YOUNG, GRAEME MPhil, BSc, FCOptom; RILEY, COLLEEN M. OD, MS; CHALMERS, ROBIN L. OD; HUNT, CHRIS MSc
As outdoor air quality deteriorates because of increased air pollution from automobiles and industrial sources, building designers and managers depend more heavily on air-conditioning or central heating systems to clean and condition the interior environment. The result of this effort is to create increasingly artificial conditions in which we work and live. Researchers who study the effect of indoor air on workers or building residents report that low relative humidity, increased air movement, higher room temperature, and ambient smoke in a building are all associated with a higher degree of general skin, mucous membrane, and ocular symptoms.1, 2 In a survey of nearly 900 subjects, Backman and co-workers found that 29% of office workers reported ocular discomfort.3 This matches the proportion found in another study by Doughty et al. after controlling for the effect of contact lens wear and medication use.4 In the Doughty study, the proportion with ocular discomfort was significantly higher (63%) when contact lens wearers and workers who used drying medications were included.
Computer screen use has also been implicated as a trigger for ocular discomfort in several studies of patients without contact lens wear.1,5,6 Wolkoff et al. propose that a work environment with demanding task content, low relative humidity and high room temperature, and use of contact lenses all contribute to ocular discomfort by increasing water evaporation and thinning of the precorneal or prelens tear film.6 Early work by Nilsson found that ambient humidity below 30% was associated with ocular discomfort in contact lens wearers, although the precise mechanism was unknown.7 Nilsson implicated lens deposits on traditional nondisposable hydrogel lenses in the development of discomfort. Since that time the proposed remedies set out in that article; more frequent lens replacement and better cleaning systems, have both been put into routine contact lens practice. Nevertheless, we still have a significant problem with environmentally triggered discomfort with hydrogel contact lenses.
The role of hydrogel contact lens material in promoting ocular comfort is a complex one that could involve the dehydration profile of the lens material and its effect on lens fit; the tendency for the surface to attract hydrophobic deposits; the smoothness of the lens surface in addition to the oxygen transmissibility. In theory, these factors could be studied in isolation while changing only one variable if the appropriate prototype lenses were available. In reality, lenses fabricated of any unique material also have unique properties with regard to dehydration, depositing profile and surface quality, and clinical trials that utilize available lenses are constrained by the fact that these features are predetermined by the lens material and cannot be studied in isolation.
In addition to high oxygen transmissibility, the group of silicone hydrogel lens materials have other material properties in common; some have a relatively low water content and low depositing profile.8,9 Those material properties may contribute to fewer symptoms of discomfort and dryness during lens wear as have been found in a clinical trial with silicone hydrogels.10 Although the in vitro and in vivo deposit characteristics of silicone hydrogels are unique to each lens type, as a class they deposit significantly less protein on the lens surface when compared with mid-water hydrogel lenses.8,9 In another in vitro study, Jones et al. correlated in vitro lens dehydration to the initial water content of the material, yielding significantly less dehydration for the silicone hydrogels tested (balafilcon A and lotrafilcon A) and that the rate of air flow over the lens surface had a greater impact on lens dehydration than relative humidity in the test chamber.11 In a clinical trial, Morgan et al. found that balafilcon A silicone hydrogel lenses dehydrated significantly less than etafilcon A hydrogel lenses over a 2-week period of wear.12
Although the effects of contact lens dehydration and evaporation have been widely studied in the laboratory, there is still a gap in our understanding of the conditions under which contact lens wearers actually use their lenses. How much do environments known to affect the comfort of the natural surface of the eye such as low humidity, high temperature, and air turbulence, affect the comfort of hydrogel and silicone hydrogel contact lenses? To what extent do these environments limit lens wear? Do contact lens wearers actively avoid situations that are known to exacerbate feelings of discomfort?
The purpose of this analysis was to query the proportion of hydrogel soft contact lens wearers who wear lenses in a range of adverse environments and challenging tasks and to assess the resulting lens comfort in those conditions. A second objective was to determine the degree to which refitting with second generation silicone hydrogel lenses affects lens comfort among subjects who wear their lenses in challenging environments.
Subjects in this analysis were 496 former daily wear hydrogel lens wearers from 48 United States clinical sites. The subjects were from mountainous, desert, and maritime areas in both urban and rural settings. Subjects were existing soft lens wearers between 18 and 40 years of age, who had used daily wear hydrogel lenses within the following range of prescriptions: −1.00 to −6.00 DS with refractive astigmatism of 1.00 DC or less in both eyes. All subjects had minimum visual acuity of 20/30 with spherical soft lenses. Subjects were excluded if they were suffering from any systemic or infectious disease, had previous refractive surgery, or any eye injury or surgery within 8 weeks. Any women who were pregnant, lactating, or planning pregnancy were also excluded.
Questionnaires were completed at the baseline visit that queried how much subjects were exposed to a range of environments and demanding tasks and whether or not they wore their lenses during those exposures. Exposure and lens comfort results were stratified by the region of the United States in which the subjects resided (Fig. 1). Baseline data for subjects from all regions were analyzed for overall use patterns and the subjective comfort response to many environments. All subjects were then randomized to be refit with one of three silicone hydrogel lenses for daily wear use (Table 1 for lens specifications). Subjects were masked to their new lens type. Subjects were instructed to continue use of their previous lens care system with the silicone hydrogel lenses. After 2 weeks, the subjects again completed the subjective questionnaires.
The subjective questionnaire included questions on the subjects’ average and comfortable wearing times, current attitudes about contact lenses, and wearing habits. Although the data are not the subject of this article, the study visits also included routine clinical examinations with visual acuity and subjective refraction, keratometry, measurement of tear-prism height, slit-lamp examination, and tear break-up time.
Descriptive results include the proportion of subjects who reported that they “always” or “frequently” wore lenses during various environments and the level of comfort that they reported in those environments. Regional comparisons were performed with chi-square analysis. Baseline and 2-week comparisons of comfort for each environment or task were then computed only for subjects who had a high level of exposure with habitual and test lenses. For each lens type, nonparametric statistics were performed (Wilcoxon signed rank test) on the proportion of subjects who changed between the baseline and 2-week visits. Note that there were unequal sample sizes across lens groups and for each environmental exposure. A few environments (air travel and exposure to mountainous or high altitudes) had too few subjects who experienced them in 2 weeks of wear of test lenses and so were not analyzed for comparison between hydrogel and test lenses.
The demographics, habitual lens, and refractive factors for all enrolled subjects and by randomized silicone hydrogel lens are shown in Table 2. The subjects’ habitual lenses and lens care systems were similar in distribution, with the majority (69.3–77.9%) of subjects in each group having worn twice-monthly replacement lenses from FDA group 3. Fig. 2 shows the proportion of subjects who reported “always” or “frequently” wearing their habitual lenses under the listed conditions.
Fig. 3 illustrates the subjects’ assessment of comfort with their habitual contact lenses while wearing them in various activities and environmental conditions. Note that only those subjects who reported a high level of exposure to an environment, as shown in Fig. 2, were included in this figure, with a range from 126 subjects for napping in lenses to 455 for driving at night while wearing contact lenses.
Comparative analysis between regions showed that Western subjects were more likely to be exposed to high altitude or mountainous environments (p < 0.0001). Subjects from the West and Northeast were more likely to wear lenses while napping (p = 0.012). When compared with subjects from other regions, significantly fewer Western subjects reported being comfortable while sitting in an air-conditioned or heated car (p = 0.012) as shown in Fig. 4.
Figures 5A and B show the proportion of subjects with comfort ratings of “always” or “frequently” with habitual and after 2 weeks with each of the three test lenses after refitting. Table 3 shows the sample size and statistical results for comparison of comfort ratings in each environmental exposure with habitual and silicone hydrogel lenses, again for subjects who reported a high degree of exposure during the 2-week test. Note that the sample size for some activities and lens combinations is very small, in particular for the galyfilcon A and lotrafilcon B cells.
Characterizing how contact lens wearers use their lenses is important because it helps to understand the environmental challenges to their ocular and contact lens surfaces. Analysis of these data provides new information about the environmental stressors to which lens-wearing eyes are exposed and the ability of subjects to cope with their effects. It also reveals situations that may limit lens wear.
This survey shows that the most common “exposures” to challenging environments involve routine everyday activities included in the wearer’s lifestyle. Over 90% (92%) of these subjects reported wearing their contact lenses while driving at night, 89% while using a computer, 87% while in a heated or air-conditioned car, and 79% while sitting under a heating or air-conditioning vent in a building. These activities define the typical routine of everyday life for adults with jobs and active lifestyles. Even though highly air-conditioned environments can disrupt the prelens tear film13 and can result in ocular,3,6,14 skin, and mucous membrane symptoms,1,2,15,16 this study shows that hydrogel contact lens wearers must and do maintain lens wear in those environments. Use of lenses during occupational and domestic activities is the norm and therefore contact lens wear must be comfortable enough for the wearer to continue lens wear. If silicone hydrogels can help deliver better lens comfort during everyday activities and environments, perhaps their use could help slow the rate of discontinuation of lens wear17–19 as lens discomfort or dryness are most often cited as the reason to cease lens wear.20
Interestingly, the least common environmental exposures (sitting under an air vent, being in low humidity and dry air, being in a smoky, dusty or polluted environment) were also associated with lower comfort ratings with habitual hydrogel lenses. That is, lens wearers seemed to avoid wearing lenses in the most uncomfortable environments such as dusty, smoky, or windy environments as shown in Fig. 2. Harsher environments like these are probably more able to predict and therefore avoid, such as going to a smoky tavern with friends or working with a sanding machine on a weekend project. Because of the ability to remove lenses when they please, lens wearers are able to and do self-manage their lens wear in order to avoid the situations that may prove unpleasant while wearing lenses.
Napping while wearing lenses was the only factor that theoretically could be experienced by all subjects but, in the study, was reported by only a few. Only 27% of this group reported napping while wearing their habitual daily wear hydrogel lenses, and only 14% reported doing so “always” when they took a nap. That represents fair compliance with the warning against closed-eye wear of the low transmissibility hydrogel lenses that they were wearing on entering the study. The higher transmissibility materials have the advantage of avoiding corneal hypoxia during brief periods of closed-eye wear for patients who nap in lenses while also maintaining good comfort. Lower water content in the silicone hydrogel materials reduces the amount of on-eye dehydration during closed-eye wear as well.12
For many lens wearers, after being refit with one of the silicone hydrogel test lenses, many environments that had previously challenged comfort with their habitual hydrogel lenses no longer appeared to pose such a challenge. The subjects with senofilcon A, and galyfilcon A lenses reported significantly improved comfort in most situations. One exception was for galyfilcon A while using a computer. Subjects who were refit with lotrafilcon B lenses, however, reported fewer symptoms in many environments but did not report a significant improvement in comfort in the most frequently experienced challenging environments; night driving, computer use, or while sitting in a car with heat or air-conditioning. The authors note that the galyfilcon A and lotrafilcon B groups were smaller than the other test lens groups, but were similar in size for most of the exposures as shown in Table 3. This smaller sample size for these lenses would have an impact on the power to detect a difference in the test vs. habitual lens in those environments. Because the first goal of this analysis was to determine the usage patterns, it was not possible to balance the sample of subjects who were exposed to each lens type and environment in combination. Although the exposed number of subjects for night driving, computer use, sitting in air-conditioned or heated rooms, and reading was nearly identical between the galyfilcon A and lotrafilcon B lens groups, as shown in Table 3, the results were quite different. The data displayed in Figs. 5 A and B shows the proportions of subjects with good comfort with habitual or test silicone hydrogel lenses so that the patterns of change in symptoms can be viewed regardless of the number of subjects in the sample.
Although a study such as this cannot pinpoint the cause of the discomfort from habitual lenses, an improvement that resulted from refitting with a new lens type may be due to use of materials that resist dehydration, stay cleaner, avoid corneal hypoxia, or have smoother surfaces. Provision of a new pair of lenses alone cannot account for all of the improvement reported in this study, as approximately 70% of the subjects habitually wore 2-week replacement disposable lenses and more than 7% wore daily disposable lenses. Although not a feature of this study, a design in which the subjects were crossed back into their habitual lens design would have more clearly identified the role of lens replacement in the improvement in symptoms.
The environments in which the subjects reported the worst comfort with habitual lenses improved the most after refitting with silicone hydrogel lenses, regardless of lens type. These exacerbating conditions included sitting under an air-conditioning or heating vent, spending time in a low humidity or dry air environment, being in a smoky, dusty or polluted environments, and napping while wearing lenses and comprise the activities that may limit lens wear if not managed properly. This study shows that lens wearers continue to put up with environmentally triggered discomfort because they need to continue wearing lenses while working or in other situations. In these situations, the option of removing the lenses may be unavailable or inconvenient. Improved comfort with silicone hydrogel lenses in environments that caused discomfort from particulates, such as dusty or windy conditions may occur because the lens surface retains more surface moisture which, in turn, facilitates clearance of particles from the surface through blinking.
This study was limited primarily by uneven sample size across environmental exposures and lens groups, and the short duration of lens wear (2 weeks) before sampling the subjective assessment of the silicone hydrogel test lenses. The lotrafilcon B group was under-represented in the West, which may have reduced the baseline dryness reports in that group. However, because a paired analysis was applied, each subject is compared to themselves, thereby reducing the effect of differences across groups at baseline. In addition, because of the 2 week sampling time, only a small number of subjects in each lens type experienced air travel or spending time in high altitude. These small sample sizes make it unwise to conduct statistical tests on these variables. However, examination of the slopes in Figures 5A and B between the proportions of subjects who reported their lenses were always or frequently comfortable in environments before and after refitting will show the relative improvement within that cohort regardless of sample size.
How much do environmental factors that are known to affect the comfort of the natural surface of the eye, such as low humidity, high temperature, and air turbulence, affect the comfort of hydrogel and silicone hydrogel contact lenses? This study indicates that the use of hydrogel lenses is avoided in a few harsh environments, such as windy, polluted, and dusty areas. These may be environments that actually limit lens wear. However, to function in their everyday life, contact lens wearers must wear lenses in a wide variety of other dry or turbulent conditions to ride to work in their car, and heat or cool their homes and offices. The sampling of experience with silicone hydrogel lenses in this study indicates that they were tolerated more easily and worn more comfortably in the wide range of conditions when compared with the subjects’ habitual hydrogel lenses. If silicone hydrogel lenses begin to be prescribed as the standard of care for soft lens wearers, the proportion of patients experiencing discomfort and poor tolerance of lenses should decrease over time in the next few years. Lens materials that were primarily designed to increase the oxygen transmissibility to the cornea may have provided another very tangible benefit for contact lens wearers.
This study was sponsored by Vistakon, a division of Johnson & Johnson Vision Care, Inc. Graeme Young, Chris Hunt and Robin Chalmers are paid consultants for both Vistakon and CIBA Vision, a Novartis Company. Colleen Riley is employed by Vistakon.
Robin L. Chalmers
2097 East Lake Rd,
Atlanta, GA 30307
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