Extended Wear

Conventional Soft Extended Wear

The original soft lenses, designed for long-term repeated usage, are now referred to as ‘conventional’, ‘traditional’ or ‘unplanned-replacement’ hydrogel lenses to distinguish them from ‘frequent-replacement’ or ‘disposable’ lenses. Soft hydrophilic lenses were introduced around the world in the late 1960s and early 1970s as a result of the pioneering work of Wichterle. These lenses were very well received by the public, which was principally due to the comfort afforded. Contact lens sales promptly soared. But the inconvenience of caring for the lenses and the need to insert and remove them on a daily basis led to increased experimentation with extended periods of wear.

Early reports focused on the use of prolonged periods of wear for therapeutic use, particularly in aphakia. Perceived advantages included alleviation of the possible risks associated with removal and handling of lenses from diseased eyes and relief for patients with limited dexterity. The first material promoted for use in cosmetic EW was perfilcon A (Permalens, CooperVision, Rochester, NY). It was suggested at the time that this could be worn continuously, day and night, for many months or even years ( ).

Numerous studies of soft lens EW for cosmetic use soon appeared with encouraging results. The remainder of this chapter deals largely with EW lens usage for such a purpose. Following clearance by the US Food and Drug Administration (FDA) for cosmetic EW in 1981, a large proportion of contact lens prescriptions, particularly in the United States, were written for EW. An intense and exciting period of research followed during which many of the problems preventing complication-free EW were identified.

The reports of early clinical experiences with hydrogel EW lenses are too numerous to review here, but even a cursory review shows dramatic variation in quoted success rates. Such differences appear to depend upon patient selection, the type of lenses fitted, fitting approach (tight or loose), the diligence of follow-up, and criteria used by investigators in assessing the severity of adverse reactions and in the categorization of success. For example, the study of reports a success rate as high as 81% following 3 years’ of EW compared with 48% reported by . Variation in study design remains a common problem in the modern evaluation of EW success.

Despite the apparently low success rate, the retrospective study of provides good insight into the success of these trials. This article reviewed over 1000 patients entered into a number of FDA regulatory studies of EW lenses, with intended wearing times of 2–4 weeks. As noted above, nearly half (48.5%) of patients ‘survived’ EW with only minor problems for 3.5 years. Of the discontinuations, almost a third (31.3%) of the subjects did so prior to beginning EW, 16.2% were lost to follow-up, 14.5% found lens comfort inadequate, and 12% experienced ocular complications. The frequency of individual complications was as follows: injection 3.7% (of the discontinued group), abrasion 1.6%, conjunctivitis 1.4%, contact lens-related papillary conjunctivitis (CLPC) 1.4%, neovascularization 1.1%, dry eye, epithelial staining and oedema all less than 1%, and infections 0.2%.

The relative success observed in these trailblazing studies was quite astounding and provided considerable scope for optimism that relatively minor adjustments to the lens parameters would provide a safe, effective correction. By modern standards though, these studies used lenses and modalities that were grossly inappropriate for EW. The thick hydrogel lenses had oxygen transmissibility ( Dk / t ) levels that were later deemed to be inadequate. The period between lens removal was also up to 6 months in many of the early studies, and more recent research has arrived at the conclusion that this interval is too long for uncomplicated wear. But by far the greatest hazard with these early EW lenses was the emerging picture of severe complications due to infectious keratitis. A study conducted in the United States in 1987 and sponsored by the Contact Lens Institute (CLI) demonstrated that sleeping in contact lenses posed a significant risk over and above that of contact lens wear alone ( ). The adverse publicity subsequent to the publication of this study meant that EW usage decreased dramatically during the 1990s.

Nonhydrophilic Materials

The high oxygen permeability ( Dk ) of silicone elastomer led to an interest in using this material for extended contact lens wear. In the late 1970s, a number of fitting trials were undertaken. Unfortunately, the hydrophobic nature of the lens surface resulted in poor wetting and surface deposition ( Fig. 23.1 ). The highly elastic nature of the material and resistance of the material to water permeation also brought about lens binding. These factors prevented the success of this material except for limited use in the paediatric and aphakic fitting.

Towards the mid-1980s, rigid gas-permeable materials became a popular alternative to hydrogels for EW, the principal attraction being a higher Dk / t without the adverse properties of silicone elastomer. Other perceived advantages of rigid lenses over hydrogel lenses include a higher rate of tear exchange beneath these lenses, less corneal coverage and a more inert lens surface.

A considerable body of literature provided evidence for successful EW in patients using these lenses ( ). Certainly, preclinical evaluations confirmed that rigid lenses produced fewer oxygen-related physiological changes, such as corneal oedema, than hydrogels. However, there remained a range of limitations with rigid lenses for EW. Complications found with hydrogels, such as infectious keratitis, infiltrative keratitis and CLPC, were not eliminated. The elevated risk of infectious keratitis caused by sleeping in contact lenses observed with hydrogels was also evident with rigid lenses ( ). As well, rigid lenses induce a greater degree of initial discomfort than hydrogels and complications largely unseen with hydrogels, such as 3 and 9 o’clock staining, corneal distortion and lens binding.

Most practitioners have been unwilling to devote the additional time required to achieve a suitable fit and deal with patient complaints of discomfort, so rigid lenses are nowadays rarely fitted for traditional cosmetic EW. However, overnight wear of rigid lenses to achieve temporary reversal of refractive errors, known as orthokeratology, maintains a fervent, if specialized, following and has become a specialty area of contact lens practice ( Chapter 30 ).

Disposable Soft Lenses

Efficiencies of manufacture allowed Johnson & Johnson Vision Care (Jacksonville, FL) to bring low-cost disposable lenses made of etafilcon A material (Acuvue) to the US market in 1987. The original intention was that the lenses be worn continuously for 1 week at a time. At the end of each week, the lenses were to be discarded and replaced by a new set of lenses. In essence, this was a simultaneous launch of the concepts of weekly EW and lens disposability ( ).

Frequent replacement of lenses offers a range of potential advantages for increasing EW success. Practitioners perceived that the most significant problem with conventional hydrogel lenses was the build-up of surface deposits and associated complications, such as CLPC ( ). Frequent replacement restricts exposure of the eye to accumulated aged or denatured protein, which seems to act as an antigen in inducing inflammatory reactions such as CLPC and infiltrative keratitis. Control of deposit build-up by frequent replacement has the further advantage of reducing patient symptoms related to vision and comfort.

While reducing exposure of the eye to lens deposition is the outstanding advantage of disposable lenses, the regular provision of fresh, clean lenses also showed promise in other areas. There was hope that frequent lens replacement would lead to fewer bacteria being introduced to the eye, thereby reducing the risk of infectious keratitis during EW. In regard to lens maintenance, disposability offers simplification of cleaning procedures, easier lens fitting and replacement, and may serve to enhance patient compliance.

In practice, the benefits with respect to ocular physiology, symptomatology and convenience are compelling, and replacement of lenses every day to every 2 weeks to 1 month now dominates contact lens prescribing around the world ( ). Clinical studies have certainly confirmed that frequent replacement reduces the occurrence of inflammatory events during EW. Both noninfectious corneal infiltrative events (CIEs) and CLPC show reduced incidence with more frequent replacement. However, these complications are not entirely eliminated, as will be discussed further below.

The early enthusiasm for prescribing EW with disposable hydrogel lenses was not maintained. Although the CLI-sponsored study was restricted to conventional replacement contact lenses, damage to the reputation of EW had been done ( ). A number of publications reported on corneal infections in association with frequent-replacement lenses. Academics and educators delivered widespread warnings of the potential complications of EW. By and large, practitioners around the world fell in line and EW prescribing dropped to very low levels (less than 1% of fits) globally by the end of the 1990s ( ).

Moreover, despite the apparent benefits and contrary to the hopes and expectations of the contact lens industry, frequent contact lens replacement failed to achieve the desired impact on the rate of infectious keratitis. Reports in the early 1990s suggested that the frequency of infections with disposable lenses was equal to or even greater than that with conventional replacement. In a nationwide survey of ophthalmologists in the Netherlands in 1996, demonstrated that rates of infection with disposable lenses, in both daily and EW, were essentially the same as those observed in the CLI study ( ). Despite the significant advantages offered by disposability, it was evident that the industry had to look elsewhere for answers to the challenge posed by infectious keratitis with EW.

Silicone-Hydrogel Contact Lenses

With the failure of frequent-replacement hydrogel lenses to solve the EW infection problem and persistent physiological compromise to the cornea during closed-eye wear, the industry turned its attention to the development of materials with high Dk . In the late 1990s, SiHy contact lenses were introduced to the market. The details of the advances incorporated in these materials are presented in Chapter 4 . In brief, the high Dk and good handling characteristics of silicone are combined with the flexibility and comfort of hydrophilic materials. Considerable advances in technology over previously manufactured lenses were required to combine these two ostensibly incompatible materials, not the least of which was new technology to produce a wettable, deposit-resistant surface. The early lenses used plasma surface coatings, but later generations of lenses managed to circumvent the need for this additional manufacturing step.

Clinical research demonstrated that EW of SiHy lenses produces fewer physiological changes, such as microcysts, corneal striae and endothelial blebs and less limbal and bulbar conjunctival injection, than did hydrogel lenses ( ). These benefits arise from the lowered resistance of the materials to oxygen flow. SiHy lenses may also, on occasion, provide the added benefits of less corneal staining, less subjective dryness and discomfort, and better handling, owing to properties such as hydration, modulus, surface and design characteristics.

These advantages of SiHy lenses were quickly recognized and some countries such as Australia, which had previously shunned EW, enthusiastically adopted these new materials. Other countries such as the United States and the United Kingdom, following the failure of the EW foray of the 1980s, were more cautious in approach. Nonetheless, by 2006 some 12% of all contact lens fits worldwide were for EW ( ).

Although the increased corneal oxygenation afforded by SiHy lenses virtually eliminated physiological or metabolic corneal disorders during EW, epidemiological studies revealed that, despite the hopes of the contact lens community, there was little impact on corneal infection rates ( ). Alongside this reality, daily disposability was increasingly seen as a safe, relatively affordable and convenient mode of wear.

As a result of the above factors, the fitting of soft lens EW in practice has been declining throughout the 21st century. Fig. 23.2 presents data for 17 nations between 2000 and 2020 ( ). The mean of all countries is shown by the black dotted line. A gradual decline in EW fitting, commencing around 2008, is apparent. The percentage of EW fits in relation to all soft lens fits, stratified by lens material type, is shown for the year 2020 in Fig. 23.3 ( ). This graph shows that all but 5 of the 23 countries surveyed in 2020 have a prescribing rate of ≤6% of all soft lens fits. As well, the vast majority of EW fits were with silicone-hydrogel lenses.

Despite the low rate of soft lens EW being prescribed, practitioners should bear in mind the considerable proportion of patients who sleep in their contact lenses and the accompanying implications for ocular health. In one survey of soft contact lens wearers, 16% said they sleep and 63% reported napping in their lenses ( ). Further, a small number of rigid gas-permeable fits (no more than 2% of total contact lens fitting) are for EW ( ). Orthokeratology constitutes around 3% of total worldwide fits and also should be considered in discussion with EW as these lenses are worn overnight, despite being removed during the daytime ( ).

Summary

As explained, EW prescribing ‘failed to break through the “glass ceiling” of 15%’ and it is therefore no surprise that it failed to become a mainstream lens-wearing modality. The continuing EW microbial keratitis rate of around 20 per 10,000 wearers per year remains a barrier to more widespread adoption and, given the industry’s reluctance to invest in further research, we are unlikely to see the substantial expansion of the EW market in the near term. A serendipitous breakthrough in an associated technology would seem to be necessary to revive interest.