Two-Week Versus Monthly Replacement for Silicone Hydrogels
A comparison of clinical and compliance differences with these two recommended replacement schedules.
By Peter D. Bergenske, OD, FAAO, Marian Miller, & Inma Perez-Gomez, PhD, FAAO
Dr. Bergenske is currently director of Professional Support for CIBA Vision North America.
Marian Miller is manager of Claims Development in Global Professional Affairs at CIBA Vision.
Dr. Perez-Gomez is head of Professional Affairs for CIBA Vision Europe.
The vast majority of soft contact lenses prescribed by clinicians today are designed to be replaced at predetermined intervals. Soft lenses were originally worn until deposition caused discomfort or until lenses became damaged or lost. Planned, frequent disposability has significantly improved the clinical performance of soft lenses, resulting in fewer unscheduled visits and enhanced patient satisfaction. The concept of frequent soft lens replacement is well accepted by clinicians around the globe. Most are prescribed to be replaced between one day and one month, including lenses made from newer silicone hydrogel materials that now represent a major portion of soft lens new fits and refits (Morgan et al, 2008).
The popularity of these highly oxygen permeable silicone hydrogel materials has significantly reduced the number of hypoxic complications observed in both daily and overnight wear. Conditions such as microcysts, striae, limbal hyperemia, and myopic creep have essentially been eliminated for patients using these materials (Stapleton et al, 2006; Brennan et al, 2002; Jalbert et al, 2004).
Currently, U.S. practitioners fitting patients with daily wear silicone hydrogel lenses choose among lenses that the manufacturers have recommended for either two- or four-week replacement. One exception is a made-to-order, lathe-cut, silicone hydrogel lens, with a recommended replacement schedule of three months. Data from Morgan (2008, Figure 1) indicates that most silicone hydrogel lenses fit around the globe are prescribed on a monthly rather than a two-week replacement schedule.
Figure 1. Percentage of silicone hydrogel lenses prescribed for one- to two-week, one month, or longer, replacement schedule in various markets worldwide. Data is for new fits and refits of existing wearers, for both daily and overnight wear. (Data courtesy of P Morgan, July 2008.)
Although you may choose to simply follow the manufacturer's recommendation for replacement frequency, it is reasonable for practitioners and patients to question the justification of these intervals. Replacing lenses significantly more frequently than necessary is associated with economic impact for consumers. On the other hand, more frequent replacement could be justified if it truly reduced the frequency of even minor complications. Although many studies on traditional lens materials indicate that shorter replacement times provide enhanced clinical performance, to-date minimal data are available on this topic with regard to silicone hydrogel materials.
The purpose of this work is to determine whether there is any substantial evidence to support either a two-week or a monthly replacement period for silicone hydrogel materials.
Clinical Benefits, Complications
The first studies on the clinical performance of silicone hydrogel materials focused on those replaced every month, with recent studies looking at shorter replacement periods of two weeks. To-date, the clinical performance of silicone hydrogel materials replaced after one month has been excellent on both a daily wear and an overnight wear schedule.
Thus far, there have been no published studies directly comparing schedules with identical silicone hydrogel materials for overnight or daily wear. Therefore it is difficult to draw conclusions about clinical benefits of two-weekly replaced silicone hydrogel materials over those replaced monthly.
Traditional, polyHEMA-based hydrogel lenses, particularly those that are negatively charged, rapidly uptake high levels of protein from the tear film in addition to other tear film components such as lipid, both of which alter the surface characteristics of the lens material. Prior to the introduction of frequent replacement soft lenses, practitioners reported that the greatest problem at aftercare visits was lens deposition, with up to 80 percent of extended wear conventional lenses attracting a visible buildup of tear film-related deposits. Tear film deposits have been associated with discomfort. It's been estimated that deposition is the prime reason for patients seeking aftercare in about one-third of all aftercare visits. Problems include reduced visual acuity and comfort, and increased immunological responses such as contact lens-associated papillary conjunctivitis.
Many studies have shown that frequent replacement of traditional, polyHEMA-based materials reduces the degree of deposition either clinically observed or analytically measured, with improved clinical performance occurring as a result. To-date, no published studies have determined whether there is an observed clinical difference over time in deposits that occur with silicone hydrogel lenses replaced on a two- or four-week replacement schedule. Two studies have examined the degree to which clinically observed deposits occur with twoweek replacement silicone hydrogel lenses. In one study (Nichols, 2006) significant deposits were shown to occur in approximately 10 percent of patients after two weeks, which were reduced to insignificant amounts when patients began using a rub-and-rinse step with a multipurpose system. The value of incorporating a "rub step" with silicone hydrogel lens materials, some of which are prone to attract lipids, has also been reported by other authors (Ghormley, Jones, 2006).
Several in vitro studies have examined the kinetics of deposit buildup on silicone hydrogel materials. Protein deposition on these materials is substantially lower than that seen with traditional polyHEMA-based hydrogels, with different studies showing up to or more than 1,000μg of lysozyme typically being deposited on FDA Group 4 polyHEMA materials after seven days as compared with <30μg on silicone hydrogel materials, with certain silicone hydrogel materials (such as lotrafilcon A, Night & Day, CIBA Vision) depositing <5μg after four weeks. Although the amount of lysozyme deposited on silicone hydrogel lenses virtually doubles between weeks two and four of wear, this small increase in total amount is unlikely to be of any clinical significance.
A similar progressive accumulation in lipid deposition on silicone hydrogel materials over time has also been shown by Carney et al (2008). However, this was an in vitro study with no cleaning. Given the known impact of rubbing and rinsing it is likely that most patients adopting this step would limit the degree of deposition to clinically acceptable levels over a four-week period.
Thus, to-date, no difference in deposition over time has been shown to occur that would support the concept of a significant benefit in replacing silicone hydrogel lenses every two weeks as compared to every four. There likely are some who benefit from shorter replacement periods, particularly those with heavy lipid contamination of their tear film, as may occur in patients who have meibomian gland dysfunction or blepharitis. For these patients, introducing lid hygiene measures and ensuring lenses are rubbed and rinsed may help keep levels of lens deposition clinically acceptable over a monthly period.
Unfortunately, noncompliance with frequency of replacement of soft lenses is high, and evidence exists to show that patients are noncompliant with the lens replacement schedules specified by their practitioner.
At best, noncompliance may result in reduced comfort and clinical satisfaction with lenses; however, a Singapore-based study (Saw et al, 2007) showed that such behavior may be far more serious. They found that 54 percent of patients who developed Fusarium keratitis wore lenses past the recommended replacement date. There was a statistically significant risk of developing keratitis if patients abused their replacement period, and using lenses past their recommended replacement date increased the likelihood of developing keratitis by 2.2 times. By contrast, 34 percent of control subjects in the same study were noncompliant with replacement schedule.
Noncompliance with replacement frequency appears to be particularly prevalent in those wearing lenses on a recommended two-week schedule. A 2002 survey conducted in Canada and the United States showed that 43 percent of patients were noncompliant with replacement of two-week lenses, as opposed to 33 percent wearing one-month replacement lenses. Results of a 2005 survey indicated that 26 percent of patients wearing two-week replacement lenses were compliant with the recommended schedule, as compared to 56 percent of patients wearing monthly replacement lenses. A 2007 U.S. survey showed better compliance with replacement schedules of one day, one week, and one month, with fewer patients adhering to a two-week schedule.
An extensive survey across several European countries indicated that 17 percent of patients always wear their lenses for more days than they should, and only 23 percent would never wear their lenses beyond the recommended period. Morgan (2007) found an overall compliance rate of 34 percent with two-week replacement, as compared with 60 percent for lenses replaced every month. Interestingly, the percentages of noncompliant patients differed widely among countries. More recently, Dumbleton (2009) reported on compliance rates with silicone hydrogel use in the United States, finding 48 percent compliance with a two-week replacement schedule and 72 percent compliance with monthly schedules.
Potential reasons for these differences may be explained in an emerging area of study in psychology called "prospective memory." Prospective memory may be defined as "remembering to remember" or "remembering to perform an intended action." It is vastly different from the kind of memory involved in remembering people, events, and other things in the past. When remembering something from the past, we call on context-specific "cues" from our memory (e.g. a face, an event). In contrast, "prospective memory," or remembering to do something in the future, has no such built-in cues. Instead, we rely on setting artificial cues for reminders.
Patients wearing lenses on a two-week replacement schedule have fewer cues to rely on than those replacing lenses daily or monthly. Patients wearing monthly replaced contact lenses can rely on details such as the name of a new month, a regular date (e.g. the first day of the month) and other events that readily signal the fact that the lenses need replacing.
Although much published research supports shorter replacement periods with wear of traditional poly- HEMA-based hydrogels, no evidence yet exists that would suggest any clinical advantage to replacing silicone hydrogels at intervals of less than one month. Clinical performance to-date would appear to show that monthly replacement is sufficient with most silicone hydrogels and the schedule is associated with at least equivalent clinical performance and patient satisfaction. Patient behavior appears to support this, as in most countries, noncompliance rates are far higher for two-week replacement lenses as compared to monthly replacement lenses.
One factor that remains to be explored is the role that practitioner behavior plays, as it is likely that practitioners may be recommending replacement schedules that exceed manufacturers' suggestions, thus driving "noncompliance." More work is needed to determine optimal replacement periods. CLS
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