Future of Contact Lenses
Contact Lenses 2020: What’s in Store for the Future?
A look ahead shows myriad ways that contact lenses are evolving and expanding their use.
Associate Professor Papas is executive director of Research & Development and director of Post Graduate Studies, Brien Holden Vision Institute and Vision Cooperative Research Centre, and senior visiting fellow, School of Optometry & Vision Science, University of New South Wales, Sydney, Australia. The Brien Holden Vision Institute and Vision Cooperative Research Centre have received research funds from B+L, AMO, and Allergan and have proprietary interest in products from Alcon, CooperVision, and Carl Zeiss. You can reach him at email@example.com
By Eric Papas, PhD, MCOptom, DCLP, FAAO
The date 2020 is one that is loaded with significance for vision care professionals. Perhaps unsurprisingly, therefore, it has been adopted as a popular marker indicating where the future lies. Scarily, that point is now less than seven years away, and so the way the world will look at that particular future time should be becoming increasingly well defined and clear. How do contact lenses fit into this vision? Will they still have a place, and how will they be used?
Ironically, as we look forward in time, one of the major current trends in contact lens practice takes us backward to a lens type that seemed to many to have become almost extinct. The revival of interest over the last few years in scleral and semi-scleral lenses has been remarkable and is essentially due to the inherent stability that these large-diameter options bring, combined with their relative comfort during wear. With the advent of newer materials and modern designs, the circumstances in which such devices are useful have broadened beyond the occasional, heroic, mangled cornea case to include their regular use in keratoconic, post-refractive surgery, high astigmatic, and even dry eye work (Alipour et al, 2012). As more practitioners become acquainted with the requirements for perilimbal fitting, it seems certain that these lenses will increasingly move toward the mainstream and be a major tool for clinicians in the years to come.
Continuing the theme of looking backward to go forward, it is fascinating to discover that the original soft lens manufacturing patent of Wichterle and Lim (1965) raised the prospect of their being used for the purpose of drug delivery. This was almost 50 years ago now, and the fact that there have been no really effective devices of this nature in the intervening period provides a clue to the technical difficulties involved in achieving the goal.
The primary problem for hydrogel-like materials is that their uptake and release kinetics are not well suited to the task of drug delivery. Basically, this means that even if a therapeutically useful quantity of drug can be absorbed into the lens bulk, it emerges too quickly once the lens is applied. Effectively, there is then no benefit compared with a traditional topical application, as the majority of the drug is quickly released and washed away.
A more desirable situation would be to have the active agent released slowly over an extended period so that a therapeutically useful dose is delivered more or less continuously. Several proposals for achieving this end have been made including embedding a drug-bearing film into the contact lens bulk (Ciolino et al, 2009), incorporating barriers into the polymer that lengthen the diffusion pathway for molecules seeking to make their way to the outside (Kim et al, 2010), encapsulating the drug into nano-particles dispersed throughout the lens matrix (Peng et al, 2012), and molecular imprinting (White and Byrne, 2010). This last method involves forming a molecular template in the polymer that interacts with the molecules of the pharmaceutical agent in a way that delays their release. Conceptually, this is similar to fitting the drug into a series of snuggly fitting pockets within the lens material.
Technologies such as this can extend release times from a few tens of minutes to up to tens of days and have the ability to deliver more than one drug simultaneously. This would obviously be useful for cases in which there was a concurrent need for more than one therapeutic agent, but there could be other strategic uses. For example, one entity might act to enhance local permeability so as to make it easier for another drug to cross tissue boundaries and reach the active site. Attributes of this kind are clearly attractive for treating conditions in the anterior segment, but they also offer exciting possibilities for drug delivery to posterior segment structures as well. Could these technologies eliminate the need for retro-bulbar injection in the treatment of macular degeneration, perhaps?
As well as being a vehicle for treating disease, contact lenses also seem set to have a monitoring role in the future. One such device, the Sensimed Triggerfish (Sensimed AG), is designed to give a continuous readout of intraocular pressure (IOP) and is already on limited release in Europe. Consisting of two circumferentially orientated strain gauges incorporated into a soft contact lens, it works by detecting variations in the diameter of the corneo-scleral junction in response to pressure changes inside the globe. Data are wirelessly transferred to an external recorder via additional onboard electronic circuitry. As the appliance is meant to be continuously worn, IOP profiles over a full 24-hour period can be derived, providing greater insight into the need for medication.
The ability to mount electronics within lenses opens avenues for monitoring and detection of other disease processes, and the next most likely to benefit is diabetes. More than one group has demonstrated that glucose levels can be measured in vivo with contact lens-based measurement systems (Chu et al, 2011; Yao et al, 2012). Again, the facility of having a continuous readout as opposed to, for example, the single point assessments provided by the finger prick test provides considerable advantages for those designing the treatment strategy. Given the bioavailability of markers for other diseases in the tear film—lacryglobulin is elevated in sufferers of some cancers, for example (Evans et al, 2001)—it is likely that other diseases will follow this detection pathway if it proves to be valuable in glaucoma and diabetes.
Figure 1. Telescopic contact lens.
Low vision services are a generally under-resourced area of eye care. In most professional groups globally, less than 10 low vision health workers are available per 10 million population, and even in the United States and Canada the situation is similar to this (Chiang et al, 2011). It is pleasing, therefore, to be able to report a development that may help some patients who have this problem.
A recent patent by Ford and Tremblay (2012) discloses the details of a contact lens-based telescope consisting of a soft outer skirt surrounding an inner portion carrying the optical elements. The Cassegrain principle, familiar from school physics lessons, is used to provide the telescopic function via a system of aspheric reflectors embedded within the lens (Figure 1). Light entering the telescope does so through a peripheral annulus, leaving the center of the lens available to allow normal vision. Intriguingly, the device description also includes a blink activated switching system so that the telescope can be turned on and off as desired. When compared to traditional, spectacle-mounted telescopic visual aids, the appeal of an arrangement like this to visually impaired individuals would be massive, both from a functional and from a cosmetic point of view. It would also not be surprising to find considerable interest from other individuals whose needs were less critical such as those interested in watching a live sporting event or attending the theatre.
One of the major advantages of a contact lens is, of course, its unobtrusiveness. Some wearers, however, want to use them to create quite the opposite effect and seek to alter their appearance by changing eye color or iris shape, or by having a dramatic, theatrical look. One new way in which this may be achieved is by using liquid crystal micro-tube technology (Burton, 2012). These elements are sandwiched into the lens and are thermo-graphic; that is, they can alter their color in response to temperature variation. According to the invention description, such color changes would occur as body temperature changed, and wearers would then be able to have eye color that reflected their moods. While law enforcement agencies and suspicious spouses may relish the prospect of having these contact lenses function as lie detectors, it is not yet clear how sensitive the color elements will be to the small temperature changes typical for the ocular surface. One wonders whether the variation in external environments encountered by most people during the course of their normal activities might override those changes occurring at the cornea/lens interface. Nevertheless, the dynamic nature of the result will certainly appeal to some.
Another feature of the way in which contact lenses work is that they completely cover the entrance pupil of the eye. As they reduce the risk of damage caused by inadvertent, stray reflections, this makes them attractive for applications such as radiation protection, where it is desirable to control the amount of incident light in the nonvisible wavelengths. Naturally, the critical requirement is that the lens strongly absorbs these wavelengths while permitting the visible spectrum to enter normally. In a recent development this behavior has been achieved by using the vehicle of plasmon resonant nano-particles. Composed of a silica core coated with a nanometerthin layer of gold, these are essentially tiny spheres that can be wavelength tuned by varying the relative size of the core and the thickness of the shell. In this way, very high extinction coefficients can be attained, meaning that the undesirable wavelengths can be almost totally blocked. As the particles are apparently non-toxic and photo-stable, applying them to a contact lens potentially creates a highly efficient filter that would be useful for protection against infra-red laser light, for example. Eliminating the need for large goggles or clumsy visors would be a further attraction, and there might be an upsurge in the business of gold nano-particle contact lens salvage.
Of all the possible future applications for contact lenses, without doubt the ones that evoke the most animated responses are those involving visual augmentation. This term covers a range of possible applications, all of which have in common the desire to present visual information to the eye that is either additional to or replaces that already available in the normal environment. One way this might be accomplished would be to project the new detail onto screens arranged to be worn as a pair of spectacles or goggles. The role of the contact lens is to enable the wearer to focus onto these projected images even though they are positioned extremely close to the eye. At least part of the contact lens optics would thus need to be highly positive in power, although the configuration as suggested provides for other refractive regions that will permit the outside world to be clearly seen at the same time (Legerton and Sprague, 2012).
Alternative approaches being researched include incorporating on-board electronics into the contact lens. Although currently quite crude and primarily intended for measurement purposes, these arrays have the capacity to directly receive, transmit, and display data (Lingley et al, 2011). In theory at least, imaging systems could be created on this platform that would be able to project visual scenes directly into the eye. Depending on the particular arrangement, the result could provide functionality ranging from heads up displays that place information about almost anything imaginable into the visual field (you could watch the game or a movie anywhere you liked) to a full virtual reality headset—think Star Trek and the Holodeck!
As an example of how far these concepts could progress, a European consortium is working on the concept of BEAMING (BEing in Augmented MultImodal Naturally Networked Gathering). While not quite the teleportation device familiar from science fiction (yes, Star Trek again I’m afraid), the idea is that an individual can effectively transfer his awareness to another place by interfacing with an avatar (essentially a robot) situated in the remote location. Sensory information is received from the avatar and commands sent back to control its behavior. Virtual reality goggles, like those outlined earlier in this article, would be a key component of the system, permitting the wearer to see the same images that the avatar “sees.”
While there are clearly many hurdles to overcome before these systems become available, applications in the business, leisure, and military spheres are extensive and not a little confronting. The way in which human beings interact with one another will certainly become altered from what we have been used to for millennia. Imagine sending an avatar to an overseas business meeting or to school while your sick child stays to do the same lessons at home. For some, the delights of a full-immersion virtual world may well be so tempting that they will never emerge. Let us hope that, as a species, we are intellectually and emotionally capable of coping with the psychological and social tidal wave of change that seems destined to follow these remarkable technological advances.
It’s a heavy responsibility to ponder while you are fitting those visual augmentation contact lenses isn’t it? CLS
Acknowledgements: Grateful thanks are due to Professor Lyndon Jones for help with sections of this article.
For references, please visit www.clspectrum.com/references.asp and click on document #207.