Risk of corneal inflammatory events with silicone hydrogel and low dk hydrogel extended contact lens wear: a meta-analysis

Host defense at the ocular surface

Microbial infections of the cornea frequently cause painful, blinding and debilitating disease that is often difficult to treat and may require corneal transplantation. In addition, sterile corneal infiltrates that are associated with contact lens wear cause pain, visual impairment and photophobia. In this article, we review the role of Toll-Like Receptors (TLR) in bacterial keratitis and sterile corneal infiltrates, and describe the role of MD-2 regulation in LPS responsiveness by corneal epithelial cells. We conclude that both live bacteria and bacterial products activate Toll-Like Receptors in the cornea, which leads to chemokine production and neutrophil recruitment to the corneal stroma. While neutrophils are essential for bacterial killing, they also cause tissue damage that results in loss of corneal clarity. These disparate outcomes, therefore, represent a spectrum of disease severity based on this pathway, and further indicate that targeting the TLR pathway is a feasible approach to treating inflammation caused by live bacteria and microbial products. Further, as the P. aeruginosa type III secretion system (T3SS) also plays a critical role in disease pathogenesis by inducing neutrophil apoptosis and facilitating bacterial growth in the cornea, T3SS exotoxins are additional targets for therapy for P. aeruginosa keratitis.

Tear cytokine response to multipurpose solutions for contact lenses

PURPOSE

An increased risk of corneal infiltrative events has been noted with the use of certain contact lenses and multipurpose solutions (MPS). This study was designed to evaluate tear cytokine assay as a sensitive, objective, and quantitative measure of the ocular surface response to contact lens/MPS and to consider the assay's clinical relevance in the context of other measures of ocular surface response.

METHODS

Two MPS, ReNu® Fresh™ (RNF) and Opti-Free® RepleniSH (OFR), were used with daily wear silicone hydrogel contact lenses in a randomized, prospective crossover study involving 26 subjects. Clinical data collection (conjunctival hyperemia, ocular surface sensitivity, solution induced corneal staining (SICS) test score, and subjective responses) and tear cytokine assays were conducted masked. Responses were tracked as change from baseline throughout the experimental schedule.

RESULTS

SIMILAR RESPONSE PATTERNS FOR SEVERAL INFLAMMATORY CYTOKINES WERE SEEN THROUGHOUT BOTH PHASES: subjects who received OFR in Phase I had mean tear concentrations that were generally higher than those of the RNF Phase I group. OFR Phase I subjects had significant (P < 0.01) increases over baseline at day 1 and/or following washout for 13 cytokines (cc chemokine ligands [CCL] 3, CCL5, CCL11, granulocyte-macrophage colony-stimulating factor [GM-CSF], interferon [INF]-γ, interleukin [IL]-2, IL-4, IL-5, IL-6, IL-13, IL-15, IL-17, tumor necrosis factor [TNF]-α). These changes were not observed in RNF Phase I subjects, even though SICS test scores increased. Phase I OFR subjects also had increased dryness, while RNF Phase I subjects had decreased bulbar hyperemia. No changes were detected with respect to limbal hyperemia or surface sensitivity thresholds.

CONCLUSION

The tear cytokine assay can detect and differentiate contact lens/MPS induced increases in inflammatory cytokines. Changes in cytokine levels were consistent with measurement of hyperemia and dryness but not with SICS scores, thereby suggesting a proinflammatory response to OFR compared to RNF that is not related to SICS test score. Tear cytokine profiles may be useful for reconciling clinical relevance of test results and in revealing signaling involved in the development of corneal infiltrative events.

The effects of silicone hydrogel lens wear on the corneal epithelium and risk for microbial keratitis

Previous studies using animal models and human clinical trials have demonstrated that the use of low-oxygen-transmissible contact lens materials produce corneal epithelial surface damage resulting in increased Pseudomonas aeruginosa (PA) adhesion and raft-mediated internalization into surface corneal epithelial cells. These findings led to the testable clinical predictions that (1) microbial keratitis (MK) risk is expected to be the greatest during the first 6 months of wear; (2) there is no difference between 6 and 30 night extended wear; and (3) that wear of hyperoxygen-transmissible lenses would reduce the reported incidence of infection. Subsequent epidemiologic studies have confirmed the first two predictions; however, increased oxygen transmissibility with silicone hydrogel (SiHy) lens wear has not altered the overall incidence of MK. In this review, more recent clinical and basic studies that investigate epithelial alterations and bacterial adhesion to corneal epithelial cells after the wear of SiHy lenses with and without concomitant exposure to chemically preserved multipurpose solutions (MPS) will be examined. The collective results of these studies demonstrate that even in the absence of lens-related hypoxia, MPS induce ocular surface changes during SiHy lens wear that are associated with a pathophysiologic increase in PA adherence and internalization in the corneal epithelium, and therefore, predict a greater risk for PA-MK. In addition, new data supporting an interactive role for inflammation in facilitating PA adherence and internalization in the corneal epithelium will also be discussed.

Corneal inflammation is inhibited by the LFA-1 antagonist, lifitegrast (SAR 1118)

PURPOSE

Sterile corneal infiltrates can cause pain, blurred vision, and ocular discomfort in silicone hydrogel contact-lens users. The current study investigates the potential for the synthetic lymphocyte functional antigen-1 (LFA-1) antagonist lifitegrast (SAR 1118) to block corneal inflammation using a murine model.

METHODS

The role of LFA-1 (CD11a/CD18) was examined either in CD18(-/-) mice, by intraperitoneal injection of anti-CD11a, or by topical application of lifitegrast. Corneal inflammation was induced by epithelial abrasion and exposure to either tobramycin-killed Pseudomonas aeruginosa or Staphylococcus aureus in the presence of a 2-mm-diameter punch from a silicone hydrogel contact lens. After 24 h, corneal thickness and haze were examined by in vivo confocal microscopy, and neutrophil recruitment to the corneal stroma was detected by immunohistochemistry.

RESULTS

Neutrophil recruitment to the corneal stroma and development of stromal haze were significantly impaired in CD18(-/-) mice or after injection of anti-CD11a. Topical lifitegrast also inhibited P. aeruginosa- and S. aureus-induced inflammation, with the optimal application being a 1% solution applied either 2 or 3 times prior.

CONCLUSION

As LFA-1-dependent neutrophil recruitment to the corneal stroma can be blocked by topical lifitegrast, this reagent could be used in combination with antibiotics to prevent leukocyte infiltration to the corneal stroma in association with contact-lens wear.

Innate immune regulation of Serratia marcescens-induced corneal inflammation and infection

PURPOSE

Serratia marcescens is frequently isolated from lenses of patients with contact lens-associated corneal infiltrates. In the current study, we examined the role of toll-like receptors (TLRs) and interleukin-1 receptor type 1 (IL-1R1) in S. marcescens-induced corneal inflammation and infection.

METHODS

The central corneal epithelium of C57BL/6 and gene knockout mice was abraded, and 1 × 10(7) S. marcescens were added in the presence of a silicone hydrogel contact lens, and we examined corneal inflammation by confocal microscopy and neutrophil enumeration. Viable bacteria were quantified by colony-forming units (CFU).

RESULTS

S. marcescens induced neutrophil recruitment to the corneal stroma, and increased corneal thickness and haze in C57BL/6 mice. Conversely, CFU was significantly lower by 48 hours post infection. In contrast, MyD88(-/-), IL-1R(-/-), TLR4(-/-), and TLR4/5(-/-) corneas infected with S. marcescens had significantly increased CFU, indicating impaired clearance. However, there was no significant difference in CFU among C57BL/6, TIRAP(-/-), and TRIF(-/-) mice. Tobramycin-killed S. marcescens induced corneal inflammation in C57BL/6 mice, which was impaired significantly in MD-2(-/-) mice and in C57BL/6 mice pretreated topically with the MD-2 antagonist eritoran tetrasodium.

CONCLUSIONS

S. marcescens induces corneal inflammation by activation of TLR4/MD-2/MyD88 and the IL-1R1/MyD88 pathways, which are potential therapeutic targets for inhibition of S. marcescens-induced corneal inflammation.

Dendritic immune cell densities in the central cornea associated with soft contact lens types and lens care solution types: a pilot study

BACKGROUND

The purpose of this study was to assess whether differences in central corneal dendritic immune cell densities associated with combinations of soft contact lenses and lens care solutions could be detected by in vivo confocal microscopy.

METHODS

Participants were adults naïve to contact lens wear (n = 10) or who wore soft contact lenses habitually on a daily-wear schedule (n = 38) or on a study-assigned schedule for 30 days with daily disposable silicone hydrogel lenses (n = 15). Central corneas were scanned using an in vivo confocal microscope. Cell densities were compared among groups by demographic parameters, lens materials, and lens care solutions (polyhexamethylene biguanide [PHMB], polyquaternium-1 and myristamidopropyl dimethylamine [PQ/MAPD], peroxide, or blister pack solution [for daily disposable lenses]).

RESULTS

Among lens wearers, no associations were observed between immune cell densities and age, gender, or years of lens-wearing experience. Mean cell density was significantly lower (P < 0.01) in nonwearers (29 ± 23 cells/mm(2), n = 10) than in lens wearers (64 ± 71 cells/mm(2), n = 53). Mean cell density was lower (P = 0.21) with traditional polymer lenses (47 ± 44 cells/mm(2), n = 12) than with silicone hydrogel lenses (69 ± 77 cells/mm(2), n = 41). Lowest to highest mean density of immune cells among lens wearers was as follows: PQ/MAPD solution (49 ± 28 cells/mm(2)), blister pack solution (63 ± 81 cells/mm(2)), PHMB solution (66 ± 44 cells/mm(2)), and peroxide solution (85 ± 112 cells/mm(2)).

CONCLUSION

In this pilot study, in vivo confocal microscopy was useful for detecting an elevated immune response associated with soft contact lenses, and for identifying lens-related and solution-related immune responses that merit further research.

The impact of cellular debris on Pseudomonas aeruginosa adherence to silicone hydrogel contact lenses and contact lens storage cases

OBJECTIVES

To evaluate neutrophil-enhanced Pseudomonas aeruginosa (PA) biofilm formation on silicone hydrogel contact lenses and to determine the effect of epithelial biodebris on PA adherence in contact lens storage cases.

METHODS

A fully invasive PA corneal isolate stably conjugated to green fluorescent protein was used. Unworn lotrafilcon A contact lenses were incubated at various ratios of PA to polymorphonuclear neutrophil (PMN) for 24 hours at 37°C. Lens-associated PA was evaluated using laser scanning confocal microscopy and nonviable PA were visualized using propidium iodide. Viable bacteria were enumerated by colony-forming unit (CFU) analysis. For acute epithelial cell studies, PA viability was determined after coincubation with freeze-thaw epithelial cell lysates in 96-well polystyrene plates. Levels of residual cellular debris and bacterial viability were further assessed in used contact lens storage cases.

RESULTS

Laser scanning confocal microscopy demonstrated that cotreatment with PMA-stimulated neutrophils increased PA adherence over 24 hours to lens surfaces with a striking alteration of PA architecture. Propidium iodide staining showed that the adherent bacteria consisted of a mixture of viable and nonviable PA; a PMN-associated increase in viable PA was confirmed by CFU (PA:PMN 0.1:1, P = 0.025; PA:PMN 1:1, P = 0.005). Acute epithelial cell debris studies revealed a significant increase in viable PA in 96-well plates in the presence of epithelial freeze-thaw lysates (PA:debris 1:1, P = 0.002; PA:debris 100:1, P = 0.002). Crystal violet staining of used lens storage cases revealed residual cellular debris at all time points, which was independent of microbial contamination; all lens cases used for periods of 9 months or more were uniformly associated with high levels of viable microorganisms.

CONCLUSION

These results demonstrate that prolonged corneal inflammation with the presence of PMNs when confronted with simultaneous PA challenge in extended contact lens wear has the potential to stimulate biofilm formation on silicone hydrogel contact lenses. These findings further suggest that a persistent buildup of extracellular debris in lens storage cases may contribute to the heavy biofilms reported on these surfaces.

The association between mucin balls and corneal infiltrative events during extended contact lens wear

PURPOSE

To determine the association between mucin ball formation and corneal infiltrative events (CIEs) during continuous wear with lotrafilcon A silicone hydrogel contact lenses.

METHODS

Subjects (n = 205) in the Longitudinal Analysis of Silicone Hydrogel Contact Lens Study wore lotrafilcon A contact lenses for 12 months of continuous wear. The primary outcome was a CIE. Kaplan-Meier methods were used to estimate the unadjusted cumulative incidence of remaining CIE free stratified by mucin ball presence. Cox proportional hazards regression was used to model the hazard of developing a CIE as a function of mucin ball formation and other covariates.

RESULTS

Over half (54.2%) of the subjects displayed some presence of mucin balls during at least 1 visit and about one third (32.8%) displayed repeated episodes. Mucin ball scores were correlated between the 2 eyes and weakly correlated with corneal curvature (P ≤ 0.005). Univariate analyses revealed that the relative hazard for a CIE was 0.35 [95% confidence interval (CI), 0.19-0.68] if a single episode of mucin balls was detected and 0.17 (95% CI, 0.06-0.43) if repeated episodes were detected. Upon multivariate analysis, repeated presence of mucin balls was associated with an 84% decreased hazard of experiencing a CIE (hazard ratio: 0.16; 95% CI, 0.06-0.44).

CONCLUSIONS

The presence of mucin balls is significantly associated with a decreased incidence of CIEs, and the effect is greatest when they are repeatedly present over time. We hypothesize that the mucin ball presence represents a more concentrated or viscous mucus layer, which prevents upregulation of the immune response against bacterial ligands.

Risk factors for corneal inflammatory and mechanical events with extended wear silicone hydrogel contact lenses

PURPOSE

To identify risk factors for contact lens-related corneal inflammatory events and mechanical events in wearers of silicone hydrogel lenses on a 30-night extended wear (EW) schedule in India.

METHODS

An interventional study with 188 subjects wearing silicone hydrogel lenses bilaterally on a 30-night EW schedule. Subjects were dispensed with lenses and reviewed at scheduled visits up to 6 months of EW. Multivariate logistic regression, after adjusting for within subject correlation, was used to develop the statistical model.

RESULTS

Occupations in non-ideal environments were found to predispose a lens wearer to inflammatory events (p = 0.003). Wearers in the non-ideal group, who had varying degrees of exposure to ocular irritants in their work environment had highest incidence of inflammatory events (19.2%). Wearers in a controlled, ideal environment had lowest levels of events (3.3%). Students occupied a position between the two groups (9.3%). Inflammatory rate was higher among wearers with increased microbial contamination of lenses (p = 0.002). Wearers with an inflammatory event had mean colony forming unit of 1.97 log compared with mean colony forming unit of 1.45 log in group with no inflammatory event. Corneal vascularization was associated with the development of inflammatory events (p = 0.001) with 50% of wearers with vascularization experiencing events compared with 7.6% of subjects with no vascularization. Reduced lens movement was associated with inflammatory events with subjects more likely to develop inflammatory events compared with those wearers with optimal lens movement (p = 0.027).

CONCLUSIONS

A multitude of factors, including environmental influences, lens contamination, ocular characteristics, and lens fit, contributes to the development of inflammatory events, information that is of clinical relevance to practitioners worldwide. Occupational environment was also a contributory factor, confirming that a duty of clinicians is to ascertain the nature of the work environment of lens wearers (and potential wearers) and to balance the needs of the wearer with the potential risks.

Ability of silver-impregnated contact lenses to control microbial growth and colonisation

Purpose

To examine the ability of silver nano-particles to prevent the growth of Pseudomonas aeruginosa and Staphylococcus aureus in solution or when adsorbed into contact lenses. To examine the ability of silver nano-particles to prevent the growth of Acanthamoeba castellanii.

Methods

Etafilcon A lenses were soaked in various concentrations of silver nano-particles. Bacterial cells were then exposed to these lenses, and numbers of viable cells on lens surface or in solution compared to etafilcon A lenses not soaked in silver. Acanthamoeba trophozoites were exposed to silver nano-particles and their ability to form tracks was examined.

Results

Silver nano-particle containing lenses reduced bacterial viability and adhesion. There was a dose-dependent response curve, with 10 ppm or 20 ppm silver showing > 5 log reduction in bacterial viability in solution or on the lens surface. For Acanthamoeba, 20 ppm silver reduced the ability to form tracks by approximately 1 log unit.

Conclusions

Silver nanoparticles are effective antimicrobial agents, and can reduce the ability of viable bacterial cells to colonise contact lenses once incorporated into the lens.

Risk factors for corneal infiltrative events during continuous wear of silicone hydrogel contact lenses

PURPOSE

This study determined which microbiologic, clinical, demographic, and behavioral factors are associated with corneal infiltrative events (CIEs) during continuous wear of silicone hydrogel (SH) contact lenses.

METHODS

Subjects (n = 205) were fitted with lotrafilcon A lenses for continuous wear and observed for 1 year. The main exposures of interest were corneal staining and bacterial lens contamination. Kaplan-Meier (KM) plots were used to estimate the cumulative unadjusted probability of remaining CIE free, and Cox proportional hazards regression was used to model the hazard of having a CIE, as a function of key predictor variables.

RESULTS

The KM-unadjusted cumulative probability of remaining CIE free was 73.3%. Approximately 53% of subjects had repeated episodes of corneal staining (mild or greater), and 11.3% had repeated episodes of moderate or greater corneal staining. Corneal staining was not associated with the development of a CIE. The frequency of substantial bacterial bioburden on worn lenses at the time of a CIE was 64.7%, compared with only 12.2% during uncomplicated wear. The presence of substantial lens bacterial bioburden was associated with the development of a CIE (adjusted hazards ratio [HR], 8.66; 95% confidence interval [CI], 2.88-26.01). Smoking was also associated with a CIE (adjusted HR, 4.13; 95% CI, 1.27-13.45).

CONCLUSIONS

Corneal staining is common during continuous wear of SH lenses, but it is not associated with the development of a CIE. Smoking and substantial lens bacterial bioburden pose prominent risks of a CIE. In this study, more than 70% of the total risk of CIE in those with substantial lens bioburden is attributable to this exposure. (ClinicalTrials.gov number, NCT00727402).

Microbial contamination of contact lenses, lens care solutions, and their accessories: a literature review

PURPOSE

A contact lens (CL) can act as a vector for microorganisms to adhere to and transfer to the ocular surface. Commensal microorganisms that uneventfully cohabitate on lid margins and conjunctivae and potential pathogens that are found transiently on the ocular surface can inoculate CLs in vivo. In the presence of reduced tissue resistance, these resident microorganisms or transient pathogens can invade and colonize the cornea or conjunctiva to produce inflammation or infection.

METHODS

The literature was reviewed and used to summarize the findings over the last 30 years on the identification, enumeration, and classification of microorganisms adherent to CLs and their accessories during the course of normal wear and to hypothesize the role that these microorganisms play in CL infection and inflammation.

RESULTS

Lens handling greatly increases the incidence of lens contamination, and the ocular surface has a tremendous ability to destroy organisms. However, even when removed aseptically from the eye, more than half of lenses are found to harbor microorganisms, almost exclusively bacteria. Coagulase-negative Staphylococci are most commonly cultured from worn lenses; however, approximately 10% of lenses harbor Gram-negative and highly pathogenic species, even in asymptomatic subjects. In storage cases, the incidence of positive microbial bioburden is also typically greater than 50%. All types of care solutions can become contaminated, including up to 30% of preserved products.

CONCLUSIONS

The process of CL-related microbial keratitis and inflammation is thought to be preceded by the presence or transfer or both of microorganisms from the lens to the ocular surface. Thus, this detailed understanding of lens-related bioburden is important in the understanding of factors associated with infectious and inflammatory complications. Promising mechanisms to prevent bacterial colonization on lenses and lens cases are forthcoming, which may decrease the incidence of microbially driven CL complications.

Corneal thinning associated with recurrent microbial keratitis resulting from 7-day extended wear of low Dk hydrogel contact lenses: a case report

CASE DESCRIPTION

Corneal thinning and an increased risk of corneal perforation, resulting from recurrent episodes of microbial keratitis, required a 38-year-old Caucasian female to undergo bilateral corneal grafting. Although strongly advised otherwise, the patient had been a long time user of low oxygen permeability hydrogel contact lenses in a flexible wear regime, with frequent overnight use.

DISCUSSION

Microbial keratitis is a potentially severe contact lens related complication which, if not properly treated, may lead to permanent visual loss. The introduction of silicone-hydrogel materials and daily replacement modalities has not resulted in a significant decrease in the incidence of microbial keratitis, thus suggesting that the condition is mainly dependent on patient hygiene and wearing habits. Non-compliance, which is endemic in contact lens wear, may be combated by increasing patient awareness of the potential risk factors of contact lens misuse. This is accomplished through constant, rigorous information provided by contact lens practitioners.

Increased resistance of contact lens-related bacterial biofilms to antimicrobial activity of soft contact lens care solutions

PURPOSE

To determine if clinical and reference strains of Pseudomonas aeruginosa, Serratia marcescens, and Staphylococcus aureus form biofilms on silicone hydrogel contact lenses and ascertain antimicrobial activities of contact lens care solutions.

METHODS

Clinical and American Type Culture Collection reference strains of P. aeruginosa, S. marcescens, and S. aureus were incubated with lotrafilcon A lenses under conditions that facilitate biofilm formation. Biofilms were quantified by quantitative culturing (colony-forming units, CFUs), and gross morphology and architecture were evaluated using scanning electron microscopy and confocal microscopy. Susceptibilities of the planktonic and biofilm growth phases of the bacteria to 5 common multipurpose contact lens care solutions and 1 hydrogen peroxide care solution were assessed.

RESULTS

Pseudomonas aeruginosa, S. marcescens, and S. aureus reference and clinical strains formed biofilms on lotrafilcon A silicone hydrogel contact lenses, as dense networks of cells arranged in multiple layers with visible extracellular matrix. The biofilms were resistant to commonly used biguanide-preserved multipurpose care solutions. Pseudomonas aeruginosa and S. aureus biofilms were susceptible to a hydrogen peroxide and a polyquaternium-preserved care solution, whereas S. marcescens biofilm was resistant to a polyquaternium-preserved care solution but susceptible to hydrogen peroxide disinfection. In contrast, the planktonic forms were always susceptible.

CONCLUSION

Pseudomonas aeruginosa, S. marcescens, and S. aureus form biofilms on lotrafilcon A contact lenses, which in contrast to planktonic cells are resistant to the antimicrobial activity of several soft contact lens care products.

Toll-like receptors at the ocular surface

The Toll-like receptor (TLR) family of pathogen recognition molecules has an important role in recognizing microbial pathogens and microbial breakdown products. Activation of TLRs in the corneal epithelium induces CXC chemokine production and recruitment of neutrophils to the corneal stroma. Although essential for pathogen killing, neutrophils can cause extensive tissue damage, leading to visual impairment and blindness. In this review, we examine the role of TLRs in microbial keratitis and in noninfectious corneal inflammation, most commonly associated with contact lens wear. we present recent findings on TLR signaling pathways in the cornea, including MyD88- and TRIF-dependent responses and discuss the role of resident macrophages and dendritic cells. Finally, we examine the potential for targeting the TLR pathway as a potential therapeutic intervention for microbial keratitis and contact lens-associated corneal inflammation.

Are inflammatory events a marker for an increased risk of microbial keratitis?

PURPOSE

To consider whether inflammatory events, such as contact lens-induced peripheral ulcers, contact lens-induced acute red eye, and infiltrative keratitis are a marker for an increased risk for the occurrence of microbial keratitis.

METHODS

A review of relevant studies was undertaken with the view to answering two questions: 1) Do inflammatory events associated with contact lens wear progress to infection or microbial keratitis; and 2) Do episodes of inflammatory events predispose a patient to having an event of microbial keratitis?

RESULTS

The large body of laboratory work, along with the epidemiologic data on incidence rates and clinical data with regard to differences between the nature of inflammatory events and infection, supports the supposition that inflammatory events are not a marker for increased risk of microbial keratitis.

CONCLUSIONS

Inflammatory events are not a marker for increased risk of microbial keratitis, nor will they progress to infection because they are separate disease entities.