The majority of contact lens wearers continue to use planned-replacement lenses, accounting for 61% of all soft lenses prescribed worldwide in 2012 (USA 82%, Australia 50%).1 The contact lens storage case is therefore an integral component of lens wear for the majority of lens wearers. A large part of successful lens wear is reliant on compliance with an effective case cleaning regime because microbial contamination of contact lens cases has been associated with relatively rare but potentially devastating microbial keratitis,2,3 as well as relatively common sterile corneal inflammation.4 Microbes isolated from the corneal lesion of microbial keratitis patients are similar to those found in the contact lens case,5 and many of the pathogens isolated from contact lenses during an infectious or inflammatory event6 have also been found in contaminated contact lens cases.7 Contamination of a contact lens case also appears to be independent of contact lens type.7
There is a general consensus that noncompliance with prescribed contact lens care regimes is high8–15 with noncompliance estimates ranging from 24% to 79%.8,9 Contact lens case hygiene is not exempt from this noncompliant behavior,12,15–17 possibly a result of the perceived onerous and time-consuming task of routinely cleaning a case that does not appear to be soiled.18 However, improving lens case compliance in general is made difficult when instructions relating to case maintenance vary between regulatory authorities, contact lens solutions manufacturers, and eye-care practitioners.19
Guidelines relating to contact lens care also change with time. In the 1990s, the reported Acanthamoeba case-contamination rate was around 8%,20,21 and several studies recommended cases be rinsed with very hot water (>70°C) to minimize Acanthamoeba20,22 and bacterial contamination.23 However, modern guidelines do not recommend tap water be used to rinse contact lens cases.12,15,24–28
Acanthamoeba keratitis is a subset of microbial keratitis. While the incidence of Acanthamoeba keratitis is low,29–33 up to 93% of all contact lens–related microbial keratitis are caused by bacteria, most commonly by Gram-negative bacteria (GNB) and Pseudomonas aeruginosa in particular.29,34 However, the literature is focused on the increased risk of Acanthamoeba contamination with tap-water use, possibly a result of the historical association of Acanthamoeba keratitis with this risk factor.35,36 There is a paucity of information on the increased risk of case contamination with organisms more commonly associated with microbial keratitis when tap water is used.
The purpose of this retrospective analysis was to determine the efficacy of written instructions on contact lens case hygiene and to quantify the effect of noncompliance on contact lens case contamination.
Participants, Contact Lenses, and Lens Care Solutions
Data collected from 16 prospective, non-simultaneous, unmasked, 3-month daily-wear trials conducted at the Clinical Research and Trials Centre of the Brien Holden Vision Institute in Sydney were retrospectively analyzed. All trials received ethics approval through a local Human Research Ethics Committee and were conducted in accordance with the principles of the Declaration of Helsinki.
All trials followed a similar protocol in which participants attended four clinical visits at 2 weeks, 1 month, and 3 months after the initial baseline visit. Approximately 40 participants were enrolled into each trial. At the baseline visit, eligibility for a trial was assessed and contact lenses were fitted. To be eligible, participants had to be at least 18 years old, be myopic in both eyes, and have no underlying ocular or systemic findings that would prevent safe contact lens wear. Both experienced and new lens wearers were eligible to participate. Participants were also excluded from a trial if a successful contact lens fit was not achieved or if visual acuity with contact lenses was worse than 6/12 (20/40) in either eye. The visual acuity criteria was not applied to participants wearing monovision, provided they were able to achieve 6/12 or better with spherical over-refraction through the eye used for near work. All trials used spherical contact lenses with a power range of −0.75 D to −6.00 D. Participants were instructed to wear contact lenses a minimum of 5 days per week, 6 hours per day, and not to sleep overnight in contact lenses.
Each trial used one of five commercially available silicone hydrogel contact lenses: senofilcon A (Johnson & Johnson Vision Care, Jacksonville, FL), lotrafilcon A and lotrafilcon B (CIBA VISION, Duluth, GA), balafilcon A (Bausch + Lomb, Rochester, NY), and comfilcon A (CooperVision, Fairport, NY). Contact lenses were replaced as per manufacturer’s instructions, i.e., two-weekly for senofilcon A and monthly replacement for all other lenses.
In nine of the 16 trials, participants were given verbal instructions about lens case hygiene: to rinse case with fresh lens care solution (LCS), not to use tap water, and to leave cases to air dry (position not specified) between disinfection cycles. Participants in these trials were labeled group 1, and comprised 325 participants and five LCS: ClearCare (hydrogen peroxide), AQuify (PHMB, CIBA VISION), OPTI-FREE Express and OPTI-FREE RepleniSH (polyquaternium-1/myristamidopropyl dimethylamine; Alcon Laboratories, Fort Worth, TX), and renu fresh (PHMB, Bausch + Lomb). In the other seven trials, participants were given the same instructions both verbally and in written form. Participants in these trials were labeled group 2, and comprised 263 participants and three LCS: RevitaLens OcuTec (polyquaternium-1/alexidine dihydrochloride; Abbott Medical Optics, Inc., Santa Ana CA), Biotrue (polyquaternium-1/PHMB; Bausch + Lomb), and OPTI-FREE Puremoist (polyquaternium-1/myristamidopropyl dimethylamine; Alcon Laboratories).
Participants were instructed to use their LCS as per manufacturer’s recommendation, i.e., rinse only in group 1 and rub and rinse in group 2. The rinse-only regime consisted of rinsing each side of a lens with LCS for 5 seconds, overnight storage in the same LCS, and insertion straight from the lens case the next morning. The rub-and-rinse regime consisted of rubbing each side of a lens with LCS, rinsing each side of lens with LCS for 5 seconds, overnight storage in same LCS, and insertion straight from the lens case the next morning. Contact lenses were rubbed as per manufacturer’s instructions; 2–4 seconds with RevitaLens OcuTec and 20 seconds with Biotrue and Puremoist.
History was taken at each scheduled visit, and investigators probed participants regarding any problems or issues they might be experiencing. Instructions were only reinforced if there appeared to be any deficiencies in a participant’s care regime.
Participants completed a survey on their habitual method of contact lens hygiene (rinsing of lenses, lens cleaning methodology after lens removal, and procedure before lens insertion), LCS hygiene (frequency of changing LCS in the case, “topping off” LCS in the case, and leaving lid off LCS bottle), and contact lens case hygiene (frequency and methodology of case cleaning). Surveys were completed at both the 1- and 3-month visits, and thus a maximum of two surveys were collected for each participant.
A participant was categorized as a “non tap-water user” (compliant) if no survey was positive for tap-water use to rinse the contact lens case or a “tap-water user” (non-compliant) if at least one survey was positive for tap-water use to rinse the case. Tap-water use was defined as any water obtained from the tap, i.e., hot or cold water straight from the tap, boiled water from a kettle, or cold water previously boiled in a kettle.
Contact Lens Cases
Five different contact lens cases were used during the 16 trials. Participants who used ClearCare LCS were given the stand-up, cylindrical contact lens case as supplied by the manufacturer to enable neutralization of hydrogen peroxide before lens insertion. All other participants were given horizontal, deep-welled cases. Participants who used AQuify, OPTI-FREE Express, and OPTI-FREE RepleniSH were given the same polypropylene contact lens case (CIBA VISION) while all other participants were given cases as supplied by the manufacturer of the LCS, i.e., RevitaLens OcuTec: acrylonitrile butadiene base and polypropylene lids, and Biotrue, renu fresh, and Puremoist: polypropylene case. No case used in any study had any specific antimicrobial properties. The design features of each contact lens case and the number of each type of case used with each LCS is given in Table 1.
Participants were instructed to use each case for 1 month. Cases were collected at the 1- and 3-month visits, and so a maximum of two cases were collected for each participant per trial. Used cases that were not collected were disposed of by the participant. Collected cases were analyzed for the presence of microbial contamination by using standard procedures to identify and enumerate the types of microbes as have been described elsewhere.7 Briefly, the lids and wells of contact lens cases were swabbed with calcium alginate and dissolved in phosphate buffered saline. These samples were then cultured onto appropriate culture plates for recovery of bacteria and fungi. Cases collected from group 1 participants were also analyzed for Acanthamoeba.
Before the analysis of outcome variables, demographic factors were compared between the two study groups. Factors that were significantly different were added into the model when comparing the two groups of studies. Case contamination rates as a percentage of participants were analyzed for its association with participant noncompliance using logistic regression with robust estimate of variance. Case contamination represented as colony forming unit (CFU)/case was log transformed before analysis and analyzed using linear mixed model with subject random intercepts. The proportion of noncompliant participants, represented as a percentage, was compared between the two groups of studies using logistic regression with robust estimate of variance. The linear mixed model with random subject intercepts and logistic regression with robust estimate of variance accounted for any intrasubject correlations because of multiple visits and enrollments. LCS, study group (i.e., group 1 or group 2), and lens case design were accounted as possible confounders. Study group accounted for instructions (verbal vs. written) and lens care regime (rinse only vs. rub and rinse) differences between both groups. Because there was no LCS that was used with more than one type of lens case, LCS and lens case design could not be factored into the same model and so results are presented as adjusted for group-LCS and group-lens case design. Analysis within group 1 was adjusted for LCS and lens case design. In group 2, analysis was only adjusted for LCS because each lens case design was only used with the one LCS and so adjustment for lens case yielded the same result as adjustment for LCS. Odds ratios (OR) and its confidence limits described the strength of association, and p value less than or equal to 0.05 was considered statistically significant.
The final dataset comprised 588 participants of which 61% were female, 15% were new lens wearers, and the mean age ± SD was 29 ± 11 years. Demographic differences between participants in group 1 and group 2 are shown in Table 2. Demographic factors that were significantly different between the two groups of studies were accounted for in the model as possible confounders.
Eighty-two percent (n = 481) of all participants were categorized as non–tap-water users (compliant) and 18% (n = 107) were tap-water users (noncompliant). Categorization as non–tap-water and tap-water users for participants in groups 1 and 2 are shown in Table 3. After adjusting for the confounding effects of age, gender, and ethnicity, the logistic model showed that group 1 had a significantly higher odds of using tap water to clean cases compared to group 2 (OR = 2.19, p = 0.001; 95% confidence interval [CI]: 1.40–3.44).
Contact Lens Case Contamination
Eighty-five percent of all cases were returned, with a total of 1000 cases (517 and 483 cases from group 1 and group 2 participants, respectively) analyzed. The overall case contamination (i.e., contamination by any organism) rate was 79%. The case contamination rates for Gram-positive bacteria (GPB), Gram-negative bacteria (GNB), and fungi were 76%, 14%, and 14%, respectively. The overall, GPB, GNB, and fungal case contamination rates for non–tap-water users and tap-water users are shown in Fig. 1. Significantly more cases were contaminated with GNB when tap water was used to rinse the case compared to when tap water was not used (30% vs. 10%, p < 0.001) while there were no significant differences in the rates of overall, GPB, and fungal case contamination (p > 0.05). Similar results were found for both groups 1 and 2 in that tap-water rinsing of cases was only associated with increased GNB case contamination (Figs. 2 and 3, respectively). Acanthamoeba was not cultured from any case (group 1 participants only). No other hygiene behavior (contact lens or LCS) was associated with a significant increase in either the overall or GNB case contamination rate (p > 0.05).
The OR for case contamination and mean CFU/case (overall, GPB, GNB, and fungal) when tap water was used to rinse the case are shown in Table 4. Similar results were also found for both groups 1 and 2, with tap-water use associated with an increased risk for GNB case contamination (group 1: OR = 2.63, 95% CI = 1.40–4.95, p ≤ 0.003 [adjusted for LCS or lens case design]; group 2: OR = 3.63, 95% CI = 1.51-8.70, p = 0.004). Group 1 tap-water users showed a significantly higher mean GNB CFU/case (42,787 ± 160,611 vs. 12,583 ± 85,676, p ≤ 0.004 [adjusted for LCS or lens case design]). Group 2 tap-water users had a lower mean CFU/case (39 ± 176 vs. 673 ± 9449) because of one non–tap-water user presenting a case with GNB (Pseudomonas sp.) CFU = 68,500. However, mean log GNB CFU/case was significantly higher in tap-water users compared to non–tap-water users in group 2 (0.8 vs. 0.3, p = 0.024). There was no increased risk or significant difference in mean CFU/case with tap-water rinsing of cases for overall, GPB, or fungal case contamination (p > 0.05) for either group 1 or group 2. Of the 107 participants categorized as tap-water users, 54% (n = 58) answered positively on only one survey for tap-water use and 46% (n = 49) answered positively on both surveys. This increased frequency of tap water to rinse the case (non–tap-water user/positive for tap-water use on one survey/positive for tap water use on both surveys) was associated with an increase in OR for GNB case contamination (1.00/1.86/5.01, p < 0.001) and an increase in the mean GNB CFU/case (6477 ± 60,447/17,511 ± 83,503/42,078 ± 175,197, p < 0.001) when adjusted for either group-LCS or group-lens case design.
Commonly recovered GNB from contaminated cases included Stenotrophomonas maltophilia, Delftia acidovorans, Achromobacter sp., Serratia marcescens, and Pseudomonas sp. The case contamination rates and mean CFU found in contaminated cases for each of these species of GNB when tap water was used to rinse cases are shown in Table 5.
One of the outcomes of this analysis was that contact lens case hygiene can be improved depending on the method of instruction delivery. This finding of improved compliance when written instructions are given has been previously reported.10,11,18,37 However, despite written instructions, 13% of group 2 participants still used tap water as part of their case cleaning regime. It can be argued that this result demonstrates some contact lens wearers will never be compliant,8,11 and a 13% noncompliance rate, as measured by this analysis, is acceptable when compared against the high published rates of noncompliance.8,9 An alternate argument is that written instructions are an effective way of improving compliance, but they need to be complemented with other methods. A number of methods aimed at improving compliance are discussed in detail in two papers by McMonnies.18,37 Briefly, compliance with the prescribed contact lens care regime is a long-term goal, commencing with education at the prescribing visit but the postponement of non-essential instructions until follow-up visits. Practical demonstration can be used to reinforce both verbal and written instructions.
Several studies have reported on the association between demographic factors and various types of compliance related to contact lens wear. Gender does not appear to be a factor in compliance with replacing lenses as per manufacturer’s recommendation, while the effect of age is inconsistent between studies.38,39 A web-based survey of 4021 contact lens wearers across 14 countries by Morgan et al.12 found better compliance for a range of modifiable behaviors (including case cleaning) in females and older contact lens wearers; however, neither of these demographic factors was significant for compliance (i.e., using LCS to rinse the case and not tap water ) in our study. This was probably a result of participants in this study being involved in a clinical trial while those analyzed by Morgan et al.12 were contact lens wearers from a general population. The minor demographic differences in age and ethnicity between groups 1 and 2 in this study did not appear to impact on results as neither were significant for compliance.
The overall case contamination rate in this study (79%) falls within the range of published data estimates of 53% to 85% from studies in the UK,40 USA41, New Zealand,20 and Australia.7,42,43 Moreover, our results indicate that GNB case contamination was around three times more likely, and the mean CFU/case for GNB was significantly higher when tap water was used to rinse the contact lens case compared to when tap water was not used. Furthermore, GNB case contamination was more likely and the mean CFU/case for GNB was higher as the frequency of tap-water use increased.
This increase in GNB case contamination with tap-water rinsing of cases might have been a result of compliance issues as participants who were noncompliant with instructions for case cleaning could also be noncompliant in other areas of contact lens–wear hygiene. However, this appears unlikely for this analysis as no other hygiene procedure was associated with a significant increase in either the overall or GNB case contamination rate.
Another possible mechanism for increase GNB case contamination with tap-water use is biofilm formation. Early biofilm formation is characterized by cell surface attachment to the contact lens case.44,45 Even though rubbing, rinsing with LCS, and tissue wiping of contact lens cases is the most effective way to reduce biofilm formation,27,28,43 a degree of efficacy is also achieved in a regime involving rinsing with LCS and air drying,27,28 possibly from a residual film of LCS remaining on the lens case. Tap-water rinsing of the case washes away the LCS so that a residual film does not form on the case surface. Any forming biofilm would be left relatively undisturbed, allowing it to form stronger adhesions to the case surface,43 which ultimately leads to increased resistance to the LCS.45,46
While biofilm formation might be more likely in contact lens cases rinsed with tap water, neither GPB nor fungal case contamination was significantly different in non–tap-water users compared to tap-water users. A study by Wu et al.43 that examined the impact on case contamination with two different case cleaning regimes (rinsing case with LCS/air drying compared to rubbing case/rinsing with LCS/tissue wiping/air drying) during daily wear of contact lenses found no significant difference in CFU count for GNB or fungus, while GPB was significantly less for the latter regime. In terms of the effect of case cleaning regime on fungal case contamination, our results are similar to those of Wu et al.43 It appears that rinsing the case with LCS and air drying is effective against GNB; however, rubbing the case/rinsing with LCS/tissue wiping/air drying will also reduce the presence of GPB while fungal contamination seems unaffected by the case cleaning regime. Indeed, a study by Chang et al.47 found re-use of LCS (“topping off”) to be the only behavioral factor associated with an outbreak of Fusarium keratitis in 2006 and no association was found with contact lens case hygiene. An in vitro study has also confirmed fungal protection to LCS disinfection with “topping off”.48
A few reports49,50 have demonstrated rubbing and rinsing of silicone hydrogel contact lenses to be more effective in removing pathogenic microbes (GNB, GPB, fungus, and Acanthamoeba sp.) from the contact lens surface than rinsing alone. Even though the case contamination rate and mean CFU/case for GNB in this study were generally lower when lenses were rubbed and rinsed (i.e., generally lower in group 2 compared to group 1), it is difficult to compare the efficacy of rubbing and rinsing versus rinsing only in this study as each group used different LCS. Regardless, our finding of similar OR with overlapping 95% CI in groups 1 and 2 for GNB case contamination in tap-water users compared to non–tap-water users indicates that tap-water rinsing of cases increases GNB case contamination irrespective of lens care regime or LCS efficacy. Perhaps this is not a surprising result as the contact lens case is usually the first source of biofilm formation.44
All five species of identified GNB in contaminated cases had significantly higher case contamination rates in tap-water users, but only Pseudomonas sp. S. maltophilia and Achromobacter sp. were significantly worse for mean CFU/case. The role of Pseudomonas sp. in contact lens–related eye disease and inflammation is well established.6,29,34,51 A recent study by Wiley et al.52 reported D. acidovorans, S. maltophilia, and Achromobacter sp. to be emerging pathogens in contact lens–related disease. In 28 contact lens wearers referred to an eye clinic with either keratitis, corneal infiltrates, or corneal ulcers, Achromobacter sp. was the most common bacteria found in contact lens cases followed by S. maltophilia.52
Finding microbes on the contact lens and the contact lens case is an expected result if they are present at the ocular surface, but the reverse might not be true, i.e., microbes in the case do not imply that microbes will also be on the contact lens or ocular surface.53 Indeed, contamination of the contact lens is less frequent than contamination of the lens case.3,52 However, a contaminated case can be a replenishable source of pathogenic microbes,20 potentially contaminating the contact lens. The corneal epithelium that is compromised or modified from contact lens wear might allow these microbes to attach, invade, and replicate, leading to infectious or inflammatory keratitis.54,55
In this study, none of the assessed contact lens cases from group 1 were contaminated with Acanthamoeba. There are a few factors that could account for this outcome. First, the Sydney water supply is generally clean with no reported issues since a Giardia and Cryptosporidium contamination in 1998,56 and mains water is used to supply Sydney residential bathrooms. Conversely, one of the factors associated with the outbreak of Acanthamoeba keratitis in Chicago was a decrease in disinfection by-products in the mains water supply,57 while the use of storage tanks to supply cold water to bathrooms in England22 and Hong Kong26 have been associated with Acanthamoeba contamination. Second, contact lens cases in this study were used for only 1 month, and regular replacement of contact lens cases has long been advocated to reduce Acanthamoeba contamination.20,21
Even though no cases were contaminated with Acanthamoeba in this study, previous studies have found cases contaminated with Acanthamoeba to be often contaminated with GNB.20,21 Indeed, some species of GNB might not only be beneficial to Acanthamoeba growth but might also alter the ocular surface to increase the possibility of Acanthamoeba keratitis.58 Hence, minimizing GNB case contamination might also be beneficial in indirectly reducing the incidence of atypical keratitis.
Lens case hygiene can be improved by effective communication of instructions. Contact lens wearers should be actively discouraged from rinsing contact lens cases with tap water because of the increased risk of GNB contamination.
Brien Holden Vision Institute
Level 5, Rupert Myers Building North Wing
University of New South Wales
Sydney, NSW 2052
The studies used in this analysis have been sponsored by CIBA VISION, Abbott Medical Optics, Inc., and the Brien Holden Vision Institute.
Received May 17, 2013; accepted October 10, 2013.
1. Morgan PB, Woods CA, Tranoud, is IG, Helland M, Efron N, Carrillo-Orihuela G, Grupcheva CN, Jones D, Tan KO, Pesinova A, Ravn O, Santodomingo J, Malet F, Sze L, Cheng P, Végh M, Erdinest N, Ragnarsdóttir JB, Montani G, Davila-Garcia E, Itoi M, Chu BS, Bendoriene J, van der Worp E, Awasthi S, Lam W, González-Méijome JM, Johansson O, Silih MS, Hsiao J, Nichols JJ. International contact lens prescribing in 2012. Contact Lens Spectrum 2013; 28 (1): 31–44.
2. Stapleton F, Keay L, Edwards K, Naduvilath T, Dart JK, Brian G, Holden BA. The incidence of contact lens-related microbial keratitis in Australia. Ophthalmology 2008; 115: 1655–62.
3. McLaughlin-Borlace L, Stapleton F, Matheson M, Dart JK. Bacterial biofilm on contact lenses and lens storage cases in wearers with microbial keratitis. J Appl Microbiol 1998; 84: 827–38.
4. Bates AK, Morris RJ, Stapleton F, Minassian DC, Dart JK. ‘Sterile’ corneal infiltrates in contact lens wearers. Eye 1989; 3 (Pt. 6): 803–10.
5. Mayo MS, Schlitzer RL, Ward MA, Wilson LA, Ahearn DG. Association of Pseudomonas
corneal ulcers with use of contaminated solutions. J Clin Microbiol 1987; 25: 1398–400.
6. Willcox MD. Pseudomonas aeruginosa
infection and inflammation during contact lens wear: a review. Optom Vis Sci 2007; 84: 273–8.
7. Willcox MD, Carnt N, Diec J, Naduvilath T, Evans V, Stapleton F, Iskandar S, Harmis N, de la Jara PL, Holden BA. Contact lens case contamination during daily wear of silicone hydrogels. Optom Vis Sci 2010; 87: 456–64.
8. Bui TH, Cavanagh HD, Robertson DM. Patient compliance during contact lens wear: perceptions, awareness, and behavior. Eye Contact Lens 2010; 36: 334–9.
9. de Oliveira PR, Temporini-Nastari ER, Ruiz Alves M, Kara-Jose N. Self-evaluation of contact lens wearing and care by college students and health care workers. Eye Contact Lens 2003; 29: 164–7.
10. Donshik PC, Ehlers WH, Anderson LD, Suchecki JK. Strategies to better engage, educate, and empower patient compliance and safe lens wear: compliance: what we know, what we do not know, and what we need to know. Eye Contact Lens 2007; 33: 430–3.
11. Efron N. The truth about compliance. Cont Lens Anterior Eye 1997; 20: 79–86.
12. Morgan PB, Efron N, Toshida H, Nichols JJ. An international analysis of contact lens compliance. Cont Lens Anterior Eye 2011; 34: 223–8.
13. Claydon BE, Efron N. Non-compliance in contact lens wear. Ophthalmic Physiol Opt 1994; 14: 356–64.
14. Robertson DM, Cavanagh HD. Non-compliance with contact lens wear and care practices: a comparative analysis. Optom Vis Sci 2011; 88: 1402–8.
15. Hickson-Curran S, Chalmers RL, Riley C. Patient attitudes and behavior regarding hygiene and replacement of soft contact lenses and storage cases. Cont Lens Anterior Eye 2011; 34: 207–15.
16. Yung MS, Boost M, Cho P, Yap M. Microbial contamination of contact lenses and lens care accessories of soft contact lens wearers (university students) in Hong Kong. Ophthalmic Physiol Opt 2007; 27: 11–21.
17. Yung AM, Boost MV, Cho P, Yap M. The effect of a compliance enhancement strategy (self-review) on the level of lens care compliance and contamination of contact lenses and lens care accessories. Clin Exp Optom 2007; 90: 190–202.
18. McMonnies CW. Improving contact lens compliance by explaining the benefits of compliant procedures. Contact Lens Anterior Eye 2011; 34: 249–52.
19. Wu Y, Carnt N, Willcox M, Stapleton F. Contact lens and lens storage case cleaning instructions: whose advice should we follow? Eye Contact Lens 2010; 36: 68–72.
20. Gray TB, Cursons RT, Sherwan JF, Rose PR. Acanthamoeba
, bacterial, and fungal contamination of contact lens storage cases. Br J Ophthalmol 1995; 79: 601–5.
21. Larkin DF, Kilvington S, Easty DL. Contamination of contact lens storage cases by Acanthamoeba
and bacteria. Br J Ophthalmol 1990; 74: 133–5.
22. Seal D, Stapleton F, Dart J. Possible environmental sources of Acanthamoeba
spp. in contact lens wearers. Br J Ophthalmol 1992; 76: 424–7.
23. Larragoiti ND, Diamos ME, Simmons PA, Edrington TB. A comparative study of techniques for decreasing contact lens storage case contamination. J Am Optom Assoc 1994; 65: 161–3.
25. Asia Pacific Contact Lens Summit II, Melbourne, Australia, 2011. Guidelines for Safe and Effective Uses of Contact Lenses in the New Century for All Contact Lens Wearers. Available at: http://www.amo.com.hk/zh/CONSUMER.pdf
. Accessed: September 20, 2012.
26. Boost M, Cho P, Lai S, Sun WM. Detection of Acanthamoeba
in tap water and contact lens cases using polymerase chain reaction. Optom Vis Sci 2008; 85: 526–30.
27. Wu YT, Zhu H, Willcox M, Stapleton F. The effectiveness of various cleaning regimens and current guidelines in contact lens case biofilm removal. Invest Ophthalmol Vis Sci 2011; 52: 5287–92.
28. Wu YT, Zhu H, Willcox M, Stapleton F. Removal of biofilm from contact lens storage cases. Invest Ophthalmol Vis Sci 2010; 51: 6329–33.
29. Stapleton F, Keay LJ, Sanfilippo PG, Katiyar S, Edwards KP, Naduvilath T. Relationship between climate, disease severity, and causative organism for contact lens-associated microbial keratitis in Australia. Am J Ophthalmol 2007; 144: 690–8.
30. Schaumberg DA, Snow KK, Dana MR. The epidemic of Acanthamoeba keratitis: where do we stand? Cornea 1998; 17: 3–10.
31. Radford CF, Minassian DC, Dart JK. Acanthamoeba keratitis in England and Wales: incidence, outcome, and risk factors. Br J Ophthalmol 2002; 86: 536–42.
32. Lam DS, Houang E, Fan DS, Lyon D, Seal D, Wong E. Incidence and risk factors for microbial keratitis in Hong Kong: comparison with Europe and North America. Eye 2002; 16: 608–18.
33. Butler TK, Males JJ, Robinson LP, Wechsler AW, Sutton GL, Cheng J, Taylor P, McClellan K. Six-year review of Acanthamoeba keratitis in New South Wales, Australia: 1997–2002. Clin Experiment Ophthalmol 2005; 33: 41–6.
34. Saeed A, D’Arcy F, Stack J, Collum LM, Power W, Beatty S. Risk factors, microbiological findings, and clinical outcomes in cases of microbial keratitis admitted to a tertiary referral center in Ireland. Cornea 2009; 28: 285–92.
35. Moore MB, McCulley JP, Newton C, Cobo LM, Foulks GN, O’Day DM, Johns KJ, Driebe WT, Wilson LA, Epstein RJ, et al. Acanthamoeba
keratitis. A growing problem in soft and hard contact lens wearers. Ophthalmology 1987; 94: 1654–61.
36. Stehr-Green JK, Bailey TM, Visvesvara GS. The epidemiology of Acanthamoeba keratitis in the United States. Am J Ophthalmol 1989; 107: 331–6.
37. McMonnies CW. Improving patient education and attitudes toward compliance with instructions for contact lens use. Contact Lens Anterior Eye 2011; 34: 241–8.
38. Dumbleton K, Woods C, Jones L, Fonn D, Sarwer DB. Patient and practitioner compliance with silicone hydrogel and daily disposable lens replacement in the United States. Eye Contact Lens 2009; 35: 164–71.
39. Yeung KK, Forister JF, Forister EF, Chung MY, Han S, Weissman BA. Compliance with soft contact lens replacement schedules and associated contact lens-related ocular complications: the UCLA Contact Lens Study. Optometry 2010; 81: 598–607.
40. Devonshire P, Munro FA, Abernethy C, Clark BJ. Microbial contamination of contact lens cases in the west of Scotland. Br J Ophthalmol 1993; 77: 41–5.
41. Bowden FW 3rd, Cohen EJ, Arentsen JJ, Laibson PR. Patterns of lens care practices and lens product contamination in contact lens associated microbial keratitis. Clao J 1989; 15: 49–54.
42. Wu YT, Zhu H, Harmis NY, Iskandar SY, Willcox M, Stapleton F. Profile and frequency of microbial contamination of contact lens cases. Optom Vis Sci 2010; 87: 152–8.
43. Wu YT, Teng YJ, Nicholas M, Harmis N, Zhu H, Willcox MD, Stapleton F. Impact of lens case hygiene guidelines on contact lens case contamination. Optom Vis Sci 2011; 88: 1180–7.
44. Szczotka-Flynn LB, Pearlman E, Ghannoum M. Microbial contamination of contact lenses, lens care solutions, and their accessories: a literature review. Eye Contact Lens 2010; 36: 116–29.
45. Szczotka-Flynn LB, Imamura Y, Chandra J, Yu C, Mukherjee PK, Pearlman E, Ghannoum MA. Increased resistance of contact lens-related bacterial biofilms to antimicrobial activity of soft contact lens care solutions. Cornea 2009; 28: 918–26.
46. Wilson LA, Sawant AD, Ahearn DG. Comparative efficacies of soft contact lens disinfectant solutions against microbial films in lens cases. Arch Ophthalmol 1991; 109: 1155–7.
47. Chang DC, Grant GB, O’Donnell K, Wannemuehler KA, Noble-Wang J, Rao CY, Jacobson LM, Crowell CS, Sneed RS, Lewis FM, Schaffzin JK, Kainer MA, Genese CA, Alfonso EC, Jones DB, Srinivasan A, Fridkin SK, Park BJ. Multistate outbreak of Fusarium
keratitis associated with use of a contact lens solution. JAMA 2006; 296: 953–63.
48. Zhang S, Ahearn DG, Noble-Wang JA, Stulting RD, Schwam BL, Simmons RB, Pierce GE, Crow SA Jr. Growth and survival of Fusarium solani-F. oxysporum
complex on stressed multipurpose contact lens care solution films on plastic surfaces in situ and in vitro. Cornea 2006; 25: 1210–6.
49. Kilvington S, Lonnen J. A comparison of regimen methods for the removal and inactivation of bacteria, fungi and Acanthamoeba
from two types of silicone hydrogel lenses. Cont Lens Anterior Eye 2009; 32: 73–7.
50. Zhu H, Bandara MB, Vijay AK, Masoudi S, Wu D, Willcox MD. Importance of rub and rinse in use of multipurpose contact lens solution. Optom Vis Sci 2011; 88: 967–72.
51. Willcox MD. Management and treatment of contact lens-related Pseudomonas
keratitis. Clin Ophthalmol 2012; 6: 919–24.
52. Wiley L, Bridge DR, Wiley LA, Odom JV, Elliott T, Olson JC. Bacterial biofilm diversity in contact lens-related disease: emerging role of Achromobacter
, and Delftia
. Invest Ophthalmol Vis Sci 2012; 53: 3896–905.
53. Keay LJ, Gower EW, Iovieno A, Oechsler RA, Alfonso EC, Matoba A, Colby K, Tuli SS, Hammersmith K, Cavanagh D, Lee SM, Irvine J, Stulting RD, Mauger TF, Schein OD. Clinical and microbiological characteristics of fungal keratitis in the United States, 2001–2007: a multicenter study. Ophthalmology 2011; 118: 920–6.
54. Dart JK, Radford CF, Minassian D, Verma S, Stapleton F. Risk factors for microbial keratitis with contemporary contact lenses: a case-control study. Ophthalmology 2008; 115: 1647–54.
55. Fleiszig SM, Evans DJ. Pathogenesis of contact lens-associated microbial keratitis. Optom Vis Sci 2010; 87: 225–32.
56. Mazounie P, Bernazeau F, Alla P. Removal of Cryptosporidium
by high rate contact filtration: the performance of the Prospect Water Filtration Plant during the Sydney water crisis. Water Sci Technol 2000; 41: 93–101.
57. Joslin CE, Tu EY, McMahon TT, Passaro DJ, Stayner LT, Sugar J. Epidemiological characteristics of a Chicago-area Acanthamoeba keratitis outbreak. Am J Ophthalmol 2006; 142: 212–7.
58. Bottone EJ, Madayag RM, Qureshi MN. Acanthamoeba
keratitis: synergy between amebic and bacterial cocontaminants in contact lens care systems as a prelude to infection. J Clin Microbiol 1992; 30: 2447–50.