Incidence of contact-lens-associated microbial keratitis and its related morbidity

Current concepts: contact lens related Pseudomonas keratitis

Despite the development of silicone hydrogel lenses, Pseudomonas aeruginosa (PA) continues to be the leading cause of contact lens related microbial keratitis. Understanding the pathogenesis of PA-mediated corneal infection is critical to the development of new prevention and treatment strategies. Recently intracellular invasion of surface corneal epithelial cells by PA has been revisited as an important element in the infection process. This review identifies the mechanisms involved, and examines the roles of the lens, hypoxia alone, PA stain, cystic fibrosis transmembrane receptor protein (CFTR), and membrane lipid rafts in mediating intracellular invasion in both in vitro and in vivo conditions. Non-toxic blockade of raft formation in vitro or in vivo effectively abrogates PA internalization and may represent a unique, new strategy to prevent or ameliorate lens-related PA microbial keratitis.

Rethinking contact lens associated keratitis

This review presents a critical analysis of the literature relating to the use of binomial and polynomial classification schemes for categorising corneal infiltrative events (CIEs) associated with contact lens wear and the epidemiology of such events. The results of the Manchester Keratitis Study-a 12-month, prospective, hospital-based epidemiological study of contact lens wearer suffering from CIEs-are used as a tool to challenge and test traditional thinking in relation to contact lens associated keratitis. An innovative aspect of this study is the use of a novel clinical severity matrix to systematically score the severity of CIEs based on 10 key signs and symptoms. The ambiguities inherent in using binomial classification schemes (such as, microbial versus sterile, ulcerative versus non-ulcerative etcetera) are highlighted. The failure of a polynomial scheme-due to extensive classification overlap between proposed sub-types of CIEs-is demonstrated using a Venn diagram. A cartographic analysis reveals that infiltrates tend to occur in the superior cornea of patients wearing extended wear silicone hydrogel lenses, in the central cornea of patients wearing daily wear hydrogel daily disposable lenses and in the peripheral cornea of patients wearing daily wear hydrogel (excluding daily disposable) lenses. Infiltrates that occur more towards the limbus are less severe. The incidence of CIEs is higher when contact lenses are worn overnight. Logistic analysis reveals that the risk of developing a severe CIE is five times greater with conventional hydrogel extended wear versus silicone hydrogel extended wear. The male gender, smoking, a healthy eye and body, and the late Winter months are associated with an increased risk of developing CIEs. The rate of significant visual loss as a result of developing a CIE is low. Two key conclusions are drawn from this work, which represent a radical rethinking of this potentially sight-threatening condition. CIEs should be considered as a continuous spectrum of ocular disease. If a contact lens wearer presents with a sore eye that is becoming progressively worse and a CIE is observed in that eye, lens wear should be suspended and anti-microbial therapy initiated immediately.

Cytotoxicity and antimicrobial activity of six multipurpose soft contact lens disinfecting solutions1

OBJECTIVES

To assess and compare the cytotoxicity and antimicrobial activity of six multipurpose disinfecting contact lens solutions (MPDS).

METHOD

Six MPDS were assessed and compared: MeniCare Soft, Complete Moisture Plus, Solo-Care Aqua, Opti-Free Express, ReNu MultiPlus and ReNuMoistureLoc. Cytotoxicity was evaluated by means of the colony-forming assay (ISO 10993-5) using one cell line. One hundred Chinese hamster's fibroblast V79 cells in 2 mL of medium were inoculated into 6-well plates and cultured for 24 h. After incubation, the medium was removed and 2 mL of each MPDS was diluted with physiological saline and medium and added individually into wells at 1.25, 2.5, 5 and 10% concentrations. After an additional 6 days of incubation, cells were fixed and stained with Giemsa solution. Subsequently, the number of colonies was counted. Cytotoxicity was expressed in terms of the concentration of the MPDS that suppresses colony formation. Antimicrobial activity was evaluated by means of the stand-alone contact lens disinfection test (ISO 14729).

RESULTS

Cytotoxicity--MeniCare Soft and Complete Moisture Plus were not cytotoxic at any of the concentrations tested. The cytotoxicity ranking of the other MPDS was as follows: Solo-Care Aqua approximately equal to Opti-Free Express < ReNu MultiPlus < ReNu MoistureLoc. Antimicrobial activity--All MPDS met the primary criteria of the stand-alone test for bacterial species. ReNu MoistureLoc showed borderline values for Serratia marcescens and Staphylococcus aureus. Complete Moisture Plus failed to meet the stand-alone test criteria for Fusarium solani.

CONCLUSIONS

Large differences in cytotoxicity and antimicrobial activity were found among the MPDS under investigation. Multipurpose disinfecting contact lens solutions with identical concentrations of polyhexamethylene biguanide can behave differently depending on solution formulation. The new MeniCare Soft showed effective antimicrobial activity and minimal cytotoxicity.

Efficacy of multipurpose solutions for rigid gas permeable lenses

The use of multipurpose solutions for cleaning and disinfecting rigid gas permeable lenses has replaced single purpose solutions, but there are no reports of the efficacy of these multipurpose solutions, or of the effects of storage conditions on their disinfecting capacities. This study investigated activity against four bacterial and two fungal species, and the effects of storage in a refrigerator, at room temperature, at elevated temperature in both dry and humid conditions and with exposure to sunlight. The disinfecting solutions were challenged with the micro-organisms initially upon opening and then at 2-weekly intervals up to 12 weeks after being stored under the different conditions. Solutions were opened daily to simulate use. One solution failed to meet Food and Drug Administration (FDA) criteria to reduce numbers of bacteria by three log dilutions and of fungi by one log dilution. Storage reduced activity of all solutions over the 12-week period, but not below the requirements of the FDA. Storage in the refrigerator tended to reduce disinfecting capacity more quickly. Multipurpose solutions for rigid gas permeable (RGP) lenses lose activity over the 3 months recommended time of use but remain satisfactory for use over this time in the conditions tested. Practitioners need to remind patients to replace their solutions regularly and should advise against storage in the refrigerator. Multipurpose solutions for RGP lenses have simplified cleaning and disinfecting processes and the current formulations have improved disinfecting capacity compared to former disinfecting solutions, which is particularly important for wearers of orthokeratology lenses.

Acanthamoeba: biology and increasing importance in human health

Acanthamoeba is an opportunistic protozoan that is widely distributed in the environment and is well recognized to produce serious human infections, including a blinding keratitis and a fatal encephalitis. This review presents our current understanding of the burden of Acanthamoeba infections on human health, their pathogenesis and pathophysiology, and molecular mechanisms associated with the disease, as well as virulence traits of Acanthamoeba that may be targets for therapeutic interventions and/or the development of preventative measures.

Type III secretion system-associated toxins, proteases, serotypes, and antibiotic resistance of Pseudomonas aeruginosa isolates associated with keratitis

The association between possession of toxin gene-related type III secretory system, protease profiles, O serotypes, and antibiotic resistance patterns was characterized genetically and phenotypically in 46 keratitis isolates of Pseudomonas aeruginosa. There was no significant difference in exoU or exoS prevalence among the keratitis strains. Distinct protease profiles were seen in isolates harboring either exoU or exoS genes. One hundred percent (13/13) of serotype E (O:11) strains contained type III secretion system-associated cytotoxin gene exoU. Multidrug resistance was identified in 4% of Australian and 29% of Indian isolates. None of the Australian isolates was resistant to ciprofloxacin. In general, the rate of multidrug resistance in the exoU positive cytotoxic and serotype E (O:11) strains was significantly higher than in exoS positive invasive strains (p < 0.01). The results suggest that multidrug resistance may be more commonly associated with the corneal isolates of P. aeruginosa having type III secretion system-associated cytotoxin gene exoU and belonging to serotype E (O:11) group.

Prolonged hypoxia induces lipid raft formation and increases Pseudomonas internalization in vivo after contact lens wear and lid closure

PURPOSE

To investigate the effects of hypoxia on lipid raft formation and Pseudomonas aeruginosa internalization by the corneal epithelium with and without the physical effects of contact lens wear.

METHODS

One eye of each rabbit was randomly fitted with a low-Dk rigid gas-permeable contact lens (LDCTL) or closed with sutures, with the other as a control. After 1 day or 3 days, the rabbits were killed and bacterial invasion was assessed by gentamicin survival assay. Lipid rafts were identified by staining with FITC-conjugated beta subunit of cholera toxin. Corneal epithelial Bcl-2 expression was detected by Western blotting; surface epithelial cell size and thickness (epithelium and stroma) were measured by confocal microscopy.

RESULTS

One-day hypoxia induced no significant changes in P. aeruginosa internalization, Bcl-2 expression, or lipid raft formation except in one of four eyelid-closed eyes. After 3 days, P. aeruginosa internalization was increased significantly (P < 0.05) in LDCTL-wearing eyes and not significantly (P = 0.10) increased in eyelid-closed eyes. Both 3-day test conditions also induced lipid raft-forming cells that bound P. aeruginosa, albeit in different regions of the cornea (peripherally in LDCTL-wearing eyes and centrally in closed eyes); did not alter epithelial thickness or surface cell size; and appeared to decrease epithelial Bcl-2 expression.

CONCLUSIONS

This is the first direct comparison in vivo between two different methods inducing hypoxia on the corneal surface. Association of P. aeruginosa internalization with lipid raft formation in both conditions suggests a critical link among prolonged hypoxia, lipid raft formation, and susceptibility to P. aeruginosa infection. However, different distribution patterns of lipid raft-forming cells suggest physical effects of contact lens wear may direct localization of lipid raft-associated P. aeruginosa internalization on the corneal surface.

Efficacy of Contact Lens Disinfecting Solutions Against Staphylococcus aureus and Pseudomonas aeruginosa

PURPOSE

To evaluate the disinfection properties of multipurpose contact lens disinfection solutions, based on the International Organization for Standardization (ISO) 14729 guidelines.

METHODS

ReNu with MoistureLoc Multi-Purpose Solution, OPTI-FREE Express with Aldox Multi-Purpose Solution, Betadine 5% sterile ophthalmic preparation solution (povidone iodine), and 0.9% normal saline solution were inoculated with strains of Staphylococcus aureus and Pseudomonas aeruginosa. Surviving bacteria were quantified at specified times.

RESULTS

ReNu with MoistureLoc, OPTI-FREE Express, and 5% ophthalmic povidone iodine were effective in achieving a 5-log reduction in bacterial count. Additionally, all three products maintained their effectivity at 72 hours. However, ReNu with MoistureLoc and povidone iodine resulted in the greatest reduction in bacterial colonization.

CONCLUSIONS

ReNu with MoistureLoc, OPTI-FREE Express, and 5% ophthalmic povidone iodine meet the ISO 14729 guidelines for standalone contact lens solutions. However, ReNu with MoistureLoc and 5% ophthalmic povidone iodine are most efficient in reducing and maintaining low bacterial count for a period of 72 hours.

Orthokeratology review and update

Orthokeratology (OK) is a clinical technique that uses specially designed rigid contact lenses to reshape the cornea to temporarily reduce or eliminate refractive error. This article reviews the history of traditional daily-wear OK (1960s to 1980s) and discusses the reasons for the recent resurgence in interest in the new modality of overnight OK, using reverse-geometry lens designs (1990s to the present). The clinical efficacy of the current procedure is examined and outcomes from clinical studies in terms of refractive error change and unaided visual acuity are summarised. Onset of the effects of overnight OK lens wear is rapid, with most change after the first night of lens wear and stability of refractive change after seven to 10 days. Mean reductions in myopic refractive error of between 1.75 and 3.33 D and individual reductions of up to 5.00 D have been reported. There appear to be slight reductions or minimal changes in astigmatism with the use of reverse-geometry lenses and most patients are reported to achieve 6/6 unaided vision or better. The induction of higher order aberrations, in particular, spherical aberration, has been reported and this may affect subjective vision under conditions of low contrast and pupil dilation. Patient satisfaction with overnight OK has been reported as similar to or better than with other popular modalities of contact lens wear. Available evidence suggests that the corneal changes induced by overnight OK are fully reversible. The refractive effect in OK is achieved by central epithelial thinning and this has raised concerns about compromise of the epithelial barrier to microbial infection. Recent reports of microbial keratitis in the modality are reviewed and the overall safety of the procedure is examined critically. Recent research on stromal contributions to the OK effect, particularly relating to overnight oedema, is summarised. Emerging issues in OK, including myopic control, correction of other refractive errors and permanency of the OK effect, are discussed.

Influence of Day and Night Wear on Surface Properties of Silicone Hydrogel Contact Lenses and Bacterial Adhesion

PURPOSE

The aim of this study was to determine the effect of continuous wear on physicochemical surface properties of silicone hydrogel (S-H) lenses and their susceptibility to bacterial adhesion.

METHODS

In this study, volunteers wore 2 pairs of either "lotrafilcon A" or "balafilcon A" S-H contact lenses. The first pair was worn continuously for a week and the second pair for 4 weeks. One lens of each pair was used for surface characterization and the other one for bacterial adhesion experiments. Lens surfaces were characterized by examination of their wettability, roughness, elemental composition, and proteins attached to their surfaces. Adhesion of Staphylococcus aureus 835 and Pseudomonas aeruginosa #3 to a lens was studied using a parallel plate flow chamber.

RESULTS

Before use, the lotrafilcon A lens was rougher than the balafilcon A lens and had a lower water contact angle and a higher affinity for S. aureus 835. After wear, both lens types had similar water contact angles, whereas the differences in elemental surface composition decreased as well. S. aureus 835 adhered in higher numbers to worn balafilcon A lenses, whereas the opposite was seen for P. aeruginosa #3. The initial deposition rates of both bacterial strains to lotrafilcon A lenses decreased by wearing and were found to correlate significant (P < 0.001) with the surface roughness of worn lenses.

CONCLUSIONS

In this study, the differences in surface properties between 2 types of S-H lenses were found to change after 1 week of continuous wear. Generally, bacteria adhered in lower numbers and less tenaciously to worn lenses, except S. aureus 835, adhering in higher numbers to worn balafilcon A lenses.

Can Subtypes of Contact Lens-Associated Corneal Infiltrative Events Be Clinically Differentiated?

PURPOSE

A schema has recently been described for clinical differentiation among 4 symptomatic subtypes of contact lens-associated corneal infiltrative events (CIEs): microbial keratitis (MK), contact lens-induced peripheral ulcer (CLPU), contact lens-induced acute red eye (CLARE), and infiltrative keratitis (IK). The clinical utility of this schema has been challenged in the literature. The aim of this study is to determine whether it is possible to clinically differentiate among these conditions.

METHODS

Criteria for MK, CLPU, CLARE, and IK were applied to a data set of 111 contact lens-associated CIEs, spanning a wide range of clinical severities, presenting consecutively to a hospital clinic. A Venn diagram analysis was used to determine the extent to which these conditions can be clinically differentiated.

RESULTS

Of the 111 CIEs, 20% could be classified unambiguously as MK, CLPU, CLARE, or IK, 56% could be classified as 1 of 2 conditions, 13% could be classified as 1 of 3 conditions, and 0% could be classified as 1 of 4 conditions. Eleven percent of CIEs could not be classified as any of the 4 conditions.

CONCLUSIONS

Although the etiology of CIEs is multifactorial, the considerable overlap between the clinical presentation of MK, CLPU, CLARE, and IK is such that it is not possible to clinically differentiate between them with any degree of certainty. A preferred approach might be to consider CIEs as part of a disease continuum whereby these events can manifest in various degrees of severity, depending as well on the point at which the condition is observed in the course of the natural history of the disease.

Contact lens-related corneal ulcers requiring hospitalization: A 7-year retrospective study in Belgium

PURPOSE

To evaluate the clinical and epidemiological aspects of contact lens-related infectious corneal ulcers requiring hospitalization.

METHODS

A retrospective analysis was performed on the files of patients hospitalized for contact lens-induced corneal ulcer in the eight Belgian university hospitals over a 7-year period (January 1997 to December 2003). Diagnoses for all hospitalized patients are obligatorily registered using the ICD-9 code.

RESULTS

A total of 107 patients with contact lens-related corneal ulcers were documented: the number increased from five in 1997 to 22 in 2003. A total of 99 subjects used soft contact lenses, of whom nine used disposables, 73 planned replacement and 17 conventional lenses. Only six patients used extended wear lenses. Three patients used daily disposable lenses. The most frequently cultured organisms were Pseudomonas and other Gram-negative germs (70%) and Acanthamoeba (16%). The majority (77%) of the corneal ulcerations were centrally located and resulted in an average visual loss of four lines.

CONCLUSION

During the study period, the number of patients hospitalized rose, which is only partially explained by the increasing prevalence of lens wearers: 3.5% and 6.5% of the Belgian population used lenses in 1995 and 2003, respectively. These factual data highlight the need for improvements in patient education.

Evaluation of povidone-iodine as a disinfectant solution for contact lenses: Antimicrobial activity and cytotoxicity for corneal epithelial cells

Povidone-iodine (PVP-I) possesses broad-spectrum antimicrobial activity and is used clinically as a disinfectant. We evaluated the disinfectant properties and safety of PVP-I for use as a contact lens solution. The concentrations of PVP-I required to reduce the number of Staphylococcus aureus or Candida albicans by 3 log units were lower than were those of hydrogen peroxide, polyhexamethylene biguanide (PHMB), and benzalkonium chloride (BAK). The cytotoxicity of PVP-I for cultured human corneal epithelial (HCE) cells was less than that of the other three agents. The safety margin for PVP-I was thus greatest among the tested compounds. PVP-I appears suited for use as a contact lens disinfectant.

A decade of contact lens prescribing trends in the United Kingdom (1996–2005)

PURPOSE

To document contact lens prescribing trends in the United Kingdom over the past decade (between 1996 and 2005).

METHODS

An annual survey of contact lens prescribing trends was conducted each year by asking a random selection of optometrists and dispensing opticians to provide information relating to 10 consecutive contact lens fits between January and March.

RESULTS

Over the 10-year survey period, 1251 practitioners returned survey forms representing a total of 12,050 contact lens fits. The mean (+/-standard deviation) age of lens wearers was 33+/-13 years of which 64% were female. Over the survey period, rigid lens new fits decreased from 22% to 4%. Low water content lenses reduced from 20% to 2% of new soft lens fits. Soft toric lenses gradually increased to the point where they accounted for the expected proportion of patients with astigmatism>or=1.00DC (i.e. >20% of soft lens fits). Monthly and daily disposable lenses accounted for >90% of all soft lens fits between 2003 and 2005. The proportion of new soft fits and refits prescribed as extended wear has gradually increased, stabilizing at about 5% of new fits and 12% of refits. Multi-purpose lens care solutions increased from 60% of all care systems in 1997 to 91% in 2005. Rigid lenses and monthly replacement soft lenses are predominantly worn on a full time basis, whereas daily disposable soft lenses are mainly worn part time.

CONCLUSIONS

This survey indicates that technological advancements such as the development of new lens materials, manufacturing methods and lens designs have had a significant impact on the contact lens market over a relatively short period of time.

Pellucid marginal corneal degeneration: evaluation of the corneal surface and contact lens fitting

AIM

To quantify corneal irregularities, to describe the fitting with contact lenses, and to answer the question whether or not contact lenses with a special back surface design could improve visual acuity in patients with pellucid marginal corneal degeneration (PMCD).

METHODS

13 eyes were fitted with contact lenses with a special back surface. Videokeratographic data were assessed. The patients were followed up for an average period of 22.2 months. Lens tolerance and corrected visual acuity were evaluated.

RESULTS

The mean eccentricity did not exceed 0.7 in all patients. Either the superior or the inferior eccentricity, or both, were negative in all patients. Using Fourier analysis all PMCD subjects showed an increased irregular astigmatism of the anterior cornea. Using Zernike coefficients seven eyes (53.8%) had a higher order aberration root mean square error (HOA RMS error) out of the normal range. The visual acuity with contact lenses improved in all eyes with an average increase of 2.7 lines (maximum eight lines). No serious complications were observed.

CONCLUSIONS

Quantitative evaluation of videokeratographic data may help to diagnose PMCD and to distinguish PMCD from other ectatic corneal diseases. Contact lenses with a special back surface design can improve visual acuity and lens tolerance.

Impact of Differences in Diagnostic Criteria When Determining the Incidence of Contact Lens-Associated Keratitis

PURPOSE

The purpose of this study is to examine the effect of differences in within-study and between-study diagnostic criteria in determining the incidence of contact lens-associated keratitis.

METHODS

We applied the sets of criteria for "microbial keratitis" as described in five previous studies to the dataset of Morgan et al., which documents 118 cases of contact lens-associated keratitis across a wide range of clinical severities. For each set of criteria, the incidence of contact lens-associated keratitis was calculated for the following five lens type/modality combinations: daily-wear rigid, daily-wear daily disposable hydrogel, daily-wear hydrogel, extended-wear hydrogel, and extended-wear silicone hydrogel. The effect of varying the clinical severity score for the differentiation of nonsevere versus severe keratitis was also examined with respect to the dataset of Morgan et al.

RESULTS

The size and location of the corneal infiltrative events identified as representing "microbial keratitis" for each of the different sets of criteria are illustrated in a series of cartograms. A key between-study difference in the incidence values calculated for the various sets of criteria relates to the categories of extended-wear hydrogel and extended-wear silicone hydrogel lenses. Specifically, the incidence of "microbial keratitis" was found to be statistically significantly greater for extended-wear hydrogel compared with extended-wear silicone hydrogel lenses when the set of criteria of Morgan et al. was applied, but not when the other sets of criteria were applied, to the dataset of Morgan et al. Increasing the threshold clinical severity criterion for differentiating between nonsevere and severe keratitis within this dataset resulted in lower incidence values; however, such changes in threshold had a minimal impact on relative risk values.

CONCLUSIONS

The choice of criteria for diagnosing contact lens-associated "microbial keratitis" has a significant impact on calculations of the incidence of this condition.

Staphylococcus aureus Ulcer Associated With Continuous Wear of Silicone Hydrogel Contact Lenses

PURPOSE

To report a case of culture-positive Staphylococcus aureus keratitis associated with continuous wear of lotrafilcon A lenses.

METHODS

The case report of a patient who developed microbial keratitis while wearing lotrafilcon A contact lenses is presented.

RESULTS

A 41-year-old white man had worn polymacon contact lenses successfully for at least 10 years. He habitually replaced the lenses every 1 to 2 years and frequently wore them continuously for up to 3 months. He was refitted with silicone hydrogel lenses and was advised to remove and replace the lenses monthly. Approximately 18 months later, he developed a midperipheral, culture-positive S. aureus ulcer in his right eye. He was treated with fortified cefazolin and gentamicin for 2 weeks, followed by ciprofloxacin for 2 weeks. The ulcer resolved completely. The patient's final visual acuity was 20/20 in the affected eye.

CONCLUSIONS

The increased oxygen permeability of silicone hydrogel contact lens materials may reduce the risk of hypoxic complications of continuous contact lens wear. As this case shows, however, even patients who have continuously worn lenses with very low oxygen permeability without incident can develop microbial keratitis when wearing silicone hydrogel lenses. Contact lens practitioners should inform patients of the potential risks of continuous wear and of factors that may increase those risks.

Contact lenses and special back surface design after penetrating keratoplasty to improve contact lens fit and visual outcome

AIMS

To describe the fitting of patients with high or irregular astigmatism following penetrating keratoplasty with contact lenses and to answer the question whether or not contact lenses with special back surface design can improve visual acuity in complex cases after penetrating keratoplasty.

METHODS

28 eyes were included. They were fitted with contact lenses with a special back surface that was designed for optical rehabilitation after penetrating keratoplasty. Four different types of these lenses (tricurve, keratoconus, reverse, oblong) were used selectively depending on abnormal eccentricity determined by videokeratoscope. The patients were followed up for an average period of 15.5 months. Lens tolerance and corrected visual acuity were evaluated and compared with that corrected with spectacles.

RESULTS

The visual acuity was significantly improved in nearly all eyes with an average increase of 3.6 lines (maximal nine lines) accompanied by good contact lens tolerance and satisfactory contact lens fit. No noticeable complications were observed.

CONCLUSION

Contact lenses with special back surface design can improve visual results and lens tolerance, and minimise problems in contact lens fitting. This is in favour of contact lenses as an alternative to surgical procedures for correction of high or irregular astigmatism after penetrating keratoplasty. This procedure is recommended especially in cases of patients who decline further operative interventions.

Prolonging contact lens wear and making contact lens wear safer

PURPOSE

To summarize the present status of safety and efficacy of contact lens wear.

DESIGN

Literature review.

METHODS

Ovid Medline searches were performed on records from 1966 through 2005 using keywords: keratitis, contact lens complications, extended-wear contact lenses, and silicone-hydrogel contact lenses.

RESULTS

Patients desire comfort, clarity of vision, and prolonged contact lens wear when contact lenses are used to correct refractive error. Practitioners desire patient satisfaction but also require maintenance of the integrity of the eye and no complications that jeopardize vision or health of the eye. Improvements in the oxygen permeability of the contact lens materials, design of the contact lens and its surface, and solutions for the maintenance of the lens have reduced but not eliminated the risks of infection, inflammation, and conjunctival papillary reaction associated with contact lens wear. The lessons of past and recent history suggest that patient education and practitioner participation in the management of contact lens wear continue to be critical factors for patient satisfaction and safety in the extended wear of contact lenses.

CONCLUSIONS

The availability of highly oxygen permeable contact lenses has increased the tolerance and safety of extended contact lens wear, but patient instruction and education in proper use and care of lenses is required and caution is advised.

Resistance to a polyquaternium-1 lens care solution and isoelectric points of Pseudomonas aeruginosa strains

OBJECTIVES

The aim of this study was to correlate the cell surface hydrophobicity and charge of various strains of Pseudomonas aeruginosa with their resistance to a polyquaternium-1 lens care solution.

METHODS

The 11 P. aeruginosa strains included were isolated from eyes, contact lenses, lens cases and lens care solutions. Cell surface hydrophobicities were determined from water contact angle measurements and surface charges were measured as a function of pH using particulate micro-electrophoresis.

RESULTS

Strains resistant to polyquaternium-1 had an isoelectric point (IEP; pH where the bacterial zeta potential is zero) ranging from 4.0 to 5.5, whereas susceptible strains were more negatively charged than resistant strains and had an IEP between 1.3 and 1.9. Water contact angles ranged from hydrophilic (34 degrees) to hydrophobic (124 degrees), without showing a relation with antimicrobial resistance.

CONCLUSIONS

Results suggest that electrostatic repulsion between cationic molecules on the cell surface and quaternary ammonium compounds impedes the antimicrobial entering the cell.

A Quality of Life Comparison of People Wearing Spectacles or Contact Lenses or Having Undergone Refractive Surgery

PURPOSE

To demonstrate the use of the Quality of Life Impact of Refractive Correction (QIRC) questionnaire for comparing the quality of life of pre-presbyopic individuals with refractive correction by spectacles, contact lenses, or refractive surgery.

METHODS

The 20-item QIRC questionnaire was administered to 104 spectacle wearers, 104 contact lens wearers, and 104 individuals who had undergone refractive surgery (N = 312). These groups were similar for gender, ethnicity, socioeconomic status, and refractive error. The main outcome measure was QIRC overall score (scaled from 0 to 100), a measure of refractive correction related quality of life. Groups were compared for overall QIRC score and on each question by analysis of variance, adjusted for age, with post hoc significance testing (Sheffé).

RESULTS

On average, refractive surgery patients scored significantly better (mean QIRC score 50.2 +/- 6.3, F(2,309) = 15.18, P < .001) than contact lens wearers (46.7 +/- 5.5, post hoc P < .001) who were in turn significantly better than spectacle wearers (44.1 +/- 5.9, post hoc P < .01). Convenience questions chiefly drove the differences between groups, although functioning, symptoms, economic concerns, heath concerns, and well being were also important. Spectacle wearers with low strength prescriptions (46.18 +/- 5.05) scored significantly better than those with medium strength prescriptions (42.74 +/- 6.08, F(2,190) = 3.66, P < .05, post hoc P < .05). A small number (n = 7, 6.7%) of refractive surgery patients experienced postoperative complications, which impacted quality of life (37.86 +/- 2.13).

CONCLUSIONS

Quality of life was lowest in spectacle wearers, particularly those with higher corrections. Contact lens wearers had significantly better QIRC score than spectacle wearers. Refractive surgery patients scored significantly better than both. However, this was accompanied by a small risk of poor quality of life due to postoperative complications. The QIRC is an effective outcome measure for quality of life impact of refractive correction.

Silicone Hydrogel Contact Lenses and the Ocular Surface

For 30 years, contact lens research focused on the need for highly oxygen-permeable (Dk) soft lens materials. High Dk silicone hydrogel contact lenses, made available in 1999, met this need. The purpose of this review is to examine how silicone hydrogel lens wear affects the ocular surfaces and to highlight areas in which further research is needed to improve biocompatibility. Silicone hydrogel lenses have eliminated lens-induced hypoxia for the majority of wearers and have a less pronounced effect on corneal homeostasis compared to other lens types; however, mechanical interaction with ocular tissue and the effects on tear film structure and physiology are similar to that found with soft lens wear in general. Although the ocular health benefits of silicone hydrogel lenses have increased the length of time lenses can be worn overnight, the risk of infection is similar to that found with other soft lens types, and overnight wear remains a higher risk factor for infection than daily wear, regardless of lens material. Future contact lens research will focus on gaining a better understanding of the way in which contact lenses interact with the corneal surface, upper eyelid, and the tear film, and the lens-related factors contributing to infection and inflammatory responses.

Microbial Keratitis

PURPOSE

To examine predisposing factors, treatment costs, and visual outcome of microbial keratitis in an ophthalmic casualty and inpatient population.

DESIGN

Retrospective medical records review.

PARTICIPANTS

Fifteen- to 64-year-olds with microbial keratitis treated at the Royal Victorian Eye and Ear Hospital between May 2001 and April 2003 (n = 291).

METHODS

Risk factors were identified from patient files. Demographic, clinical, and microbiological data; severity; outpatient visits; hospital bed days; and vision loss were examined.

MAIN OUTCOME MEASURES

Cost to treat (Australian dollars), vision loss, and factors influencing these outcomes.

RESULTS

Ocular trauma (106/291 [36.4%]) and contact lens (CL) wear (98/291 [33.7%]) were the most commonly identified predisposing factors; 18 (6.1%) had multiple predisposing factors; 17 (5.8%), ocular surface disease; 20 (6.9%), herpetic eye disease; 4 (1.4%), systemic associations; 5 (1.7%), other; and 23 (7.9%), unknown cause. Of trauma cases, 90.6% involved males, compared with 44% to 57% for other groups (P<0.001). Contact lens wearers were younger than the other groups--mean age 30 years, compared with 40 to 47 years (P<0.01). Gram-negative organisms were isolated more frequently in CL wearers than trauma cases (18.7% vs. 6.5%, P = 0.01). The number of outpatient visits was 4+/-1 (median +/- interquartile range), and 19.6% (57/291) were hospitalized for 5+/-2 days. Hospital resource use and vision loss were similar for predisposing factors but differed by causative microorganism. Eighty-eight percent of cases were scraped: acanthamoeba keratitis was the most expensive to treat, followed by fungal and herpetic keratitis and, lastly, culture-proven bacterial keratitis or culture-negative cases (P<0.0001). After treatment, 21.7% exhibited >2 lines of vision loss, and 1.6% of cases had > or =10 lines of vision loss. Vision loss was associated with clinical severity (P = 0.005).

CONCLUSIONS

Ocular trauma and CL wear are the major predisposing factors for microbial keratitis in this age range. These cases require significant hospital resources during treatment, and the keratitis may result in loss of vision.

Attachment of Acanthamoeba to first- and second-generation silicone hydrogel contact lenses

PURPOSE

To investigate the attachment of Acanthamoeba to first- and second-generation silicone hydrogel contact lenses, and to determine if patient wear or the presence of a bacterial biofilm coating affects attachment characteristics.

DESIGN

Experimental study.

PARTICIPANTS AND CONTROLS

Attachment to the silicone hydrogel lenses was compared with that to a conventional hydrogel control lens. Sixteen replicates (n = 16) were carried out for unworn, worn, and biofilm-coated lenses of each type.

METHODS

Unworn, worn, and Pseudomonas aeruginosa biofilm-coated first-generation (lotrafilcon A) and second-generation (galyfilcon A) silicone hydrogel and conventional hydrogel (etafilcon A) lens quarters were incubated for 90 minutes in suspensions of plate-cultured Acanthamoeba castellanii trophozoites.

MAIN OUTCOME MEASURES

Trophozoites attached to one surface of each lens quarter were counted by direct light microscopy. Logarithmic transformation of data allowed the use of parametric analysis of variance for statistical analysis.

RESULTS

Attachment of Acanthamoeba was affected significantly by lens material type (P<0.001), with higher numbers of trophozoites attaching to the first-generation lotrafilcon A silicone hydrogel lens, compared with the second-generation galyfilcon A lens and the conventional hydrogel lens. Attachments to the latter 2 lenses did not differ significantly from each other (P = 0.126). Patient wear and the presence of a bacterial biofilm had no significant effect on attachment to the lotrafilcon A lens (P = 0.426) but did significantly increase attachment to the galyfilcon A (P<0.001) and the etafilcon A (P = 0.009) lenses; attachment to the latter 2 lenses was still significantly less than that found with the first-generation silicone hydrogel (P<0.001).

CONCLUSIONS

Acanthamoeba demonstrated a significantly greater affinity for the first-generation silicone hydrogel lens as compared with the second-generation silicone hydrogel and the conventional hydrogel. If exposed to Acanthamoeba (e.g., when showering or swimming, through noncontinuous wear and ineffective lens care regimes), first-generation silicone hydrogel lenses may promote a greater risk of Acanthamoeba infection due to the enhanced attachment characteristics of this lens material. However, prospective studies in patients are required to determine if these experimental results are clinically significant.

Acanthamoeba keratitis during orthokeratology

PURPOSE

To report an infectious complication of overnight rigid gas-permeable contact lenses.

METHODS

Case report and medical literature review.

RESULTS

A 16-year-old girl developed laboratory-confirmed acanthamoebic keratitis during orthokeratology for myopic reduction. Recent case reports suggest that Acanthamoeba is a cause of microbial keratitis associated with gas-permeable contact lenses among teenagers and young adults undergoing orthokeratology.

CONCLUSIONS

Acanthamoeba keratitis is an emerging complication of orthokeratology in young myopes.

Efficacy of multipurpose solutions against Acanthamoeba species

AIM

The disinfection efficacy of contact lens multipurpose solutions (MPSs) against Acanthamoeba polyphaga (Ros) and Acanthamoeba castellanii (ATCC30868) cysts and trophozoites was determined by both biocidal and manufacturer-recommended no-rub/rinse regimen testing.

METHODS

A biocidal assay using four MPSs (ReNu with MoistureLoc, Opti-free Express, Solo-care Plus, and Complete MoisturePlus) was conducted with or without the presence of organic soil. A second test procedure compared the ability of five MPSs (ReNu with MoistureLoc MPS, ReNu MultiPlus, Opti-free Express, Solo-care Aqua, and Complete MoisturePlus) to remove and kill Acanthamoeba species cysts and trophozoites from SofLens 38 and Surevue conventional hydrogel lenses, and Focus Night & Day silicone hydrogel lenses using the manufacturer-recommended regimen.

RESULTS

In the biocidal assay, only ReNu with MoistureLoc successfully killed both trophozoites and cysts (>3 log) within the manufacturer-recommended soak time. A >3 log decrease in trophozoites, but not cysts, was reported for Opti-free Express; however, Solo-care Plus and Complete MoisturePlus did not reduce the number of cysts or trophozoites by >3 log during the manufacturer-recommended soak time. In the no-rub/rinse regimen tests, only ReNu with MoistureLoc removed an inoculum of 2 x 10(5) trophozoites or cysts from SofLens 38 and Surevue hydrogel lenses, as well as Focus Night & Day silicone hydrogel lenses. Less than 10 viable organisms were recovered from the lenses after the 10s rinse and 4h soak. Opti-free Express, Solo-care Aqua, and ReNu MultiPlus were effective at removing trophozoites and cysts from SofLens 38 and Surevue conventional hydrogel lenses, but not from Focus Night & Day silicone hydrogel lenses. In excess of 10 viable organisms were recovered from all lenses after the manufacturer-recommended regimen using Complete MoisturePlus.

CONCLUSIONS

These data suggest that some MPSs, when used as recommended by the manufacturer, are more effective at killing representative strains of Acanthamoeba than others.

The Incidence of Microbial Keratitis among Wearers of a 30-Day Silicone Hydrogel Extended-Wear Contact Lens

PURPOSE

To estimate the incidence of presumed microbial keratitis with and without loss of visual acuity among wearers of a silicone hydrogel contact lens (Lotrafilcon A, Night & Day, CIBA Vision, Inc., Duluth, GA), recently approved for up to 30 days of continuous wear.

DESIGN

Prospective cohort postmarket surveillance study.

PARTICIPANTS

Contact lens wearers (recruited from 131 practices) who had been prescribed the lens for intended continuous wear of as many as 30 nights.

METHODS

The occurrence of a corneal infiltrate was ascertained through a combination of center report and direct contact with participants at 3 and 12 months. Whenever a corneal infiltrate was suspected, study and treatment medical records were systematically reviewed by an Endpoints Committee using a predetermined classification scheme for corneal infiltration. Cases of presumed microbial keratitis were determined based on the constellation of presenting signs and symptoms and clinical course.

MAIN OUTCOME MEASURES

The incidence of presumed microbial keratitis with and without loss of visual acuity.

RESULTS

A total of 6245 participants were recruited between August 13, 2002 and July 2, 2003. Of these, 4999 subjects (80%) completed 12 months of follow-up, and these participants contributed a total of 5561 person years of lens wearing experience. Approximately 80% of participants routinely wore their lenses continuously for 3 or more weeks. The overall annual rate of presumed microbial keratitis was 18 per 10,000 (95% confidence interval (CI): 8.5-33.1). There were 2 cases of presumed microbial keratitis with loss of visual acuity, an annual rate of 3.6 per 10,000 (95% CI: 0.4-12.9), and an additional 8 cases without loss of visual acuity, an annual rate of 14.4 per 10000 (95% CI: 6.1-28.4). The rate of presumed microbial keratitis was lower for users reporting typical wear of 3 or more weeks than for those wearing the lens for less than a 3-week continuous period (P = 0.02).

CONCLUSIONS

The incidence of loss of visual acuity due to microbial keratitis among users of the silicone hydrogel contact lens was low. The overall rate of presumed microbial keratitis with the wearing schedule of as many as 30 nights was similar to that previously reported for conventional extended-wear soft lenses worn for fewer consecutive nights.

Incidence and morbidity of hospital-presenting corneal infiltrative events associated with contact lens wear

AIM

To determine the incidence and morbidity (visual loss) of hospital-presenting corneal infiltrative events (CIEs) associated with the wearing of current generation contact lenses.

METHODS

All contact lens wearers presenting with any form of corneal infiltrate/ulcer to a hospital centre in Manchester, UK, were surveyed in this 12-month, prospective, hospital-based epidemiological study. A clinical severity matrix was used to quantify the overall severity of presenting signs and symptoms. The size of the hospital catchment population and the wearing modalities (daily wear [DW] or extended wear [EW]) and lens types used in that population were estimated from relevant demographic and market data to facilitate the calculation of incidence. We also attempted to ascertain, from their eye care practitioners, the visual acuity (VA) of patients suffering from CIEs prior to and at about six months following attendance at the hospital.

RESULTS

During the survey period, 118 patients presented with CIEs of varying severity. The annual incidence (cases per 10,000 wearers) for all wearing modalities and lens types is 21.3 (95 per cent confidence interval 17.8 to 25.5). The incidence of CIEs for each wearing modality and lens type is: DW rigid, 8.6 (3.9 to 18.7); DW hydrogel daily disposable, 14.0 (9.3 to 21.0); DW hydrogel (excluding daily disposable), 20.4 (15.9 to 26.2); DW silicone hydrogel, 55.9 (9.9 to 309.6); EW rigid, zero (0.0 to 1758.8); EW hydrogel, 144.6 (66.4 to 311.8) and EW silicone hydrogel, 118.6 (75.2 to 186.7). The risk of developing a CIE with EW lenses was 8.1 (5.3 to 12.5) times greater than that with DW lenses (p < 0.0001). Although there was no difference between EW hydrogel and EW silicone hydrogel lenses with respect to the risk of developing CIEs, the clinical severity of CIEs was greater with EW hydrogel lenses (p = 0.04). Results of VA for pre- and post-hospital attendance were obtained from 38 patients, none of whom lost more than one line of VA. For the study population, zero patients (95 per cent CI: 0 to 9.2 per cent) suffered a significant loss of VA as a result of developing a CIE.

CONCLUSIONS

Overall, there is an eight times higher incidence of CIEs in wearers who sleep in contact lenses compared with wearers who use lenses only during the waking hours. For those who choose to routinely or intermittently sleep in soft contact lenses, silicone hydrogels are the lens of first choice because CIEs are less clinically severe with this lens type compared with hydrogel lenses. The rate of significant visual loss as a result of developing a CIE is low.

Actin cytoskeleton disruption by ExoY and its effects on Pseudomonas aeruginosa invasion

Three of the Type III-secreted effectors of Pseudomonas aeruginosa (ExoS, ExoT, and ExoY) each alter mammalian cell morphology in culture without causing a loss of cell viability. For ExoS and ExoT this property involves RhoGAP activity, and leads to actin cytoskeleton disruption and a reduced capacity for internalizing bacteria. ExoY does not possess RhoGAP activity. Instead, cell rounding depends upon its adenylate cyclase catalytic region. Since anti-phagocytic activities of ExoS and ExoT are associated with cell rounding and cytoskeleton disruption, we hypothesized that ExoY would also inhibit P. aeruginosa invasion of epithelial cells coinciding with adenylate cyclase-mediated cytoskeleton disruption. The results showed actin disruption of epithelial cells at 2 h post-infection associated with both adenylate cyclase-active ExoY and its catalytic mutant form ExoYK81M, and which coincided with inhibition of bacterial invasion (76% inhibition by ExoY, and 37% by ExoYK81M). Surprisingly, at 4h post-infection, neither form of ExoY inhibited invasion despite extensive actin disruption. These data suggest that ExoY, like ExoS and ExoT, contains more than one active domain affecting mammalian cell function. The data also suggest that cytoskeleton disruption does not necessarily predict invasion inhibitory activity, supporting the recently proposed model that P. aeruginosa internalization can proceed through more than one pathway.

Serratia Corneal Ulcers

PURPOSE

To study the clinical and microbiological profile of Serratia corneal ulcers at the Cornea Service of the Wills Eye Hospital.

METHODS

This was a retrospective, observational case series. The clinical records of patients with Serratia marcescens corneal ulcers seen at the Cornea Service of the Wills Eye Hospital between January 1, 1998 and December 31, 2002 were reviewed.

RESULTS

Twenty-four cases of Serratia keratitis were identified in 21 patients. Two patients (9.5%) had recurrent keratitis, 1 of which recurred twice. Both had corneal graft edema and were on topical steroids and antiglaucoma drops. The Serratia infection in 15 patients (71%) was associated with an abnormal corneal surface. Twelve of these patients (57%) had the ulcer in a corneal graft, 4 (19%) of which were associated with suture infiltrates. Fifteen patients (71%) were on topical medications-15 used corticosteroids and 13 used antiglaucoma drops. Six patients (29%) were contact lens wearers-1 had a concomitant suture infiltrate associated with a corneal graft, and 5 had otherwise healthy corneas. One isolate lacked in vitro susceptibility to ciprofloxacin and ofloxacin but was susceptible to gentamicin and tobramycin. Nineteen patients had a favorable response to medical therapy. Two patients with poor outcome had large corneal ulcers with severe necrosis and thinning associated with delay in treatment.

CONCLUSIONS

Serratia marcescens keratitis is associated with the presence of an abnormal corneal surface, use of topical medications, and contact lens wear. Prompt medical therapy results in a good clinical response in the majority of cases.

Orthokeratology for myopic children: wolf in sheep's clothing?

Orthokeratology attempts to reduce myopia by remoulding the corneal shape with contact lenses. A recent resurgence is predicated on new contact lens designs with a prefigured back contact surface and higher oxygen transmissibility. This Clinical Controversy presents an analysis of the risk factors associated with orthokeratology and its suitability for children, followed by commentaries from specialists who have an interest in the method. Some state that there is a lack of data on relative risks of corneal infection and that there is a need for large-scale randomized controlled studies; however, opinion is expressed by others that orthokeratology is a clinically safe procedure using modern lenses. It is noted that the physiological and biophysical bases of orthokeratology are virtually unknown, and further research on the human cornea is indicated to scientifically establish the safety of orthokeratology. Prospective patients, and their parents in the case of children, should be fully informed of the risks.

Mutation of retS, encoding a putative hybrid two-component regulatory protein in Pseudomonas aeruginosa, attenuates multiple virulence mechanisms

Two-component regulatory systems play an important role in bacterial virulence. We report that mutation of a Pseudomonas aeruginosa gene designated retS (previously designated fimK; accession number PA4856) encoding a putative hybrid two-component regulator, attenuates multiple virulence mechanisms. The retS mutant was selected from a Tn5 transposon library of the cytotoxic P. aeruginosa strain PA103 based upon expression of a small-colony phenotype suggestive of reduced surface-associated "twitching" motility, a property dependent upon type IV pili. Subsequent analysis revealed that the mutant expressed pilin, albeit at lower levels than wild-type PA103. In a murine model of corneal infection, retS mutation was associated with delayed disease development and altered pathology. In vitro, retS mutants demonstrated loss of acute cytotoxic activity towards corneal epithelia as determined by trypan blue exclusion and by LDH release assays (P<0.0001). This coincided with loss of ExsA-regulated type III secretion. Mutation of retS also impaired ExsA-independent pathogenic mechanisms. When compared to the exsA mutant of PA103, retS mutants exhibited reduced epithelial adherence and invasion and reduced intracellular survival within the cells after invasion. Time-lapse video microscopy revealed that retS mutants, compared to exsA mutants, had a reduced capacity to access, and move along, the basal cell surfaces of corneal epithelial cell monolayers. Taken together, these data suggest that the protein encoded by retS regulates various properties of P. aeruginosa including both ExsA-dependent and ExsA-independent virulence mechanisms.

ExsE, a secreted regulator of type III secretion genes in Pseudomonas aeruginosa

Type III secretion systems are toxin delivery systems that are present in a large number of pathogens. A hallmark of all type III secretion systems studied to date is that expression of one or more of their components is induced upon cell contact. It has been proposed that this induction is controlled by a negative regulator that is itself secreted by means of the type III secretion machinery. Although candidate proteins for this negative regulator have been proposed in a number of systems, for the most part, a direct demonstration of their role in regulation is lacking. Here, we report the discovery of ExsE, a negative regulator of type III secretion gene expression in Pseudomonas aeruginosa. Deletion of exsE deregulates expression of the type III secretion genes. We provide evidence that ExsE is itself secreted by means of the type III secretion machinery and physically interacts with ExsC, a positive regulator of the type III secretion regulon. Taken together, these data demonstrate that ExsE is the secreted negative regulator that couples triggering of the type III secretion machinery to induction of the type III secretion genes.

Incidence of keratitis of varying severity among contact lens wearers

AIM

To determine the incidence of non-severe keratitis (NSK) and severe keratitis (SK) among wearers of current generation contact lenses.

METHODS

A 12 month, prospective, hospital based epidemiological study was conducted by examining all contact lens wearers presenting with a corneal infiltrate/ulcer to a hospital centre in Manchester. A clinical severity matrix was used to differentiate between NSK and SK, based on the severity of signs and symptoms. The size of the hospital catchment population and the wearing modalities (daily wear (DW) or extended wear (EW)) and lens types being used were estimated from relevant demographic and market data.

RESULTS

During the survey period, 80 and 38 patients presented with NSK and SK, respectively. The annual incidences (cases per 10,000 wearers) for each wearing modality and lens type were: DW rigid--NSK 5.7, SK 2.9; DW hydrogel daily disposable--NSK 9.1, SK 4.9; DW hydrogel (excluding daily disposable)--NSK 14.1, SK 6.4; DW silicone hydrogel--NSK 55.9, SK 0.0; EW rigid--NSK 0.0, SK 0.0; EW hydrogel--NSK 48.2, SK 96.4; EW silicone hydrogel--NSK 98.8, SK 19.8. The difference in SK between EW hydrogel and EW silicone hydrogel was significant (p = 0.04).

CONCLUSIONS

A clinical severity matrix has considerable utility in assessing contact lens related keratitis. There is a significantly higher incidence of SK in wearers who sleep in contact lenses compared with those who only use lenses during the waking hours. Those who choose to sleep in lenses should be advised to wear silicone hydrogel lenses, which carry a five times decreased risk of SK for extended wear compared with hydrogel lenses.

Microbial Keratitis in Prospective Studies of Extended Wear With Disposable Hydrogel Contact Lenses

PURPOSE

To report the annualized incidence of microbial keratitis with extended wear of low oxygen transmissible (Dk/t) disposable soft contact lenses from prospective postmarket clinical trials.

METHODS

Seven hundred ninety subjects were enrolled at the L.V. Prasad Eye Institute (LVPEI), Hyderabad, India from March 1993 to March 2000, resulting in 1231 patient eye years, and 167 subjects were enrolled at the Cornea and the Contact Lens Research Unit (CCLRU), Sydney, Australia from July 1987 to December 1999, resulting in 842 patient eye years.

RESULTS

The annualized incidence of microbial keratitis per 10,000 eyes per year of lens wear was 32.5 (95% CI 8.9 to 83.2) for LVPEI, 23.8 (95% CI=2.9 to 85.8) for CCLRU; when data are combined across both centers, the incidence was 28.9 (95% CI=10.6 to 63) per 10,000 eyes per year of lens wear. This equates to 57.0 per 10,000 wearers or 1 in 173 wearers per year of lens wear. All events were rated as slight to moderate in severity and did not result in visual loss. Two events were described to highlight the challenges in diagnosis and treatment of microbial keratitis.

CONCLUSIONS

The incidence of microbial keratitis with extended wear of low-Dk/t disposable lenses was higher in these prospective studies (1 in 210 wearers per year at CCLRU and 1 in 154 wearers per year at LVPEI) than that seen in retrospective population-based surveillance studies (1 in 500 wearers per year). Practitioners and patients should always be alert to signs and symptoms, and practitioners should adopt conservative strategies for diagnosis and management of contact lens-related adverse events.

Trends in Contact Lens???Related Corneal Ulcers

PURPOSE

To analyze the frequency of contact lens-related corneal ulcers and its relationship to the type of contact lens and care.

METHODS

Charts of 376 patients with corneal ulcers seen at the Cornea Service of Wills Eye Hospital from July 1, 1999 to December 31, 2002 were retrospectively reviewed. All patients with contact lens-related corneal ulcers were identified, and information regarding cultures, lens type, usage, and cleaning was obtained.

RESULTS

Of the 376 cases, 113 (30%) were related to contact lens use. The contact lens history was recorded in 83 of 113 cases (73%). The soft daily wear frequent replacement lens was the most common lens type associated with corneal ulcers (n = 36/83, 43%). Corneal cultures were performed in 71 of 113 cases (63%) and were positive in 51 of 71 cases (72%). The most common microorganism involved was Pseudomonas aeruginosa (n = 17/51, 33%). The frequency of contact lens-related corneal ulcers from 1999-2002 (n = 113/376, 30%) was significantly greater than that from years 1996-1999 (n = 37/299, 12%) at our institution (P < 0.05).

CONCLUSION

There was a significant increase in the number of contact lens-related corneal ulcers between 1999 and 2002 compared with previous years (P < 0.05). The contact lens type most frequently associated with corneal ulcers was the soft daily-wear frequent-replacement contact lens (43%). Contact lens-related corneal ulcers continue to be a serious problem despite a shift in the market to the use of frequent-replacement daily-wear contact lenses and advances in contact lens technology.

Corneal Oxygen Deficiency

OBJECTIVES

To compare the ocular effects of low Dk hydrogel and high Dk silicone hydrogel contact lenses.

METHODS

A review of recent literature was conducted to determine the effects of wearing low and high Dk soft lenses on corneal swelling, vascular response, refractive error and the corneal epithelium.

RESULTS

High Dk silicone hydrogel contact lenses became available for research and clinical practice almost 10 and 5 years ago respectively. During that time many studies have been conducted and it has been demonstrated repeatedly how much improvement there has been to the physiological response of the eye particularly when wearing the lenses on an overnight basis.

CONCLUSIONS

Although silicone hydrogels only constitute about 2% of current wearers, their positive effects on the eye compared with low Dk hydrogel lenses should make them the most dominant lenses in the near future.

Polarisation of type III translocation by Pseudomonas aeruginosa requires PcrG, PcrV and PopN

Type III secretion (TTS) mediated translocation of exoenzymes is a key virulence strategy utilised by the opportunistic pathogen Pseudomonas aeruginosa to deliver exoenzyme effectors into the eukaryotic cell. We have previously shown that type III mediated translocation is a contact dependent process, which requires the secreted translocator proteins PcrV, PopB and PopD. To further analyse this mechanism, HeLa cells were infected with the wild-type strain PAK as well as isogenic pcrV, popB, popD, pcrG and popN mutants. In the presence of eukaryotic cells, expression of exoenzyme S (ExoS) increased. When cells were infected with the wild-type strain PAK no ExoS was detected in the tissue culture medium. This confirms that ExoS translocation by P. aeruginosa occurs by a polarised mechanism. In contrast, high levels of ExoS were recovered in the tissue culture medium when cells were infected with pcrG, pcrV and popN mutants. Additionally, ExoS expression levels were higher for these mutants regardless of inducing conditions. This suggests that PcrG, PcrV and PopN are involved in negative regulation of ExoS expression and secretion, and are required to ensure polarised delivery of effectors into target cells.

Pseudomonas aeruginosa corneal binding after 24-hour orthokeratology lens wear

PURPOSE

To examine the effect of short-term 24-hr orthokeratology lens (OKL) wear on Pseudomonas aeruginosa binding, epithelial surface cell morphology, epithelial sheet thickness, and stromal thickness in a rabbit model.

METHODS

Seventeen New Zealand white rabbits were treated according to the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research. Partial membranectomy was performed on all rabbits 1 week before the experiments. Baseline values for epithelial and stromal thickness and epithelial surface cell size were determined by in vivo confocal microscopy in one randomly chosen eye (n = 6). One week later, rabbits were fitted in the same eye with a hyper oxygen-transmissible OKL. Twenty-four hours later, confocal microscopy was repeated. The second group of rabbits (n = 6) was fitted with an OKL in one randomly chosen eye for 24 hr. P. aeruginosa binding to the corneal epithelium was assessed for the control corneas and those exposed to the test lens. Scanning electron microscopy was performed on a third group of rabbits to assess epithelial surface damage (n = 5).

RESULTS

There was a statistically significant difference (P<0.001) in P. aeruginosa binding between the control (1.11 +/- 0.74 x 10(5) colony-forming units per cornea) and the OKL-wearing eyes (2.74 +/- 0.69 x 10(5) colony-forming units per cornea). The central epithelium thinned by 6.5% after lens wear (48.2 +/- 1.9 microm to 45 +/- 1.7 microm, P=0.005); however, central stromal thickness increased by 7.3% (322 +/- 22 microm to 345 +/- 29 microm, P=0.006). Compared with the baseline value, central epithelial cell size increased significantly from 1,253 +/- 140 mm(2) to 1,627 +/- 393 mm(2) (29.4%, P=0.02). Scanning electron microscopy showed increased surface epithelial damage associated with OKL wear.

CONCLUSIONS

This prospective, masked, pilot study showed that 24-hr hyper oxygen-transmissible OKL wear induced a statistically significant increase in P. aeruginosa binding to the epithelium of the rabbit cornea, accompanied by central epithelial thinning, stromal thickening, and surface cell damage assessed by scanning electron microscopy. Collectively, the data suggest that despite adequate lens oxygen transmissibility, the mechanical pressure inherent in the OKL design exerted on the corneal surface appears to be associated with increased adherence of P. aeruginosa to surface corneal epithelial cells, which may pose an increased risk for lens-related microbial keratitis, especially in overnight (i.e., closed-eye) wearing conditions. Future studies are needed to determine whether these results are similar in human wear and how P. aeruginosa binding during OKL wear compares with other lens-wearing modalities, such as daily or continuous soft lens wear.

Physicochemical factors influencing bacterial transfer from contact lenses to surfaces with different roughness and wettability

The aim of this study was to determine the transfer of Pseudomonas aeruginosa No. 3 and Staphylococcus aureus 835 from contact lenses to surfaces with different hydrophobicity and roughness. Bacteria were allowed to adhere to contact lenses (Surevue, PureVision, or Focus Night & Day) by incubating the lenses in a bacterial suspension for 30 min. The contaminated lenses were put on a glass, poly(methylmethacrylate), or silicone rubber substratum, shaped to mimic the eye. After 2 and 16 h, lenses were separated from the substrata and bacteria were swabbed off from the respective surfaces and resuspended in saline. Appropriate serial dilutions of these suspensions were made, from which aliquots were plated on agar for enumeration. Bacterial transfer varied between 4 and 60%, depending on the combination of strain, contact time, contact lens, and substratum surface. For P. aeruginosa No. 3, transfer was significantly higher after 16 h than after 2 h, whereas less increase with time was seen for S. aureus 835. Bacterial transfer from all tested contact lenses was least to silicone rubber, the most hydrophobic and roughest substratum surface included.

What Does Overnight Lens Wear Do to the Corneal Epithelium?

The corneal epithelium plays a central role in preventing infectious keratitis. It is a layer that functions both as a physical barrier and as an active component of the ocular surface defense system. Contact lens wear is capable of altering the structure and physiology of the corneal epithelium, potentially increasing the risk of infectious keratitis. This brief review summarizes the effects of continuous contact lens wear and corneal refractive therapy on the physiology and structure of the corneal epithelium.

Evaluation of surveillance methods for an epidemiological study of contact lens related microbial keratitis

PURPOSE

To evaluate surveillance methods in a pilot epidemiological study of contact lens related microbial keratitis (MK) cases identified by ophthalmic practitioners in Australia and New Zealand between May and August 2003 inclusive.

METHODS

Twelve ophthalmologists and 55 optometrists from rural and metropolitan locations were sent a study information pack with postal reporting forms. After 2 months, practitioners were emailed a link to a website for Internet reporting. After 4 months, practitioners were prompted by email and then by telephone if a response was not received. Passive response rates were the rate of returns after posting information and emailing the website link. Active response rates included personalized email and telephone follow-up.

RESULTS

Ten cases of MK were identified by optometrists and five by ophthalmologists. The passive response rates were 79% and 58% for the first and second reporting periods, respectively. There was a lower response rate in the second reporting period compared to the first (P = 0.02). With active surveillance the response rate increased to 97% and 96%. A large proportion of optometrists (62%) and ophthalmologists (55%) used the website for at least one reporting period. Internet reporting was used by all New Zealand practitioners (5/5).

CONCLUSIONS

A surveillance study to estimate the incidence of contact lens related MK in Australia and New Zealand is feasible and acceptable. Internet-based reporting offers a reliable, rapid and cost-effective means of running a large scale, international surveillance study. Active surveillance methods are necessary to enhance reporting rates.

Effect of storage temperatures and time on the efficacy of multipurpose solutions for contact lenses

PURPOSE

To determine the effect of storage time and temperature on the efficacy of four multipurpose solutions for soft contact lenses.

METHOD

Aliquots of multipurpose solutions (OPTI-FREE Express, ReNu MultiPlus, COMPLETE and SOLO-care) stored at different temperatures over a 3-month period, were challenged with contact lens-related ocular pathogens, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans.

RESULTS

The results showed that OPTI-FREE Express had the best activity against Ps. aeruginosa at all temperatures; ReNu MultiPlus performed well at 25 degrees C; COMPLETE barely achieved activity requirements at all temperatures, and lost efficacy after 2 months. SOLO-care maintained its activity best against Ps. aeruginosa at 30 degrees C. Storage at fridge temperature reduced activity of all solutions. Regardless of storage temperature, activities of all solutions against S. aureus markedly decreased by 2 months. Only OPTI-FREE Express met FDA requirements against C. albicans.

CONCLUSION

Performance of multipurpose solutions is affected by time and temperature of storage. Contact lens users should be aware that the efficacy of opened solutions may not be sustained for as long as 3 months. Manufacturers should reconsider their recommendations to further safeguard the ocular health of contact lens wearers.

Continuous wear silicone hydrogel contact lenses and microbial keratitis

Like other lens types, the new generation of silicone hydrogel contact lenses can be associated with a spectrum of ocular complications. Most tend to be very minor, but serious and sight-threatening complications can occur. We present four such cases with microbial keratitis following extended wear of these lenses. Cultures were positive for Pseudomonas aeruginosa in three cases and all three of these suffered lasting visual impairment. We describe our findings and discuss possible risk factors.

Pathogenicity islands in bacterial pathogenesis

In this review, we focus on a group of mobile genetic elements designated pathogenicity islands (PAI). These elements play a pivotal role in the virulence of bacterial pathogens of humans and are also essential for virulence in pathogens of animals and plants. Characteristic molecular features of PAI of important human pathogens and their role in pathogenesis are described. The availability of a large number of genome sequences of pathogenic bacteria and their benign relatives currently offers a unique opportunity for the identification of novel pathogen-specific genomic islands. However, this knowledge has to be complemented by improved model systems for the analysis of virulence functions of bacterial pathogens. PAI apparently have been acquired during the speciation of pathogens from their nonpathogenic or environmental ancestors. The acquisition of PAI not only is an ancient evolutionary event that led to the appearance of bacterial pathogens on a timescale of millions of years but also may represent a mechanism that contributes to the appearance of new pathogens within a human life span. The acquisition of knowledge about PAI, their structure, their mobility, and the pathogenicity factors they encode not only is helpful in gaining a better understanding of bacterial evolution and interactions of pathogens with eukaryotic host cells but also may have important practical implications such as providing delivery systems for vaccination, tools for cell biology, and tools for the development of new strategies for therapy of bacterial infections.

Relative primary adhesion of Pseudomonas aeruginosa, Serratia marcescens and Staphylococcus aureus to HEMA-type contact lenses and an extended wear silicone hydrogel contact lens of high oxygen permeability

PURPOSE

To compare multiple strains of Pseudomonas aeruginosa and representative isolates of Staphylococcus aureus and Serratia marcescens for their relative primary adhesion to a high Dk silicone hydrogel lens (36% H2O) with that of a HEMA-type lens (58% H2O).

METHODS

A radiolabeled cell procedure with a 2-h cell exposure was employed for enumerating bacteria on unworn and worn silicone hydrogel (balafilcon A) and HEMA-type (etafilcon A) hydrogel lenses.

RESULTS

The degree of primary adhesion of P. aeruginosa to 7-day worn balafilcon A lens was similar to the degree of adhesion to unworn balafilcon A lenses. The degree of primary adhesion by clinical strains to unworn balafilcon A lenses and etafilcon lenses was strain variable, but did not differ markedly for the two lenses with a given strain of P. aeruginosa. Relative to most of the pseudomonad strains, adhesion to the hydrogel lenses by S. aureus and S. marcescens was non-significant.

CONCLUSION

Adhesion of strains of P. aeruginosa to a hydrogel contact lens does not appear to differ appreciably between the HEMA-type etafilcon A and the high Dk silicone hydrogel balafilcon A lens.