1040-5488/15/9206-0665/0 VOL. 92, NO. 6, PP. 665Y670 OPTOMETRY AND VISION SCIENCE Copyright * 2015 American Academy of Optometry
ORIGINAL ARTICLE
Ocular Discomfort Responses after Short Periods of Contact Lens Wear Eric Papas*, Daniel Tilia†, John McNally‡, and Percy Lazon de la Jara§
ABSTRACT Purpose. To investigate if contact lensYrelated discomfort is a function of the time of day at which lenses are worn. Methods. This was a randomized, crossover, open-label clinical trial where subjective responses, with and without contact lenses, were assessed every 2 hours during five stages (A to E). Each stage began at the time when subjects would normally have inserted their contact lenses (T0). During stage A, no lenses were worn, whereas in stage B, lenses were worn continuously for 12 hours. In stages C to E, lenses were worn for only 4 hours. Contact lenses were inserted at T0 for stage C, but for stages D and E, lenses were not inserted until T0 + 4 and T0 + 8 hours, respectively. Mixed linear models were used for statistical analysis. Results. In the absence of contact lenses, ocular comfort and dryness remained reasonably constant throughout the observation period. Ocular comfort and dryness decreased during 12 hours of continuous lens wear and became significantly worse from the 8-hour time onward compared with insertion (p G 0.023). There were no significant differences in terms of ocular comfort and dryness between any of the 4-hour lens wear stages (p G 0.82). During each 4-hour stage, both comfort and dryness behaved in a similar fashion (p 9 0.05) to the first 4 hours of continuous contact lens wear. Comparing the scores of each of these stages with the no-lens response at the corresponding time showed no significant differences for comfort (p 9 0.23) or dryness (p 9 0.37). Conclusions. Short periods of wear can be experienced at any time of day without significant change in ocular discomfort and dryness. This suggests that subjective responses at the end of the day are determined by the length of time lenses are in contact with the eye, rather than the time of day at which lenses are worn. (Optom Vis Sci 2015;92:665Y670) Key Words: ocular comfort, ocular discomfort, ocular dryness, contact lenses
C
ontact lensYrelated ocular discomfort and dryness are well-recognized phenomena that have been implicated as major causes of failure among wearers.1,2 The typical ocular discomfort and dryness sensations are low or absent immediately after insertion but increase in severity over the course of a day of wear.3 Many subjects find these sensations at the end of the day to be unsatisfactory, and in some cases, it is intolerable, prompting lens removal before the desired wearing time. The dryness and discomfort response has been attributed to, or associated with, a series of potential causative factors including
*PhD, FAAO † MOptom, FAAO ‡ OD, FAAO § PhD Brien Holden Vision Institute, Sydney, New South Wales, Australia (EP, DT, PLdlJ); Vision Cooperative Research Centre, Sydney, Australia (EP, PLdlJ); School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia (EP, PLdlJ); and CIBA Vision, Duluth, Georgia (JMc).
disturbance of the tear film, lens design, material characteristics, and interaction between the contact lens and its care system.4Y11 Considerable effort has been devoted to strategies that will improve contact lens performance including recent work indicating that switching from a reusable to a daily disposable wearing schedule may reduce the magnitude of the problem.12 Given this result, it appears reasonable to ask if further gains can be achieved by increasing the frequency of disposal still further. Unfortunately, in a study where twice daily replacement was investigated, no net gain in end-of-day comfort resulted, despite some short-term benefit being noted immediately after the midday insertion of a new lens.13 This result has been interpreted as indicating that changes occurring to the lens itself, in the time frame of the wearing day, are not responsible for driving the discomfort sensation; rather, it is some factor, or factors, associated with the eye that appear to be implicated. The fact that discomfort sensations increase in intensity with time suggests that the duration of contact between the eyes and
Optometry and Vision Science, Vol. 92, No. 6, June 2015
Copyright © American Academy of Optometry. Unauthorized reproduction of this article is prohibited.
666 Ocular Discomfort after Contact Lens WearVPapas et al.
lens is a critical element in the process. Before that conclusion can be drawn, however, it is important to eliminate the alternative possibility that the discomfort is simply an expression of normal fatigue; that is, lenses feel worse at the end of the day because the subject is more tired at that time. To phrase the question a different way, is it time in the lens, or the time of day, that is driving the sensation of discomfort? The aim of the present study, therefore, was to investigate the hypothesis that contact lensYrelated discomfort is a function of the time of day at which lenses are worn. To do this, an attempt was made to determine if the comfort profile typically experienced by contact lens wearers during the course of the day would be replicated from a series of shorter periods of wear undertaken at different times during the day.
METHODS This was a prospective, crossover, bilateral, open-label, randomized clinical trial in which participants’ subjective responses, with and without contact lenses, were assessed every 2 hours during five stages. A total of 34 participants were enrolled, and 31 completed the trial. The study received ethics approval and was conducted in accordance with the Declaration of Helsinki (October 2008). All participants gave written informed consent. To be eligible for this trial, participants were required to be at least 18 years old, to be experienced contact lens wearers, to be myopic in both eyes, to be correctable to at least 20/40 (6/12) distance visual acuity with spherical contact lenses, and to have no ocular or systemic findings that would prevent safe lens wear. Participants were fitted bilaterally with a monthly replacement, commercial silicone hydrogel contact lens (Lotrafilcon B, Alcon, USA). Lenses were worn only on one occasion and then discarded; hence, no contact lens care product was necessary for cleaning or disinfection. This study consisted of five stages (A to E). Each phase began at the time when subjects would normally have inserted their contact lenses (T0), with the proviso that the latest allowed starting time was 9:00 AM. During stage A, no lenses were worn, whereas in stage B, lenses were worn continuously for 12 hours. In stages C to E, lenses were worn for only 4 hours, but the time point of insertion was different in each case. For stage C, wear began at T0, but for stages D and E, lenses were not inserted until T0 + 4 and T0 + 8 hours, respectively. The order of stages was randomized and a new pair of lenses was used for each relevant stage. Participants were instructed to complete stages on consecutive days, but if their eyes felt uncomfortable the day after 12 hours of continuous wear, they were permitted to not wear lenses (and not complete the takehome questionnaire) on that day. Subjective ocular comfort and ocular dryness were evaluated using 1 to 100 numerical rating scales,14 where 1 = poor and 100 = excellent. Participants were asked ‘‘please rate your ocular comfort/dryness for both eyes’’ at each time point. For dryness rating, a high score indicated less dryness. Participants rated their ocular comfort and dryness within 5 minutes of contact lens insertion and every 2 hours from the beginning of each stage using takehome questionnaires. A series of actions were undertaken to ensure compliance with the collection of subjective responses. The take-home questionnaires
for each stage was printed on different colored paper and included specific information about the stage such as starting time, time to insert the lenses, and for how long they needed to be worn. Participants were verbally instructed on how to complete the takehome questionnaires before commencement and were required to return all documents at the final visit.
STATISTICAL ANALYSIS A sample size of 30 participants was required to detect a paired difference between five crossover stages of 10 T 15 points in subjective ratings with 80% power at the 5% level of significance and corrected for multiple comparisons.15 All participants who completed study treatment were eligible to be included in the analysis data set. The analysis of efficacy variables such as subjective ratings used only scheduled and evaluable visits. Subjective rating variables were compared between stages at each time point and across time within each stage using a linear mixed model with subject random intercepts to adjust for intrasubject correlations and repeated visits. Post hoc multiple comparisons were adjusted using Bonferroni correction. A p value less than or equal to 0.05 was considered statistically significant. Analysis was performed using SPSS 15.0.
RESULTS Demographics A total of 34 participants were enrolled. There were three discontinuations during the trial, and data for these subjects were not included in the analysis. The sample (n = 31) consisted of 59% female and 41% male subjects. The mean (TSD) age was 29.6 (T13.4) years with an average (TSD) auto-refraction sphere and cylinder of j3.33 (T1.34) diopters and j0.71 (T0.37) diopters, respectively.
Take-home Questionnaire Compliance All participants who completed the study (n = 31) returned the set of take-home questionnaires at the end of the five stages. Out of a maximum number of 713 data points, 647 (91%) were included in the data analysis.
Subjective Responses Summary statistics for comfort responses during stages A to E are shown in Table 1, whereas those for dryness are given in Table 2. To assist with interpretation, group mean scores are also plotted in Figs. 1 and 2, for comfort and dryness, respectively.
No Lens Wear (Stage A) In the absence of contact lenses, both comfort and dryness remained reasonably constant throughout the observation period, with no significant differences being found between any of the time points (comfort, p = 0.82; dryness, p = 0.72).
Optometry and Vision Science, Vol. 92, No. 6, June 2015
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Ocular Discomfort after Contact Lens WearVPapas et al.
667
TABLE 1.
Summary of comfort scores at each time point Stage A Time
n
0 2 4 6 8 10 12
29 29 29 29 29 29 29
Mean
Stage B SD
90.3 13.8 90.8 10.7 91.7 9.7 91.0 10.0 91.5 8.9 91.8 8.9 90.0 8.6 p = 0.82*
n 28 30 30 30 30 27 27
Mean
Stage C SD
87.8 10.4 89.2 10.5 88.4 11.0 86.3 15.2 81.1 18.7 78.6 18.7 76.9 17.9 p G 0.0005*
Stage D
n
Mean
SD
29 30 25
88.0 89.6 87.4
11.6 10.0 15.2
Stage E
n
Mean
SD
25 28 24
87.8 89.6 88.3
20.5 12.4 13.5
p = 0.25*
n
25 29 27
p = 0.22*
Mean
SD
85.8 12.6 88.9 12.1 87.1 11.7 p = 0.18*
Stage A, no lens wear; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8. *p values refer to differences within each stage.
12-Hour Continuous Contact Lens Wear (Stage B) After the first few hours, comfort scores reduced in a fashion typical of that commonly experienced during soft contact lens wear and consistent with that reported previously.3,13 The magnitude of this reduction was such that at T8 and beyond, comfort was significantly worse than at T0 (p G 0.023). Comfort while wearing contact lenses was significantly inferior to the no-lens condition (stage A) at all times after T6 (p G 0.003). Similar behavior was also observed for dryness. Again, the scores during lens wear indicated that dryness was significantly greater from T8 onward than at T0 (p G 0.013), as well as being more severe than that experienced during the no-lens condition for all times after T6 (p G 0.017).
Ocular dryness response also showed no significant differences between these three stages (p = 0.81) and again showed a consistent response profile between stages. In this case, however, scores declined successively and significantly (p e 0.041) across the 4 hours of wear for each stage (Fig. 2). During each, individual, 4-hour stage, both comfort and dryness behaved in similar fashion to the first 4 hours of continuous contact lens wear. That is, stages C to E were statistically indistinguishable from the 0- to 4-hour portion of stage B, for both comfort (p = 0.80) and dryness (p = 0.90) (Figs. 1 and 2). Comparing the scores of each of these 4-hour stages with the nolens response at the corresponding time showed no significant differences for comfort (p 9 0.23) or dryness (p 9 0.37) (Figs. 1 and 2).
Phased 4-Hour Wear (Stages C to E)
DISCUSSION
For comfort, although there was no significant difference between these three stages (p = 0.66), or between the time points within each stage (p 9 0.07), a characteristic pattern of response was discernible within each stage. Thus, in each of the 4-hour stages, scores increased slightly between insertion and the 2-hour point, before declining toward the 4-hour time point. A similar result was also found for the first 4 hours of the continuous wear stage (Fig. 1).
The hypothesis for this study was that contact lens discomfort is related to the general level of fatigue and therefore increases as a function of time during waking hours. On this basis, a number of observations would be expected. First, a wearing period that occurs late in the day, such as stage E, should be associated with more discomfort than those coming earlier, that is, stages C and D. Second, each short stage should roughly match its corresponding portion of the continuous wear profile. Thus, stage C would
TABLE 2.
Summary of dryness scores at each time point Stage A Time
n
0 2 4 6 8 10 12
29 29 29 29 29 29 29
Mean 89.8 91.2 90.4 90.1 89.8 89.6 87.8 p = 0.72*
Stage B SD
n
14.8 11.9 11.0 11.7 12.6 12.7 12.2
28 30 30 30 30 27 27
Mean
Stage C SD
90.0 11.7 89.4 10.5 87.5 11.5 85.1 17.1 80.9 20.7 76.9 22.6 76.5 20.6 p G 0.0005*
Stage D
n
Mean
SD
29 30 25
90.4 88.6 86.9
13.5 12.5 14.5
Stage E
n
Mean
SD
25 28 24
91.5 88.3 88.0
8.8 14.9 13.5
p = 0.007*
n
25 29 27
p = 0.04*
Mean
SD
90.1 12.1 88.3 13.8 85.9 13.1 p = 0.04*
Stage A, no lens wear; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8. *p values refer to differences within each stage. Optometry and Vision Science, Vol. 92, No. 6, June 2015
Copyright © American Academy of Optometry. Unauthorized reproduction of this article is prohibited.
668 Ocular Discomfort after Contact Lens WearVPapas et al.
FIGURE 1. Group mean ocular comfort scores during the following stages of contact lens wear: stage A, no lens; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8.
mirror what occurred during stage B between the times T0 and T4, stage D would resemble stage B at T4 to T8, and stage E would look like stage B for T8 to T12. Third, this sequence of short, 4-hour periods of wear, when added together in series, would reconstruct the stage B, 12-hour continuous profile. The results of the study indicate very clearly that none of these patterns of behavior actually occurred. Not only were the 4-hour stages very similar to one another, they were all essentially identical with the first 4-hour period of continuous wear. Furthermore,
constructing a profile by sequentially linking stages C to E produces a picture that has more in common with the no-lens pattern of stage A than it does with the continuous wear curve of stage B. It appears then that short periods of wear can be undertaken at any time of day without significant changes in subjective comfort being noted. This means that the typical end-of-day discomfort experienced by many wearers, that is reflected in the stage B data is unlikely to be attributed to the simple fact that it is late in the day and the wearer is generally fatigued.
FIGURE 2. Group mean ocular dryness scores during the following stages of contact lens wear: stage A, no lens; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8. Optometry and Vision Science, Vol. 92, No. 6, June 2015
Copyright © American Academy of Optometry. Unauthorized reproduction of this article is prohibited.
Ocular Discomfort after Contact Lens WearVPapas et al.
Clinically, this phenomenon might be exploited by wearers whose total, comfortable wearing time is less than they would ideally wish. Adopting shorter periods of wear and moving these to coincide with times of day that are convenient for lifestyle needs may offer a way to optimize the experience of comfortable contact lens wear. Anecdotally, it is apparent that some subjects have already adopted this strategy. Looking more closely at the individual 4-hour segment profiles for comfort (Fig. 1), the pattern of slight increase followed by decline is consistent across stages C to E and is closely replicated by the first 4 hours of the continuous wear stage B. Accordingly, it appears reasonable to assume that this contour represents the starting profile for any period of lens wear lasting longer than 4 hours. Discomfort resulting from such wear then follows the 12-hour continuous wearing pathway in showing a steady and continuous decline. Previous work has shown that this outcome is unlikely to be attributed to lens-based deterioration or deposition, as replacing lenses after 5 hours of wear had no impact on endof-day comfort.13 That study also suggested that increasing discomfort is likely to be a consequence of the length of time for which the contact lens is on the eye and the present data are strongly supportive of this proposal. Thus, although general fatigue is not a factor, the eye does appear to ‘‘tire’’ of its interaction with the lens, in a way that manifests to the wearer as discomfort over a longer wearing period. The situation for dryness was broadly similar to that outlined above for comfort, but with one exception. Whereas comfort essentially remained constant during the first 4 hours of wear, the sensation of dryness significantly increased (as indicated by decreasing dryness scores) over the same period. A possible explanation for this lag may involve the state of the lens immediately upon insertion. Although mechanical factors and phenomena associated with lens settling probably act to slightly reduce the overall comfort sensation initially, it would be usual for there to be a degree of excess fluid on the lens from its packing or soaking solution as the lens is inserted. This liquid fully hydrates the lens at the point of insertion and contributes some amount of additional moisture to the conjunctival sac. Subjective impressions of dryness at this time are thus likely to be reduced. As time goes on, small improvements in overall comfort occur owing to the completion of lens settling, but as the benefits associated with initial hydration are gradually lost, sensations of dryness progressively increase. Although the magnitude of these changes may not initially be subjectively noticeable to the subject,15 they clearly become so as the length of exposure to the lens increases, and thus it is interesting to consider if the overall impression of discomfort is produced by an underlying sensation of dryness. As has been pointed out previously,13 there is a physiological basis for dryness sensations to be mediated by contact lens wear by virtue of the responses of cold nociceptors on the ocular surface.16,17 It remains to be seen if the current data prove to be a reflection of this kind of mechanism. It is evident from the similarity between the comfort scores of no-lens wear and the very early stages of lens wear that contact lenses initially constitute extremely comfortable vision correction devices. Prolonging the period over which this remains true requires a deeper understanding of the nature and location of the changes that begin in the eye during this time.
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It can be argued that a possible limitation of the current study is the use of a single contact lens type. Therefore, these results cannot be generalized to other contact lenses. However, the ocular comfort and dryness response encountered after 12 hours of contact lens wear in this study was similar to that widely reported as a common experience with different contact lens types.3,13,18,19 The addition of other contact lens types to a crossover study design will run the risk of a higher discontinuation rate of study participants, which might influence the study outcome.
CONCLUSIONS The magnitudes of the discomfort and dryness sensations experienced at the end of a period of contact lens wear are not related to the absolute time of day at which that wear takes place and therefore are not simply a result of general physical fatigue. These findings support previous work suggesting that end-of-day discomfort increases as a function of the length of time the lens is on the eye and is not related to the time of day at which lenses are worn.
ACKNOWLEDGMENTS This study was sponsored by CIBA Vision (Duluth, GA), the Brien Holden Vision Institute (Sydney, New South Wales, Australia), and the Vision Cooperative Research Centre (Sydney, New South Wales, Australia). Received November 5, 2014; accepted February 28, 2015.
REFERENCES 1. Young G, Veys J, Pritchard N, Coleman S. A multi-centre study of lapsed contact lens wearers. Ophthalmic Physiol Opt 2002;22:516Y27. 2. Richdale K, Sinnott LT, Skadahl E, Nichols JJ. Frequency of and factors associated with contact lens dissatisfaction and discontinuation. Cornea 2007;26:168Y74. 3. Santodomingo-Rubido J, Barrado-Navascues 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. 4. Fonn D, Dumbleton K. Dryness and discomfort with silicone hydrogel contact lenses. Eye Contact Lens 2003;29:S101Y4. 5. Carnt N, Jalbert I, Stretton S, Naduvilath T, Papas E. Solution toxicity in soft contact lens daily wear is associated with corneal inflammation. Optom Vis Sci 2007;84:309Y15. 6. Carnt NA, Evans VE, Naduvilath TJ, Willcox MD, Papas EB, Frick KD, Holden BA. Contact lens-related adverse events and the silicone hydrogel lenses and daily wear care system used. Arch Ophthalmol 2009;127:1616Y23. 7. Young G, Efron N. Characteristics of the pre-lens tear film during hydrogel contact lens wear. Ophthalmic Physiol Opt 1991;11:53Y8. 8. Nichols JJ, Sinnott LT. Tear film, contact lens, and patient-related factors associated with contact lens-related dry eye. Invest Ophthalmol Vis Sci 2006;47:1319Y28. 9. Efron N, Jones L, Bron AJ, Knop E, Arita R, Barabino S, McDermott AM, Villani E, Willcox MDP, Markoulli M. The TFOS International Workshop on Contact Lens Discomfort: report of the contact lens interactions with the ocular surface and adnexa subcommittee. Invest Ophthalmol Vis Sci 2013;54:TFOS98Y122. 10. Craig JP, Willcox MDP, Argu¨eso P, Maissa C, Stahl U, Tomlinson A, Wang J, Yokoi N, Stapleton F. The TFOS International Workshop
Optometry and Vision Science, Vol. 92, No. 6, June 2015
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670 Ocular Discomfort after Contact Lens WearVPapas et al.
11.
12.
13.
14.
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on Contact Lens Discomfort: report of the contact lens interactions with the tear film subcommittee. Invest Ophthalmol Vis Sci 2013;54:TFOS123Y56. Jones L, Brennan NA, Gonza´lez-Me´ijome J, Lally J, MaldonadoCodina C, Schmidt TA, Subbaraman L, Young G, Nichols JJ. The TFOS International Workshop on Contact Lens Discomfort: report of the contact lens materials, design, and care subcommittee. Invest Ophthalmol Vis Sci 2013;54:TFOS37Y70. Lazon de la Jara P, Papas E, Diec J, Naduvilath T, Willcox MD, Holden BA. Effect of lens care systems on the clinical performance of a contact lens. Optom Vis Sci 2013;90:344Y50. Papas EB, Tilia D, Tomlinson D, Williams J, Chan E, Chan J, Golebiowski B. Consequences of wear interruption for discomfort with contact lenses. Optom Vis Sci 2014;91:24Y31. Papas EB, Schultz BL. Repeatability and comparison of visual analogue and numerical rating scales in the assessment of visual quality. Ophthalmic Physiol Opt 1997;17:492Y8. Papas EB, Keay L, Golebiowski B. Estimating a just-noticeable difference for ocular comfort in contact lens wearers. Invest Ophthalmol Vis Sci 2011;52:4390Y4.
16. Belmonte C, Gallar J. Cold thermoreceptors, unexpected players in tear production and ocular dryness sensations. Invest Ophthalmol Vis Sci 2011;52:3888Y92. 17. Parra A, Gonzalez-Gonzalez O, Gallar J, Belmonte C. Tear fluid hyperosmolality increases nerve impulse activity of cold thermoreceptor endings of the cornea. Pain 2014;155:1481Y91. 18. Diec J, Evans VE, Tilia D, Naduvilath T, Holden BA, Lazon de la Jara P. Comparison of ocular comfort, vision, and SICS during silicone hydrogel contact lens daily wear. Eye Contact Lens 2012;38:2Y6. 19. Diec J, Papas E, Naduvilath T, Xu P, Holden BA, de la Jara PL. Combined effect of comfort and adverse events on contact lens performance. Optom Vis Sci 2013;90:674Y81.
Eric Papas Level 4, Rupert Myers Bldg University of New South Wales Sydney, NSW 2052 Australia e-mail: [email protected]
Optometry and Vision Science, Vol. 92, No. 6, June 2015
Copyright © American Academy of Optometry. Unauthorized reproduction of this article is prohibited.
ORIGINAL ARTICLE
Ocular Discomfort Responses after Short Periods of Contact Lens Wear Eric Papas*, Daniel Tilia†, John McNally‡, and Percy Lazon de la Jara§
ABSTRACT Purpose. To investigate if contact lensYrelated discomfort is a function of the time of day at which lenses are worn. Methods. This was a randomized, crossover, open-label clinical trial where subjective responses, with and without contact lenses, were assessed every 2 hours during five stages (A to E). Each stage began at the time when subjects would normally have inserted their contact lenses (T0). During stage A, no lenses were worn, whereas in stage B, lenses were worn continuously for 12 hours. In stages C to E, lenses were worn for only 4 hours. Contact lenses were inserted at T0 for stage C, but for stages D and E, lenses were not inserted until T0 + 4 and T0 + 8 hours, respectively. Mixed linear models were used for statistical analysis. Results. In the absence of contact lenses, ocular comfort and dryness remained reasonably constant throughout the observation period. Ocular comfort and dryness decreased during 12 hours of continuous lens wear and became significantly worse from the 8-hour time onward compared with insertion (p G 0.023). There were no significant differences in terms of ocular comfort and dryness between any of the 4-hour lens wear stages (p G 0.82). During each 4-hour stage, both comfort and dryness behaved in a similar fashion (p 9 0.05) to the first 4 hours of continuous contact lens wear. Comparing the scores of each of these stages with the no-lens response at the corresponding time showed no significant differences for comfort (p 9 0.23) or dryness (p 9 0.37). Conclusions. Short periods of wear can be experienced at any time of day without significant change in ocular discomfort and dryness. This suggests that subjective responses at the end of the day are determined by the length of time lenses are in contact with the eye, rather than the time of day at which lenses are worn. (Optom Vis Sci 2015;92:665Y670) Key Words: ocular comfort, ocular discomfort, ocular dryness, contact lenses
C
ontact lensYrelated ocular discomfort and dryness are well-recognized phenomena that have been implicated as major causes of failure among wearers.1,2 The typical ocular discomfort and dryness sensations are low or absent immediately after insertion but increase in severity over the course of a day of wear.3 Many subjects find these sensations at the end of the day to be unsatisfactory, and in some cases, it is intolerable, prompting lens removal before the desired wearing time. The dryness and discomfort response has been attributed to, or associated with, a series of potential causative factors including
*PhD, FAAO † MOptom, FAAO ‡ OD, FAAO § PhD Brien Holden Vision Institute, Sydney, New South Wales, Australia (EP, DT, PLdlJ); Vision Cooperative Research Centre, Sydney, Australia (EP, PLdlJ); School of Optometry and Vision Science, University of New South Wales, Sydney, New South Wales, Australia (EP, PLdlJ); and CIBA Vision, Duluth, Georgia (JMc).
disturbance of the tear film, lens design, material characteristics, and interaction between the contact lens and its care system.4Y11 Considerable effort has been devoted to strategies that will improve contact lens performance including recent work indicating that switching from a reusable to a daily disposable wearing schedule may reduce the magnitude of the problem.12 Given this result, it appears reasonable to ask if further gains can be achieved by increasing the frequency of disposal still further. Unfortunately, in a study where twice daily replacement was investigated, no net gain in end-of-day comfort resulted, despite some short-term benefit being noted immediately after the midday insertion of a new lens.13 This result has been interpreted as indicating that changes occurring to the lens itself, in the time frame of the wearing day, are not responsible for driving the discomfort sensation; rather, it is some factor, or factors, associated with the eye that appear to be implicated. The fact that discomfort sensations increase in intensity with time suggests that the duration of contact between the eyes and
Optometry and Vision Science, Vol. 92, No. 6, June 2015
Copyright © American Academy of Optometry. Unauthorized reproduction of this article is prohibited.
666 Ocular Discomfort after Contact Lens WearVPapas et al.
lens is a critical element in the process. Before that conclusion can be drawn, however, it is important to eliminate the alternative possibility that the discomfort is simply an expression of normal fatigue; that is, lenses feel worse at the end of the day because the subject is more tired at that time. To phrase the question a different way, is it time in the lens, or the time of day, that is driving the sensation of discomfort? The aim of the present study, therefore, was to investigate the hypothesis that contact lensYrelated discomfort is a function of the time of day at which lenses are worn. To do this, an attempt was made to determine if the comfort profile typically experienced by contact lens wearers during the course of the day would be replicated from a series of shorter periods of wear undertaken at different times during the day.
METHODS This was a prospective, crossover, bilateral, open-label, randomized clinical trial in which participants’ subjective responses, with and without contact lenses, were assessed every 2 hours during five stages. A total of 34 participants were enrolled, and 31 completed the trial. The study received ethics approval and was conducted in accordance with the Declaration of Helsinki (October 2008). All participants gave written informed consent. To be eligible for this trial, participants were required to be at least 18 years old, to be experienced contact lens wearers, to be myopic in both eyes, to be correctable to at least 20/40 (6/12) distance visual acuity with spherical contact lenses, and to have no ocular or systemic findings that would prevent safe lens wear. Participants were fitted bilaterally with a monthly replacement, commercial silicone hydrogel contact lens (Lotrafilcon B, Alcon, USA). Lenses were worn only on one occasion and then discarded; hence, no contact lens care product was necessary for cleaning or disinfection. This study consisted of five stages (A to E). Each phase began at the time when subjects would normally have inserted their contact lenses (T0), with the proviso that the latest allowed starting time was 9:00 AM. During stage A, no lenses were worn, whereas in stage B, lenses were worn continuously for 12 hours. In stages C to E, lenses were worn for only 4 hours, but the time point of insertion was different in each case. For stage C, wear began at T0, but for stages D and E, lenses were not inserted until T0 + 4 and T0 + 8 hours, respectively. The order of stages was randomized and a new pair of lenses was used for each relevant stage. Participants were instructed to complete stages on consecutive days, but if their eyes felt uncomfortable the day after 12 hours of continuous wear, they were permitted to not wear lenses (and not complete the takehome questionnaire) on that day. Subjective ocular comfort and ocular dryness were evaluated using 1 to 100 numerical rating scales,14 where 1 = poor and 100 = excellent. Participants were asked ‘‘please rate your ocular comfort/dryness for both eyes’’ at each time point. For dryness rating, a high score indicated less dryness. Participants rated their ocular comfort and dryness within 5 minutes of contact lens insertion and every 2 hours from the beginning of each stage using takehome questionnaires. A series of actions were undertaken to ensure compliance with the collection of subjective responses. The take-home questionnaires
for each stage was printed on different colored paper and included specific information about the stage such as starting time, time to insert the lenses, and for how long they needed to be worn. Participants were verbally instructed on how to complete the takehome questionnaires before commencement and were required to return all documents at the final visit.
STATISTICAL ANALYSIS A sample size of 30 participants was required to detect a paired difference between five crossover stages of 10 T 15 points in subjective ratings with 80% power at the 5% level of significance and corrected for multiple comparisons.15 All participants who completed study treatment were eligible to be included in the analysis data set. The analysis of efficacy variables such as subjective ratings used only scheduled and evaluable visits. Subjective rating variables were compared between stages at each time point and across time within each stage using a linear mixed model with subject random intercepts to adjust for intrasubject correlations and repeated visits. Post hoc multiple comparisons were adjusted using Bonferroni correction. A p value less than or equal to 0.05 was considered statistically significant. Analysis was performed using SPSS 15.0.
RESULTS Demographics A total of 34 participants were enrolled. There were three discontinuations during the trial, and data for these subjects were not included in the analysis. The sample (n = 31) consisted of 59% female and 41% male subjects. The mean (TSD) age was 29.6 (T13.4) years with an average (TSD) auto-refraction sphere and cylinder of j3.33 (T1.34) diopters and j0.71 (T0.37) diopters, respectively.
Take-home Questionnaire Compliance All participants who completed the study (n = 31) returned the set of take-home questionnaires at the end of the five stages. Out of a maximum number of 713 data points, 647 (91%) were included in the data analysis.
Subjective Responses Summary statistics for comfort responses during stages A to E are shown in Table 1, whereas those for dryness are given in Table 2. To assist with interpretation, group mean scores are also plotted in Figs. 1 and 2, for comfort and dryness, respectively.
No Lens Wear (Stage A) In the absence of contact lenses, both comfort and dryness remained reasonably constant throughout the observation period, with no significant differences being found between any of the time points (comfort, p = 0.82; dryness, p = 0.72).
Optometry and Vision Science, Vol. 92, No. 6, June 2015
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Ocular Discomfort after Contact Lens WearVPapas et al.
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TABLE 1.
Summary of comfort scores at each time point Stage A Time
n
0 2 4 6 8 10 12
29 29 29 29 29 29 29
Mean
Stage B SD
90.3 13.8 90.8 10.7 91.7 9.7 91.0 10.0 91.5 8.9 91.8 8.9 90.0 8.6 p = 0.82*
n 28 30 30 30 30 27 27
Mean
Stage C SD
87.8 10.4 89.2 10.5 88.4 11.0 86.3 15.2 81.1 18.7 78.6 18.7 76.9 17.9 p G 0.0005*
Stage D
n
Mean
SD
29 30 25
88.0 89.6 87.4
11.6 10.0 15.2
Stage E
n
Mean
SD
25 28 24
87.8 89.6 88.3
20.5 12.4 13.5
p = 0.25*
n
25 29 27
p = 0.22*
Mean
SD
85.8 12.6 88.9 12.1 87.1 11.7 p = 0.18*
Stage A, no lens wear; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8. *p values refer to differences within each stage.
12-Hour Continuous Contact Lens Wear (Stage B) After the first few hours, comfort scores reduced in a fashion typical of that commonly experienced during soft contact lens wear and consistent with that reported previously.3,13 The magnitude of this reduction was such that at T8 and beyond, comfort was significantly worse than at T0 (p G 0.023). Comfort while wearing contact lenses was significantly inferior to the no-lens condition (stage A) at all times after T6 (p G 0.003). Similar behavior was also observed for dryness. Again, the scores during lens wear indicated that dryness was significantly greater from T8 onward than at T0 (p G 0.013), as well as being more severe than that experienced during the no-lens condition for all times after T6 (p G 0.017).
Ocular dryness response also showed no significant differences between these three stages (p = 0.81) and again showed a consistent response profile between stages. In this case, however, scores declined successively and significantly (p e 0.041) across the 4 hours of wear for each stage (Fig. 2). During each, individual, 4-hour stage, both comfort and dryness behaved in similar fashion to the first 4 hours of continuous contact lens wear. That is, stages C to E were statistically indistinguishable from the 0- to 4-hour portion of stage B, for both comfort (p = 0.80) and dryness (p = 0.90) (Figs. 1 and 2). Comparing the scores of each of these 4-hour stages with the nolens response at the corresponding time showed no significant differences for comfort (p 9 0.23) or dryness (p 9 0.37) (Figs. 1 and 2).
Phased 4-Hour Wear (Stages C to E)
DISCUSSION
For comfort, although there was no significant difference between these three stages (p = 0.66), or between the time points within each stage (p 9 0.07), a characteristic pattern of response was discernible within each stage. Thus, in each of the 4-hour stages, scores increased slightly between insertion and the 2-hour point, before declining toward the 4-hour time point. A similar result was also found for the first 4 hours of the continuous wear stage (Fig. 1).
The hypothesis for this study was that contact lens discomfort is related to the general level of fatigue and therefore increases as a function of time during waking hours. On this basis, a number of observations would be expected. First, a wearing period that occurs late in the day, such as stage E, should be associated with more discomfort than those coming earlier, that is, stages C and D. Second, each short stage should roughly match its corresponding portion of the continuous wear profile. Thus, stage C would
TABLE 2.
Summary of dryness scores at each time point Stage A Time
n
0 2 4 6 8 10 12
29 29 29 29 29 29 29
Mean 89.8 91.2 90.4 90.1 89.8 89.6 87.8 p = 0.72*
Stage B SD
n
14.8 11.9 11.0 11.7 12.6 12.7 12.2
28 30 30 30 30 27 27
Mean
Stage C SD
90.0 11.7 89.4 10.5 87.5 11.5 85.1 17.1 80.9 20.7 76.9 22.6 76.5 20.6 p G 0.0005*
Stage D
n
Mean
SD
29 30 25
90.4 88.6 86.9
13.5 12.5 14.5
Stage E
n
Mean
SD
25 28 24
91.5 88.3 88.0
8.8 14.9 13.5
p = 0.007*
n
25 29 27
p = 0.04*
Mean
SD
90.1 12.1 88.3 13.8 85.9 13.1 p = 0.04*
Stage A, no lens wear; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8. *p values refer to differences within each stage. Optometry and Vision Science, Vol. 92, No. 6, June 2015
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668 Ocular Discomfort after Contact Lens WearVPapas et al.
FIGURE 1. Group mean ocular comfort scores during the following stages of contact lens wear: stage A, no lens; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8.
mirror what occurred during stage B between the times T0 and T4, stage D would resemble stage B at T4 to T8, and stage E would look like stage B for T8 to T12. Third, this sequence of short, 4-hour periods of wear, when added together in series, would reconstruct the stage B, 12-hour continuous profile. The results of the study indicate very clearly that none of these patterns of behavior actually occurred. Not only were the 4-hour stages very similar to one another, they were all essentially identical with the first 4-hour period of continuous wear. Furthermore,
constructing a profile by sequentially linking stages C to E produces a picture that has more in common with the no-lens pattern of stage A than it does with the continuous wear curve of stage B. It appears then that short periods of wear can be undertaken at any time of day without significant changes in subjective comfort being noted. This means that the typical end-of-day discomfort experienced by many wearers, that is reflected in the stage B data is unlikely to be attributed to the simple fact that it is late in the day and the wearer is generally fatigued.
FIGURE 2. Group mean ocular dryness scores during the following stages of contact lens wear: stage A, no lens; stage B, 12 hours continuous wear; stage C, 4 hours wear beginning at T0; stage D, 4 hours wear beginning at T4; stage E, 4 hours wear beginning at T8. Optometry and Vision Science, Vol. 92, No. 6, June 2015
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Ocular Discomfort after Contact Lens WearVPapas et al.
Clinically, this phenomenon might be exploited by wearers whose total, comfortable wearing time is less than they would ideally wish. Adopting shorter periods of wear and moving these to coincide with times of day that are convenient for lifestyle needs may offer a way to optimize the experience of comfortable contact lens wear. Anecdotally, it is apparent that some subjects have already adopted this strategy. Looking more closely at the individual 4-hour segment profiles for comfort (Fig. 1), the pattern of slight increase followed by decline is consistent across stages C to E and is closely replicated by the first 4 hours of the continuous wear stage B. Accordingly, it appears reasonable to assume that this contour represents the starting profile for any period of lens wear lasting longer than 4 hours. Discomfort resulting from such wear then follows the 12-hour continuous wearing pathway in showing a steady and continuous decline. Previous work has shown that this outcome is unlikely to be attributed to lens-based deterioration or deposition, as replacing lenses after 5 hours of wear had no impact on endof-day comfort.13 That study also suggested that increasing discomfort is likely to be a consequence of the length of time for which the contact lens is on the eye and the present data are strongly supportive of this proposal. Thus, although general fatigue is not a factor, the eye does appear to ‘‘tire’’ of its interaction with the lens, in a way that manifests to the wearer as discomfort over a longer wearing period. The situation for dryness was broadly similar to that outlined above for comfort, but with one exception. Whereas comfort essentially remained constant during the first 4 hours of wear, the sensation of dryness significantly increased (as indicated by decreasing dryness scores) over the same period. A possible explanation for this lag may involve the state of the lens immediately upon insertion. Although mechanical factors and phenomena associated with lens settling probably act to slightly reduce the overall comfort sensation initially, it would be usual for there to be a degree of excess fluid on the lens from its packing or soaking solution as the lens is inserted. This liquid fully hydrates the lens at the point of insertion and contributes some amount of additional moisture to the conjunctival sac. Subjective impressions of dryness at this time are thus likely to be reduced. As time goes on, small improvements in overall comfort occur owing to the completion of lens settling, but as the benefits associated with initial hydration are gradually lost, sensations of dryness progressively increase. Although the magnitude of these changes may not initially be subjectively noticeable to the subject,15 they clearly become so as the length of exposure to the lens increases, and thus it is interesting to consider if the overall impression of discomfort is produced by an underlying sensation of dryness. As has been pointed out previously,13 there is a physiological basis for dryness sensations to be mediated by contact lens wear by virtue of the responses of cold nociceptors on the ocular surface.16,17 It remains to be seen if the current data prove to be a reflection of this kind of mechanism. It is evident from the similarity between the comfort scores of no-lens wear and the very early stages of lens wear that contact lenses initially constitute extremely comfortable vision correction devices. Prolonging the period over which this remains true requires a deeper understanding of the nature and location of the changes that begin in the eye during this time.
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It can be argued that a possible limitation of the current study is the use of a single contact lens type. Therefore, these results cannot be generalized to other contact lenses. However, the ocular comfort and dryness response encountered after 12 hours of contact lens wear in this study was similar to that widely reported as a common experience with different contact lens types.3,13,18,19 The addition of other contact lens types to a crossover study design will run the risk of a higher discontinuation rate of study participants, which might influence the study outcome.
CONCLUSIONS The magnitudes of the discomfort and dryness sensations experienced at the end of a period of contact lens wear are not related to the absolute time of day at which that wear takes place and therefore are not simply a result of general physical fatigue. These findings support previous work suggesting that end-of-day discomfort increases as a function of the length of time the lens is on the eye and is not related to the time of day at which lenses are worn.
ACKNOWLEDGMENTS This study was sponsored by CIBA Vision (Duluth, GA), the Brien Holden Vision Institute (Sydney, New South Wales, Australia), and the Vision Cooperative Research Centre (Sydney, New South Wales, Australia). Received November 5, 2014; accepted February 28, 2015.
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Eric Papas Level 4, Rupert Myers Bldg University of New South Wales Sydney, NSW 2052 Australia e-mail: [email protected]
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