Contact lens extended wear (EW) offers the potential convenience of (a) not having to insert, remove, and maintain lenses on a daily basis, and (b) sharp vision at any time, including when awoken during the night or first thing in the morning.1 The term “extended wear” has evolved to mean the continuous wear of contact lenses, day and night, for up to 30 days, after which time the lenses are discarded and a new pair of lenses are inserted, with this cycle continuing.
After the introduction of hydrogel lenses onto the international market in the early 1970s, various industry-driven attempts have been made to launch EW as a mainstream contact lens option. The first lens promoted for EW was the Permalens (CooperVision, Pleasanton, CA), which entered the market in the late 1970s.2 This was in the era that preceded regular lens replacement (disposable lenses). It was suggested at the time that Permalens contact lenses could be worn continuously for many months or even years, day and night, until they became uncomfortable or there was some other clinical need to remove or replace them.3 This concept failed as a result of an unacceptably high rate of ocular adverse reactions.4
Johnson & Johnson Vision Care (Jacksonville, FL) introduced the original Acuvue lens into the market in the late 1980s,5 with the suggestion that 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. The notion of disposability was well accepted; however, practitioners preferred fitting these lenses for daily wear (DW), probably as a result of the negative experiences relating to previous problems fitting the Permalens and similar products for EW. Reports also began to emerge highlighting adverse ocular reactions with the EW of Acuvue lenses.6,7 As well, two important epidemiological studies were published in the late 1980s documenting the increased incidence of ulcerative keratitis with EW lenses.8,9
Researchers soon demonstrated that a major problem with the original Permalens and Acuvue lenses was the lack of sufficient corneal oxygenation during closed-eye lens wear10,11 to allow normal corneal metabolism.12 This problem was resolved in 1999 with the introduction of highly oxygen permeable silicone hydrogel contact lenses.13 The silicone hydrogel lenses that were launched at the time—PureVision (Bausch & Lomb, Rochester, NY) and Focus Night & Day (CIBA Vision, Atlanta, GA)—were originally promoted for 30 days EW; however, just as occurred with the launch of the Acuvue lens, many practitioners preferred fitting these lenses for DW only. In 2004, silicone hydrogel lenses specifically designed and promoted for DW were released into the market.
Scant data exist in the scientific literature on the rate of prescribing EW lenses over the past 40 years. Available data include a series of single-year surveys spanning 13 years, conducted in Australia over 20 years ago, which indicate that EW ranged between 2 and 15% of all contact lenses fitted in that country between 1976 and 1989.14–16 Here, we examine trends in EW contact lens prescribing over the past 14 years (1997–2010) and undertake a detailed analysis of contemporary world-wide prescribing of this modality over the past 5 years (2006–2010).
Conduct of the Annual Survey
Between January and March each year from 2006 to 2010, a survey was undertaken in 39 countries. This was achieved through the offices of members of the International Contact Lens Prescribing Survey Consortium, which is a network of academics, industry representatives, and clinical colleagues who have agreed to manage the survey in their country or geographic region, as outlined below.
In each country, a paper or electronic (e-mail) survey form was sent to up to 1000 contact lens practitioners (opticians, optometrists, and/or ophthalmologists, depending on the market). In some countries, such as Australia, survey forms were sent to virtually every practitioner in the country. In other countries, such as the United Kingdom, survey forms were sent to a selection of practitioners throughout the country; this process varied among countries, ranging, for example, from a computer-generated random list from the national practitioner register in the United Kingdom to list of practitioner prescribers to contact lens trade publications in the United States and Russia. In large countries with dispersed populations, such as China and Russia, survey forms were sent to practitioners in a select number of major urban cities. The survey forms were sent along with a request that they be completed and returned within 3 months of receipt. Although there is no clear evidence for seasonal variation in the types of contact lenses prescribed, the survey was conducted at approximately the same time of year to minimize any possible seasonal effects.
The same survey format was used each year, as published previously.17 This survey was a one-sided form, on which practitioners were requested to enter a number of background details and to supply generic information about the first 10 contact lens fits performed after receipt of the survey form. Practitioners were asked to return the form irrespective of the number of patients seen (if fewer than 10). The information gathered about lenses and care systems is detailed in Table 1. The returned forms were logged and data from each form were manually entered into an Excel (Microsoft Corporation, Redmond, WA) spreadsheet to facilitate data analysis.
The Office of Research Ethics at the University of Waterloo, Canada, advised that, as the data being collected were (1) part of normal practice care provision, (2) transcribed from the practice patient records, and (3) deidentified in respect of the patients, then the requirement for patient informed consent was waived.
Although this paper reports a detailed analysis of survey data collected between 2006 and 2010, we have been collecting information on EW fitting every year since 1997, initially in the United Kingdom (1997–1999) and then gradually increasing the number of countries surveyed since 2000. To illustrate trends in EW prescribing between 1997 and 2010, the proportion of EW soft lenses prescribed in all countries each year during this period was determined.
Differences among practitioners in relation to the amount of contact lens fitting performed were taken into accounted by assigning an appropriate weighting to each recorded contact lens fit. This was achieved by estimating the number of contact lens fits performed each year by each respondent (based on the date information provided on the survey form) and using this as a weighting factor. For example, the data generated by a practitioner completing all 10 fits in 1 week were given twice the weighting of a practitioner who fitted 10 patients in 2 weeks.
Data were mined with the aid of the Excel Pivot Table function. Statistical analysis of differences was conducted using logistic regression models (JMP, SAS Institute, Cary, North Carolina) for soft lens fits. A separate linear regression analysis was undertaken to evaluate the relationship between the proportion of silicone hydrogel EW fits (as a function of all EW fits) vs. the gross domestic product at purchasing parity per capita for year 2010. Wilson's method was used to determine 95% confidence limits.18,19
During the 5-year survey period (2006–2010), data about lens modality were collected in relation to 107,094 rigid and soft lens fits, of which 88,392 were for soft lens DW and 7470 were for soft lens EW. The median country response rate was 1345 fits (range from 59 fits in Nepal to 22,802 fits in Japan). The number of fits recorded in each country between 1997 and 2010 is shown in the Appendix (available online at https://links.lww.com/OPX/A72). EW represented 7.8% of all soft lens fits; however, there was considerable variance in EW fitting among the 39 countries surveyed, ranging from 0.6% in Malaysia to 27% in Norway (Fig. 1).
The mean age (±SD) of those fitted with EW lenses (32.7 ± 13.6 years) was greater than for DW lenses (29.4 ± 12.0 years;χ2 = 87.0, p < 0.0001). Males were over-represented among those wearing extend wear lenses; specifically, males represented 41% of all those wearing EW lenses vs. only 32% of those wearing DW lenses (χ2 = 180.9, p < 0.0001).
The ratio of new fits to refits was 27:73 for EW and 34:66 for DW (χ2 = 101.3, p < 0.0001). Silicone hydrogel lenses were used for 72% of EW fits (the balance being conventional hydrogel materials; Fig. 1); this compared with silicone hydrogel lenses representing 30% of DW fits (χ2 = 2605.8, p < 0.0001).
The proportion spherical, toric, presbyopic, and other designs used for EW and DW fits is shown in Fig. 2. The distributions of designs used for these two modalities of wear were significantly different (χ2 = 130.3, p < 0.0001). The proportion of spherical and presbyopia designs were higher for EW fits (71 and 10%) compared with DW fits (68 and 7%).
Data for the replacement frequency recommended by practitioners for EW and DW lenses are presented in Fig. 3; these distributions were significantly different (χ2 = 2127.1, p < 0.0001). The proportion of monthly replacement lens fits was far greater for EW (66%) compared with DW (40%).
Fig. 4 shows the proportion of care systems used (or not used) for EW and DW; these distributions were significantly different (χ2 = 1406.9, p < 0.0001). Eighty percent of those wearing EW lenses use multipurpose solutions, whereas 9% do not use any care system.
The trend in EW fitting in all countries surveyed between 1997 and 2010 is displayed in Fig. 5. Between 1997 and 1999, the rate of EW prescribing decreased from 5 to 1% of all soft lens fits. It then increased to a peak of 12% in 2006, and then settled back to 8% by 2010. The proportion of silicone hydrogel EW fits (as a function of all EW fits) was positively related to the gross domestic product at purchasing parity per capita for year 2010 (r2 = 0.51, F = 6.7, p = 0.014; Fig. 6).
Interpretation of the statistical findings of this survey needs to be placed in the context of the very large data set analyzed. Even small numeric differences in the percentages presented are likely to be “statistically significant,” because this outcome is directly related to sample size. Thus, although a given difference or change might be statistically significant, we need to consider the broad implications of our findings. For example, the global contact lens market is worth an estimated U.S. $6 billion at retail values.20 Therefore, a global difference in prescribing EW of, say, 1% would have a potential fiscal impact of $60 million, which is a meaningful shift. However, from a clinical perspective, such a small change may not necessarily influence practitioner perceptions or behavior.
There are many possible reasons for the difference between nations with respect to the extent of EW contact lens fitting. Differences may exist between nations with respect to the training, attitudes, and collective confidence of the predominant practitioner groupsa—opticians, optometrists, and ophthalmologists—in relation to EW fitting. Differences in the extent and nature of commercial and professional promotion of EW may also influence the volume of EW contact lens prescribing in different regions. Access to therapeutics has little apparent impact on EW prescribing; for example, Japan, where virtually all contact lenses are prescribed by ophthalmologists, has the third lowest rate of EW prescribing (1%), whereas the United States, in which most contact lens practitioners are able to prescribe therapeutics, has a much higher EW prescribing rate (10%). Differences between nations with respect to the likelihood of litigation arising from clinical problems because of EW may also impact on the uptake of this modality.
There will also be variations in EW prescribing in different regions of the world, and even within some large countries, relating to socioeconomic factors and levels of public awareness of eye care. For example, in China, the provision of contact lenses and associated eye care in large urban centers, with ready access to large hospitals and other forms of sophisticated urban infrastructure, is likely to be very different from that in remote, rural areas. In some parts of East Asia, standards of contact lens care possibly lag behind those in the western world.
We speculate that the relatively high rate of EW fitting in Australia, which is largely with silicone hydrogel lenses, is attributed to the fact that much of the initial trial work for silicone hydrogel EW lenses was conducted in that country. This activity generated considerable interest among local practitioners, who were apparently keen to try out these new products as soon as they became available. However, the low rate of EW fitting in Japan may be linked to the belated release of silicone hydrogel lenses in that country, primarily as a result of stringent regulatory constraints and resultant delays in obtaining approvals to launch these products. Additionally, Japanese contact lens fitters—who are primarily ophthalmologists—may harbor more conservative attitudes and concerns relating to the ocular health risks of overnight lens wear.8,9,21,22
The higher age at which people are fitted with EW lenses could be attributed to a variety of factors. The strategy of fitting patients with DW lenses before moving on to EW has the advantage of familiarizing them with lens handling and lens maintenance procedures, resulting in a higher age when EW is commenced. In view of the known increased ocular health risks associated with EW generally,8,9,21,22 practitioners may prefer to fit such lenses to more mature (and therefore older) patients who would perhaps better understand the risks and responsibilities involved in overnight wear and be more likely to adopt a more sensible approach to solving any problems that arise during wear. A higher age might also be associated with a higher disposable income and less resistance to purchase the more expensive EW option.b
The reason for the over-representation of males being fitted with EW lenses is unclear but could relate to gender differences in lifestyle. More males are involved in sport23,24 and may prefer the convenience of EW when engaging in such activities.
The greater tendency for EW lenses to be dispensed as a refit could be explained by a preference of practitioners for lens wearers to first become accustomed to the lens handling and maintenance rituals of DW before progressing to EW. Practitioners also may be interested in gauging the ocular response to DW, which can serve as a baseline reference against which any adverse reactions to subsequent EW can be measured. The higher proportion of EW lenses prescribed as refits is commensurate with the necessarily higher age of those fitted with EW (as discussed above).
The majority of lenses prescribed for EW are made from silicone hydrogel materials. There is disagreement in the literature as to whether lenses made from these materials reduce the risk of severe microbial keratitis with EW compared conventional hydrogel lenses.8,9,21,22 Nevertheless, the superior oxygen transmissibility of silicone hydrogel lenses5 is known to alleviate hypoxic ocular complications—such as corneal edema, stromal neovascularization, and endothelial polymegethism25—which can be more pronounced with extended lens wear because of reduced oxygen availability beneath the closed eyelid during sleep.26 Therefore, the health benefits of silicone hydrogel lenses for closed-eye lens wear demand that EW patients are only fitted with this lens type.
It is somewhat disappointing to observe that 28% of EW fits were with conventional hydrogel lenses. A possible reason for the continued use of conventional hydrogel lenses for EW is their lower cost. If this were to be the case, greater use of conventional hydrogel lenses may be observed in poorer countries. Our demonstration of a lower rate of prescribing silicone hydrogel lenses for EW in nations with a lower gross domestic product at purchasing parity per capita tends to support this hypothesis.
The finding that a higher proportion of presbyopic designs are fitted for EW compared with DW is commensurate with the observation that those wearing EW lenses are slightly older. The lower rate of prescribing toric lenses for EW (14%) vs. DW (19%) may relate to clinical considerations of the oxygen performance of these lenses. Toric lenses have regions of increased thickness to mediate in-eye orientation. The oxygen transmissibility in these thicker regions is reduced,27 which may be problematic in EW in view of already reduced corneal oxygen availability during closed eye lens wear.26 For this reason, practitioners may prefer to prescribe thinner spherical designs, thus avoiding fitting toric lenses for EW at the expense of vision decrement resulting from a degree of uncorrected astigmatism. Throughout our survey period (2006–2010), there has been a progressive increase in the number of silicone hydrogel toric lens designs introduced into the market, which could also explain why the total proportion of toric lenses fitted is lower for EW (which are predominantly made from silicone hydrogel materials) than for DW.
The majority of EW lenses are prescribed for monthly replacement. This perhaps reflects lens availability at the time of our survey, whereby monthly replacement lenses have dominated the market in respect of lenses that are suitable for EW.28 It is unclear why 2.5% of EW fits were designated as daily replacement. This could be due to the occasional use of daily disposable lenses for 24 h (e.g., one day and one night) as a social convenience, a practice that would be contrary to the recommendations of manufacturers and most practitioners.29
Eighty one percent of those wearing lenses on an EW basis use some form of care solution. This indicates a need among most EW patients for occasional lens removal and subsequent maintenance and storage between scheduled lens disposal time points. The majority of patients use multipurpose solutions. The rate of use of hydrogen peroxide with EW is greater than for DW, possibly because of the perceived superior antimicrobial efficacy of hydrogen peroxide systems.30 Those who do not use lens care solutions (a) are generally able to wear lenses continuously for the full-designated lens wear replacement frequency interval, (b) replace lenses whenever a problem occurs (e.g., sudden discomfort), which may be sooner than the scheduled lens replacement time point, or (c) are non-compliant, e.g., using tap water to rinse lenses that need to be temporarily removed.
An Historical Perspective
The contact lens industry launched silicone hydrogel contact lenses onto the market around the turn of the century with the recommendation that they be worn exclusively on an EW basis. Market penetration of EW increased dramatically between 1999 and 2003, before levelling off from 2003 to 2007, and declining slightly thereafter. The slowing down of EW prescribing in the mid-2000s is possibly because, at least in part, of the introduction in 2004 of silicone hydrogel lenses specifically designed and promoted for DW.
A key factor that is likely to influence the prescribing of EW lenses is the perceived safety of this modality. Numerous epidemiological studies have addressed this issue, as outlined above. The muted world-wide prescribing of silicone hydrogel lenses for EW suggests that practitioners and lens wearers generally judge the health risks of this modality to outweigh the potential benefits.
Despite the obvious benefits of lifestyle convenience offered by the EW modality, and the enhanced biocompatibility of silicone hydrogel lenses that are available for this purpose, it appears that practitioners still prefer to prescribe, and patients prefer to wear, contact lenses for DW. Throughout the 40-year history of soft lenses, repeated efforts at promoting EW by the contact lens industry have failed to result in this modality exceeding a global average “glass ceiling” prescribing rate of about 15%. EW is unlikely to become the mainstream lens wearing modality until the already low risks of severe keratitis with this modality (around 20 cases per 10,000 wearers/yr9,21,22) become equivalent to that for DW (around four cases per 10,000 wearers/yr9,21,22). In the mean time, if contact lenses are to be fitted to a patient for EW, then silicone hydrogel lenses are the preferred option in view of their superior oxygen performance compared with conventional hydrogel lenses.
The International Contact Lens Prescribing Survey Consortium
Nathan Efron, Australia; Philip B. Morgan, United Kingdom; Craig A. Woods, Canada; Suresh Awasthi, Nepal; Joseph T. Barr, U.S.; Vadim Belousov, Russia; Jolanta Bendoriene, Lithuania; Aris Chandrinos, Greece; Byoung Sun Chu, South Korea; Nir Erdinest, Israel; Philip Fine, Israel; Martha Y Gonzalez, U.S.; José Manuel González-Méijome, Portugal; Hans-Jürgen Grein, Germany; Christina N. Grupcheva, Bulgaria; Jorgen Gustafsson, Sweden; Magne Helland, Norway; Hreinn Ingi Hreinsson, Iceland; John C. J. Hsiao, South Korea; Lee Kai Hung, Singapore; Motozumi Itoi, Japan; Deborah Jones, Canada; Razmig Knajian, Lebanon; Carla J. Mack, U.S.; Florence Malet, France; Edoardo Marani, Italy; Sebastian Marx, Germany; Giancarlo Montani, Italy; Jason J. Nichols, U.S.; Alex Ong, Singapore; Alice Pesinova, The Czech Republic; Geraint Phillips, New Zealand; Simona Radu, Romania; Ole Ravn, Denmark; Svend-Erik Runberg, Denmark; Jacinto Santodomingo, Spain; Mirna Stabuc Silih, Slovenia; Kah-Ooi Tan, Singapore; Inga-Lill Thunholm-Henriksson, Sweden; Ioannis G. Tranoudis, Greece; Eef van der Worp, The Netherlands; and Edit Vodnyanszky, Hungary.
School of Optometry
Queensland University of Technology
Kelvin Grove, Queensland 4059
e-mail: [email protected]
The appendix is available online at https://links.lww.com/OPX/A72.
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a Unregistered merchants are regrettably also involved in contact lens fitting in certain unregulated parts of the world, but this category of lens supplier was not surveyed in this work.
b Some practitioners charge a higher professional fee for fitting EW lenses in view of the additional costs relating to (a) greater chair time required for the higher frequency of follow-up visits, (b) logistical considerations (a requirement for 24-hour access), and (c) additional administration (e.g., gaining informed consent and more frequent reminders).