Nicole Carnt

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.

Solution toxicity in soft contact lens daily wear is associated with corneal inflammation

Purpose. Contact lens-associated solution toxicity manifests as generalized, mild punctate epithelial fluorescein staining and usually is widely reported as asymptomatic, with no substantial clinical sequelae. This study examined the relationship between solution toxicity and corneal infiltrative events (CIEs) in soft contact lens daily wear. Methods. Several nonrandomized interventional clinical trials conducted between May and November 2005 were analyzed retrospectively. Subjects wore commercially available soft contact lenses bilaterally, on a daily schedule, disinfected overnight using marketed lens care solutions for 3 months with monthly disposal. Solution toxicity was defined as diffuse punctate staining in at least four of five areas of the cornea after instillation of sodium fluorescein. First events of corneal staining or corneal infiltrates were used to calculate incidence (per 100 eye months). Results. Toxic staining was detected in 77 of 609 subjects and all CIEs were mild and symptomatic or asymptomatic. The incidence of CIEs in eyes with a predisposition to toxic staining was 6.7% and in unaffected eyes was 2.3%. CIEs were 3-times more likely to occur in eyes that exhibited solution toxicity compared to unaffected eyes (odds ratio = 3.08, p = 0.008, 95% CI 1.40 to 6.76). Previous events of limbal redness (≥grade 2.0) were not associated with CIEs (odds ratio = 1.53, p = 0.364, 95% CI 0.63 to 3.70). The rate of CIEs increased as the rate of toxic staining increased for specific lens type-solution combinations (Spearman’s rho = 0.558, p = 0.025, n = 16), and peroxide-based solutions consistently resulted in the lowest rates of toxic staining and corneal inflammation. Conclusions. Eyes that experience solution toxicity are more likely to experience a CIE. Daily wear soft lens wearers should be routinely examined with sodium fluorescein soon after lenses are inserted and alternative solution/lens type combinations should be investigated if toxic staining is detected.

Care regimen and lens material influence on silicone hydrogel contact lens deposition

Purpose. To quantitatively detect proteins and cholesterol extracted from worn silicone hydrogel contact lenses and determine the effect of various lens care solutions on deposit accumulation. Methods. Contact lenses, made from different polymers and worn on a daily wear schedule with different lens care solutions, were collected. Lipid and protein deposits were extracted by methanol:chloroform (1:1, v/v) and protein extraction solution (containing urea and surfactant), respectively. Lipid extracts were separated and cholesterol quantified using thin layer chromatography. Protein extracts were quantified using standard techniques. Results. Among all lenses tested, Balafilcon A lenses exhibited greatest extracted cholesterol (4.1 to 8.2 μg/lens) and total protein (5.4 to 23.2 μg/lens). AQuify was the most effective solution in reducing extracted deposits, especially extracted protein, from Balafilcon A lenses. AQuify and Opti-Free RepleniSH solutions were most effective in reducing extracted cholesterol from Senofilcon A and Galyfilcon A lenses, respectively. Use of Opti-Free Express solution resulted in more extracted protein from Lotrafilcon B lenses than use of other solutions. Generally, Lotrafilcon B, Senofilcon A, and Galyfilcon A lenses accumulated relatively low amount of proteins. Lotrafilcon B lenses accumulated the least amount of cholesterol deposit among all lenses tested regardless of solution used. Conclusions. Lens polymer (possibly associated with surface characteristics) is a prominent factor affecting lipid and protein accumulation. Within a lens polymer type, lens care solutions exhibit varying effectiveness in reducing protein and lipid accumulation.

Contact Lens–Related Adverse Events and the Silicone Hydrogel Lenses and Daily Wear Care System Used

OBJECTIVEnTo investigate the incidence of adverse events related to the use of varying silicone hydrogel contact lens and lens solution combinations.nnnMETHODSnIndividuals with myopia (N = 558) participated in 1 or more of approximately 40-participant trials in a matrix of 20 silicone hydrogel contact lens and lens-solution combinations. Visits were at baseline, 2 weeks, 1 month, and 3 months. The mean study completion rate was 90% of the expected participant-months (final data set: 840 lens-solution combinations and 2271 participant-months). Adverse events were reported as the first occurrence of each type per 100 participant-months for each lens-solution combination.nnnRESULTSnThe rate of all corneal infiltrative events (CIEs) was 3.1 per 100 participant-months (range, 0-10.5), and the rate of symptomatic CIEs was 1.7 per 100 participant-months (range, 0-10.5), including 1 case of microbial keratitis (0.04 per 100 participant-months). Rates for CIEs differed substantially among solution groups, with hydrogen peroxide having the lowest rate (0.6 per 100 participant-months; range, 0-0.9). The rate was 0.8 per 100 participant-months (range, 0-8.0) for superior epithelial arcuate lesions, which varied by lens type, 0.04 per 100 participant-months (1 case only) for corneal erosion, and 0.4 per 100 participant-months (range, 0-2.0) for contact lens papillary conjunctivitis, which was modified by type of solution. The rate of solution-induced corneal staining for all lens-solution combinations was 4.7 per 100 participant-months (range, 0-23) and varied significantly based on lens-solution combination (P < .001).nnnCONCLUSIONSnThe frequency of adverse events varied with silicone hydrogel contact lens and lens solution combinations, with hydrogen peroxide having the lowest incidence of CIEs and solution-induced corneal staining, indicating that lens material and design, type of solution, and solution-lens interactions are likely contributing factors in this mode of lens wear.

Contact lens user profile, attitudes and level of compliance to lens care

PURPOSEnTo identify the demographics profile of lens wearers, and to evaluate the scope and level of noncompliant, behaviours in lens wearers.nnnMETHODSn210 contact lens wearers who attended an optometry clinic at an education and research institute, were surveyed using a self-administered questionnaire. The questionnaire was constructed to gather information regarding contact lens wearer demographics, contact lens hygiene behaviours and, attitudes toward lens care. Multivariate testing between lens wearers demographic, hygiene, behaviours and attitude to aftercare visit were analysed.nnnRESULTSnOne hundred and eleven (62%) of participants responded, with a mean age of 33.8+/-12 years. 55% of the respondents were female. Major non-compliance aspects identified were poor hand hygiene (11%), inadequate cleaning of lenses (13%) and lens storage cases (61%), and wearers not remembering how often they were advised to return for an aftercare (50%). Lens wearers who purchased contact lenses, from the internet were 3.8 times more likely to forget their aftercare schedule than those who purchased contact lenses from the optometrists (95% CI=1.2-12.2, p=0.024).nnnCONCLUSIONnPoor hand hygiene, inadequate lens care, and not remembering when to come back for aftercares are the common non-compliant behaviours in lens wearers. Purchase of lenses via the internet was associated with lack of awareness of aftercare visit.

Microbial keratitis and vision loss with contact lenses.

Purpose. Microbial keratitis is the only sight-threatening adverse event that occurs with contact lens wear. This article gives a preliminary estimation of the incidence of microbial keratitis and vision loss with continuous-wear contact lenses made from highly oxygen permeable (Dk) materials. Methods. The most up-to-date data available on microbial keratitis and vision loss are collected from a range of sources including industry, private practice, and publications and is reviewed. Results. There have been 16 cases of microbial keratitis with high-Dk silicone hydrogel lenses. Of the 13 where data are available, none have lost two or more lines of best-corrected visual acuity (BCVA). Conclusion. First approximation indicates that the incidence of microbial keratitis with high-Dk silicone hydrogel lenses may be lower than the incidence with low-Dk soft lenses during extended wear. The rate of loss of more than two lines of BCVA is low in patients that develop microbial keratitis with low- and high-Dk soft lenses.

Contact lens case contamination during daily wear of silicone hydrogels.

Purpose. Contamination of contact lens cases has been associated with the production of adverse responses in the eye during contact lens wear. This study aimed to evaluate the contamination rate and types of microbes contaminating cases during use of contact lens disinfecting solutions and silicone hydrogel lenses. Methods. Two hundred thirty-two participants were allocated to one or more groups. The participants wore one or more of three silicone hydrogel lenses and used one or more of four contact lens disinfecting solutions. Cases were collected after use for 1 month and sent for routine microbial testing. The rate of contamination of cases and the types of microbes contaminating cases were evaluated. Results. Between 76 and 92% of all cases were contaminated. Use of different contact lenses did not affect contamination rate or the types of microbes isolated from cases. Use of AQuify (PHMB as disinfectant) was associated with the highest contamination rate (92%; p = 0.015) of cases for any microbe. Level and type of contamination with use of ClearCare (H2O2) was similar to use of PHMB (polyhexamethylene biguanide)- or Polyquat/Aldox-containing solutions. There was no difference in contamination rate of cases by fungi or Gram-positive bacteria, but for Gram-negative bacteria, use of Opti-Free Express (Polyquat and Aldox as disinfectants) resulted in a lower contamination rate (7% vs. 29 to 45%; p < 0.001). The average number of microbes contaminating a case was significantly less for Opti-Free Express (223 ± 1357 cfu/case) compared with Opti-Free RepleniSH (Polyquat and Aldox as disinfectants; 63,244 ± 140,630 cfu/case; p < 0.001), driven mostly by differences in numbers of Gram-negative bacteria, particularly contamination by Delftia acidovorans in cases exposed to Opti-Free RepleniSH. Conclusions. Different disinfecting solutions used during storage in cases result in different levels of contamination and contamination by different types of microbes. These differences are not simply because of the types of disinfectants used, suggesting that other excipients in, or formulation of, the solution affect contact lens storage case contamination.

Contact lens deposits, adverse responses, and clinical ocular surface parameters.

Purpose. To correlate clinical responses during contact lens wear with the amount of protein or cholesterol extracted from lenses after wear. Methods. Clinical parameters, including adverse response rates and corneal staining, and symptomatology rating during lens wear were collected from a series of clinical tests comprising four different silicone hydrogel lenses with four different multipurpose solutions. To test for correlates, the amount of total protein or cholesterol extracted from lenses after daily wear were compared statistically to clinical parameters. Results. The amount of protein (p = 0.008) or cholesterol (p = 0.01) extracted from lenses was higher for those subjects who showed solution-induced corneal staining. Amount of protein extracted was correlated (p < 0.01) with conjunctival staining (R = −0.23), lens front surface wetting (r = 0.14), and lens fit tightness (R = −0.20). These clinical parameters accounted for 48% of lens protein deposition. The amount of cholesterol extracted from lenses was much more weakly associated with clinical variables. Amount of protein or cholesterol extracted from lenses was not associated with the production of any corneal infiltrative or mechanical adverse event during wear and was only very weakly correlated with insertion comfort of lenses. Conclusions. These results suggest that there may be no physiologically relevant consequence of cholesterol depositing on silicone hydrogel lenses. The amount of protein that deposits onto silicone hydrogel lenses during wear may have more affect on lens performance on-eye. However, the correlations were generally small and may still not indicate any causative relevant physiological response. Further work is required to determine whether there is any direct causative effect to support these correlative findings.

Complications associated with care product use during silicone daily wear of hydrogel contact lens.

Increased use of silicone hydrogel contact lenses for daily wear has necessitated a parallel rise in the use of multipurpose care solutions (MPS). This in turn has been accompanied by substantially more reports of solution related complications, in particular corneal staining and low grade infiltrates. Management of these problems involves reducing the impact of care system components on the ocular surface. Options for achieving this include use of low impact lens/MPS combinations, daily disposable lenses or hydrogen peroxide based disinfection systems.

Higher risk taking propensity of contact lens wearers is associated with less compliance

PURPOSEnTo determine whether risk taking personality is associated with compliance in contact lens wear, and how practitioner perception of compliance compares with wearer risk taking and non-compliant behaviour.nnnMETHODnOptometrists in Australia, recruited through professional organizations, were asked to enroll up to 10 current contact lens wearers each. Wearers completed a questionnaire assessing risk-taking propensity (20-item instrument), non-compliant behaviour and demographics. Non-compliance was scored on four components (maximum score 40, lens disinfection, 20; hand hygiene, 8; case hygiene, 6; case replacement, 6). Independently, practitioners ranked each wearers non-compliance on a 1-5 scale. Associations between wearer risk taking propensity, non-compliant behaviour and practitioner perceived non-compliance were investigated using Pearson correlation. Significant associations were entered into a linear regression model predicting overall non-compliant behaviour.nnnRESULTSnSeventy-three wearers were recruited by 18 optometrists (mean 4, range 1-10). Wearer risk taking was associated with less compliance (p<0.01) as was younger age (p<0.01) and male gender (p=0.02). Years of lens wear was not associated with non-compliant behaviour (p=0.8), nor was practitioner perception of compliance (p>0.6) Linear regression indicated that risk taking was the only independent significant factor predicting non-compliance, explaining 24% of the variation in behaviour.nnnCONCLUSIONnA higher risk taking personality style of contact lens wearers in Australia is associated with less compliant behaviour. Risk taking is a better predictor of compliance than age, gender and practitioner perception and helps explain the individual characteristics of wearers that may influence lens care and maintenance.