A Look at the Future of Contact Lens R&D
BY ERIC PAPAS, PHD, MCOPTOM, DIPCL
As computer scientist Alan Kaye once said, “The best way to predict the future is to invent it.” In the contact lens world, it could be argued that all the easy stuff has already been invented, which should clarify for us what still needs to be done. By default this means we're left to address the difficult stuff, but these problems hold the key to wider and more satisfactory use of contact lenses as a modality. Where then, can we expect this activity to be focused in the next few years?
The first area that comes to mind is convenience. Reducing the paraphernalia and effort associated with keeping lenses clean and sterile would surely be on the “wish list” for most wearers. The FDA and other regulatory bodies are tightening antimicrobial standards for care systems and these heightened regulations aren't likely to foster a simplification of the cleaning, disinfection and storage process. Indeed the value of each step in the regimen to its overall efficacy is becoming more evident (Butcko et al, 2007).
In that light, maybe changing the focus of anti-pathogenic activity from the care system to the lens itself would be a more user-friendly strategy. Attempts have been made to produce an antimicrobial contact lens but, so far, nothing has reached the marketplace. While finding and incorporating into the lens an agent that can kill microbes appears to be relatively straightforward, it's more challenging to extend this activity to deal effectively and continuously with pathogens that invade the conjunctival sac, while simultaneously avoiding ocular toxicity. As we begin to understand more about the multiple defense mechanisms utilized by the eye (Evans et al, 2007) it's evident that not all involve the direct eradication of microbes. Future contact lenses may be able to make use of these principles to lower their contamination rate independently of preservative concentration. It remains to be seen whether these strategies will be effective enough to succeed where more oxygen failed, and reduce the rate of contact lens-related infection. If this can be done during eye closure, the ultimate convenience of safe extended wear is the tantalizing prize.
Having developed a safer lens, it would be nice to be able to wear it comfortably all of the time. Increasing discomfort during the wearing cycle affects large numbers of wearers and continues to be the major reason for discontinuation (Young et al, 2002).
Based on the experience gained in dry eye research, one avenue of investigation is sure to be the extent to which contact lenses induce inflammatory responses during the course of normal wear. Inflammation has been strongly implicated as a major factor in dry eye (Dry Eye Workshop, 2007) and so it is reasonable to hypothesize that it has a role in creating the dryness and discomfort symptoms that are a feature of contact lens wear for many users.
Several companies have taken an alternative approach of incorporating internal wetting agents into their lenses, presumably on the basis that this will maintain hydration during the wearing cycle and reduce friction between the lens surface and the eyelid. Somewhat surprisingly, there's little published evidence that this strategy has the desired effect on subjective comfort. Nevertheless, it's likely that material developments will focus on the enhancement of the properties of the contact lens surface. With the eye as the model, perhaps we may see lenses whose back and front aspects have different characteristics in an effort to present an evolutionarily familiar surface to the corneal epithelium on one side, and the palpebral conjunctiva on the other.
While the aim of most research activity is to reduce the impact of contact lenses on the ocular environment, in the area of refractive status, there's likely to be considerable interest in making them do just the opposite. Orthokeratology is familiar as a means of manipulating refractive error within a certain range, but evidence is building that contact lenses may be a vehicle whereby refractive errors can be prevented in the first place. Work carried out over a number of years, across many species, has shown that it's possible to influence the amount of ocular growth, and thus the degree of myopia, using purely optical means. Confirmation that humans respond in a comparable manner opens the prospect that suitably designed lenses would have “anti-myopic” properties. Clinical trials to assess the value of these interventions have begun and their results will be keenly watched to see how they compare with previous interventions in arresting myopic progression. The high prevalence of myopia, particularly among children of school age in the emerging markets of China and Asia (Liang et al, 2009; He et al, 2009) guarantees that this will be an area of considerable endeavor over the next few years.
Apart from discomfort, another major factor in contact lens dropout is presbyopia. Many previously happy wearers seem unable to accept the visual compromise associated with changing from a single-element optical system to one that is bifocal, multifocal or uses monovision. The lens designs that predominate in this landscape are of the simultaneous vision type, largely due to their simpler fitting. While it's undoubtedly the case that significant improvements in performance have been achieved in recent years, the extent to which this process can continue is limited by the optical and perceptual factors associated with having multiple images coincident on the retina. An obvious way around this difficulty is to create a device that is capable of dynamically changing its focal length so that the quality of the retinal image is maximized for any given viewing distance. Alternating, or translating, bifocal contact lenses work in this way, have been around for many years and can work successfully in rigid gas permeable form. Though there are some interesting candidates, a comfortable, consistently translating, soft bifocal contact lens is still an unmet need.
These difficulties might be happily overcome by having an active optical element that can repeatedly change its dioptric power over time, as the eye does during accommodation. When considering how this might be achieved, recent reports emanating from the University of Washington in Seattle come to mind. The reports (Hickey, 2010) suggest that sophisticated electronic arrays have been successfully embedded into contact lenses. Though the short-term use of these devices is likely to be for measurement, a useful enough research tool in its own right, the ability to send and receive signals raises the prospect of being able to control, for example, the refractive index of a lens segment. At least in theory, such an arrangement could form the basis for a true bifocal, or even a lens with continuously variable focus.
Exciting though this prospect may be, more far-reaching applications are being envisioned for this technology. These include the creation of contact lens-mounted information displays and full-field scene projection as a means of facilitating total immersion virtual reality. It seems that contact lenses may have a very interesting future. Welcome to the Holo-deck! CLS
For references, please visit www.clspectrum.com/references.asp and click on document SE2010.
Associate Professor Papas is Executive Director of Research & Development and Director of Post Graduate Studies, Institute for Eye Research and Vision Cooperative Research Centre, and Senior Visiting Fellow, School of Optometry & Vision Science, University of New South Wales, Sydney, Australia. He has received research funding from Alcon, AMO, Allergan and Ciba Vision.