Holden B. Extended- and continuous- wear lenses. In: Phillips A, Speedwell L, eds. Contact Lenses. 5th ed. Edinburgh: Butterworth Heinemann Elselvier; 2007:273-309.
10.  BAUSCH AND LOMB. It’s going to be a Biotrue day.2016.
11.  Heiler D. Data on file. Bausch and Lomb. 2012.
12.  Bomgardner M. Making better contact lenses. Chem Eng News. 2017;5(13):29-33.
13. Ensley R, The Fight against Discomfort: Innovations in Daily Disposables, Review of Cornea and Contact Lenses, 2015, http://www.reviewofcontactlenses.com/content/c/55085/. Accessed June 5, 2017.
14.  Steffen R, Merchea M, Rah M, Reindel W. Clinical performance of Samilfilcon A Silicone Hydrogel Contact Lenses. Contact Lens Spectr. 2014;(Special Edition):30-38.
15.  Wygladacz K, Hook DJ, Steffen R, Reindel W. Breaking the Cycle of Discomfort. Contact Lens Spectr. 2014:23-28. www.clspectrum.com/content/bl/5/CLS_BL_704.pdf.
16.  Hoteling A, Nichols W, Harmon P, et al. Characterization of Bulk PVP Content of Samfilcon A Silicone Hydrogel Lenses.; 2013.
17.  Crnovrsanin T, Wang Y, Ma K. Stimulating a blink: reduction of eye fatigue with visual stimulus. Proc SIGCHI Conf Hum Factors Comput Syst. 2014:2055-2064. doi:10.1145/2556288.2557129.
18.  Hovinga KR, Ludington PD, Merchea M, Steffen R. Preventing dehydration blur. Contact Lens Spectr. 2014;(Special Edition):39-42.
19.  BAUSCH AND LOMB. Data on File. 2013.
20.  Saxon J, Hovinga K. Translating Insight Into Innovation. 2016;(January 2013):2016.
21.  Vogt AKS, Hovinga KR. Consistency of Multifocal Contact Lens Designs. Data File, Bausch Lomb.
22.  Bausch + Lomb data on file. Merchea MM et al. Clinical performance of a novel silicone hydrogel contact lens with optimized chemical and physical attributes
*Model cornea used to mimic the optics and physical dimensions of an average human eye. One or two drops of a rewetting solution were used to simulate a fresh tear film after a blink.(23)
© 2017 Bausch & Lomb Incorporated. ®/TM denote trademarks of Bausch & Lomb Incorporated and its affiliates. Other product names/ brand names are trademarks of their respective owners. iNova Pharmaceuticals (Australia) Pty Limited. ABN 88 000 222 408. Level 10, 12 Help Street, Chatswood NSW 2067 Australia. Ph (AUS) 1800 251 150. LOTJ : 2017-06—034
  • ULTRA┬« resists water loss for significantly better image quality with reduced blinking rates*(23)
  • Consistent power in the near, intermediate and distance zones for improved visual performance(24)
  • Accurate Add power at every power for a successful and easy fit(20)
  • MoistureSealTM technology features a unique two-phase polymerisation process for an exceptional combination of oxygen transmissibility (Dk/t), modulus and water content(16,22)

' the successful interaction of these components creates amazing opportunities and productivity '