Contact Lens-related Microbial Keratitis Research Articles

Impact of contact lens hygiene risk factors on the prevalence of contact lens-related keratitis in Alexandria-Egypt

BackgroundThis study aimed at measuring the effect of contact lens hygiene risk factors on the prevalence of contact lens-related keratitis and identifying the specific risk factors to both microbial and non-microbial keratitis independently.MethodsA cross-sectional study was conducted at Alexandria Ophthalmology Hospital from May to October 2023. All contact lens wearers attending the outpatient clinic had undergone face-to-face interviews using a standardized validated questionnaire which included demographic data and contact lenses (CLs) hygiene risk factors. Participants were classified into two groups; normal group and keratitis group. Keratitis group was further subdivided into non-microbial and microbial group.ResultsThe study included 245 contact lens wearers; 149 normal cases, 50 (20.4%) contact lens-related non-microbial keratitis (CLNK) cases, and 46 (18.8%) contact lens-related microbial keratitis (CLMK) cases. Sharing contact lenses and eye trauma were significant risk factors for both CLNK (p=0.036), (p=0.001) and CLMK (p=0.003), (p=0.017). CLs wear duration for more than 12 hours was associated with an increased risk of CLNK by about 4 times (p=0.030) and overnight wear of contact lenses increased the risk of CLNK by 2.6 times (p=0.030). Showering or swimming in lenses was identified as a significant risk factor for CLMK (p=0.012), moreover washing lenses with tap water increased the risk of CLMK (p=0.030).ConclusionsPoor compliance with contact lenses hygiene rules results in a high prevalence of contact lens-related keratitis. Eye trauma and sharing contact lenses were significant hygiene risk factors for both contact lens-related non-microbial keratitis and contact lens-related microbial keratitis.

Hydroquinine Enhances the Efficacy of Contact Lens Solutions for Inhibiting Pseudomonas aeruginosa Adhesion and Biofilm Formation.

P. aeruginosa is one of the most common bacteria causing contact lens-related microbial keratitis (CLMK). Previous studies report that disinfecting solutions were ineffective in preventing biofilm formation. Solutions containing novel natural agents may be an excellent alternative for reducing the risk of CLMK. Here, we investigate the disinfecting properties of hydroquinine in combination with multipurpose solutions (MPSs) to prevent P. aeruginosa adhesion and biofilm formation. We examined the antibacterial, anti-adhesion, and anti-biofilm properties of hydroquinine-formulated MPSs compared to MPSs alone. Using RT-qPCR, hydroquinine directly affected the expression levels of adhesion-related genes, namely, cgrC, cheY, cheZ, fimU, and pilV, resulting in reduced adhesion and anti-biofilm formation. Using ISO 14729 stand-alone testing, hydroquinine met the criteria (>99.9% killing at disinfection time) against both P. aeruginosa reference and clinical strains. Using the crystal violet retention assay and FE-SEM, MPSs combined with hydroquinine were effective in inhibiting P. aeruginosa adhesion and destroying preexisting biofilms. This report is the first to highlight the potential utility of hydroquinine-containing formulations as a disinfecting solution for contact lenses, specifically for inhibiting adhesion and destroying biofilm. These findings may aid in the development of novel disinfectants aimed at combating P. aeruginosa, thereby potentially reducing the incidence of CLMK.

Topical Review: Contact Lens Eye Health and Safety Considerations in Government Policy Development.

SIGNIFICANCEAs new federal or state policies are introduced in the United States to shape the evolving contact lens market, it has never been more important to amplify the importance of patient health and safety during contact lens wear and promote the value of the eye care professional–patient relationship.Within the United States, contact lenses are regulated by the Food and Drug Administration as class II or III medical devices that require additional regulatory and professional oversight to keep consumers safe. The contact lens market and broader eye health landscape are rapidly changing. Recently, the U.S. Federal Trade Commission finalized its 10-year review of the Contact Lens Rule, implementing new policies that will shape the contact lens market in the United States for years to come. The purpose of this clinical perspective was to compile and review key data regarding contact lens–related adverse events, including their economic impact on the health care system, to inform government policy development. Although contact lenses provide many benefits to the wearer, a variety of complications can occur ranging from asymptomatic events or mild discomfort to severe sight-threatening adverse events such as microbial keratitis. Patients who do not routinely visit their eye care professional or do not receive the lenses prescribed to them are at a greater risk of contact lens–related adverse events. Nearly 1 million people in the United States experience ocular infections or inflammation annually, resulting in significant health care costs. The economic burden of contact lens–related microbial keratitis in the United States has been estimated to be approximately $175 million annually. The importance of eye care professional oversight of contact lens wear cannot be emphasized enough to key stakeholders, including lawmakers, government regulators, contact lens manufacturers and distributors, and the broader eye health community.

Therapy for contact lens-related ulcers.

The current review covers the current literature and practice patterns of antimicrobial therapy for contact lens-related microbial keratitis (CLMK). Although the majority of corneal ulcers are bacterial, fungus and acanthamoeba are substantial contributors in CLMK and are harder to treat due to the lack of commercially available topical medications and low efficacy of available topical therapy. Topical antimicrobials remain the mainstay of therapy for corneal ulcers. Fluoroquinolones may be used as monotherapy for small, peripheral bacterial ulcers. Antibiotic resistance is a persistent problem. Fungal ulcers are less responsive to topical medications and adjunct oral or intrastromal antifungal medications may be helpful. Acanthamoeba keratitis continues to remain a therapeutic challenge but newer antifungal and antiparasitic agents may be helpful adjuncts. Other novel and innovative therapies are being studied currently and show promise. Contact lens-associated microbial keratitis is a significant health issue that can cause vision loss. Treatment remains a challenge but many promising diagnostics and procedures are in the pipeline and offer hope.

Contact Lens Associated Bacterial Keratitis: Common Organisms, Antibiotic Therapy, and Global Resistance Trends: A Systematic Review.

Contact lens wearing has been increased globally during recent decades, which is one of the main risk factors for developing microbial keratitis. Microbial keratitis is a severe and dangerous condition that causes cornea inflammation. It can lead to corneal scarring and perforation or even endophthalmitis and visual loss if it remains untreated. Among bacterial, fungal, protozoal, and viral agents which can cause microbial keratitis, bacteria are the most common cause. Therefore, in this study, we aim to find common causative bacteria, sensitivity, and resistance to antibiotics and the outcome of antibiotic therapy in contact lens-related bacterial keratitis. A systematic search was carried out in PubMed/Medline, EMBASE, and Web of Science for published studies and medRxiv for preprints up to February 30, 2021, and May 14, 2021, respectively. A combination of the following keywords was used: "Infection", "Corneal infection", "Keratitis", "Microbial keratitis", and "Contact lens", Also,we used the "Contact lenses" MeSH term. Lists of references for each selected article and relevant review articles were hand-searched to identify further studies. Twenty-six articles were included. From 1991 to 2018, 2,916 episodes of contact lens-related microbial keratitis) CLMK(with 1,642 episodes of proven bacterial keratitis have been reviewed in these studies. Studies were conducted in 17 countries with different geographical regions, and four studies were conducted in Iran, which is the highest number of studies among these countries. According to 20 studies, the mean age of patients was 30.77 years. Females with 61.87% were more than males in 19 studies. Apercentage of 92.3% of patients used soft contact lenses, and 7.7% of patients used hard contact lenses (including RGP), according to 16 studies. Pseudomonas aeruginosa, Staphylococcus spp., and Serratia marcescens were the three most common bacteria isolated from samples of patients with contact lens-related bacterial keratitis. Overall,isolated bacteria were most sensitive to fluoroquinolones and aminoglycosides, especially ciprofloxacin and gentamicin respectively, and most resistant against penicillin and cephalosporins especially cefazolin and chloramphenicol. Almost all patients responded well to antibiotic therapy, with some exceptions that needed further surgicalinterventions. Antibiotics are efficient for treating almost all patients with contact lens-related bacterial keratitis if they are appropriately chosen based on common germs in every geographical region and the sensitivity and resistance of these germs against them. In this regard, Pseudomonas aeruginosa is the most common causative germ of contact lens-associated bacterial keratitis all over the world and is almost fully sensitive to ciprofloxacin. Because of some different results about the sensitivity and resistance of germs against some antibiotics like gentamicin, vancomycin, and chloramphenicol in the Middle East region, especially Iran, more in vitro and clinical studies are suggested.

Risk Factors for Contact Lens-Related Microbial Keratitis and Associated Vision Loss in a South Indian Population.

To identify risk factors associated with contact lens-related microbial keratitis (CL-MK) and subsequent vision loss in a south Indian population. A retrospective study of medical records at the LV Prasad Eye Institute in Hyderabad, India, of patients diagnosed with CL-MK and of controls who had no history of corneal inflammation during contact lens wear was undertaken. Variables such as demographic data, contact lens wear details, duration of the event, visual acuity, epithelial defect and infiltrate size, and microbiology of the cornea during the event were collected. Differences between cases and controls were analyzed using parametric and nonparametric tests. Logistic regression was used to calculate the odds ratio (OR) and associated 95% confidence intervals in univariate and multivariate analyses for cases vs. controls and for factors associated with vision loss. One hundred sixty-seven cases of CL-MK and 153 controls were included in the analyses. Risk factors associated with the greatest increased OR for CL-related MK were: being in professional employment vs. a student (OR=3.9), disposing lenses yearly versus monthly or biweekly (OR=2.2), and any overnight wear (OR=2.8). Risk factors associated with vision loss were: high myopia (OR=3.6), severe vs. mild severity (OR=16.0), and hypopyon (OR=4.3). Identification of these risk factors may help inform safe contact lens wear habits and management strategies.

Personal hygiene risk factors for contact lens-related microbial keratitis

ObjectiveMicrobial keratitis is a sight-threatening complication of contact lens wear, which affects thousands of patients and causes a significant burden on healthcare services. This study aims to identify compliance with...

Different contact lens case treatment methods for the elimination of pathogen biofilms associated with contact lens related microbial keratitis

Objective To investigate the biofilm-forming abilities of pathogens associated with contact lens related microbial keratitis and to compare the efficacies of different treatments in eliminating biofilms in contact lens cases (CLCs). Methods Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Candida albicans biolm formation in polypropylene CLCs was examined by using a static biofilm formation model, which was incubated at 37 ℃ for 24 hours.According to the CLC treatment methods, the experimental groups were divided into a control group, a room temperature air-drying group, a contact lens care solution soaking group, a heat-drying group and a soaking-heating group.A pathogen colony counting-based serial dilution micro-counting method was applied to evaluate the biofilm elimination efficacies and pathogen killing rates of treatments. Results All four tested strains formed biofilms on the inner walls of the CLC, and the biomasses of S. aureus, P. aeruginosa, E.coli and C. albicans biofilm were (10.78±2.12), (9.19±0.57), (8.03±0.30), and (7.50±0.07)lg CFU/ml, respectively.The S. aureus biofilm biomass was significantly higher than those of the other strains (P<0.05). The biofilm biomasses of all the tested strains in the heat-drying and the soaking-heating groups were significantly lower than those in the control group (all at P<0.05); and the biofilm biomasses of S. aureus and E. coli in the soaking group were significantly lower than that in the control group (all at P<0.05). The heat-drying treatment resulted in a killing rate of (51.76±16.75)% for S. aureus, (68.63±4.43)% for P. aeruginosa, (83.51±13.97)% for E. coli, and (97.13±5.19)% for C. albicans, respectively (F=31.806, P<0.001). Significant differences were observed between the killing rates for each bacterium (all at P<0.05). The E. coli and C. albicans killing rates of the soak-heating treatment were (100.00±0.00) % and (97.79±7.67)%, respectively, and were significantly higher than (81.13±14.86)% of S. aureus and (74.22±11.91)% of P. aeruginosa (all at P<0.05). Conclusions Heating alone or combined with the use of contact lens care solution treatment can improve the pathogen killing rates and effectively eliminate the bacterial and fungal contaminations in CLCs. Key words: Microbial keratitis; Contact lens cases; Biofilm; Heating

Hand hygiene is linked to microbial keratitis and corneal inflammatory events.

Lack of or inadequate hand washing is a risk factor in the development of contact lens related microbial keratitis and corneal inflammatory events. In the public health domain there is compelling evidence that proper hand washing with soap can save lives. The purpose of this review is to draw attention to some of the public health literature in support of hand washing and how education can influence patients' hand hygiene behavior. Contact lens wearers are also guilty of poor hand washing behavior but there is scant evidence that education of hand washing procedures of lens wearers alters patient non-compliance. It is well known that pathogenic microbial contamination of contact lenses, lens cases, care solutions and anterior ocular components have been found with contact lens wear. However while the originating source may be hands or water, it is most likely both of these. Besides proper hand washing this paper will include mitigating strategies for avoiding microbial contamination.

Emerging trends in contact lens-related infections.

This article reviews the literature on past and recent trends in contact lens-related microbial keratitis from bacterial, fungal, and Acanthamoeba infections. Contact lens wear is the most important risk factor for microbial keratitis. Despite increased use of daily disposable contact lens wear, the incidence of bacterial ulcers related to contact lens wear remains high. Overnight contact lens wear is the leading risk factor in contact lens-related bacterial infections. There may be a trend towards increasing antibiotic resistance of Gram-positive bacteria to fourth-generation fluoroquinolones. The incidence of Acanthamoeba and fungal infections, despite resolution of two outbreaks involving multipurpose solutions, are also on the rise. Contact lens-related microbial keratitis is rising and may be associated with more severe, vision threatening, infections.

Microbial Bioburden of Orthokeratology Contact Lens Care System.

To assess the bioburden in an orthokeratology contact lens (OK) care system (defined by microbial identification from OK case fluid) and to identify the risk factors causing high bioburden for pediatric OK wearers in southern Taiwan. A prospective study for the investigation of bioburden in the OK care system was performed in a tertiary medical center in southern Taiwan. Microbial isolates from the case fluids soaking OKs were analyzed, and pathogenicity was determined. Age, gender, OK experiences, and contact lens care habits were considered the potential risk factors of microbial bioburden (colony-forming units per milliliter) for causal analysis. Forty-one OK wearers (20 female and 21 male subjects) participated in this study. The mean age was 12.7 years, and the mean OK-wearing experience was 3.5 years. A total of 86 microbial strains were isolated from 38 culture-positive specimens. Frequently reported pathogens in contact lens-related microbial keratitis were less common in the current study, but still present, including 4 strains (5%) of Serratia marcescens, 1 strain (1%) of Pseudomonas aeruginosa, and 1 strain (1%) of Staphylococcus aureus. Microbial bioburden of the OK care system was significantly higher (P<0.05) in male subjects. The contamination rate of the OK care system was high, and many isolated microorganisms had potential pathogenicity. Reinforcement of proper contact lens care and education should be mandatory for OK wearers, particularly for male subjects, to decrease the risk of high bioburden of the OK care system.

Risk factors for contact lens-related microbial keratitis in Singapore.

To investigate independent risk factors for contact lens-related microbial keratitis in Singapore and estimate their impact on disease load. Cases were contact lens wearers presenting to Singapore National Eye Centre with microbial keratitis between 2008 and 2010. Community contact lens wearers were recruited as controls. All wearers completed a previously validated questionnaire describing contact lens wear history, hygiene and compliance habits, and demographics. Risk factors significant in univariate analysis (P<0.2) were evaluated in a multivariate model. In all, 58 cases of microbial keratitis and 152 contemporaneous controls were identified. When controlling for other variables, Chinese had a 7 × lower risk compared with other races (95% CI: 2.3-21.3, P=0.001). Those aged between 25 and 44 years were at 3 × increased risk compared with younger wearers (95% CI: 1.1-9.6, P=0.04). Occasional overnight contact lens wear (less often than one night per week) was associated with a 4 × higher risk (95% CI: 1.2-15.4, P=0.03) compared with daily use. Not washing hands before handling was associated with a 13 × increased risk (95% CI: 1.9-84.8, P=0.008). Use of multipurpose solution A carried a 16 × higher risk compared with hydrogen peroxide (95% CI: 1.5-174.0, P=0.02). The combined PAR% for modifiable risk factors (occasional overnight wear, not washing of hands, and MPS A) was 82%. Consistent with previous findings, independent risk factors for contact lens-related microbial keratitis include poor hand hygiene, occasional overnight wear, and type of lens care solution. Prolonged overnight or extended contact lens use was infrequent in this population.

Clinical Presentation and Antibiotic Susceptibility of Contact Lens Associated Microbial Keratitis.

Introduction. In recent years, the number of contact lens wearers has dramatically increased in Iran, particularly in youngsters. The purpose of current study was to assess the clinical presentation and antibiotic susceptibility of contact lens related microbial keratitis in Ahvaz, southwest of Iran. Methodology. A cross-sectional investigation of 26 patients (33 eyes) with contact lens induced corneal ulcers who were admitted to Imam Khomeini Hospital, Ahwaz City, from June 2012 to June 2013 was done. In order to study microbial culture and susceptibility of corneal ulcers, all of them were scraped. Results. Eight samples were reported as sterile. Pseudomonas aeruginosa (80%) in positive cultures was the most widely recognized causative organism isolated. This is followed by Staphylococcus aureus 12% and Enterobacter 8%. The results showed that 84% of the microorganism cases were sensitive to ciprofloxacin, while imipenem, meropenem, and ceftazidime were the second most effective antibiotics (76%). Conclusion. Results of current study show the importance of referring all contact lens wearers with suspected corneal infection to ophthalmologists for more cure. The corneal scraping culture and contact lens solution should be performed to guide antibiotic therapy.

Effektivität antibiotischer Initialtherapie in der Behandlung der kontaktlinsenassoziierten bakteriellen Keratitis

Contact lens-related microbial keratitis is a cause of potentially sight-threatening corneal opacification. Effective initial antimicrobial therapy is crucial to prevent long-term complications. This investigation was undertaken to test the effectiveness of current routine empirical antibiotic treatment regimens. All consecutive cases of contact lens-related keratitis presenting in the outpatient clinic of the Department of Ophthalmology at the Medical University of Innsbruck between January 2010 and April 2012 were retrospectively analyzed. Cultures were positive in 69 out of the 123 cases included in the study. Culture results identified 59.4 % Gram positive strains, 50.7 % Gram negative strains and 7.2 % fungal strains. Mixed infections accounted for 29 % of cases. The combination of an aminoglycoside and a second generation quinolone antibiotic was the most common initial treatment regimen (87.8 %). In vitro this regimen was less effective compared to combinations of moxifloxacin and ciprofloxacin or moxifloxacin and gentamicin. Empirical combined regimens remain an effective treatment of contact lens-related keratitis. Fluoroquinolones proved to be inadequate for monotherapy.

In-vitroanalysis of the microbicidal activity of 6 contact lens care solutions

BackgroundContact lens-related infections are often associated with inadequate contact lens hygiene, and therefore, contact lens care products should be able to sufficiently minimise the amount of pathogens that are responsible for these infections. In 2001, the EN ISO 14729 was introduced to ensure adequate disinfection efficacy of contact lens care solutions, but this norm has recently been criticised.MethodsIn this study, six frequently used contact lens care solutions were retested according to the Stand Alone Test of the EN ISO 14729 (2001). The Stand Alone Test is a quantitative suspension test. In addition, the products were tested in a modified setting adding an organic load. The load was a mixture of human blood serum, lysozyme, and mucine, which resembles tear fluid.ResultsThe criteria of the Stand Alone Test recommended in EN ISO 14729 were only met by Aosept Plus. This 3% hydrogen-peroxide-based contact lens care solution attained a reduction factor of > 5 log units for bacteria and > 4 for fungi in all cases. Two further contact lens care solutions, Blue Vision and Optifree Replenish, met the criteria of a reduction factor of > 3 log units for bacteria and > 1 log unit for fungi, but only in the presence of artificial tear fluid. The three remaining products did not exhibit adequate disinfecting efficacy, at least against one of the tested microorganisms.ConclusionsThrough the observation that the artificial tear fluid used in this study influences the disinfecting efficacy of contact lens care solutions, especially that of multi-purpose solutions, in a different way than does albumin, mucine, or even the organic load suggested in EN ISO 14729, it becomes obvious that the test conditions in the EN ISO 14729 should be revised in order to create more realistic conditions, e.g., by using a more realistic artificial tear fluid. Furthermore, we suggest adapting the EN ISO 14729 to the European test hierarchy for chemical disinfectants and antiseptics, which consists of three test phases and also requests meeting stricter criteria in order to pass the test. Unless the test conditions guarantee a sufficient reduction of potential pathogens, the risk of contact lens-related microbial keratitis and other infections will remain for the users.

Contact lens-related microbial keratitis: how have epidemiology and genetics helped us with pathogenesis and prophylaxis

Contact lens wear is a common predisposing factor in microbial keratitis and is one of the two preventable risk factors for corneal infection in a working age population. Our understanding of the prevention and prophylaxis of contact lens-related corneal infection is informed by recent epidemiological studies describing the incidence of and risk factors for the disease, the effect of causative organism on disease severity, and an appreciation of individual immune profiles in susceptibility to and severity of the disease. Although contemporary contact lenses have not reduced the overall incidence of keratitis, a reduction in morbidity may be achievable through recognition of appropriate risk factors in severe disease, including avoiding delays in presenting for appropriate treatment, and attention to storage case hygiene practise. Severe keratitis is most commonly associated with an environmental causative organism, and daily disposable lenses are associated with less severe disease. Pseudomonas aeruginosa remains the commonest cause of contact lens-related corneal infection probably because of its unique virulence characteristics and ability to survive in the contact lens/storage case/ocular environment. In two recent outbreaks of contact lens-related infections, there has been a strong association demonstrated with particular contact lens solutions. Since the recall of these specific contact lens solutions, the rate of Acanthamoeba keratitis has remained above the expected baseline, indicating unidentified risk factors that may include environmental exposures. Individual differences in susceptibility to microbial keratitis may be partly explained by differences in single-nucleotide polymorphisms in certain cytokine genes, particularly those with a proven protective role in corneal infection.

Contact lens related microbial keratitis – avoidable blindness

Aim: The aim of this article is to review the literature on microbial keratitis, exploring the pathophysiology, causes, diagnosis, and management strategies of this ocular condition which can lead to blindness and can be avoided. The main focus is contact lens-related microbial keratitis. The author analyzed some statistics for this condition from his work place (Birmingham and Midland eye hospital) in order to provide an indication of the number of patients attending the eye hospital with contact lens-related microbial keratitis and non contact lens-related microbial keratitis. Methods: Extensive review of the literature on microbial keratitis and a retrospective review of all cases with contact lens-related microbial keratitis over a period of 4 months (August 2010 and November 2010). Case files were retrieved and relevant information was extracted and analyzed. Results: The data collected indicated that 192 patients attended the eye casualty with contact lens-related problems. Out of these 110 cases were diagnosed as infective microbial keratitis and were treated with intensive antibiotics. Conclusion: Microbial keratitis is one of the main eye traumas for people using contact lenses and can lead to blindness. One feature of bacterial keratitis is rapid progression if left untreated — microbial keratitis is a true ocular emergency that requires immediate and intensive evaluation and treatment. Understanding the pathophysiology of microbial keratitis and its relationship to contact lenses is key in choosing the right treatment and ensuring a good prognosis.

Pilot Study of Contact Lens Practitioner Risk-Taking Propensity

To determine risk-taking propensity of optometrists and the association with the volume of contact lens practice and prescribing profile. Other factors associated with high practitioner risk taking and larger volume contact lens practices were also investigated. Sixty-four practitioners were recruited through Australian professional associations. Practitioners completed a risk-taking propensity survey and rated the importance of risk factors for contact lens-related microbial keratitis on prescribing decisions and wearer advice (prescribing profile). Demographics and the number of contact lens wearers seen per week were documented. Risk-taking propensity was estimated after adjusting for item difficulty using Rasch analysis, then scaled 0 to 100. Prescribing profile, practice type, practitioner age, and gender were tested for association with risk-taking propensity. Risk-taking propensity, practitioner age, personal contact lens wear, and the socioeconomic status of the practice location were investigated for association with the volume of contact lens patients with regression. Rasch analysis of the risk-taking questionnaire indicated good person separation and reliability (2.44, 0.86) but some item redundancy (1.69, 0.74). Risk taking (mean 35, range 0 to 71) was associated with increasing number of contact lens patients (p = 0.02). The perceived importance of risk factors (p = 0.9) and likelihood of discussing them with patients (p = 0.7) were not associated with risk-taking propensity. Risk taking (p = 0.02) and socioeconomic status of the practice location (p = 0.03) were predictors of higher volume contact lens practices. Practitioners who see a higher volume of contact lens patients tend to have higher risk-taking personalities. However, increased risk taking did not affect the perceived importance and type of advice given to contact lens wearers. Higher socioeconomic status of the practice location is also associated with larger volume of contact lens patients. This information gives insight into what drives higher volume contact lens practice within Australia and may have applications to the contact lens and wider optical industry.

Surface thermodynamics and adhesion forces governing bacterial transmission in contact lens related microbial keratitis

Contact lens induced microbial keratitis results from bacterial transmission from one surface to another. We investigated the adhesion forces of Pseudomonas aeruginosa, Staphylococci and Serratia to different contact lenses, lens cases and corneal surfaces using AFM, and applied a Weibull analysis on these adhesion forces to calculate bacterial transmission probabilities from lens case to corneas with a contact lens as an intermediate. Also a new surface thermodynamic parameter was introduced, the interfacial free energy of transmission, which in essence compares the interfacial free energies of bacterial adhesion, calculated from measured contact angles with liquids on the donating and receiving surfaces in the transmission process. Bacterial adhesion forces were generally strongest among all eight strains for the lens case (−6.5 to −12.0 nN) and corneas (−3.5 to −11.5 nN), while contact lenses (−0.6 to −13.1 nN) exerted slightly smaller adhesion forces. Consequently, bacterial transmission from lens case to contact lens yielded a smaller contribution in the final transmission than from contact lens to cornea. Bacterial transmission probabilities as derived from force analyses were higher when the interfacial free energies of transmission were more negative, which is in line with surface thermodynamic principles. Therewith this parameter could provide useful in analyzing other bacterial transmission phenomena between donating and receiving surfaces as well.

Antimicrobial efficacy of multi-purpose contact lens disinfectant solutions following evaporation

Non-compliance is a significant factor in contact lens related microbial keratitis and includes solution reuse and failure to recap the lens storage case resulting in evaporation effects. To address this, impact of partial evaporation on the antimicrobial efficacy of multipurpose contact lens care solutions was investigated. Solutions were evaporated under a stream of air to 2× and 4× concentration and challenged with Fusarium solani (ATCC 36031), Candida albicans (ATCC 10231) and Acanthamoeba castellanii (ATCC 50370). The level of organism kill at 6h was compared to the non-evaporated product. ReNu with MoistureLoc(®) (RML) lost 90-100% of biocidal activity against C. albicans on evaporation, 75-99% for F. solani and 29-33% with A. castellanii at 2× or 4× concentration, respectively. OPTI-FREE(®) RepleniSH(®) lost 72-90% efficacy against C. albicans and F. solani, and 61% at 2× and 10% at 4× concentration with A. castellanii. ReNu(®) MultiPlus, AQuify(®) Multi-Purpose and Biotrue™ showed only loss in efficacy with C. albicans at 4× concentration giving 79%, 34.5% and 48% reduction, respectively. No loss in biocidal activity on evaporation was obtained with Complete(®) Revitalens for all organisms. Partial evaporation can affect biocidal efficacy of multi-purpose solutions and may have been a significant factor in an outbreak of Fusarium keratitis cases associated with RML. Evaporation results in increased binding of cationic disinfectants to counter-ions in the formulation, reducing ability to attach and rupture anionic microbial cell walls. Interaction may also occur between the biocidal ingredient and other components, such as surfactants, resulting in sequestration of activity through micelle formation.