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Soft Contact Lens-Related Dryness with and without Clinical Signs

Young, Graeme; Chalmers, Robin; Napier, Leslie; Kern, Jami; Hunt, Chris; Dumbleton, Kathryn

doi: 10.1097/OPX.0b013e3182640af8
Original Articles

Purpose. To report demographics, wearing patterns, and symptoms from soft contact lens (SCL) wearers with significant SCL-related dryness symptoms with and without significant ocular signs of dryness.

Methods. In a multicenter, prospective observational clinical trial, symptomatic SCL wearers reported significant SCL-related dryness via self-administered questionnaire of frequency and intensity of dryness after a dry eye (DE) examination. DE etiology was assigned post hoc by an expert panel, and those with and without significant DE-related signs were analyzed by univariate logistic regression. Possible DE etiologies were aqueous tear deficiency, SCL-induced tear instability, meibomian gland dysfunction, or “other.” Wearers without signs that qualified for any DE etiology were designated as No DE Signs (NDES).

Results. Of the 226 SCL symptomatic wearers examined, 23% were without signs, 30% had aqueous tear deficiency, 25% had SCL-induced tear instability, 14% had meibomian gland dysfunction, and 8% had “other” diagnoses. The NDES wearers had significantly longer pre-lens break-up time (9.8 vs. 6.6 s, p < 0.0001), better lens wetting (3.4 vs. 2.4 0 to 4 scale, p < 0.0001), lower levels of film deposits on lenses (0.45 vs. 0.92, 0 to 4 scale, p < 0.0001), and of most slit lamp signs. The NDES wearers were significantly more likely to be male (36% vs.19%, p = 0.013), were less likely to have deteriorating comfort during the day (81% vs. 97%, p = 0.001), reported longer average hours of comfortable wear (11 ± 3 vs. 9 ± 4 h, p = 0.014), had older contact lenses (18 ± 14 vs. 13 ± 12 days, p = 0.029), and greater intensity of photophobia early and late in the day (p = 0.043 and 0.021).

Conclusions. Symptoms of dryness in SCL wearers stem from a variety of underlying causes. However, nearly one-quarter of these symptomatic SCL wearers appear to be free of signs of dryness. The effective management of CL-related dryness requires a comprehensive range of clinical assessments and the use of a diverse range of management strategies.

*PhD, FCOptom, FAAO





MSc, MCOptom, FAAO

Visioncare Research Ltd, Farnham, United Kingdom (GY, CH), Clinical Trial Consultant, Atlanta, Georgia (RC), Alcon Research, Fort Worth, Texas (LN, JK), and Centre for Contact Lens Research, University of Waterloo, Waterloo, Ontario, Canada (KD).

Supplemental digital contents are available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (

Received December 19, 2011; accepted April 26, 2012.

Robin L. Chalmers 2097 East Lake Rd Atlanta, GA e-mail:

Dryness symptoms related to soft contact lens (SCL) wear and their associated clinical signs have been researched in depth during the past 15 years.110 Compared with patients who do not wear SCLs, wearers of hydrogel lenses report a higher prevalence of dryness and experience it in greater intensity, especially late in the day.8

The introduction of newer silicone hydrogel and other biocompatible lens materials may have reduced the prevalence and degree of SCL-related dryness, although there is no complete consensus on this point. A comparison of age-matched adult hydrogel and silicone hydrogel SCL wearers showed that hydrogel wearers experienced significantly more end-of-day discomfort and dryness when using SCLs on a daily wear basis compared with wearers of silicone hydrogel lenses, and that these symptoms were related to increasing age only in wearers of hydrogel SCLs.2

When SCL wearers experience dryness symptoms, it may or may not be part of an underlying dry eye (DE) condition. In a cross-sectional comparison of patients who did not wear SCLs, and current and former SCL wearers, the lapsed SCL wearers were significantly more likely to report a previous diagnosis of DE, indicating either that DE may have been underlying their symptoms, or that they were erroneously diagnosed with DE because of SCL-related dryness symptoms.5 However, in that survey, 1.5% of the current SCL wearers reported intense late-day dryness when they were not wearing their SCLs, compared with 28.5% reporting intense late dryness while wearing SCLs. The use of SCLs themselves appears to be the exacerbating condition. In support of this point, SCL-related dryness with hydrogel SCLs was not significantly correlated with patient age or sex, although advanced age and female gender are highly correlated with DE disease in patients who do not wear SCLs. Thus, SCL-related dryness appears to be a range of conditions that affects many wearers. It can be influenced by choice of SCL materials, lens care products, wearing environment, and patient factors alike.1113

The purpose of this study was to examine a large cross-section of SCL wearers who reported significant SCL-related dryness with a protocol-driven DE workup to identify the most likely DE etiology for a given symptomatic wearer. A secondary purpose was to characterize the type of SCL wearers who reported SCL-related dryness symptoms to assist in their identification during routine SCL follow-up visits.

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In a multicenter prospective observational clinical trial, symptomatic SCL wearers were recruited from among SCL wearers who were attending 12 clinics in North America for routine after-care or other reasons. The study protocol was approved for the 10 non-university sites by the Quorum Review IRB (Seattle, WA), and by the institutional IRBs at the University of Waterloo and Indiana University. Participants signed informed consent documents before enrollment in the study. The protocol followed the tenets of the Declaration of Helsinki. Several steps were taken to ensure consistency between investigators. First, detailed written instructions were provided on how each of the assessment was to be carried out. Second, all the investigators underwent a pre-study training session on the clinical assessments and grading systems. Finally, their grading accuracy was assessed using an online test involving a series of images that the investigators were asked to grade, as shown in Appendix 1 (available online at They were also provided with a Tearscope Plus (Keeler, Windsor, UK) if they did not have one available at the clinical site.

After consent, participants were invited to complete a confidential self-administered questionnaire regarding their SCL wearing history and a DE examination. Wearers were classified as having significant SCL-related dryness based on a self-administered short questionnaire on frequency and intensity of dryness based on the Contact Lens Dry Eye Questionnaire.1,8 Responses to frequency of dryness and intensity of dryness late in the day were used to classify participants as normal, marginal, or as suffering from SCL-related dryness, as seen in Table 1. Qualifying criteria included a combined assessment of the frequency and late-day intensity of dryness.

Participants who reported SCL-related dryness (the “Dry” participants, n = 226) and 48 asymptomatic controls (“Not Dry”) subsequently received a full protocol-driven DE examination. Clinicians were masked to the participants' symptom status. The examination was conducted at least 5 h after lens insertion of the participant's habitual lenses at home, and followed a pre-determined sequence shown in Table 2.

First, using a Tearscope Plus (Keeler, Windsor UK), the pre-lens tear film lipid layer was assessed, and the non-invasive tear break-up time (NIBUT) was measured. The lens front surface was then assessed using a slit lamp for lens wettability, film deposits, and white spot deposits. The fit of participants' habitual lenses was assessed for centration, movement, and overall fit acceptance. Limbal and bulbar hyperemia were graded using reference images.14 The meibomian glands were assessed and graded on a 0 to 4 scale according to the appearance of the secretions.15

The habitual lenses were then removed and, after waiting for the tear film to re-establish itself, fluorescein tear break-up time (BUT) was measured. This was undertaken by applying a minimal amount of fluorescein with a moistened paper strip to the superior temporal bulbar conjunctiva and, after waiting 60 s, asking the participant to blink three times before measuring BUT with a stopwatch. BUT measurements were performed at least two times per eye, and the results averaged. Corneal staining was graded in each of five corneal sectors on a 0 to 4 scale for type of staining and a 0 to 10 scale for extent of staining. Lissamine green staining of the bulbar conjunctive was assessed 2 min after application of stain with a paper strip and graded using the Oxford scale.16 The normal blink pattern was observed over a number of cycles and assessed whether complete or incomplete. If incomplete, the typical blink deficit was measured in millimeters in the central lid area. Assessment of the vertical gap in blink (blink deficit) was made by observing the fluorescein pattern formed in the tear film by the incomplete closure of the lids. The lids were then everted for assessment of lid wiper epitheliopathy with a 0 to 4 scale.17 Hyperemia and roughness of the upper palpebral conjunctiva were then graded.

After these relatively invasive tests, there was a break of 15 min during which the participants completed a questionnaire covering contact lens wear history and DE symptomology. Questions were related to comfort and comfortable wearing time with participants' habitual lenses. After the 15-min break, the preocular tear film was classified for lipid layer, and NIBUT was measured. Tear meniscus height and regularity were assessed. Finally, an unanesthetized, bilateral Schirmer 1 test was undertaken with the strip placed in the lower temporal lid margin.

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Analysis Methods

After data capture, three clinical experts (authors G.Y., R.C., K.D.) independently reviewed the data from the DE examinations and assigned a probable primary etiology for CL-related dryness for each participant by applying the diagnostic rubric in Table 3 to the signs data. Reviewers were masked to details of patient symptoms or responses to the wearing patterns questionnaire during this step. Possible DE etiologies were aqueous tear deficiency (ATD), SCL-induced tear instability (SCLTI), meibomian gland dysfunction (MGD), and No Dry Eye Signs (NDES), among others. Wearers without signs that qualified for any DE etiology were designated as NDES. “Dry” participants were then stratified into those with and without significant DE-related signs for univariate logistic regression analysis.

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Statistical Analysis

Wearers with CL-related dryness symptoms were included in this study and were stratified into those with and without significant DE-related signs for the application of descriptive statistics and univariate logistic regression analysis. The analysis was undertaken using SPSS Statistics version 19 (IBM, Somers, NY) statistical software. Missing data were excluded from the analysis and not extrapolated from the collected data. A p value ≤0.050 was taken to indicate a statistically significant difference. Logistic regression was used to explore the relationship between those with or without significant DE-related signs and various factors. The four “Dry” groups with substantial populations (NDES, ATD, SCLTI, and MGD) were also compared using linear mixed models, with group as a fixed effect and site and participant as random effects (Tables 4 and 5).

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The study population included 226 SCL wearers with self- report of SCL-related dryness, and 48 asymptomatic control subjects. Approximately two-thirds of participants were wearing silicone hydrogel lenses. The mean ages for the Dry and Not Dry participants were statistically similar: 32.8 vs. 28.7 years, respectively (p = 0.44). The proportion of females was 77% for the Dry group compared with 68% for the Not Dry group (p = 0.20). The average wearing times were similar for the two groups: 12.8 and 13.0 h for the Dry and Not Dry groups respectively; however, the mean comfortable wearing time was shorter for the Dry group: 9.4 h vs. 12.1 h (p < 0.0001). Of the 226 Dry participants, the review panel found that 23% (53/226) had NDES compared with 85% of the Not Dry participants (41/48) (p < 0.0001, χ2).

For the Dry group, the most common potential etiology categorizations were ATD (30%), SCLTI (25%), and MGD (14%), as shown in Fig. 1. Demographics and other lens-related features are shown in Table 4, according to the assigned diagnostic group for the participants with SCL-related dryness.

In the 48 Not Dry control group, 15% (7/48) were categorized in one of the DE categories based on the objective assessments. Four of the Not Dry participants were categorized as such on the basis of signs in one eye only. Two Not Dry participants showed marked DE signs: one was categorized as ATD because of a low Schirmer result in both eyes and the other because of MGD.

Compared with participants with all other DE etiologies, those with NDES were more likely to be male (36% vs. 19%, p = 0.013) and had older contact lenses (17.9 ± 14.1 d vs. 13.4 ± 11.9 d, p = 0.029). Fewer of them reported deterioration in comfort during the wearing day (81% vs. 95%, p = 0.001), and they reported longer mean comfortable wearing times (10.6 ± 3.3 h vs. 9.2 ± 3.5 h, p = 0.014). Comparisons of comfortable and uncomfortable wearing times are shown in Figs. 2 and 3 by possible etiology groupings. Based on symptoms alone, the NDES wearers were not significantly different from the rest of the participants in the study for any symptom (range p = 0.11 to 0.96), except for reporting more intensity and bother from photophobia (p < 0.043).

On slit lamp examination, the NDES wearers showed significantly longer pre-lens NIBUT (9.8 s vs. 6.6s, p ≤ 0.0001), had better lens surface wetting (3.4 vs. 2.4, 0 to 4 scale, p ≤ 0.0001), significantly lower levels of film deposit on lenses (0.45 vs. 0.92, 0 to 4 scale, p ≤ 0.0001), and significantly lower levels of most slit lamp signs (Table 5).

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This study showed that participants with and without symptoms of CL-related dryness did not differ by age, gender, average hours of contact lens wear, or in the prevalence of silicone hydrogel lens use. Thus, to answer one of the study objectives, the CL-related dryness must be a result of the wearer's response to lens wear and cannot be easily predicted by demographic factors or wearing patterns alone.

The participants with CL-related dryness exhibited a wide range of signs that accompanied their habitual symptoms of dryness and discomfort that are commonly associated with DE. However, not one DE sign was present in a majority of these symptomatic participants. The most commonly noted sign was poor lens wetting (40%) followed by fast pre-lens NIBUT (39%) and preocular fluorescein BUT (39%). The diversity of clinical presentations by symptomatic participants suggests a range for causative factors of this condition. Even those participants who were given the same possible diagnosis showed a range of presentations. This diversity of clinical presentations emphasizes the need for practitioners to use a wide range of assessment techniques to screen potential CL patients and to evaluate both signs and symptoms in existing wearers, with an emphasis on symptoms. All these CL wearers had frequent and intense symptoms, but their ocular signs were less predictive of their struggle with comfortable lens wear. In addition, Table 4 shows the amount of overlap in the demographic features of the diagnostic groups, with no significant differences between groups for any of these factors.

An important finding of the study was that nearly one-quarter of these symptomatic SCL wearers showed no apparent signs of DE in a detailed DE examination. The high number of NDES participants, who presented with “occult” CL-related DE that caused symptoms but did not show itself in clinical signs, suggests that factors other than DE may contribute to CL-related dryness symptoms soft lens wearers. These possible factors include awareness of the lens edge or lens optic junctions, environmental stressors such as pollution or smoke, or choice of lens care product.

To evaluate the first of these factors, an assessment of lens fit was included in the DE work-up; however, this would not necessarily identify those participants suffering irritation from marginally small lens diameters. Because the true corneal diameter is over a millimeter larger than the horizontal visible iris diameter,18 it is not always obvious when a lens fails to give full corneal coverage. A further potential source of mechanical irritation with soft lenses arises from the front surface profile (e.g., optic zone junctions). This may explain the higher prevalence of symptoms in toric soft lens wearers noted in an earlier study.1 The lid margin, which comes into contact with the lens surface during blinking, is highly sensitive; Collins et al.19 found the upper lid margin to be only marginally less sensitive than that of the central cornea, whereas Lowther and Hill20 found that lower lid margin sensitivity sometimes exceeded that of the cornea. Another factor that might make lid margin sensitivity more critical in contact lens wear is the fact that it contains a range of mechanoreceptors, in contrast to the cornea which only contains free nerve endings whose prime function is to detect pain. It is also possible that some of the symptoms experienced by participants in this study were related to care products.

This DE examination was exhaustive, with many biomicroscopic observations of the ocular surface and tear film. Even though this battery of clinical tests went beyond what is typically done in clinical practice, tests alone would fail to identify a quarter of the symptomatic SCL wearers. It appears that for the foreseeable future, symptomatic SCL wearers will need a clear opportunity to express the degree of symptoms and guidance from their eye care practitioners on the choice of lens material, care regimen, or other aspects of lens wear that may help to alleviate them. We suggest the inclusion of simple, but systematic, symptom questions during the case history to identify symptomatic SCL wearers and then to use accompanying clinical signs to help in the differential diagnosis. Our team suggests use of the questions in Appendix 2 (available online at and scoring grid in Table 1 for this purpose.1

After symptomatic SCL wearers were identified by questionnaire, one objective of this study was to identify the most efficient objective assessment to classify affected patients. These patients may benefit from changes in lens type, lens care product, or management of environments that exacerbate dryness symptoms.3,11,20,21,22 The clinical observation of pre-lens tear stability through the PLTF-NIBUT or fluorescein TBUT tests was diagnostic in many wearers. These tests identified tear instability problems in approximately 40% of the symptomatic wearers and were the most commonly observed positive signs. This finding agrees with work done by Guillon et al. that found that, in general, lenses hold the tear film differently in symptomatic and asymptomatic SCL wearers, and that breaks in the central zones were most common.9 Tear stability tests, paired with tear volume results from the Schirmer 1 test with which nearly 20% of DE patients had low tear volume, identified a large group of patients who had underlying low tear volumes and/or poor tear stability, regardless of lens wear. Patients with this ATD type of presentation may need more aggressive management of their DE condition than a person with adequate, but unstable, tear film with SCL wear (SCLTI), where the choice of lens material or replacement schedule may help.

Observation of meibomian gland output was also an important part of the differential diagnostic tool kit in this study and identified a unique group. Not surprisingly, the participants with poor meibomian gland output were the oldest sub-group in this study. Therefore, examination for physical changes in the glands may be most efficient if used with older SCL wearers.

The biomicroscopic observation of tear meniscus height was less helpful in identifying patients with low tear volume, as <8% of participants showed poor volume by this test. A number of authors have been developing optical coherence tomography methods to measure tear meniscus height in laboratory-based research and have found significant correlation to symptoms.2325 However, the clinical observation of tear meniscus height with a biomicroscope was relatively insensitive in the current study. Tear meniscus height may be an outcome for research trials, but unlikely to be useful in multicenter trials with a broad base of clinicians. In addition, significant corneal fluorescein staining was noted in fewer than one in five of these symptomatic SCL wearers and, like conjunctival lissamine green staining and lid wiper epitheliopathy signs, was one of the least useful tests in the series.

It is notable that there was a significant difference between groups in lid wiper epitheliopathy with the NDES group showing the lowest level. The prevalence of lid wiper epitheliopathy was lower than previously noted in symptomatic contact lens wearers. This may have been due to a less rigorous technique being used compared with previous studies. For instance, in the present study, only fluorescein was used to evaluate the lid wiper whereas Korb et al. supplemented this with Lissamine green.26

The fact that seven of the control participants were categorized as showing signs of DE may appear surprising; however, most of these cases were marginal and not severe enough to cause symptoms. For instance, four of the participants were categorized for signs, which were evident in one eye only, and only two of the participants showed inferior corneal staining > Grade 1.

There are a number of obvious limitations to the approach taken in this study. The DE test battery did not include all possible DE tests. For example, we did not evaluate tear osmolarity, which has been shown in some studies, to correlate with symptoms in SCL wearers in some, but not all, studies.4 Other tear components have shown weak relationship to symptoms; Glasson et al. showed that chemical analysis of tear proteins did not correlate to symptoms in SCL wearers.7 Instead, the study was restricted to tests that can be reasonably easily undertaken in normal CL practice. Furthermore, some of the DE assessments are subject to variability because of limitations of repeatability and reproducibility. An attempt was made to reduce inter-investigator variations through pre-study training and the use of detailed instructions; nevertheless, it is inevitable that, as with any multicenter clinical study, there will have been some measurement error. Finally, the fact that the potential DE etiology was determined as a secondary exercise by a review panel who was masked to participant demographics rather than by the investigators themselves removed bias that may have occurred based on seeing the patient in person.

Although it is mentioned as one cause of DE in the DEWS 2007 Report,27 dryness related to SCL wear is not a disease condition per se. In fact, in most cases, SCL removal eliminates the symptoms.5 Symptoms of SCL-related dryness often affects SCL wear patterns. Coping techniques include removing lenses earlier in the day and eventually ceasing lens wear altogether. Dryness symptoms have long been associated with discontinuation of SCL wear.10,28,29 This is not surprising because the symptomatic SCL wearers in this study reported an average of 3.5 to 4.3 h of uncomfortable SCL wear per day, depending on diagnostic group. Those hours represent a substantial proportion of their waking hours and represent a large degree of struggle with SCL wear.

In summary, this study has demonstrated the varied nature of CL-related dryness and the diverse range of underlying causes. Most notably, the study suggests that nearly one-quarter of dryness symptoms may relate to factors other than dryness on the surface of the eyes that would generate ocular signs. The effective management of CL-related dryness requires a comprehensive range of clinical assessments, subjective symptoms, and objective tests of tear supply, tear stability, tear quality, and the ocular surface's ability to retain them as an optical surface. Diverse management strategies will be required to incorporate the appropriate treatment to reduce symptoms in SCL wearers.

Robin L. Chalmers

2097 East Lake Rd

Atlanta, GA


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This study was designed by the authors and funded by Alcon Research, Ltd. Study sites included: Carolyn Begley, OD, MS; Tom Quinn, OD; Wilson Movic, OD; Gary Osias, OD; Anthony Verachtert, OD; Stephen Cohen, OD; William Bogus, OD; David Ross, OD; Joe Schwallie, OD, MS; Larry Wan, OD; Shane Kannarr, OD; Gill Woods, OD; and Kathy Dumbleton MSc, MCOptom. Clinical monitors were Rosemary Stewart and Susanna Jones of Visioncare Research, Ltd.

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The appendices are available online at and

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1. 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;34:64–70.
2. 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;32:113–9.
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8. Begley CG, Chalmers RL, Mitchell GL, Nichols KK, Caffery B, Simpson T, DuToit R, Portello J, Davis L. Characterization of ocular surface symptoms from optometric practices in North America. Cornea 2001;20:610–8.
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11. Young G, Riley CM, Chalmers RL, Hunt C. Hydrogel lens comfort in challenging environments and the effect of refitting with silicone hydrogel lenses. Optom Vis Sci 2007;84:302–8.
12. Schafer J, Mitchell GL, Chalmers RL, Long B, Dillehay S, Barr J, Bergenske P, Donshik P, Secor G, Yoakum J. The stability of dryness symptoms after refitting with silicone hydrogel contact lenses over 3 years. Eye Contact Lens 2007;33:247–52.
13. Guillon M, Maissa C. Use of silicone hydrogel material for daily wear. Cont Lens Anterior Eye 2007;30:5–10.
14. McMonnies CW, Chapman-Davies A. Assessment of conjunctival hyperemia in contact lens wearers. Part I. Am J Optom Physiol Opt 1987;64:246–50.
15. Ong BL. Relation between contact lens wear and Meibomian gland dysfunction. Optom Vis Sci 1996;73:208–10.
16. Bron AJ, Evans VE, Smith JA. Grading of corneal and conjunctival staining in the context of other dry eye tests. Cornea 2003;22:640–50.
17. Korb DR, Herman JP, Greiner JV, Scaffidi RC, Finnemore VM, Exford JM, Blackie CA, Douglass T. Lid wiper epitheliopathy and dry eye symptoms. Eye Contact Lens 2005;31:2–8.
18. Hall LA, Young G, Wolffsohn JS, Riley C. The influence of corneoscleral topography on soft contact lens fit. Invest Ophthalmol Vis Sci 2011;52:6801–6.
19. Collins M, Seeto R, Campbell L, Ross M. Blinking and corneal sensitivity. Acta Ophthalmol (Copenh) 1989;67:525–31.
20. Lowther GE, Hill RM. Sensitivity threshold of the lower lid margin in the course of adaptation to contact lenses. Am J Optom Arch Am Acad Optom 1968;45:587–94.
21. Young G, Keir N, Hunt C, Woods CA. Clinical evaluation of long-term users of two contact lens care preservative systems. Eye Contact Lens 2009;35:50–8.
22. Fahmy M, Long B, Giles T, Wang CH. Comfort-enhanced daily disposable contact lens reduces symptoms among weekly/monthly wear patients. Eye Contact Lens 2010;36:215–9.
23. Wang J, Cox I, Reindel WT. Upper and lower tear menisci on contact lenses. Invest Ophthalmol Vis Sci 2009;50:1106–11.
24. Chen Q, Wang J, Shen M, Cai C, Li J, Cui L, Qu J, Lu F. Lower volumes of tear menisci in contact lens wearers with dry eye symptoms. Invest Ophthalmol Vis Sci 2009;50:3159–63.
25. Chen Q, Zhang X, Cui L, Huang Q, Chen W, Ma H, Lu F. Upper and lower tear menisci in Sjogren's syndrome dry eye. Invest Ophthalmol Vis Sci 2011;52:9373–8.
26. Korb DR, Greiner JV, Herman JP, Hebert E, Finnemore VM, Exford JM, Glonek T, Olson MC. Lid-wiper epitheliopathy and dry-eye symptoms in contact lens wearers. CLAO J 2002;28:211–6.
27. Definition and Classification Subcommittee of the International Dry Eye WorkShop. 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;5:75–92.
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29. Richdale K, Sinnott LT, Skadahl E, Nichols JJ. Frequency of and factors associated with contact lens dissatisfaction and discontinuation. Cornea 2007;26:168–74.

soft contact lens; dryness; symptoms; clinical signs

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