THE LAST 30 YEARS
CONTACT LENSES: THE LAST 30 YEARS
Many developments and milestones have occurred in the contact lens industry over the last three decades.
DESMOND FONN, MOPTOM, & DEBORAH SWEENEY, PHD
When Contact Lens Spectrum published its first issue in 1986, the contact lens industry was entering a period of significant evolution and growth. In the 1980s, Otto Wichterle’s innovative development of hydrogel biomaterials, combined with patients’ desire for a convenient and comfortable alternative to glasses and polymethyl methacrylate (PMMA) lenses, resulted in a surge of contact lens fittings, not only for daily wear, but also for extended and even continuous wear modalities. By 1989, it was estimated that there were 13 million wearers of hydrogel contact lenses in the United States alone, with approximately 4 million wearing soft lenses on an extended wear basis (Poggio et al, 1989).
Research then began to emerge that hydrogel lenses, including those in higher-water-content materials, compromised corneal physiology. Over the next decade, the development of high-oxygen-permeable silicone hydrogel contact lenses helped revolutionize the industry. These lenses eliminated the effects of hypoxia during overnight wear by overcoming the major hurdle of delivering adequate oxygen permeability. The high levels of oxygen permeability, however, did not significantly impact the rate of microbial keratitis with extended wear.
At the same time, issues with inflammation and care solution compatibility arose as silicone hydrogels were developed for daily wear use. Multipurpose lens care solutions dominated the market in the 1990s. In the next decade, outbreaks of Fusarium and Acanthamoeba keratitis were associated with use of multipurpose solutions. In part as a consequence, daily disposable lenses, which had been on the market in hydrogel lens materials for about a decade, were developed in silicone hydrogel.
Research efforts are now concentrated on trying to understand the remaining major impediments to contact lens wear and further growth of the market: namely lens discomfort and ensuring that all refractive errors, including presbyopia, can be fully corrected with contact lenses.
The last decade has also witnessed the growing understanding that myopia is occurring at epidemic levels. Efforts to find optical solutions, as opposed to drug interventions, have revealed novel solutions developed through a better understanding of what controls the development of a myopic eye.
Silicone hydrogel lenses now dominate the contact lens market and, as noted above, now include not only daily disposables, but also advanced toric and multifocal designs. This article will explore each of these milestone eras.
THE PROS AND CONS OF HYDROGELS
The 1980s saw a rapid rise in the number of soft lenses fit. In the early ’70s, it was estimated that half of all lenses prescribed were hydrogels, and this rose to 90% by 2000 (Ibrahim et al, 2009). The U.S. Food and Drug Administration (FDA) cleared the use of hydrogel contact lenses for extended wear in 1981, and it was estimated that there were close to 4 million wearers by the mid-1980s (Poggio et al, 1989). While the market was expanding, pioneering research studies of the late ’70s were building a case around some potential limitations of the hydrogel materials of that time and around safety issues with contact lens wear, particularly with extended and continuous wear modalities (Sarver, 1971; Polse et al, 1975; Harris et al, 1975; Ruben, 1976).
The landmark study by Holden and Mertz (1984) (Figure 1) established that to match the overnight edema with no lens wear, measured by Mertz (1980) to be 4%, contact lenses must have an oxygen transmissibility (Dk/t) of at least 87. La Hood et al (1988) and later du Toit et al (2003) established the overnight edema without lenses to be 3.2%, resulting in a revised minimum Dk/t of 125 for edema-free overnight wear. The Holden and Mertz research also specified the minimum oxygen transmissibility (24) required to avoid excessive levels of corneal edema during daily wear, setting the benchmarks for oxygen requirements for successful corneal oxygenation during contact lens wear.
Figure 1. Brien Holden and George Mertz.
The Gothenburg Study (Holden, Sweeney et al, 1985) examined the long-term effects of extended contact lens wear on the anterior eye and noted that all layers of the cornea were adversely affected. Even after cessation of lens wear, polymegethism and stromal thickness did not return to a normal level (Holden, Vannas et al, 1985). These studies were further confirmation of the earlier work of Carney and Bailey (1972), which had shown that hydrogels could cause significant edema even when worn on a daily wear basis.
The Gothenburg Study also provided insights into how these significant physiological changes could be minimized, if not avoided: contact lens materials should provide higher oxygen transmissibility, and lenses needed to be more mobile, more frequently removed, and more regularly replaced.
The largest concern for practitioners, however, was the safety of hydrogel lenses when worn overnight. In 1989, the FDA issued a statement to eyecare practitioners to limit extended wear of soft contact lenses to seven consecutive days from the previously cleared 30 days. This followed the initial reports of microbial keratitis (Ruben, 1976; Zantos and Holden, 1978) with overnight wear of hydrogels and the seminal study of Poggio et al (1989) that indicated a five-fold increased risk of microbial keratitis for extended wear compared to daily wear of hydrogel lenses. These complications and safety issues drove the search for the next generation of contact lens materials that could meet the requirements of the Holden and Mertz criteria and the recommendations of the Gothenburg Study while providing the convenience that patients desired.
SILICONE HYDROGELS: THE NEXT REVOLUTION
Silicone elastomer lenses provided more than adequate oxygen, as the levels of overnight edema with these lenses were significantly less than with no lens wear (Sweeney and Holden, 1987). However, despite this promising result, they were far from a success. Silicone elastomer lenses were associated with reports of discomfort, poor wettability, excessive lipid deposits, and lens binding (Mannarino et al, 1985).
A truly revolutionary material was required, and as summarized by Tighe (2000), many unsuccessful attempts had been made to combine the oxygen permeability of silicone with the “softness” and the fluid and ion transport benefits of hydrogels. However, in the 1990s, techniques were developed that were able to limit the phase separation of the components to produce optically clear materials. The first two innovative materials, with oxygen transmissibility of up to four to six times that of traditional hydrogels, were released in Australia, Canada, Europe, and the United States in 1999. The FDA later cleared Ciba Vision’s Focus Night & Day and Bausch + Lomb’s PureVision contact lenses for continuous wear in 2001.
Results from short- and long-term extended wear clinical trials with these high-Dk silicone hydrogel lenses demonstrated that the typical physiological changes associated with traditional low-Dk contact lenses did not occur (Dumbleton et al, 1999; Stern et al, 2004; Jalbert et al, 2004). One of the more unexpected findings relating to avoiding hypoxia was that limbal redness was significantly reduced in patients wearing high-Dk silicone hydrogel contact lenses (Papas et al, 1997). Through a series of goggle studies, it was determined that the increased limbal redness response occurred as a result of hypoxia acting directly on the limbal region rather than as an indirect consequence of corneal swelling (Papas, 1998).
The benefits of silicone hydrogels have been perhaps best summarized in a prospective masked assessment conducted by Covey and colleagues (2001). One group of subjects wore high-Dk silicone hydrogels on a continuous wear basis for an average of nine months, and the other were non-lens wearers. The markers of corneal hypoxia, namely corneal vascularization, limbal and bulbar redness, number of epithelial microcysts, and endothelial polymegethism, were not significantly different for the two groups. As a consequence of these benefits, in the past 15 years, a significant proportion of new contact lens fits have been with silicone hydrogels, although many hydrogels are still available on the market today (Figure 2).
Figure 2. Percentage of monthly replaced lenses fit—hydrogels versus silicone hydrogels.
WHAT OXYGEN COULD NOT DELIVER
The hypothesis and anticipation was that the higher levels of corneal oxygen delivery would achieve more than eliminating the physiological consequences of hypoxia. The benefit of higher oxygen levels and a healthier epithelial layer was hoped to translate to significantly lowering if not eliminating the rate of corneal infections associated with overnight lens wear (Holden et al, 2003).
Disappointingly, incidents of microbial keratitis began to be reported with the release of silicone hydrogel lenses (Lim et al, 2002; Schein et al, 2005). Studies by Stapleton and colleagues (2008, 2013) determined that the risk of infection with 30 continuous nights of silicone hydrogel lens wear was equivalent to six nights of hydrogel lens extended wear; perhaps more importantly, the rate of vision loss due to corneal infection with silicone hydrogel contact lenses was similar to that with hydrogel lenses. They hypothesized that the lack of change in the absolute risk of disease suggested that exposure to a large number of pathogenic organisms overcame any advantage from eliminating the hypoxic effects of contact lenses.
Unfortunately, several reports also demonstrated that extended wear of silicone hydrogel materials did not reduce inflammatory adverse events, and there was also an increase in mechanical events such as contact lens papillary conjunctivitis (CLPC) and superior epithelial arcuate lesions (SEALs) (Carnt et al, 2002; Szczotka-Flynn and Diaz, 2007; Chalmers et al, 2012). As a consequence, silicone hydrogel lenses were increasingly prescribed for daily wear use, and new-generation silicone hydrogel lenses were developed specifically for this modality.
The first-generation extended wear materials had high oxygen transmissibility, low water content, and were relatively stiff (high lens modulus), but second-generation lenses incorporated internal wetting agents. These lenses were higher in water content and lower in modulus. Third-generation products also had decreased modulus and higher water content, but they broke the traditional inverse relationship between Dk and water content by having a higher Dk than what the water content would predict and by being inherently wettable silicone hydrogel materials.
DAILY WEAR DEVELOPMENTS
During the silicone hydrogel lens revolution, daily wear prescribing underwent a parallel revolution in which frequent replacement regimens became routine. Soft lenses initially were replaced only when damaged, lost, or spoiled, which resulted in replacement intervals as long as two or three years. In the mid-1980s, the concept of planned or frequent replacement for soft contact lenses emerged. Reduced lens deposition and the consequential improvement in many facets of clinical performance, particularly the reduction of conjunctival papillary changes, resulted in widespread adoption of monthly, two-week, and weekly replacement options for daily and extended wear (Kotow et al, 1987; Grant at al, 1989, Pritchard et al, 1996).
Prior to the release of silicone hydrogel lenses in the late ’90s, it was estimated that there were approximately 70 million contact lens wearers worldwide; but within two decades, that number amazingly increased to approximately 140 million (Nichols, 2015). Close to 75% of all soft contact lens fits are with silicone hydrogel lenses (Efron et al, 2015), and more than 80% of silicone hydrogels are prescribed on a daily wear basis (Morgan, 2016) (Figure 3).
Figure 3. Use of silicone hydrogel materials for extended and daily wear.
Notwithstanding the increase, prescribing silicone hydrogel lenses for daily wear posed further problems. Contact lens care regimens had been developed for traditional hydrogel lenses, and for some patients, certain components of these care regimens resulted in corneal staining when used with silicone hydrogel materials (Jones et al, 2002; Carnt et al, 2007). There are divided opinions about the clinical relevance of this staining. Hydrogen peroxide systems, new formulations of multipurpose care solutions, and the development of silicone hydrogel daily disposable lenses appear to have reduced this problem.
Of much greater concern were the outbreaks of Fusarium and Acanthamoeba keratitis during the first decade of the 21st century (Saw et al, 2007; Tu and Joslin, 2010). These infections were associated with certain multipurpose disinfecting solutions, necessitating their recall, but patient noncompliance was also implicated (Tu and Joslin, 2010).
The other great nirvana for contact lens wearers and practitioners alike is comfort, especially at the end of the day. Although not a safety issue, discomfort continues to limit the number of contact lens wearers and is the major contributor to the significant numbers of dropouts from contact lens wear (Pritchard et al, 1999). This enigma has plagued the industry for the last three decades, and while some patients’ end-of-day discomfort may be remedied, there is general agreement that the etiology of discomfort remains unresolved (Dumbleton et al, 2008; Jones et al, 2013; Guillon, 2013).
Daily disposable hydrogels were launched in the early 1990s. The modality has grown steadily since that time—particularly in Europe, but now globally (Efron et al, 2013) as the benefits of avoiding routine lens care and maintenance requirements and for part-time wear are evident. For practitioners, daily disposables eliminate the issues of solution-lens interactions, while reducing risks of infection, deposits, and complications (Dumbleton et al 2009, 2010; Morgan et al 2009; Solomon et al, 1996). Although compliance should be easier with this modality, studies have indicated that patient noncompliance (reuse, often without solutions) can be an issue (Dumbleton et al, 2009) and can have serious consequences (Stapleton et al, 2012).
Silicone hydrogel daily disposable lenses were introduced in 2008 and provided the additional physiological benefits of higher oxygen transmissibility. These were proclaimed to be revolutionary, for although all are siloxane-based, they all have unique properties and/or use revolutionary manufacturing technology (Griffiths 2009; Draper et al, 2013; Dunn et al, 2013) to ensure improved surface lubricity (low friction) along with reduced modulus.
A study by Morgan and colleagues (2013) compared neophytes who wore daily disposable silicone hydrogel lenses to non-lens-wearing controls. After one year, bulbar and limbal hyperemia were clinically equivalent between the silicone hydrogel daily disposable lens wearers and the non-wearing controls, confirming their physiological benefits.
A more recent study by Chalmers et al (2015) reported that there was no significant difference in the rate of adverse events between hydrogels and silicone hydrogels when used on a daily disposable basis (0.4% per year for silicone hydrogels lenses and 0% per year for hydrogels). These rates are significantly lower compared to the rates reported for reusable lenses, and they support the safety of the daily disposable modality. Silicone hydrogel daily disposable lenses have recently been introduced in sphere, toric, and multifocal designs, resulting in a considerable increase in the use/prescribing of daily disposable lenses made from these materials (Efron et al, 2013) (Figure 4).
Figure 4. Use of silicone hydrogel materials for monthly and daily replacement.
TORICS AND MULTIFOCALS
The phenomenal improvement in toric soft lenses and their consequential growth in market penetration over the last two decades has primarily resulted from computer-controlled manufacturing capabilities coupled with extraordinarily imaginative lens designs. The same can be said for multifocal soft lenses, but the comparative growth of the presbyopic contact lens market has been disappointingly low for what is the fastest growing demographic of the world’s population.
Two studies spanning about 40 years agreed that approximately 33% of potential contact lens wearers require astigmatic correction (Holden et al, 1975; Young et al, 2011). Two separate surveys from 2015 indicate that 25% of toric lenses prescribed are soft torics (Nichols, 2016; Morgan et al, 2016). This demonstrates that soft toric lenses are accepted internationally (with a few exceptions) as the optimal mode of correction for astigmatic patients who require single-vision lenses. This is a testament to the better optics, improved stability, wide range of stock parameters, improved manufacturing accuracy, and reproducibility of these lenses today.
Simultaneous vision or, more correctly, simultaneous image-producing multifocal or bifocal soft contact lenses were designed because it was difficult for soft bifocal contact lenses to successfully translate (move) on the eye with predictable success. During the mid-to-late 1980s, concentric and diffractive bifocal contact lenses were modestly successful, but for the next 10 years, single-vision monovision was the system of choice (Back et al, 1989; 1992).
That ratio changed in the mid-1990s, with innovative designs and sophisticated manufacturing capabilities enabling production of lenses at considerably reduced cost, resulting in frequent replacement lens options. Practitioners became much more confident and willing to fit these simultaneous image lenses even though image quality and subjective vision for some patients was compromised. Fast forward to the 21st century, and multifocal lenses are the lens of choice over monovision; Efron and colleagues (2015) documented survey results of practitioners in the United States from 2002 to 2014 that demonstrate clearly the preference for multifocal contact lenses. The most recent survey reported by Nichols (2016) confirms this trend, finding that 48% of contact lens-wearing presbyopes are prescribed multifocals, compared to 31% fit with monovision.
Although it appears that multifocals are now the contact lens of choice, the survey conducted by Contact Lens Spectrum indicated that only 14% of all contact lenses prescribed are soft lens multifocals, with about 2% GP multifocals (Nichols 2016). These values have changed little in the last four years, so a “miraculous” lens design change is needed for the ever-growing presbyopic demographic.
GP LENSES, ORTHOKERATOLOGY, AND THE RE-EMERGENCE OF SCLERAL LENSES
GP lenses have been available for daily wear since the mid-1970s, and some GP materials received FDA clearance for extended wear in 1986. It was again polymer chemistry developments that resulted in fluorosilicone-acrylate and styrene-based materials that enhanced the oxygen permeability of GP lenses.
Despite their low rates of inflammatory complications (Polse et al, 2001), these lenses still represent only a small proportion of the contact lens market (Nichols, 2016) primarily due to comfort issues, although they do offer superior vision due to their great optics.
Although orthokeratology (ortho-k) was used on a daily wear basis beginning in the 1960s, the new high-Dk GP materials allowed the concept to be coupled with overnight wear in new reverse geometry designs, enabling corneal reshaping to re-emerge with some success. The technique with overnight wear is particularly effective for low myopes, controlling refractive error within a week with good predictability (Swarbrick, 2006). Unfortunately, reports of microbial keratitis have created concern about this procedure, again pointing to the risk of overnight wear (Bullimore et al, 2013).
The last decade has seen the use of large-diameter GP lenses: corneo-scleral (<15mm diameter lenses partially supported by the cornea) as well as mini-scleral (up to 6mm larger than the horizontal visible iris diameter [HVID]) and full scleral (greater than 6mm larger than the HVID) (www.sclerallens.org) lenses supported only by the conjunctiva, aimed to vault the cornea.
Although fitting rates remain low on a relative basis, this is arguably one of the fastest growing segments of the contact lens market. As well as offering options to restore and protect the ocular surface, these designs are being used to correct moderate-to-high spherical refractive errors as well as moderate-to-high regular and irregular astigmatism and presbyopia, as they offer some improvements in comfort over traditional-sized GPs (van der Worp et al, 2014).
THE MYOPIA EPIDEMIC AND MYOPIA CONTROL
A significant change in the last 30 years has been the rising prevalence of myopia. In many parts of Asia, particularly East Asia, more than 70% of teens and young adults are near-sighted (Lee et al, 2015; Wu et al, 2015). The prevalence is not equally high elsewhere, but myopia has increased—or is on the rise—in other parts of the world, with approximately half of young adults in the United States and Europe representing a doubling of the prevalence of half a century ago. Holden and colleagues (2014, 2016) have projected that 2.2 billion people could be affected by myopia by the end of this decade; by 2050, this figure will soar to 4.8 billion, afflicting half of the world’s population.
In addition to the increasing prevalence, perhaps of greater concern is the increase in the magnitude of myopia, with increasing numbers of individuals reaching high myopia (–5.00D or more) and the subsequent risk of retinal pathology (Wu et al, 2015).
Anti-muscarinic drugs, such as atropine, can significantly slow myopia progression (Chia et al, 2012). However, concern about drug interventions and possible long-term side effects when used with children spurred many researchers to seek alternative approaches to control the progression of myopia.
Contact lenses today are prescribed more frequently to children and young teens as a result of studies that have demonstrated improved self-image and self-worth in children, allowing them to both see and feel better (Walline et al, 2009). Traditional design soft and GP contact lenses are not effective in slowing myopia progression. Reverse geometry ortho-k lenses are moderately effective in decreasing the progression of myopia in the short-term (two years) (Cho et al, 2012). Studies using novel peripheral myopic defocus-correcting soft contact lenses show that they slow the progression of myopia with a 30% to 70% efficacy (Sankaridurg et al, 2015; Aller et al, 2016).
There are other meritorious contact lenses, events, organizations, and serendipitous consequences that have occurred over the last 30 years. The various new cosmetic and hybrid lenses were ingenious inventions even though they represent a very small portion of the market. The world contact lens market is now estimated to be worth $7.5 billion (Nichols, 2016).
Even though it was startling for practitioners, some would say it was inevitable that alternative sources, such as Internet purveyors, would begin selling contact lenses. The market was relatively small and undeveloped during the mid-’80s. The realization that growing the market was dependent on education created a slew of educational organizations and research societies with significant interest from the contact lens companies in those endeavours.
The last 30 years have been glorious for so many more patients, clinicians, and scientists. The hope is that momentum will continue even though mergers have significantly reduced the number of large companies. CLS
For references, please visit www.clspectrum.com/references and click on document #250.
Dr. Fonn is distinguished professor emeritus, School of Optometry and Vision Science, University of Waterloo, Ontario, Canada. He is also a consultant/advisor to CooperVision.
Prof. Sweeney is Pro vice-chancellor Research and Innovation at the Western Sydney University. Her major research interests include corneal physiology, effects of contact lens wear and refractive surgery on the cornea, and alternate forms of vision correction..