Lipopolysaccharide entry in the damaged cornea and specific uptake by polymorphonuclear neutrophils

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Corneal fibroblasts: Function and markers

Corneal stromal keratocytes contribute to the maintenance of corneal transparency and shape by synthesizing and degrading extracellular matrix. They are quiescent in the healthy cornea, but they become activated in response to insults from the external environment that breach the corneal epithelium, with such activation being associated with phenotypic transformation into fibroblasts. Corneal fibroblasts (activated keratocytes) act as sentinel cells to sense various external stimuli-including damage-associated molecular patterns derived from injured cells, pathogen-associated molecular patterns of infectious microorganisms, and inflammatory mediators such as cytokines-under pathological conditions such as trauma, infection, and allergy. The expression of various chemokines and adhesion molecules by corneal fibroblasts determines the selective recruitment and activation of inflammatory cells in a manner dependent on the type of insult. In infectious keratitis, the interaction of corneal fibroblasts with various components of microbes and with cytokines derived from infiltrated inflammatory cells results in excessive degradation of stromal collagen and consequent corneal ulceration. Corneal fibroblasts distinguish between type 1 and type 2 inflammation through recognition of corresponding cytokines, with their activation by type 2 cytokines contributing to the pathogenesis of corneal lesions in severe ocular allergic diseases. Pharmacological targeting of corneal fibroblast function is thus a potential novel therapeutic approach to prevention of excessive corneal stromal inflammation, damage, and scarring.

What Makes Cornea Immunologically Unique and Privileged? Mechanistic Clues from a High-Resolution Proteomic Landscape of the Human Cornea

Success rates of corneal transplantation are particularly high owing to its unique, innate immune privilege derived from a phenomenon known as Anterior Chamber-Associated Immune Deviation (ACAID). Of note, cornea is a transparent, avascular structure that acts as a barrier along with sclera to protect the eye and contributes to optical power. Molecular and systems biology mechanisms underlying ACAID and the immunologically unique and privileged status of cornea are not well known. We report here a global unbiased proteomic profiling of the human cornea and the identification of 4824 proteins, the largest catalog of human corneal proteins identified to date. Moreover, signaling pathway analysis revealed enrichment of spliceosome, phagosome, lysosome, and focal adhesion pathways, thereby demonstrating the protective functions of corneal proteins. We observed an enrichment of neutrophil-mediated immune response processes in the cornea as well as proteins belonging to the complement and ER-Phagosome pathways that are suggestive of active immune and inflammatory surveillance response. This study provides a key expression map of the corneal proteome repertoire that should enable future translational medicine studies on the pathological conditions of the cornea and the mechanisms by which cornea immunology are governed. Molecular mechanisms of corneal immune privilege have broad relevance to understand and anticipate graft rejection in the field of organ transplantation.

Evaluation of the proinflammatory effects of contaminated bathing water

Contaminated marine bathing water has been reported to adversely affect human health. Our data demonstrated a correlation between total endotoxin (lipopolysaccharide; LPS) levels and degree of contamination of marine bathing waters. To assess the potential health implications of LPS present in marine bathing waters, the inflammation-inducing potency of water samples collected at different time points at multiple sampling sites were assessed using a cell culture-based assay. The numbers of fecal indicator bacteria (FIB) were also examined in the same samples. Water samples were used to stimulate two cell culture models: (1) a novel non-transformed continuously growing murine cell line Max Plank Institute (MPI) characteristic of alveolar macrophages and (2) human MonoMac 6 monocyte cell line. The inflammatory potential of the samples was assessed by measuring the release of inflammatory cytokines. The presence of high levels of LPS in contaminated bathing water led to induction of inflammatory response from our in vitro cell-based bioassays suggesting its potential health impact. This finding introduces an in vitro culture assay that reflects the level of LPS in water samples. These observations further promote previous finding that LPS is a reliable surrogate biomarker for fecal contamination of bathing water.

Contact lens-related corneal infection: Intrinsic resistance and its compromise

Contact lenses represent a widely utilized form of vision correction with more than 140 million wearers worldwide. Although generally well-tolerated, contact lenses can cause corneal infection (microbial keratitis), with an approximate annualized incidence ranging from ~2 to ~20 cases per 10,000 wearers, and sometimes resulting in permanent vision loss. Research suggests that the pathogenesis of contact lens-associated microbial keratitis is complex and multifactorial, likely requiring multiple conspiring factors that compromise the intrinsic resistance of a healthy cornea to infection. Here, we outline our perspective of the mechanisms by which contact lens wear sometimes renders the cornea susceptible to infection, focusing primarily on our own research efforts during the past three decades. This has included studies of host factors underlying the constitutive barrier function of the healthy cornea, its response to bacterial challenge when intrinsic resistance is not compromised, pathogen virulence mechanisms, and the effects of contact lens wear that alter the outcome of host-microbe interactions. For almost all of this work, we have utilized the bacterium Pseudomonas aeruginosa because it is the leading cause of lens-related microbial keratitis. While not yet common among corneal isolates, clinical isolates of P. aeruginosa have emerged that are resistant to virtually all currently available antibiotics, leading the United States CDC (Centers for Disease Control) to add P. aeruginosa to its list of most serious threats. Compounding this concern, the development of advanced contact lenses for biosensing and augmented reality, together with the escalating incidence of myopia, could portent an epidemic of vision-threatening corneal infections in the future. Thankfully, technological advances in genomics, proteomics, metabolomics and imaging combined with emerging models of contact lens-associated P. aeruginosa infection hold promise for solving the problem - and possibly life-threatening infections impacting other tissues.

Increased postoperative anterior chamber inflammation secondary to heat-resistant endotoxins

PURPOSE

To evaluate the cause of clusters of increased postoperative anterior chamber inflammation after uneventful cataract surgery, and to examine its relation to the presence of endotoxins in sterile consumables.

SETTING

Tertiary eye center in north India.

DESIGN

Single-center retrospective case series.

METHODS

All cataract surgeries performed at the tertiary eye center over 12 weeks (October 1, 2017 to December 31, 2017) were noted. Any patient with a "severe reaction" postoperatively was monitored closely and the postoperative drug regimen was altered accordingly. "Severe reaction" was defined as any patient with more than 4+ cells and/or fibrin with or without hypopyon. The Hospital Infection Control committee was informed, and a root cause analysis was performed to determine the cause. All the consumables were recalled and replaced. The samples were sent for microbiological evaluations.

RESULTS

Of the 781 cataract surgeries performed, 81 patients had a severe reaction. Most patients were men (71%) and the mean age of the patients was 63 years. Twelve patients had fibrin, 3 of whom presented with hypopyon. Because all samples were negative of any growth, endotoxin tests were performed. All the samples were found to be negative, except for the ophthalmic viscosurgical device (OVD), which showed positive endotoxin levels. The OVD was changed and the anterior chamber reactions ceased to occur.

CONCLUSION

A careful, stepwise approach is necessary when investigating clusters of increased postoperative anterior chamber reactions after uneventful surgery. A high degree of suspicion is important to rule out all possible reasons and in the absence of any identifiable cause, sterile consumables should be checked for endotoxins.

Corneal Fibroblasts as Sentinel Cells and Local Immune Modulators in Infectious Keratitis

The cornea serves as a barrier to protect the eye against external insults including microbial pathogens and antigens. Bacterial infection of the cornea often results in corneal melting and scarring that can lead to severe visual impairment. Not only live bacteria but also their components such as lipopolysaccharide (LPS) of Gram-negative bacteria contribute to the development of inflammation and subsequent corneal damage in infectious keratitis. We describe the important role played by corneal stromal fibroblasts (activated keratocytes) as sentinel cells, immune modulators, and effector cells in infectious keratitis. Corneal fibroblasts sense bacterial infection through Toll-like receptor (TLR)–mediated detection of a complex of LPS with soluble cluster of differentiation 14 (CD14) and LPS binding protein present in tear fluid. The cells then initiate innate immune responses including the expression of chemokines and adhesion molecules that promote the recruitment of inflammatory cells necessary for elimination of the infecting bacteria. Infiltrated neutrophils are activated by corneal stromal collagen and release mediators that stimulate the production of pro–matrix metalloproteinases by corneal fibroblasts. Elastase produced by Pseudomonas aeruginosa (P. aeruginosa) activates these released metalloproteinases, resulting in the degradation of stromal collagen. The modulation of corneal fibroblast activation and of the interaction of these cells with inflammatory cells and bacteria is thus important to minimize corneal scarring during treatment of infectious keratitis. Pharmacological agents that are able to restrain such activities of corneal fibroblasts without allowing bacterial growth represent a potential novel treatment option for prevention of excessive scarring and tissue destruction in the cornea.

Rocking media over ex vivo corneas improves this model and allows the study of the effect of proinflammatory cytokines on wound healing

PURPOSE

The aim of this work was to develop an in vitro cornea model to study the effect of proinflammatory cytokines on wound healing.

METHODS

Initial studies investigated how to maintain the ex vivo models for up to 4 weeks without loss of epithelium. To study the effect of cytokines, corneas were cultured with the interleukins IL-17A, IL-22, or a combination of IL-17A and IL-22, or lipopolysaccharide (LPS). The effect of IL-17A on wound healing was then examined.

RESULTS

With static culture conditions, organ cultures deteriorated within 2 weeks. With gentle rocking of media over the corneas and carbon dioxide perfusion, the ex vivo models survived for up to 4 weeks without loss of epithelium. The cytokine that caused the most damage to the cornea was IL-17A. Under static conditions, wound healing of the central corneal epithelium occurred within 9 days, but only a single-layered epithelium formed whether the cornea was exposed to IL-17A or not. With rocking of media gently over the corneas, a multilayered epithelium was achieved 9 days after wounding. In the presence of IL-17A, however, there was no wound healing evident. Characterization of the cells showed that wherever epithelium was present, both differentiated cells and highly proliferative cells were present.

CONCLUSIONS

We propose that introducing rocking to extend the effective working life of this model and the introduction of IL-17A to this model to induce aspects of inflammation extend its usefulness to study the effects of agents that influence corneal regeneration under normal and inflamed conditions.

The role of toll-like receptor 4 in corneal epithelial wound healing

PURPOSE

We evaluated the role of Toll-like receptor 4 (TLR4) in corneal epithelial wound healing.

METHODS

The expression of TLR4 during in vivo corneal epithelial wound healing was examined by immunostaining in mice. The expression and activation of TLR4 was studied in primary or telomerase-immortalized human corneal epithelial cells (HCEC). Scratch assay was performed to evaluate in vitro wound closure using live time-lapse microscopy. Transwell migration assay and Ki67 immunostaining were done to evaluate migration and proliferation, respectively. Lipopolysaccharide (LPS) was used to activate TLR4, whereas CLI-095 was used for its inhibition. The expression of inflammatory cytokines was determined by RT-PCR and ELISA. The activation of p42/44 and p38 was determined by immunoblotting.

RESULTS

In the murine model, TLR4 immunostaining was noted prominently in the epithelium 8 hours after wounding. There was a 4-fold increase in the expression of TLR4 6 hours after in vitro scratch wounding (P < 0.001). Confocal microscopy confirmed the membrane localization of TLR4/MD2 complex. There was a significant increase in migration, proliferation, and wound closure in HCEC treated with LPS (P < 0.05), while there was significant decrease with TLR4 inhibition (P < 0.05). Addition of LPS to wounded HCEC resulted in a significant increase in the expression of IL-6, TNF-α, CXCL8/IL8, and CCL5/RANTES at the mRNA and protein levels. Likewise, LPS increased the activation of p42/44 and p38 in wounded HCEC.

CONCLUSIONS

These results suggest that epithelial wounding induces the expression of functional TLR4. Toll-like receptor 4 signaling appears to contribute to early corneal epithelial wound repair by enhancing migration and proliferation.

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.

Ethyl pyruvate ameliorates endotoxin-induced corneal inflammation

PURPOSE

The purpose of this study was to evaluate the anti-inflammatory effect of ethyl pyruvate (EP) in a mouse model of lipopolysaccharide (LPS)-induced corneal inflammation.

METHODS

LPS was injected intrastromally into the corneas of C57BL/6 mice followed by treatment with a solution of 2.5% EP in 0.2% hydroxypropyl methylcellulose (HPMC) every 90 minutes during the course of 12 hours. Prednisolone acetate 1% solution (PRED FORTE) was used as a positive control. Mice were sacrificed after 3 days, and corneas were examined by in vivo confocal microscopy and analyzed for infiltrated cells by flow cytometry. Gr-1, TNF-α, and pNF-κB-p65 were detected immunohistochemically, and TNF-α, IL-6, and IL-1β levels were quantified by ELISA.

RESULTS

LPS-induced haze in mice corneas was decreased by 2-fold upon EP treatment; however, it was not changed upon PRED FORTE treatment. Flow cytometry and immunohistochemistry showed infiltration of leukocytes in the LPS-treated corneas; among the infiltrated cells, neutrophils (Gr-1+ and CD11b+) and macrophages (F4/80+ and CD11b+) were 3403.4- and 4.5-fold higher in number, respectively, than in vehicle-treated control corneas. EP or PRED FORTE treatment of LPS-injected corneas decreased the number of neutrophils 7.5- and 7.2-fold and macrophages by 5.6- and 3.5-fold, respectively. Both EP and PRED FORTE decreased TNF-α and IL-6 expression considerably, and to a lesser extent IL-1β expression, in the LPS-treated corneas.

CONCLUSIONS

The present study demonstrated that EP reduces LPS-induced inflammation in the cornea and thus may have a potential therapeutic application in the inhibition of corneal inflammation.

Contact lenses as a drug delivery device for epidermal growth factor in the treatment of ocular wounds

BACKGROUND

This work was conducted to investigate the uptake and release of epidermal growth factor (EGF) from hydrogel contact lenses and to determine whether the released protein would be therapeutically active in a rabbit corneal epithelial defect model of ocular trauma, prior to use in humans.

METHODS

The uptake and release of EGF from hydrogel contact lens materials were determined by high-pressure liquid chromatography. Contact lenses composed of vasurfilcon A or lotrafilcon A (containing silicone) were incubated in a source solution containing 0.4 ppm EGF for seven hours. To determine the kinetics of drug uptake into the contact lens matrix, drug concentration in the source solution was measured at zero, one, 60, 240 and 420 minutes. To determine the kinetics of release, loaded contact lenses were immersed in a recipient solution of phosphate-buffered saline. Therapeutic activity in vivo was investigated by placing prepared lenses on the surface of abraded corneas of New Zealand White rabbits, with abraded corneas of contralateral eyes used as controls. Control eyes were treated with contact lenses placed in saline for injection. Wound closure was assessed hourly.

RESULTS

Uptake and release of EGF were demonstrated for vasurfilcon A but not lotrafilcon A contact lens materials. The retention time of EGF released from vasurfilcon A contact lenses was similar to control EGF not exposed to contact lens polymers. The greatest adsorption of EGF into the lens material occurred within approximately 120 minutes, with a flattening of the rate of uptake thereafter. Abraded eyes in rabbits showed a significantly higher overall healing rate for EGF-treated contact lenses compared with control eyes (p < 0.0001).

CONCLUSIONS

EGF can be delivered from some but not all hydrogel materials. Lens materials composed of silicone may not be useful for delivering EGF to the eye. EGF-treated contact lenses may be a useful device to facilitate healing of ocular wounds.

Lack of MD-2 expression in human corneal epithelial cells is an underlying mechanism of lipopolysaccharide (LPS) unresponsiveness

In the present study we tested the responsiveness of human corneal epithelial cells (HCECs) and corneal fibroblasts to lipopolysaccharide (LPS), a TLR4 ligand. Purified P aeruginosa LPS was used to stimulate telomerase-immortalized HCECs (HUCL) and stromal fibroblast (THK) cell lines. Exposure of cells to LPS induced a time-dependent activation of NF-κB in THK but not in HUCL cells, as assessed by an increase in IκB-α phosphorylation and degradation. Concomitant with NF-κB activation, LPS-treated THK cells, but not HUCL cells, produced significantly more cytokines than control untreated cells. A cell surface biotinylation assay revealed that HUCL cells express TLR4 intracellularly whereas TLR5 is expressed on the cell surface. Furthermore, RT-PCR analysis revealed that HUCL and primary HCECs, in contrast to THK cells, do not express MD-2. Thus, our results demonstrate that the LPS unresponsiveness of HCECs might be due to deficient expression of MD2, an essential component for LPS-TLR4 signaling.

Inhibition of corneal inflammation by the TLR4 antagonist Eritoran tetrasodium (E5564)

PURPOSE

To investigate the role of the TLR4/MD-2 antagonist eritoran tetrasodium in a murine model of contact lens-associated corneal infiltrates.

METHODS

C57BL/6 mouse corneas were abraded and treated with eritoran tetrasodium or placebo, either before or after stimulation with either LPS, the TLR2 ligand Pam(3)Cys, or antibiotic-killed Pseudomonas aeruginosa. A 2-mm punch from a silicon hydrogel contact lens was used to cover the corneal surface throughout the inhibition and stimulation period. Corneal infiltrates were detected by in vivo confocal microscopy and by immunohistochemistry for neutrophils. The effect of eritoran tetrasodium on stimulated human corneal epithelial cells (HCECs), macrophages, and neutrophils was also assessed.

RESULTS

Eritoran tetrasodium significantly inhibited CXC chemokine production in the cornea and development of corneal infiltrates, specifically neutrophils, in response to stimulation with LPS (TLR4), but not Pam(3)Cys (TLR2). When the antagonist was applied after LPS stimulation, neutrophil infiltration was also inhibited, although a higher concentration was needed. Furthermore, IL-8 production by TLR4- but not TLR2-stimulated HCECs, macrophages and neutrophils was also significantly reduced. Corneal inflammation induced by P. aeruginosa in the presence of tobramycin was found to be dependent on expression of TLR4 and MD-2 and is inhibited by eritoran tetrasodium.

CONCLUSIONS

Eritoran tetrasodium is a highly effective antagonist of TLR4/MD-2-dependent corneal inflammation.

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.

Peripheral ulcerative keratitis due to a 'long lost' hard contact lens

Peripheral ulcerative keratitis (PUK) is a disorder consisting of a crescent-shaped destructive inflammation of the perilimbal corneal stroma. PUK can occur in a variety of ocular and systemic conditions including infections, lid abnormalities, dermatological disorders and connective tissue disorders. We present a case of PUK associated with a hard contact lens (CL) retained in the superior fornix for over 16 years. After removal of the embedded CL, a superior forniceal conjunctival pedicle graft was performed to prevent corneal perforation. The patient was managed postoperatively with a combination of topical steroids and antibiotics. The use of systemic immunosuppressive therapy was not necessary. Micro-trauma and micro-keratitis may have occurred as a result of the mechanical effect of the CL but if this was the sole mechanism, one would expect presentation at a much earlier date. We discuss the pathogenetic mechanisms which may have contributed to the development of this ulceration. This report highlights the importance of lid eversion when examining patients with anterior segment pathology.

Use of Polymyxin as an Endotoxin Blocker in the Prevention of Diffuse Lamellar Keratitis in an Animal Model

PURPOSE

To determine whether bacterial endotoxin, lipopolysaccharide (LPS), could induce diffuse lamellar keratitis (DLK) in an animal model and whether DLK could be prevented by endotoxin blockers such as polymyxin.

METHODS

Laser in situ keratomileusis (LASIK) flaps were created in rabbit eyes. The stromal bed was treated with 20 microg of Burkholderia cepacia LPS or balanced salt solution (BSS). Development of DLK, histological degree of inflammation, and presence of LPS detected by anti-LPS antibody were evaluated after 48 hours. In a second experiment, all eyes received LPS and were randomly assigned to receive either polymyxin in the form of two drops of Polytrim (Allergan, Irvine, Calif) on the stromal bed or two drops of BSS.

RESULTS

In the animal model study, LPS was significantly associated with the development of DLK (P<.05, n=30). Infiltration with polymorphonuclear cells and presence of DLK were found in LPS treated eyes but not in controls. In the second experiment, 4 (27%) of 15 eyes that received polymyxin in addition to LPS developed DLK compared to 18 (95%) of 19 eyes that received only LPS (P<.05, n=34). There was a trend towards higher flap displacement in polymyxin treated eyes but this was not significant (P=.07).

CONCLUSIONS

Diffuse lamellar keratitis in a rabbit model can be caused by bacterial endotoxin (LPS). Endotoxin blockers, such as polymyxin, are effective in decreasing the incidence of endotoxin-induced DLK in a rabbit model.

Intracellularly expressed TLR2s and TLR4s contribution to an immunosilent environment at the ocular mucosal epithelium

Epithelial cells are key players in the first line of defense offered by the mucosal immune system against invading pathogens. In the present study we sought to determine whether human corneal epithelial cells expressing Toll-like receptors (TLRs) function as pattern-recognition receptors in the innate immune system and, if so, whether these TLRs act as a first line of defense in ocular mucosal immunity. Incubation of human primary corneal epithelial cells and the human corneal epithelial cell line (HCE-T) with peptidoglycan or LPS did not lead to activation, at the level of DNA transcription, of NF-kappaB or the secretion of inflammation-associated molecules such as IL-6, IL-8, and human beta-defensin-2. However, when incubated with IL-1alpha to activate NF-kappaB, the production by these cells of such inflammatory mediators was enhanced. Human corneal epithelial cells were observed to express both TLR2- and TLR4-specific mRNA as well as their corresponding proteins intracellularly, but not at the cell surface. However, even when LPS was artificially introduced into the cytoplasm, it did not lead to the activation of epithelial cells. Taken together, our results demonstrate that the intracellular expression of TLR2 and TLR4 in human corneal epithelial cells fails to elicit innate immune responses and therefore, perhaps purposely, contributes to an immunosilent environment at the ocular mucosal epithelium.

Contact lens-associated corneal infiltrates

PURPOSE This review article examines recent studies pertaining to contact lens-associated corneal infiltrates (CLACI) that occur in the absence of culture-proven microbial infection. METHODS The literature was reviewed in regard to the clinical appearance, incidence and risk, etiology, pathophysiology, differential diagnosis, and management of CLACI. Recent insights are presented in the context of future directions for prevention of CLACI. RESULTS Contact lens-associated corneal infiltrates may manifest in various forms that require careful observational skills to ensure proper diagnosis. Although the reported incidence of CLACI varies widely, even a low percentage of contact lens wearers would constitute a substantial number of affected individuals. Any one or a combination of multiple mechanical, hypoxic, or toxic stimuli associated with contact lens use can induce proinflammatory responses that lead to infiltration of inflammatory cells into the cornea. A number of candidate cytokines, chemokines, adhesion molecules, and so forth have been identified. In addition to differentiation from microbial keratitis, CLACI also should be differentiated from ocular disorders not associated with contact lenses but involving corneal infiltrates and from contact lens-associated disorders that may resemble infiltrates. Management of CLACI can range from simple monitoring of the patient to the use of pharmacologic intervention. CONCLUSIONS The small percentage of affected lens wearers translates into a notable number of individuals who, although not experiencing a vision-threatening event, are inconvenienced by the development of infiltrates. Design of preventive measures for CLACI should focus on the elimination of various mechanical, hypoxic, and toxic stimuli that can induce infiltrates and on the approaches for molecular intervention of the inflammatory cascade initiated by the stimuli.

Atopy: a patient-specific risk factor for diffuse lamellar keratitis

OBJECTIVE

To identify whether atopy is a patient-specific risk factor for the development of diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK).

DESIGN

Retrospective survey study.

PARTICIPANTS

Three hundred sixty consecutive patients who underwent same-day bilateral myopic astigmatic primary LASIK procedures during March 1, 2000, through July 31, 2000.

METHODS

We collected data for 360 consecutive patients undergoing LASIK during a 4-month period. On preoperative medical history questionnaires, patients self-identified whether they were atopic. All patients also indicated whether they were taking antiallergy medications or were untreated for allergy.

MAIN OUTCOME MEASURES

The incidence of DLK after LASIK surgery.

RESULTS

The risk of DLK in untreated atopic patients was much greater than the risk of DLK among nonatopics (odds ratio, 5.85; 95% confidence interval, 2.89-11.85; P = 0.001). However, the risk of DLK among atopic patients taking an oral systemic nonsedating histamine receptor 1 antagonist and among nonatopic patients did not differ significantly (odds ratio, 0.54; 95% confidence interval, 0.12-2.46; P = 0.43).

CONCLUSIONS

Atopy is a patient-specific risk factor for the development of DLK after primary bilateral LASIK for either myopia or myopic astigmatism. Atopic individuals benefit from preoperative treatment to minimize the incidence of DLK and the potential for visual loss.

Role of instrument cleaning and maintenance in the development of diffuse lamellar keratitis

OBJECTIVE

To determine if instrument cleaning techniques affect the rate of diffuse lamellar keratitis (DLK) after laser in situ keratomileusis (LASIK).

DESIGN

Retrospective case series.

PARTICIPANTS

Two hundred ten eyes of 109 patients.

METHODS

A record review was performed of all patients who underwent LASIK at the Jules Stein Eye Institute from April 1 through June 24, 1999. During the first 6 weeks, the instruments used in LASIK surgery were cleaned according to our conventional protocol. At the end of this 6-week period, the cleaning protocol was modified and used for a subsequent 6-week period. For each eye during the two periods, the status of DLK on the first postoperative day was recorded.

MAIN OUTCOME MEASURES

Presence of DLK.

RESULTS

During the first 6-week period, 118 eyes of 60 patients underwent LASIK surgery. In the subsequent 6 weeks, 92 eyes of 49 patients underwent LASIK surgery. The two groups included patients with similar demographic background: gender, age, and target correction. Diffuse lamellar keratitis was present in 13 of 118 eyes (11%) using our conventional protocol. In only 2 of 92 eyes (2%) did DLK develop after the protocol was modified. Using the chi-square test, the difference between the two groups was statistically significant (P = 0.01).

CONCLUSIONS

Diffuse lamellar keratitis is a fairly uncommon phenomenon after LASIK surgery. Although the cause remains to be elucidated, these results demonstrated a reduced incidence of DLK associated with alteration of cleaning procedures and a decrease in stagnant instrument cleaning fluids. The authors recommend that refractive centers avoid the use of stagnant fluids in their instrument cleaning and sterilizing protocols to minimize the occurrence of DLK outbreaks.

Endotoxin Levels in Steam and Reservoirs of Table-top Steam Sterilizers

PURPOSE

To document endotoxin levels in "Statim" cassette sterilizer reservoirs and in steam delivered to the cassette in the unwrapped instrument cycle. To document endotoxin levels in sterilizer reservoir water using different management protocols.

METHODS

Endotoxin levels were determined using the Limulus Amebocyte Lysate test. Endotoxin preparations were from Escherichia coli and Ralstonia pickettii. All samples were collected in depyrogenated glassware and stored at -20 degrees C until assayed.

RESULTS

The majority of water samples contained < 1.0 Endotoxin Unit (EU)/ml. The highest level found in sterilizers in clinical use was 5.3 EU/ml. Endotoxin was not detected in steam condensate within the limits of the assay. When the endotoxin level in the reservoir water was experimentally enhanced to 200 EU/ml, cassette steam condensate endotoxin levels were from 0.5% to 5% of the reservoir level. Daily and weekly emptying of the cassette reservoir consistently yielded low endotoxin levels as did monthly emptying, but with the latter there was a trend toward higher levels that favors weekly emptying as a precautionary measure.

CONCLUSIONS

Endotoxin levels in the reservoirs of 23 sterilizers involving 240 samplings were never high enough to yield detectable endotoxin levels in steam in the sterilizer cassette. Regular weekly emptying of sterilizer reservoirs would eliminate the risk of endotoxin transfer during steam sterilization.