1040-5488/14/9101-0024/0 VOL. 91, NO. 1, PP. 24Y31 OPTOMETRY AND VISION SCIENCE Copyright * 2013 American Academy of Optometry
ORIGINAL ARTICLE
Consequences of Wear Interruption for Discomfort With Contact Lenses Eric B. Papas*, Daniel Tilia†, Daniel Tomlinson‡, Josh Williams‡, Eddy Chan‡, Jason Chan‡, and Blanka Golebiowski§
ABSTRACT Purpose. To establish whether increased end-of-day discomfort during soft contact lens wear is associated with short-term changes occurring to the lens itself. Methods. Twenty-seven subjects wore hydrogel lenses (Focus Dailies; Alcon) bilaterally for 10 hours on two separate days. Comfort was reported using 1Y100 numerical rating scales (1 = intolerable discomfort, 100 = lens cannot be felt). Day 1 ratings were taken before lens insertion and at 0.05, 5, and 10 hours post-insertion. Day 2 ratings occurred at similar times, but lenses were removed after the 5-hour assessment and either reinserted (n = 14) or newly replaced (n = 12). An additional rating was taken 5 minutes after re-insertion. Wear then continued to the 10-hour point. In a separate study, 24 different subjects repeated these procedures using a silicone hydrogel lens (AirOptix Aqua; Alcon) with wear taking place on 3 days to permit lens replacement to be with existing as well as new lenses in all subjects. Results. For hydrogel lenses, comfort scores (mean T 95% CI) reported after 10 hours were 79.4 T 8.3 when lenses were worn un-replaced, compared with 73.2 T 9.2 for replacement with the existing lens. When replacement was with a brand new lens, the corresponding values were 72.9 T 10.9 (un-replaced) versus 69.2 T 12.8 (new lens replacement). For silicone hydrogel lenses, 10-hour comfort was 90.3 T 3.2 (un-replaced) versus 92.2 T 2.9 (replacement with existing lens) versus 90.0 T 3.3 (replacement with new lens). Differences between replacement conditions were not significant in any case (analysis of variance, p 9 0.05). Conclusions. Final comfort was not influenced by replacing lenses midway through the wearing period. Comfort decrements experienced by users of these daily contact lenses towards the later part of the wearing period are not caused by changes occurring to the lenses on this time scale. Possible alternative etiological factors include a fatigue-like response in one or more ocular tissues or stimulation of ocular surface nociceptors induced by the presence of the contact lens. (Optom Vis Sci 2014;91:24Y31) Key Words: contact lens, comfort, discomfort, replacement, daily wear, end of day, nociceptor
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any soft contact lens wearers experience a gradual decline in their wearing comfort over the course of the day. The problem was widely evident when hydrogel materials were the dominant modality1 and has not been resolved by the introduction of silicone hydrogels.2Y4 The syndrome of late-day dryness and discomfort is a major reason for contact lens discontinuation,5,6 a situation that breeds dissatisfaction among wearers and clinicians alike and ultimately limits growth in the contact lens market.5 *PhD, BScOptom, FAAO † MOptom ‡ BOptom § PhD, BOptom Brien Holden Vision Institute (EBP, DTi), Sydney; School of Optometry and Vision Science (EBP, DTo, JW, EC, JC, BG), University of New South Wales, Sydney; and Vision CRC (EBP), Sydney, New South Wales, Australia.
The reasons why comfort decays in this fashion are not well understood. Ocular discomfort also occurs in association with dry eye disease in the absence of contact lenses, and here it is generally accepted that a significant inflammatory component is involved.7 Although it is not impossible that inflammation also accompanies contact lensYrelated symptoms, it seems likely that the scenario there is rather different because of the common experience that removal of the lens brings instant relief.8 Inflammatory processes usually do not respond to stimulus removal on a time scale that would replicate this step functionYlike behavior, and so it seems probable that the primary sensation in contact lens wear is generated by other means. When considering the characteristics of the discomfort response, it is attractive to suppose that some sort of gradual change occurs to the lens, whereby it becomes increasingly irritating the longer it is worn. Possible candidates might be increased surface
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Contact Lens Wear Interruption and DiscomfortVPapas et al.
deposits, water content reduction, hydrophobization, or changes to physical parameters leading to shape or fitting variations. If such lens-associated perturbations are indeed responsible for causing discomfort, it seems evident that preventing them from progressing should improve the overall situation at the end of the wearing period. One simple way that this might be achieved is to remove the lens part way through the day and replace it with a new, clean version. A brief enough interruption would preclude the recovery from any ocular changes that may concurrently have been in progress. Our aim in the current series of experiments, therefore, was to test the hypothesis that removal and replacement of the lens midway through the day would result in an improved final comfort outcome compared to undisturbed wear of the same lens.
METHODS Throughout these procedures, the tenets of the Declaration of Helsinki 1975, as revised in 1989, were adhered to. All subjects gave informed consent and the methods employed were approved either by the Human Research Ethics Committee at the University of New South Wales or the Vision CRC Human Research Ethics Committee. Sample size calculations9 indicated that based on > = 0.05, A = 0.2, and effect size (partial G2) = 0.2, a minimum of 18 subjects were required for the planned study design. The investigation was conducted in two parts and Figs. 1 and 2 give flow charts of the procedures followed in each.
Part 1 Twenty-seven subjects were recruited with a mean age of 22 years (range 18-26). Nine were male, 18 were female, and 14 were neophytes to contact lens wear prior to the study. All were screened prior to enrollment to ensure that there was no active ocular disease. At a preliminary visit, all subjects were fitted with a trial pair of contact lenses (Focus Dailies; Alcon, Fort Worth, TX, USA) suitable to correct their spherical refractive error at 6 m. Subjects presented on two further days for evaluation. On one of these days, a new pair of lenses, to the previously determined specifications, was inserted directly from the packaging at around 8 am and worn for a period of approximately 10 hours. Subjects rated their ocular comfort with the lenses using 100-point numerical rating scales (NRS) at the following times during the day: 2Y3 minutes post-insertion (t0), and after 5 (t5) and 10 (t10) hours of wear. The instruction given was that a rating of 100 should indicate perfect comfort, lenses cannot be felt; while 1 corresponded to intolerable, lenses must be removed immediately. Procedure on the second day was identical to that on the first until just after ratings had been taken at 5 hours. At this point, both lenses were removed by the investigator and placed out of sight of the subject, in a new lens case containing fresh, unpreserved 0.9% sterile saline (Astra-Zeneca, Sydney, Australia). According to a predetermined randomization scheme, either these lenses or a new pair, fresh from the packaging, were then reinserted and additional ratings obtained 2Y3 minutes later (t5+). Lens wear then continued until the 10-hour point. The total length of wear interruption was between 1 and 2 minutes. At the time the study
FIGURE 1. Flow chart of procedures followed during part 1.
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26 Contact Lens Wear Interruption and DiscomfortVPapas et al. TABLE 1.
Comfort scores reported by subjects (n = 14) wearing Dailies lenses at each time point Time (t)
Replacement
Mean comfort (1Y100)
95% CI
0
Old lens Un-replaced Old lens Un-replaced Old lens Un-replaced Old lens Un-replaced
89.9 84.4 82.9 78.2 89.5
5.4 7.6 6.5 9.1 4.7
79.4 73.2
8.3 9.2
5 5+ 10
Lenses were worn either un-replaced throughout, or were removed after 5 hours wear (t5) and replaced (old lens) after a brief interval (t5+).
was conducted, Focus Dailies had no added polyvinylpyrrolidone, polyethylene glycol, or hydroxypropyl methyl cellulose in the packing solution. Packing solutions for current Dailies products have been modified compared with those used here. In this way, two profiles of subjective comfort responses were generated for each contact lens wearing subject over 10 hours. For the first of these profiles, wear was continuous (no replacement), while during the second there was a brief interruption midway through. After this pause, roughly half the subjects resumed wear with the same lenses as at the start of the day (old lens replacement), while the remainder continued wear with new lenses (new lens replacement). The order of the continuous and interrupted wear days was randomized and subjects were not told whether the reinserted lenses were new or not. Note that data for one subject in the ‘‘new replacement’’ group were removed from the analysis as they were incomplete.
Part 2 Twenty-four subjects, who were different from those in part I, took part in phase II. These had a mean age of 25 years (range 18Y50), seven were male and 17 were female, and all were experienced contact lens wearers. Essentially the same procedures were followed as in part I, though with the following two differences. First, to improve the generalizability of the outcomes, a different lens type was used, namely the silicone hydrogel AirOptix Aqua (Alcon). According to the package insert, the packing solution may have contained copolymer 845. Second, all subjects undertook to wear lenses on 3 days. This permitted the entire group to experience replacement with both new and existing lenses as well as having an uninterrupted wearing day. As before, the order of the days was randomized and subjects were masked as to the nature of the replaced lens.
Data Analysis
FIGURE 2. Flow chart of procedures followed during part 2.
Data were examined for statistical assumption violations with the result that deviations from both normality (Shapiro-Wilk, p G 0.05) and homogeneity of variance (Levene, p G 0.05) were detected. Nevertheless, we proceeded to utilize analysis of variance methods on the basis of their robustness to normality deviations.10
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Contact Lens Wear Interruption and DiscomfortVPapas et al.
We did, however, adopt a more than usually stringent significance level of p = 0.025 to control possible type I errors introduced by homogeneity of variance violation.10 Repeated measures analysis of variance (ANOVA) was applied to the data from each of the studies. Within-subject factors were time after lens insertion (Time) and replacement lens type (Replacement). The sphericity assumption was examined using Mauchly test, and when violated, the Hyundh-Feldt correction was applied. Bonferroni post hoc testing was conducted when the primary ANOVA indicated significance. Analysis was conducted using PASW version 18.0 (IBM SPSS, Chicago, IL, USA).
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Note that as no data were collected for the ‘‘no replacement’’ condition at the t5+ time point, values from the immediately preceding t5 time were used to permit the ANOVA to proceed.
RESULTS Part 1 Mean comfort scores reported by subjects wearing Dailies lenses at each of the four time points and who replaced the old lens after interrupting wear are shown in Table 1 and Fig. 3A. For the main effects, Time was significant, F(3, 39) = 7.36, p = 0.001, partial
FIGURE 3. A, Group mean comfort scores at each study time point when hydrogel lenses were either worn continuously for 10 hours or removed after 5 hours and replaced with the same (old) lens. Error bars indicate 95% confidence intervals. B, Group mean comfort scores at each study time point when hydrogel lenses were either worn continuously for 10 hours or removed after 5 hours and replaced with a new lens. Error bars indicate 95% confidence intervals. Optometry and Vision Science, Vol. 91, No. 1, January 2014
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28 Contact Lens Wear Interruption and DiscomfortVPapas et al. TABLE 2.
Comfort Scores Reported by Subjects (n = 12) Wearing Dailies Lenses at Each Time Point Time (t)
Replacement
Mean Comfort (1Y100)
95% CI
0
New lens Un-replaced New lens Un-replaced New lens Un-replaced New lens Un-replaced
86.3 80.8 77.8 75.7 84.4
5.8 11.3 9.7 11.9 8.3
69.2 72.9
12.8 10.9
5 5+ 10
Lenses were worn either un-replaced throughout or were removed after 5 hours of wear (t5) and replaced after a brief interval (t5+) with a new, unworn lens of the same type (New lens).
G2 = 0.36, but Replacement was not, F(1, 13) = 4.77, p = 0.05, partial G2 = 0.27. The Time Replacement interaction was not significant, F(3, 39) = 0.98, p = 0.41, partial G2 = 0.07. Although the Replacement effect was not significant at the chosen confidence level (p = 0.025), verification of this outcome was deemed to be important because an error at this point would critically alter the interpretation of the data. Fig. 3A indicated that the potential for a Replacement effect (i.e., a difference between replacement and no replacement) would most likely be driven by the fact that comfort in the ‘‘replaced’’ arm was slightly better than ‘‘un-replaced’’ at baseline, a differential that was maintained throughout that phase of the study. To control for this issue, a reanalysis was conducted after subtracting the baseline comfort values from all subsequent times, i.e., the changes relative to baseline data were analyzed. The outcome of this procedure was that again the main effect of Time was significant, F(2, 26) = 4.94, p = 0.015, partial G2 = 0.28, but Replacement was clearly not, F(1, 13) = 0.25, p = 0.63, partial G2 = 0.019. The Time Replacement interaction was also not significant, F(2, 26) = 1.51, p = 0.24, partial G2 = 0.10. On this basis, the original view that replacement with the old lens was not significantly different from the un-replaced situation appears to be entirely justified. Post hoc tests indicated that comfort just post-insertion (t0) was significantly better than that at either 5 (t5) or 10 hours (t10) later (p G 0.025). Mean comfort scores for subjects who exchanged old lenses for new ones after interrupting wear are shown in Table 2 and Fig. 3B. As before, the main effect of Time was significant, F(3, 33) = 7.59, p = 0.001, partial G2 = 0.41, but Replacement, F(1, 11) = 0.61, p = 0.45, partial G2 = 0.05, and the Time Replacement interaction, F(3, 33) = 2.20, p = 0.12, partial G2 = 0.17, were not. Only post-insertion (t0) and 10-hour (t10) comfort scores were significantly different from each other on post hoc testing (p G 0.025).
Replacement interaction, F(6, 138) = 0.79, p = 0.56, partial G2 = 0.033, were not. Comfort at 10 hours (t10) was significantly different from both that at 5 hours (t5) and just after lens replacement (t5+) on post hoc evaluation (p G 0.025).
DISCUSSION The pattern of discomfort responses seen in parts I and II of the study showed essentially the same type of behavior for both the hydrogel and silicone hydrogel lenses. However, it will be evident from Fig. 5, which shows how discomfort changed during the wearing period, that the magnitudes of the observed comfort decrements were smaller during the silicone hydrogel phase (part II). This is most likely due to the fact that around half the subjects in phase I were neophytes. As all the participants in phase II were experienced contact lens wearers, it would be expected that this greater familiarity would lead to more consistent and less extreme subjective responses. An additional contributory factor may have been the suggestion from large population studies that, while end-of-day dryness complaints remain common, silicone hydrogel lenses offer general comfort advantages over their conventional counterparts,11,12 although this has yet to be confirmed.13 Considered as a whole, the data presented above imply that removing and replacing the lens midway through the wearing period had no effect in improving the final comfort response. Similar effects have anecdotally been reported by Nic (Lally, J.; personal communication). While in each of the situations studied, replacement after 5 hours was associated with a marked comfort increase, this advantage subsequently dissipated. By the end of the observation period, reported comfort was essentially similar to how it was when lenses were worn without interruption. Of particular note here is that it did not matter whether or not the lens replacement was with the existing 5-hour-old item or a brandnew, unworn example. Evidently then, short-term changes to the lens that might occur during wear, such as dehydration, parameter alterations, tear-borne protein or inorganic debris TABLE 3.
Comfort scores reported by subjects (n = 24) wearing AirOptix lenses at each time point Time (t)
Replacement
Mean Comfort (1-100)
95% CI
0
Old lens New lens Un-replaced Old lens New lens Un-replaced Old lens New lens Un-replaced Old lens New lens Un-replaced
94.1 93.0 94.3 93.0 92.5 93.1 94.7 94.0
2.4 2.6 2.7 2.9 3.0 2.2 1.8 2.7
92.2 90.0 90.3
2.9 3.3 3.2
5
5+
10
Part 2 Mean comfort scores reported by subjects wearing AirOptix lenses at each of the four time points are shown in Table 3 and Fig. 4. Yet again, the main effect of Time was significant, F(3, 69) = 5.31, p = 0.011, partial G2 = 0.18, but both the effect of Replacement, F(2, 46) = 0.67, p = 0.49, partial G2 = 0.028, and the Time
Lenses were worn either un-replaced throughout or were removed after 5 hours of wear (t5) and replaced after a brief interval (t5+) with either the same lens (old lens) or a new, unworn lens of the same type (new lens).
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Contact Lens Wear Interruption and DiscomfortVPapas et al.
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FIGURE 4. Group mean comfort scores at each study time point when silicone hydrogel lenses were worn continuously for 10 hours or removed after 5 hours and replaced with a new lens or removed after 5 hours and replaced with the same (old) lens. Note that the new lens and old lens curves have been shifted slightly to the right for clarity. Error bars indicate 95% confidence intervals.
accumulation etc., do not seem to be responsible for driving the loss of comfort. This follows because the replacement procedure with the new item effectively resets the condition of the lens to its baseline state. While the upward spike in comfort at t5+ may appear to suggest that improving lens condition in this way was influential, the observation that a similar phenomenon occurred with the old lens indicates the reverse, as does the fact that the
slopes of the comfort decreases were steeper after replacement had taken place (i.e., between t5+ and t10) than they were before (i.e., between t0 and t5). Both these factors strongly indicate that the rate at which discomfort increased during the wearing period was independent of the state of the lens that was in the eye at the time. Clinically, this has the consequence that replacing lenses more frequently than once a day will not improve end-of-day comfort.
FIGURE 5. Mean difference in comfort score between insertion (t0) and after 10 hours of wear (t10) for hydrogel (Hy) and silicone hydrogel (SiHy) lenses. Positive values indicate poorer comfort at the 10-hour point. Error bars indicate 95% confidence intervals. Comparisons between old, new, and un-replaced conditions were not significant for either lens type (p 9 0.05). Optometry and Vision Science, Vol. 91, No. 1, January 2014
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30 Contact Lens Wear Interruption and DiscomfortVPapas et al.
If lens-based changes are not responsible for end-of-day discomfort, we must look elsewhere for an explanation. One alternative possibility is that the observed comfort decrements are rather due to processes occurring in ocular tissue. Presumably, such events are a consequence of, and initiated by, the physical presence of the contact lens. The effect appears analogous to that of an uncomfortable pair of shoes, whose wearer experiences immediate relief on removal but quickly relapses if circumstances dictate that the offending footwear be replaced. Likewise, wearing a contact lens arguably leads to the ‘‘fatiguing’’ of one or more ocular tissues which eventually begins to manifest to the wearer as discomfort that increases until the lens is removed. Re-inserting the lens too quickly simply recreates the scenario. Although no data were collected in these studies to enable identification of the specific tissues involved, a likely candidate appears to be the upper eye lid, given its continual motion relative to the contact lens. As has been pointed out by both Korb and Allensmith (Buckley, R.J.; personal communication), a typical blink rate has the consequence of moving the eyelid across the equivalent of a football field every day. Given such regular and prolonged interaction, it would not be unreasonable to expect some kind of tissue response to result if the rheological characteristics of the system were to alter from those of the typical lid/ cornea interface. In this respect, contact lens surfaces generally have been considered to generate more friction than does the cornea. For example, one recent report found coefficients of friction for versions of Focus Dailies and AirOptix Aqua to be approximately 0.4 and 0.2, respectively,14 which is roughly an order of magnitude higher than such estimates for corneal tissue.15 Note, however, that as none of these measures were made by using palpebral conjunctiva as the sliding substrate, the actual relevant values will inevitably be somewhat different. Nevertheless, a trend towards contact lenses with very low coefficients of friction14 has recently emerged among several manufacturers, and it will be interesting to see if these products have an impact on the reported levels of late-day discomfort among wearers. Changes to the eyelid, and in particular its so-called lid wiper region, have been reported recently,16 and several studies have associated this phenomenon with contact lensYrelated discomfort.16Y18 Although other work has suggested that alternative features, such as the presence of bulbar conjunctival folds running parallel to the lids, may be more predictive of discomfort,19,20 both sets of occurrences have been linked to a frictional aetiology.18 Clinical signs such as these may prove useful in understanding the overall tissue responses taking place when discomfort is present, but it remains to be seen whether they can be perceived and interpreted on the relatively short time frames needed to account for typical diurnal changes. A further alternative to this potential lid-based etiology has been raised by recent work suggesting that the sensation of dryness may be mediated by cold nociceptors on the ocular surface. These sensors respond to evaporative cooling,21 which is known to increase during contact lens wear.22 Although cold nociceptors are distributed throughout the cornea, limbus, and bulbar conjunctiva,23 it is the latter two locations that would be most likely to be involved in communicating contact lensYrelated dryness. This is because the cornea is generally covered by the lens and thus
insulated from evaporative effects. Due to edge motion and the discontinuous surface contour at the junction, the region around the lens periphery is particularly likely to experience tear film disruption, which would tend to increase evaporative loss and hence nociceptor stimulation as wear progresses. The theoretical mechanisms for discomfort by this route are present therefore. It does not seem unreasonable to conjecture that removal of the lens would normalize the situation, resulting in symptomatic relief, or that subsequently replacing it would rapidly recreate the conditions for dryness to return. This behavior would of course be consistent with the experimental observations noted above, and so a neural mechanism must also be considered when attempting to explain the discomfort phenomenon.
CONCLUSIONS Final comfort was not influenced by lens replacement midway through the wearing period. Comfort decrements experienced by users of these daily contact lenses towards the later part of the wearing period are not caused by changes occurring to the lenses on this time scale. The possibility that the presence of the contact lens induces a fatigue-like response in one or more ocular tissues, or causes stimulation of ocular surface nociceptors, are potential etiological factors.
ACKNOWLEDGMENTS The contact lenses used in this study were supplied by CibaVision, now Alcon, Fort Worth, TX, USA. Parts of this manuscript were presented as a paper at the British Contact Lens Association, June 2007, and as a poster at the Association for Research in Vision and Ophthalmology annual meeting, May 2011. Received March 4, 2013; accepted August 9, 2013.
REFERENCES 1. Brennan NA, Efron N. Symptomatology of HEMA contact lens wear. Optom Vis Sci 1989;66:834Y8. 2. Santodomingo-Rubido J, Barrado-Navascue´s E, Rubido-Crespo MJ. Ocular surface comfort during the day assessed by instant reporting in different types of contact and non-contact lens wearers. Eye Contact Lens 2010;36:96Y100. 3. Martin R, Sanchez I, de la Rosa C, de Juan V, Rodriguez G, de Paz I, Zalama M. Differences in the daily symptoms associated with the silicone hydrogel contact lens wear. Eye Contact Lens 2010; 36:49Y53. 4. Dumbleton K, Keir N, Moezzi A, Feng Y, Jones L, Fonn D. Objective and subjective responses in patients refitted to daily-wear silicone hydrogel contact lenses. Optom Vis Sci 2006;83:758Y68. 5. Young G, Veys J, Pritchard N, Coleman S. A multi-centre study of lapsed contact lens wearers. Ophthalmic Physiol Opt 2002; 22:516Y27. 6. Richdale K, Sinnott LT, Skadahl E, Nichols JJ. Frequency of and factors associated with contact lens dissatisfaction and discontinuation. Cornea 2007;26:168Y74. 7. Lemp M, Baudouin C, Baum J, Dogru M, Foulks GN, Kinoshita S, Laibson P, McCulley J, Murube J, Pfugfelder SC, Rolando M, Toda I. The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye WorkShop (2007). Ocul Surf 2007;5:75Y92.
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Contact Lens Wear Interruption and DiscomfortVPapas et al. 8. Chalmers RL, Begley CG. Dryness symptoms among an unselected clinical population with and without contact lens wear. Cont Lens Anterior Eye 2006;29:25Y30. 9. Faul F, Erdfelder E, Lang AG, Buchner A. G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods 2007;39:175Y91. 10. Keppel G, Wickens TD. Design and Analysis: A Researcher’s Handbook, 4th ed. Upper Saddle River, NJ: Pearson Prentice Hall; 2004. 11. Young G, Chalmers RL, Napier L, Hunt C, Kern J. Characterizing contact lens-related dryness symptoms in a cross-section of UK soft lens wearers. Cont Lens Anterior Eye 2011;34:64Y70. 12. Chalmers RL, Hunt C, Hickson-Curran S, Young G. Struggle with hydrogel CL wear increases with age in young adults. Cont Lens Anterior Eye 2009;32:113Y9. 13. Guillon M. Are silicone hydrogel contact lenses more comfortable than hydrogel contact lenses? Eye Contact Lens 2013;39:86Y92. 14. Roba M, Duncan EG, Hill GA, Spencer ND, Tosatti SG. Friction measurements on contact lenses in their operating environment. Tribol Lett 2011;44:387Y97. 15. Dunn AC, Uruen˜a JM, Puig E, Perez VL, Sawyer WG. Friction coefficient measurement of an in vivo murine cornea. Tribol Lett 2012;49:145Y9. 16. Korb DR, Greiner JV, Herman JP, Hebert E, Finnemore VM, Exford JM, Glonek T, Olson MC. Lid-wiper epitheliopathy and dryeye symptoms in contact lens wearers. CLAO J 2002;28:211Y6.
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17. Yeniad B, Beginoglu M, Bilgin LK. Lid-wiper epitheliopathy in contact lens users and patients with dry eye. Eye Contact Lens 2010;36:140Y3. 18. Pult H, Purslow C, Berry M, Murphy PJ. Clinical tests for successful contact lens wear: relationship and predictive potential. Optom Vis Sci 2008;85:E924Y9. 19. Berry M, Pult H, Purslow C, Murphy PJ. Mucins and ocular signs in symptomatic and asymptomatic contact lens wear. Optom Vis Sci 2008;85:930Y8. 20. Pult H, Murphy PJ, Purslow C. A novel method to predict the dry eye symptoms in new contact lens wearers. Optom Vis Sci 2009; 86:1042Y50. 21. Belmonte C, Gallar J. Cold thermoreceptors, unexpected players in tear production and ocular dryness sensations. Invest Ophthalmol Vis Sci 2011;52:3888Y92. 22. Guillon M, Maissa C. Contact lens wear affects tear film evaporation. Eye Contact Lens 2008;34:326Y30. 23. Belmonte C, Acosta MC, Gallar J. Neural basis of sensation in intact and injured corneas. Exp Eye Res 2004;78:513Y25.
Eric B. Papas Level 4 Rupert Myers Building, Gate 14 UNSW, Barker St. Kensington NSW 2052 Australia e-mail: [email protected]
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ORIGINAL ARTICLE
Consequences of Wear Interruption for Discomfort With Contact Lenses Eric B. Papas*, Daniel Tilia†, Daniel Tomlinson‡, Josh Williams‡, Eddy Chan‡, Jason Chan‡, and Blanka Golebiowski§
ABSTRACT Purpose. To establish whether increased end-of-day discomfort during soft contact lens wear is associated with short-term changes occurring to the lens itself. Methods. Twenty-seven subjects wore hydrogel lenses (Focus Dailies; Alcon) bilaterally for 10 hours on two separate days. Comfort was reported using 1Y100 numerical rating scales (1 = intolerable discomfort, 100 = lens cannot be felt). Day 1 ratings were taken before lens insertion and at 0.05, 5, and 10 hours post-insertion. Day 2 ratings occurred at similar times, but lenses were removed after the 5-hour assessment and either reinserted (n = 14) or newly replaced (n = 12). An additional rating was taken 5 minutes after re-insertion. Wear then continued to the 10-hour point. In a separate study, 24 different subjects repeated these procedures using a silicone hydrogel lens (AirOptix Aqua; Alcon) with wear taking place on 3 days to permit lens replacement to be with existing as well as new lenses in all subjects. Results. For hydrogel lenses, comfort scores (mean T 95% CI) reported after 10 hours were 79.4 T 8.3 when lenses were worn un-replaced, compared with 73.2 T 9.2 for replacement with the existing lens. When replacement was with a brand new lens, the corresponding values were 72.9 T 10.9 (un-replaced) versus 69.2 T 12.8 (new lens replacement). For silicone hydrogel lenses, 10-hour comfort was 90.3 T 3.2 (un-replaced) versus 92.2 T 2.9 (replacement with existing lens) versus 90.0 T 3.3 (replacement with new lens). Differences between replacement conditions were not significant in any case (analysis of variance, p 9 0.05). Conclusions. Final comfort was not influenced by replacing lenses midway through the wearing period. Comfort decrements experienced by users of these daily contact lenses towards the later part of the wearing period are not caused by changes occurring to the lenses on this time scale. Possible alternative etiological factors include a fatigue-like response in one or more ocular tissues or stimulation of ocular surface nociceptors induced by the presence of the contact lens. (Optom Vis Sci 2014;91:24Y31) Key Words: contact lens, comfort, discomfort, replacement, daily wear, end of day, nociceptor
M
any soft contact lens wearers experience a gradual decline in their wearing comfort over the course of the day. The problem was widely evident when hydrogel materials were the dominant modality1 and has not been resolved by the introduction of silicone hydrogels.2Y4 The syndrome of late-day dryness and discomfort is a major reason for contact lens discontinuation,5,6 a situation that breeds dissatisfaction among wearers and clinicians alike and ultimately limits growth in the contact lens market.5 *PhD, BScOptom, FAAO † MOptom ‡ BOptom § PhD, BOptom Brien Holden Vision Institute (EBP, DTi), Sydney; School of Optometry and Vision Science (EBP, DTo, JW, EC, JC, BG), University of New South Wales, Sydney; and Vision CRC (EBP), Sydney, New South Wales, Australia.
The reasons why comfort decays in this fashion are not well understood. Ocular discomfort also occurs in association with dry eye disease in the absence of contact lenses, and here it is generally accepted that a significant inflammatory component is involved.7 Although it is not impossible that inflammation also accompanies contact lensYrelated symptoms, it seems likely that the scenario there is rather different because of the common experience that removal of the lens brings instant relief.8 Inflammatory processes usually do not respond to stimulus removal on a time scale that would replicate this step functionYlike behavior, and so it seems probable that the primary sensation in contact lens wear is generated by other means. When considering the characteristics of the discomfort response, it is attractive to suppose that some sort of gradual change occurs to the lens, whereby it becomes increasingly irritating the longer it is worn. Possible candidates might be increased surface
Optometry and Vision Science, Vol. 91, No. 1, January 2014
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Contact Lens Wear Interruption and DiscomfortVPapas et al.
deposits, water content reduction, hydrophobization, or changes to physical parameters leading to shape or fitting variations. If such lens-associated perturbations are indeed responsible for causing discomfort, it seems evident that preventing them from progressing should improve the overall situation at the end of the wearing period. One simple way that this might be achieved is to remove the lens part way through the day and replace it with a new, clean version. A brief enough interruption would preclude the recovery from any ocular changes that may concurrently have been in progress. Our aim in the current series of experiments, therefore, was to test the hypothesis that removal and replacement of the lens midway through the day would result in an improved final comfort outcome compared to undisturbed wear of the same lens.
METHODS Throughout these procedures, the tenets of the Declaration of Helsinki 1975, as revised in 1989, were adhered to. All subjects gave informed consent and the methods employed were approved either by the Human Research Ethics Committee at the University of New South Wales or the Vision CRC Human Research Ethics Committee. Sample size calculations9 indicated that based on > = 0.05, A = 0.2, and effect size (partial G2) = 0.2, a minimum of 18 subjects were required for the planned study design. The investigation was conducted in two parts and Figs. 1 and 2 give flow charts of the procedures followed in each.
Part 1 Twenty-seven subjects were recruited with a mean age of 22 years (range 18-26). Nine were male, 18 were female, and 14 were neophytes to contact lens wear prior to the study. All were screened prior to enrollment to ensure that there was no active ocular disease. At a preliminary visit, all subjects were fitted with a trial pair of contact lenses (Focus Dailies; Alcon, Fort Worth, TX, USA) suitable to correct their spherical refractive error at 6 m. Subjects presented on two further days for evaluation. On one of these days, a new pair of lenses, to the previously determined specifications, was inserted directly from the packaging at around 8 am and worn for a period of approximately 10 hours. Subjects rated their ocular comfort with the lenses using 100-point numerical rating scales (NRS) at the following times during the day: 2Y3 minutes post-insertion (t0), and after 5 (t5) and 10 (t10) hours of wear. The instruction given was that a rating of 100 should indicate perfect comfort, lenses cannot be felt; while 1 corresponded to intolerable, lenses must be removed immediately. Procedure on the second day was identical to that on the first until just after ratings had been taken at 5 hours. At this point, both lenses were removed by the investigator and placed out of sight of the subject, in a new lens case containing fresh, unpreserved 0.9% sterile saline (Astra-Zeneca, Sydney, Australia). According to a predetermined randomization scheme, either these lenses or a new pair, fresh from the packaging, were then reinserted and additional ratings obtained 2Y3 minutes later (t5+). Lens wear then continued until the 10-hour point. The total length of wear interruption was between 1 and 2 minutes. At the time the study
FIGURE 1. Flow chart of procedures followed during part 1.
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26 Contact Lens Wear Interruption and DiscomfortVPapas et al. TABLE 1.
Comfort scores reported by subjects (n = 14) wearing Dailies lenses at each time point Time (t)
Replacement
Mean comfort (1Y100)
95% CI
0
Old lens Un-replaced Old lens Un-replaced Old lens Un-replaced Old lens Un-replaced
89.9 84.4 82.9 78.2 89.5
5.4 7.6 6.5 9.1 4.7
79.4 73.2
8.3 9.2
5 5+ 10
Lenses were worn either un-replaced throughout, or were removed after 5 hours wear (t5) and replaced (old lens) after a brief interval (t5+).
was conducted, Focus Dailies had no added polyvinylpyrrolidone, polyethylene glycol, or hydroxypropyl methyl cellulose in the packing solution. Packing solutions for current Dailies products have been modified compared with those used here. In this way, two profiles of subjective comfort responses were generated for each contact lens wearing subject over 10 hours. For the first of these profiles, wear was continuous (no replacement), while during the second there was a brief interruption midway through. After this pause, roughly half the subjects resumed wear with the same lenses as at the start of the day (old lens replacement), while the remainder continued wear with new lenses (new lens replacement). The order of the continuous and interrupted wear days was randomized and subjects were not told whether the reinserted lenses were new or not. Note that data for one subject in the ‘‘new replacement’’ group were removed from the analysis as they were incomplete.
Part 2 Twenty-four subjects, who were different from those in part I, took part in phase II. These had a mean age of 25 years (range 18Y50), seven were male and 17 were female, and all were experienced contact lens wearers. Essentially the same procedures were followed as in part I, though with the following two differences. First, to improve the generalizability of the outcomes, a different lens type was used, namely the silicone hydrogel AirOptix Aqua (Alcon). According to the package insert, the packing solution may have contained copolymer 845. Second, all subjects undertook to wear lenses on 3 days. This permitted the entire group to experience replacement with both new and existing lenses as well as having an uninterrupted wearing day. As before, the order of the days was randomized and subjects were masked as to the nature of the replaced lens.
Data Analysis
FIGURE 2. Flow chart of procedures followed during part 2.
Data were examined for statistical assumption violations with the result that deviations from both normality (Shapiro-Wilk, p G 0.05) and homogeneity of variance (Levene, p G 0.05) were detected. Nevertheless, we proceeded to utilize analysis of variance methods on the basis of their robustness to normality deviations.10
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Contact Lens Wear Interruption and DiscomfortVPapas et al.
We did, however, adopt a more than usually stringent significance level of p = 0.025 to control possible type I errors introduced by homogeneity of variance violation.10 Repeated measures analysis of variance (ANOVA) was applied to the data from each of the studies. Within-subject factors were time after lens insertion (Time) and replacement lens type (Replacement). The sphericity assumption was examined using Mauchly test, and when violated, the Hyundh-Feldt correction was applied. Bonferroni post hoc testing was conducted when the primary ANOVA indicated significance. Analysis was conducted using PASW version 18.0 (IBM SPSS, Chicago, IL, USA).
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Note that as no data were collected for the ‘‘no replacement’’ condition at the t5+ time point, values from the immediately preceding t5 time were used to permit the ANOVA to proceed.
RESULTS Part 1 Mean comfort scores reported by subjects wearing Dailies lenses at each of the four time points and who replaced the old lens after interrupting wear are shown in Table 1 and Fig. 3A. For the main effects, Time was significant, F(3, 39) = 7.36, p = 0.001, partial
FIGURE 3. A, Group mean comfort scores at each study time point when hydrogel lenses were either worn continuously for 10 hours or removed after 5 hours and replaced with the same (old) lens. Error bars indicate 95% confidence intervals. B, Group mean comfort scores at each study time point when hydrogel lenses were either worn continuously for 10 hours or removed after 5 hours and replaced with a new lens. Error bars indicate 95% confidence intervals. Optometry and Vision Science, Vol. 91, No. 1, January 2014
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28 Contact Lens Wear Interruption and DiscomfortVPapas et al. TABLE 2.
Comfort Scores Reported by Subjects (n = 12) Wearing Dailies Lenses at Each Time Point Time (t)
Replacement
Mean Comfort (1Y100)
95% CI
0
New lens Un-replaced New lens Un-replaced New lens Un-replaced New lens Un-replaced
86.3 80.8 77.8 75.7 84.4
5.8 11.3 9.7 11.9 8.3
69.2 72.9
12.8 10.9
5 5+ 10
Lenses were worn either un-replaced throughout or were removed after 5 hours of wear (t5) and replaced after a brief interval (t5+) with a new, unworn lens of the same type (New lens).
G2 = 0.36, but Replacement was not, F(1, 13) = 4.77, p = 0.05, partial G2 = 0.27. The Time Replacement interaction was not significant, F(3, 39) = 0.98, p = 0.41, partial G2 = 0.07. Although the Replacement effect was not significant at the chosen confidence level (p = 0.025), verification of this outcome was deemed to be important because an error at this point would critically alter the interpretation of the data. Fig. 3A indicated that the potential for a Replacement effect (i.e., a difference between replacement and no replacement) would most likely be driven by the fact that comfort in the ‘‘replaced’’ arm was slightly better than ‘‘un-replaced’’ at baseline, a differential that was maintained throughout that phase of the study. To control for this issue, a reanalysis was conducted after subtracting the baseline comfort values from all subsequent times, i.e., the changes relative to baseline data were analyzed. The outcome of this procedure was that again the main effect of Time was significant, F(2, 26) = 4.94, p = 0.015, partial G2 = 0.28, but Replacement was clearly not, F(1, 13) = 0.25, p = 0.63, partial G2 = 0.019. The Time Replacement interaction was also not significant, F(2, 26) = 1.51, p = 0.24, partial G2 = 0.10. On this basis, the original view that replacement with the old lens was not significantly different from the un-replaced situation appears to be entirely justified. Post hoc tests indicated that comfort just post-insertion (t0) was significantly better than that at either 5 (t5) or 10 hours (t10) later (p G 0.025). Mean comfort scores for subjects who exchanged old lenses for new ones after interrupting wear are shown in Table 2 and Fig. 3B. As before, the main effect of Time was significant, F(3, 33) = 7.59, p = 0.001, partial G2 = 0.41, but Replacement, F(1, 11) = 0.61, p = 0.45, partial G2 = 0.05, and the Time Replacement interaction, F(3, 33) = 2.20, p = 0.12, partial G2 = 0.17, were not. Only post-insertion (t0) and 10-hour (t10) comfort scores were significantly different from each other on post hoc testing (p G 0.025).
Replacement interaction, F(6, 138) = 0.79, p = 0.56, partial G2 = 0.033, were not. Comfort at 10 hours (t10) was significantly different from both that at 5 hours (t5) and just after lens replacement (t5+) on post hoc evaluation (p G 0.025).
DISCUSSION The pattern of discomfort responses seen in parts I and II of the study showed essentially the same type of behavior for both the hydrogel and silicone hydrogel lenses. However, it will be evident from Fig. 5, which shows how discomfort changed during the wearing period, that the magnitudes of the observed comfort decrements were smaller during the silicone hydrogel phase (part II). This is most likely due to the fact that around half the subjects in phase I were neophytes. As all the participants in phase II were experienced contact lens wearers, it would be expected that this greater familiarity would lead to more consistent and less extreme subjective responses. An additional contributory factor may have been the suggestion from large population studies that, while end-of-day dryness complaints remain common, silicone hydrogel lenses offer general comfort advantages over their conventional counterparts,11,12 although this has yet to be confirmed.13 Considered as a whole, the data presented above imply that removing and replacing the lens midway through the wearing period had no effect in improving the final comfort response. Similar effects have anecdotally been reported by Nic (Lally, J.; personal communication). While in each of the situations studied, replacement after 5 hours was associated with a marked comfort increase, this advantage subsequently dissipated. By the end of the observation period, reported comfort was essentially similar to how it was when lenses were worn without interruption. Of particular note here is that it did not matter whether or not the lens replacement was with the existing 5-hour-old item or a brandnew, unworn example. Evidently then, short-term changes to the lens that might occur during wear, such as dehydration, parameter alterations, tear-borne protein or inorganic debris TABLE 3.
Comfort scores reported by subjects (n = 24) wearing AirOptix lenses at each time point Time (t)
Replacement
Mean Comfort (1-100)
95% CI
0
Old lens New lens Un-replaced Old lens New lens Un-replaced Old lens New lens Un-replaced Old lens New lens Un-replaced
94.1 93.0 94.3 93.0 92.5 93.1 94.7 94.0
2.4 2.6 2.7 2.9 3.0 2.2 1.8 2.7
92.2 90.0 90.3
2.9 3.3 3.2
5
5+
10
Part 2 Mean comfort scores reported by subjects wearing AirOptix lenses at each of the four time points are shown in Table 3 and Fig. 4. Yet again, the main effect of Time was significant, F(3, 69) = 5.31, p = 0.011, partial G2 = 0.18, but both the effect of Replacement, F(2, 46) = 0.67, p = 0.49, partial G2 = 0.028, and the Time
Lenses were worn either un-replaced throughout or were removed after 5 hours of wear (t5) and replaced after a brief interval (t5+) with either the same lens (old lens) or a new, unworn lens of the same type (new lens).
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Contact Lens Wear Interruption and DiscomfortVPapas et al.
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FIGURE 4. Group mean comfort scores at each study time point when silicone hydrogel lenses were worn continuously for 10 hours or removed after 5 hours and replaced with a new lens or removed after 5 hours and replaced with the same (old) lens. Note that the new lens and old lens curves have been shifted slightly to the right for clarity. Error bars indicate 95% confidence intervals.
accumulation etc., do not seem to be responsible for driving the loss of comfort. This follows because the replacement procedure with the new item effectively resets the condition of the lens to its baseline state. While the upward spike in comfort at t5+ may appear to suggest that improving lens condition in this way was influential, the observation that a similar phenomenon occurred with the old lens indicates the reverse, as does the fact that the
slopes of the comfort decreases were steeper after replacement had taken place (i.e., between t5+ and t10) than they were before (i.e., between t0 and t5). Both these factors strongly indicate that the rate at which discomfort increased during the wearing period was independent of the state of the lens that was in the eye at the time. Clinically, this has the consequence that replacing lenses more frequently than once a day will not improve end-of-day comfort.
FIGURE 5. Mean difference in comfort score between insertion (t0) and after 10 hours of wear (t10) for hydrogel (Hy) and silicone hydrogel (SiHy) lenses. Positive values indicate poorer comfort at the 10-hour point. Error bars indicate 95% confidence intervals. Comparisons between old, new, and un-replaced conditions were not significant for either lens type (p 9 0.05). Optometry and Vision Science, Vol. 91, No. 1, January 2014
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30 Contact Lens Wear Interruption and DiscomfortVPapas et al.
If lens-based changes are not responsible for end-of-day discomfort, we must look elsewhere for an explanation. One alternative possibility is that the observed comfort decrements are rather due to processes occurring in ocular tissue. Presumably, such events are a consequence of, and initiated by, the physical presence of the contact lens. The effect appears analogous to that of an uncomfortable pair of shoes, whose wearer experiences immediate relief on removal but quickly relapses if circumstances dictate that the offending footwear be replaced. Likewise, wearing a contact lens arguably leads to the ‘‘fatiguing’’ of one or more ocular tissues which eventually begins to manifest to the wearer as discomfort that increases until the lens is removed. Re-inserting the lens too quickly simply recreates the scenario. Although no data were collected in these studies to enable identification of the specific tissues involved, a likely candidate appears to be the upper eye lid, given its continual motion relative to the contact lens. As has been pointed out by both Korb and Allensmith (Buckley, R.J.; personal communication), a typical blink rate has the consequence of moving the eyelid across the equivalent of a football field every day. Given such regular and prolonged interaction, it would not be unreasonable to expect some kind of tissue response to result if the rheological characteristics of the system were to alter from those of the typical lid/ cornea interface. In this respect, contact lens surfaces generally have been considered to generate more friction than does the cornea. For example, one recent report found coefficients of friction for versions of Focus Dailies and AirOptix Aqua to be approximately 0.4 and 0.2, respectively,14 which is roughly an order of magnitude higher than such estimates for corneal tissue.15 Note, however, that as none of these measures were made by using palpebral conjunctiva as the sliding substrate, the actual relevant values will inevitably be somewhat different. Nevertheless, a trend towards contact lenses with very low coefficients of friction14 has recently emerged among several manufacturers, and it will be interesting to see if these products have an impact on the reported levels of late-day discomfort among wearers. Changes to the eyelid, and in particular its so-called lid wiper region, have been reported recently,16 and several studies have associated this phenomenon with contact lensYrelated discomfort.16Y18 Although other work has suggested that alternative features, such as the presence of bulbar conjunctival folds running parallel to the lids, may be more predictive of discomfort,19,20 both sets of occurrences have been linked to a frictional aetiology.18 Clinical signs such as these may prove useful in understanding the overall tissue responses taking place when discomfort is present, but it remains to be seen whether they can be perceived and interpreted on the relatively short time frames needed to account for typical diurnal changes. A further alternative to this potential lid-based etiology has been raised by recent work suggesting that the sensation of dryness may be mediated by cold nociceptors on the ocular surface. These sensors respond to evaporative cooling,21 which is known to increase during contact lens wear.22 Although cold nociceptors are distributed throughout the cornea, limbus, and bulbar conjunctiva,23 it is the latter two locations that would be most likely to be involved in communicating contact lensYrelated dryness. This is because the cornea is generally covered by the lens and thus
insulated from evaporative effects. Due to edge motion and the discontinuous surface contour at the junction, the region around the lens periphery is particularly likely to experience tear film disruption, which would tend to increase evaporative loss and hence nociceptor stimulation as wear progresses. The theoretical mechanisms for discomfort by this route are present therefore. It does not seem unreasonable to conjecture that removal of the lens would normalize the situation, resulting in symptomatic relief, or that subsequently replacing it would rapidly recreate the conditions for dryness to return. This behavior would of course be consistent with the experimental observations noted above, and so a neural mechanism must also be considered when attempting to explain the discomfort phenomenon.
CONCLUSIONS Final comfort was not influenced by lens replacement midway through the wearing period. Comfort decrements experienced by users of these daily contact lenses towards the later part of the wearing period are not caused by changes occurring to the lenses on this time scale. The possibility that the presence of the contact lens induces a fatigue-like response in one or more ocular tissues, or causes stimulation of ocular surface nociceptors, are potential etiological factors.
ACKNOWLEDGMENTS The contact lenses used in this study were supplied by CibaVision, now Alcon, Fort Worth, TX, USA. Parts of this manuscript were presented as a paper at the British Contact Lens Association, June 2007, and as a poster at the Association for Research in Vision and Ophthalmology annual meeting, May 2011. Received March 4, 2013; accepted August 9, 2013.
REFERENCES 1. Brennan NA, Efron N. Symptomatology of HEMA contact lens wear. Optom Vis Sci 1989;66:834Y8. 2. Santodomingo-Rubido J, Barrado-Navascue´s E, Rubido-Crespo MJ. Ocular surface comfort during the day assessed by instant reporting in different types of contact and non-contact lens wearers. Eye Contact Lens 2010;36:96Y100. 3. Martin R, Sanchez I, de la Rosa C, de Juan V, Rodriguez G, de Paz I, Zalama M. Differences in the daily symptoms associated with the silicone hydrogel contact lens wear. Eye Contact Lens 2010; 36:49Y53. 4. Dumbleton K, Keir N, Moezzi A, Feng Y, Jones L, Fonn D. Objective and subjective responses in patients refitted to daily-wear silicone hydrogel contact lenses. Optom Vis Sci 2006;83:758Y68. 5. Young G, Veys J, Pritchard N, Coleman S. A multi-centre study of lapsed contact lens wearers. Ophthalmic Physiol Opt 2002; 22:516Y27. 6. Richdale K, Sinnott LT, Skadahl E, Nichols JJ. Frequency of and factors associated with contact lens dissatisfaction and discontinuation. Cornea 2007;26:168Y74. 7. Lemp M, Baudouin C, Baum J, Dogru M, Foulks GN, Kinoshita S, Laibson P, McCulley J, Murube J, Pfugfelder SC, Rolando M, Toda I. The definition and classification of dry eye disease: report of the Definition and Classification Subcommittee of the International Dry Eye WorkShop (2007). Ocul Surf 2007;5:75Y92.
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Contact Lens Wear Interruption and DiscomfortVPapas et al. 8. Chalmers RL, Begley CG. Dryness symptoms among an unselected clinical population with and without contact lens wear. Cont Lens Anterior Eye 2006;29:25Y30. 9. Faul F, Erdfelder E, Lang AG, Buchner A. G*Power 3: a flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behav Res Methods 2007;39:175Y91. 10. Keppel G, Wickens TD. Design and Analysis: A Researcher’s Handbook, 4th ed. Upper Saddle River, NJ: Pearson Prentice Hall; 2004. 11. Young G, Chalmers RL, Napier L, Hunt C, Kern J. Characterizing contact lens-related dryness symptoms in a cross-section of UK soft lens wearers. Cont Lens Anterior Eye 2011;34:64Y70. 12. Chalmers RL, Hunt C, Hickson-Curran S, Young G. Struggle with hydrogel CL wear increases with age in young adults. Cont Lens Anterior Eye 2009;32:113Y9. 13. Guillon M. Are silicone hydrogel contact lenses more comfortable than hydrogel contact lenses? Eye Contact Lens 2013;39:86Y92. 14. Roba M, Duncan EG, Hill GA, Spencer ND, Tosatti SG. Friction measurements on contact lenses in their operating environment. Tribol Lett 2011;44:387Y97. 15. Dunn AC, Uruen˜a JM, Puig E, Perez VL, Sawyer WG. Friction coefficient measurement of an in vivo murine cornea. Tribol Lett 2012;49:145Y9. 16. Korb DR, Greiner JV, Herman JP, Hebert E, Finnemore VM, Exford JM, Glonek T, Olson MC. Lid-wiper epitheliopathy and dryeye symptoms in contact lens wearers. CLAO J 2002;28:211Y6.
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17. Yeniad B, Beginoglu M, Bilgin LK. Lid-wiper epitheliopathy in contact lens users and patients with dry eye. Eye Contact Lens 2010;36:140Y3. 18. Pult H, Purslow C, Berry M, Murphy PJ. Clinical tests for successful contact lens wear: relationship and predictive potential. Optom Vis Sci 2008;85:E924Y9. 19. Berry M, Pult H, Purslow C, Murphy PJ. Mucins and ocular signs in symptomatic and asymptomatic contact lens wear. Optom Vis Sci 2008;85:930Y8. 20. Pult H, Murphy PJ, Purslow C. A novel method to predict the dry eye symptoms in new contact lens wearers. Optom Vis Sci 2009; 86:1042Y50. 21. Belmonte C, Gallar J. Cold thermoreceptors, unexpected players in tear production and ocular dryness sensations. Invest Ophthalmol Vis Sci 2011;52:3888Y92. 22. Guillon M, Maissa C. Contact lens wear affects tear film evaporation. Eye Contact Lens 2008;34:326Y30. 23. Belmonte C, Acosta MC, Gallar J. Neural basis of sensation in intact and injured corneas. Exp Eye Res 2004;78:513Y25.
Eric B. Papas Level 4 Rupert Myers Building, Gate 14 UNSW, Barker St. Kensington NSW 2052 Australia e-mail: [email protected]
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