Adaptive effects of 30-night wear of hyper-O(2) transmissible contact lenses on bacterial binding and corneal epithelium: a 1-year clinical trial

Role of Different Types of Contact Lenses in Epithelial Thickness

OBJECTIVE

To evaluate the potential role of different types of contact lenses, such as soft (SCL), hard (HCL), and mini scleral (SCCL), in corneal epithelial thickness with anterior segment optical coherence tomography (AS-OCT).

METHODS

In this cross-sectional study, patients who used contact lens at recent 6 months were recruited consecutively from September 2019 to October 2019, and the epithelial thicknesses of the cornea were obtained by AS-OCT and compared with control subjects who did not use contact lens.

RESULTS

In total, 184 eyes (115 subjects) were included; of them, 75 eyes were keratoconic (KCN) and 109 eyes were nonkeratoconic (non-KCN). Twenty eyes in KCN and 79 eyes of non-KCN group had no history of contact lens use and were included for comparison with KCN and non-KCN contact lens users, respectively. Mean duration of contact lens wearing was 75.63±50.42 months. The epithelial thickness of non-KCN SCL group was thinner than that of non-KCN control subjects all over the cornea, whereas the epithelium of non-KCN HCL was thinner at central site as well as nasal and temporal paracentral and midperipheral areas. Epithelial thickness of the KCN HCL group was not different from the KCN control subjects in all sectors. The KCN SCCL group had thinner epithelium at nearly all peripheral sectors as well as inferior, inferotemporal, inferonasal, and nasal midperipheral sectors compared with KCN control subjects.

CONCLUSION

The corneal epithelium was thinner at the peripheral zones in KCN SCCL users; at both peripheral and central zones in non-KCN SCL users and in central zones in non-KCN HCL users.

CLEAR - Effect of contact lens materials and designs on the anatomy and physiology of the eye

This paper outlines changes to the ocular surface caused by contact lenses and their degree of clinical significance. Substantial research and development to improve oxygen permeability of rigid and soft contact lenses has meant that in many countries the issues caused by hypoxia to the ocular surface have largely been negated. The ability of contact lenses to change the axial growth characteristics of the globe is being utilised to help reduce the myopia pandemic and several studies and meta-analyses have shown that wearing orthokeratology lenses or soft multifocal contact lenses can reduce axial length growth (and hence myopia). However, effects on blinking, ptosis, the function of Meibomian glands, fluorescein and lissamine green staining of the conjunctiva and cornea, production of lid-parallel conjunctival folds and lid wiper epitheliopathy have received less research attention. Contact lens wear produces a subclinical inflammatory response manifested by increases in the number of dendritiform cells in the conjunctiva, cornea and limbus. Papillary conjunctivitis is also a complication of all types of contact lenses. Changes to wear schedule (daily disposable from overnight wear) or lens materials (hydrogel from SiHy) can reduce papillary conjunctivitis, but the effect of such changes on dendritic cell migration needs further study. These changes may be associated with decreased comfort but confirmatory studies are needed. Contact lenses can affect the sensitivity of the ocular surface to mechanical stimulation, but whether these changes affect comfort requires further investigation. In conclusion, there have been changes to lens materials, design and wear schedules over the past 20+ years that have improved their safety and seen the development of lenses that can reduce the myopia development. However, several changes to the ocular surface still occur and warrant further research effort in order to optimise the lens wearing experience.

Homeostasis and Defense at the Surface of the Eye. The Conjunctival Microbiota

The literature on ocular microbiome has grown tremendously over the past decade, and our knowledge of the different aspects and roles in homeostasis and protection is continuously growing. The development of 16 S rRNA sequencing has allowed the field to characterize communities of bacteria in health and ocular disease. Efforts should continue to further elucidate the interplay between microbiome and key players, such as age, comorbidities, and contact lens usage in order to have better control of the sight-threatening complications.

Thirty years of 'quiet eye' with etafilcon A contact lenses

Frequent replacement contact lenses made from the etafilcon A hydrogel lens material were introduced onto the market over 30 years ago, and etafilcon A remains the most widely used hydrogel lens material today. Although the prescribing of silicone hydrogel lenses is increasing, millions of lens wearers globally have been wearing hydrogel lenses for many years and exhibit a physiologically-stable 'quiet eye', with a low profile of adverse events. Hydrogel lenses are demonstrated to maintain a low inflammatory response and infection risk profile during daily wear, which in the case of etafilcon A, may be related to its low modulus, and the naturally-protective, anti-microbial, non-denatured lysozyme absorbed into the lens from the tear fluid. Although improved corneal physiology from decreased hypoxia with silicone hydrogel lenses is well accepted, equivalent levels of corneal oxygenation are maintained during daily wear of low to medium powered hydrogel lenses, which do not impede the daily corneal de-swelling process, and do not induce clinically significant changes in ocular health. Therefore, hydrogel lenses remain an important alternative for daily wear in modern contact lens practice.

Contact lens wear and the diabetic corneal epithelium: A happy or disastrous marriage?

Diabetes mellitus is an epidemic in the US and abroad. With the advent of new contact lens technology, the use of contact lenses as glucose sensors in lieu of the traditional finger stick is quickly becoming realized. This has the potential to rapidly expand the contact lens market into this growing patient population. The independent cellular and physiological effects of contact lens wear and diabetes on the corneal epithelium have been described. However, little evidence exists to date to support whether there is increased risk associated with contact lens wear in diabetes. The focus of this review is to discuss what is known about the cellular effects of contact lenses on the corneal epithelium, the pathophysiological changes in the corneal epithelium that occur in diabetes, and whether an increased risk for corneal epithelial damage and/or infection may negatively impact safety in diabetic contact lens wearers. Available data indicates that there are inherent risks associated with contact lens wear in diabetics. Importantly, eye care practitioners fitting contact lenses in the diabetic patient need to carefully consider the duration of disease, the level of glycemic control, the presence of retinopathy, and the patient's overall health.

Does Long-term Soft Contact Lens Wear Affect Corneal and Anterior Chamber Parameters?

Objectives

To assess the long-term effects of soft contact lenses (SCL) on the cornea and anterior chamber by topography.

Materials and Methods

Thirty-nine eyes of 22 healthy patients were included in this prospective study. Changes in corneal and anterior chamber parameters before and after 12 months of daily SCL use (Air Optix Aqua, Air Optix Aqua for Astigmatism, Acuvue Oasys and Acuvue Oasys for Astigmatism) were evaluated with Pentacam (Oculus, Germany).

Results

Best corrected visual acuity with toric SCL was significantly better compared to spectacles in the toric SCL group (0.98±0.34 vs 0.94±0.72, p=0.004). None of the corneal (horizontal and vertical keratometry, corneal volume, anterior and posterior corneal astigmatism, corneal pachymetry of apex and thinnest location) and anterior chamber (anterior chamber depth, volume and angle) parameters showed a statistically significant change after long-term daily wear of SCLs.

Conclusion

The results of this study revealed that long-term wear of current high oxygen permeable and relatively low modulus silicone hydrogel SCLs does not impact cornea and anterior chamber morphology or volumetric parameters. Furthermore, toric silicone hydrogel SCLs can provide better visual performance than spectacles.

Epidemiology of contact lens-induced infiltrates: an updated review

Corneal infiltrative events (CIEs) are well established as a risk associated with soft contact lens wear. The incidence of symptomatic CIEs during extended soft lens wear ranges from 2.5 to six per cent; when asymptomatic CIEs are included, the incidence can be as high as 20-25 per cent. In daily soft lens wear, the annual incidence of symptomatic CIEs is about three per cent. There are various accepted methods of categorising CIEs, and a scoring system based on clinical signs and symptoms is a good approach to grade severity. Lens-related risk factors include extended wear, silicone hydrogel material, the use of multipurpose solutions, bacterial bioburden and reusable lenses. Recent studies report that daily disposable lenses reduce the risk of CIEs.

Disturbing the balance: effect of contact lens use on the ocular proteome and microbiome

Contact lens wear is a popular, convenient and effective method for vision correction. In recent years, contact lens practice has expanded to include new paradigms, including orthokeratology; however, their use is not entirely without risk, as the incidence of infection has consistently been reported to be higher in contact lens wearers. The explanations for this increased susceptibility have largely focused on physical damage, especially to the cornea, due to a combination of hypoxia, mechanical trauma, deposits and solution cytotoxicity, as well as poor compliance with care routines leading to introduction of pathogens into the ocular environment. However, in recent years, with the increasing availability and reduced cost of molecular techniques, the ocular environment has received greater attention with in-depth studies of proteins and other components. Numerous proteins were found to be present in the tears and their functions and interactions indicate that the tears are far more complex than formerly presumed. In addition, the concept of a sterile or limited microbial population on the ocular surface has been challenged by analysis of the microbiome. Ocular microbiome was not considered as one of the key sites for the Human Microbiome Project, as it was thought to be limited compared to other body sites. This was proven to be fallacious, as a wide variety of micro-organisms were identified in the analyses of human tears. Thus, the ocular environment is now recognised to be more complicated and interference with this ecological balance may lead to adverse effects. The use of contact lenses clearly changes the situation at the ocular surface, which may result in consequences which disturb the balance in the healthy eye.

Microbiological study of therapeutic soft contact lenses used in the treatment of recurrent corneal erosion syndrome

OBJECTIVE

To determine the bacteriological spectrum of the removed therapeutic soft contact lenses (TSCLs) and to establish efficacy of prophylactic antibiotics on TSCLs used for 2 weeks for treatment of patients with recurrent corneal erosion syndrome (RCES).

METHODS

This study included idiopathic RCES treated using highly oxygen-permeable silicone hydrogel contact lenses (CLs), and treated 4 times per day with topical tobramycin 3% for 2 weeks. After TSCLs were applied for 2 weeks, the lenses were removed with sterile forceps under which a speculum was inserted, and placed on blood agar with the inner face down. The TSCLs were analyzed for bacterial colonization, and antibiotic susceptibility tests were performed for the isolates, using disk diffusion.

RESULTS

Of the 40 lenses analyzed, 9 (22.5%) yielded positive cultures. Staphylococcus epidermidis was the most commonly isolated microorganism; there were five methicillin-sensitive coagulase-negative staphylococci and two methicillin-resistant coagulase-negative staphylococci. Furthermore, we found two lenses that were colonized by Enterobacter gergoviae and Citrobacter freundii. All cultured bacteria showed intermediate or complete sensitivity to ciprofloxacin, tigecycline, and tobramycin. Despite bacterial colonization in 9 CLs, no clinical signs of infectious keratitis were found in any of the patients with prophylactic topical tobramycin 3%.

CONCLUSIONS

In case of using TSCLs for 2 weeks, tobramycin or ciprofloxacin may be useful as prophylactic topical antibiotics for preventing secondary corneal infections. Considering currently growing incidence of ciprofloxacin-resistant ocular isolates, tobramycin seems to be a reasonable prophylactic topical antibiotic susceptible broad spectrum of bacteria in clinics.

In Vivo Confocal Microscopy of the Cornea: New Developments in Image Acquisition, Reconstruction, and Analysis Using the HRT-Rostock Corneal Module

The optical sectioning ability of confocal microscopy allows high magnification images to be obtained from different depths within a thick tissue specimen and is thus ideally suited to the study of intact tissue in living subjects. In vivo confocal microscopy has been used in a variety of corneal research and clinical applications since its development over 25 years ago. In this article we review the latest developments in quantitative corneal imaging with the Heidelberg Retinal Tomograph with Rostock Corneal Module (HRT-RCM). We provide an overview of the unique strengths and weaknesses of the HRT-RCM. We discuss techniques for performing 3-D imaging with the HRT-RCM, including hardware and software modifications that allow full-thickness confocal microscopy through-focusing (CMTF) of the cornea, which can provide quantitative measurements of corneal sublayer thicknesses, stromal cell and extracellular matrix backscatter, and depth-dependent changes in corneal keratocyte density. We also review current approaches for quantitative imaging of the subbasal nerve plexus, which require a combination of advanced image acquisition and analysis procedures, including wide-field mapping and 3-D reconstruction of nerve structures. The development of new hardware, software, and acquisition techniques continues to expand the number of applications of the HRT-RCM for quantitative in vivo corneal imaging at the cellular level. Knowledge of these rapidly evolving strategies should benefit corneal clinicians and basic scientists alike.

Eye rubbing-induced changes in intraocular pressure and corneal thickness measured at five locations, in subjects with ocular allergy

AIM

To assess the effects of eye rubbing on corneal thickness (CT) and intraocular pressure (IOP) measurements obtained 0-30min after habitual eye rubbing in symptomatic patients.

METHODS

Measurements of IOP and CT were obtained at five locations (central, temporal, superior, nasal and inferior) before, and every 5min for 30min interval after 30s of eye rubbing, for 25 randomly selected eyes of 14 subjects with ocular allergy and 11 age-matched normals. Differences in measurements were calculated in each group [Baseline measurements minus measurements recorded at each time interval after eye rubbing (for IOP), and for each corneal location (for CT)] and comparison were then made between groups (allergic versus control) for differences in any observed effects.

RESULTS

Within groups, baseline mean IOPs in the allergic patient-group (14.2±3.0 mm Hg) and in the control group (13.1±1.9 mm Hg) were similar at all times, after eye rubbing (P >0.05, for all). The maximum reduction in IOP was 0.8 mm Hg in the control subjects and the maximum increase was also 0.8 mm Hg in the allergic subjects. Between groups (allergic versus control), the changes in IOP remained under 1 mm Hg at all times (P=0.2) after 30min of eye rubbing. Between 0 and 30min of CT measurements after eye rubbing, the mean central CT (CCT), inferior CT (ICT), superior CT (SCT), temporal CT (TCT) and nasal CT (NCT) did not vary significantly from baseline values in the control and allergic-subject groups (P>0.05, for both). Between both groups, changes in CT were similar at all locations (P>0.05) except for the TC which was minimally thinner by about 4.4 µm (P=0.001) in the allergic subjects than in the control subjects, 30min following 30s of eye rubbing.

CONCLUSION

IOP measured in allergic subjects after 30s of habitual eye rubbing was comparable with that obtained in normal subjects at all times between 0 and 30min. Although, CT in the allergic subjects were similar to those of the control subjects at all times, it varied between +10 and -7.5 µm following eye rubbing, with the temporal cornea showing consistent reductions in thickness in the subjects with allergy. However, this reduction was minimal and was considered to not be clinically relevant.

Pseudomonas aeruginosa infectious keratitis in a high oxygen transmissible rigid contact lens rabbit model

PURPOSE

To establish a rabbit model of infectious Pseudomonas aeruginosa keratitis using ultrahigh oxygen transmissible rigid lenses and characterize the frequency and severity of infection when compared to a non-oxygen transmissible lens material.

METHODS

Rabbits were fit with rigid lenses composed of ultrahigh and non-oxygen transmissible materials. Prior to wear, lenses were inoculated with an invasive corneal isolate of P. aeruginosa stably conjugated to green fluorescent protein (GFP). Corneas were examined before and after lens wear using a modified Heidelberg Rostock Tomograph in vivo confocal microscope. Viable bacteria adherent to unworn and worn lenses were assessed by standard plate counts. The presence of P. aeruginosa-GFP and myeloperoxidase-labeled neutrophils in infected corneal tissue was evaluated using laser scanning confocal microscopy.

RESULTS

The frequency and severity of infectious keratitis was significantly greater with inoculated ultrahigh oxygen transmissible lenses. Infection severity was associated with increasing neutrophil infiltration and in severe cases, corneal melting. In vivo confocal microscopic analysis of control corneas following lens wear confirmed that hypoxic lens wear was associated with mechanical surface damage, whereas no ocular surface damage was evident in the high-oxygen lens group.

CONCLUSIONS

These data indicate that in the absence of adequate tear clearance, the presence of P. aeruginosa trapped under the lens overrides the protective effects of oxygen on surface epithelial cells. These findings also suggest that alternative pathophysiological mechanisms exist whereby changes under the lens in the absence of frank hypoxic damage result in P. aeruginosa infection in the otherwise healthy corneal epithelium.

Multipurpose care solution-induced corneal surface disruption and Pseudomonas aeruginosa internalization in the rabbit corneal epithelium

PURPOSE

To evaluate the effects of a chemically preserved multipurpose contact lens care solution (MPS) on the corneal epithelial surface and Pseudomonas aeruginosa (PA) internalization in the rabbit corneal epithelium.

METHODS

Rabbits were fit in one eye with a silicone hydrogel lens (balafilcon A) soaked overnight in a borate-buffered MPS (BioTrue). The contralateral eye was fit with a lens removed directly from the blister pack containing borate-buffered saline (control). Lenses were worn for 2 hours. Upon lens removal, corneas were challenged ex vivo with invasive PA strain 6487 and assessed for PA internalization. Ultrastructural changes were assessed using scanning electron (SEM) and transmission electron microscopy (TEM).

RESULTS

Scanning electron microscopy showed frank loss of surface epithelium in MPS-exposed eyes, while control eyes exhibited occasional loss of surface membranes but retention of intact junctional borders. Transmission electron microscopy data supported and extended SEM findings, demonstrating the presence of epithelial edema in MPS-treated eyes. There was a 12-fold increase in PA uptake into the corneal epithelium following wear of the MPS-treated lens compared to control (P = 0.008).

CONCLUSIONS

These data demonstrate that corneal exposure to MPS during lens wear damages the surface epithelium and are consistent with our previous clinical data showing an increase in bacterial binding to exfoliated epithelial cells following MPS use with resultant increased risk for lens-mediated infection. These findings also demonstrate that the PA invasion assay may provide a highly sensitive quantitative metric for assessing the physiological impact of lens-solution biocompatibility on the corneal epithelium.

Ethnic differences in dry eye symptoms: effects of corneal staining and length of contact lens wear

PURPOSE

To explore the relationships among length of contact lens (CL) wear, degree of corneal staining and severity of dryness symptoms, and to determine whether these relationships differ between Asians and non-Asians.

METHODS

Adapted soft CL wearers (n=395; 180 Asian, 215 non-Asian) were required to discontinue CL wear for at least 24h and report to the University of California, Berkeley Clinical Research Center (UCB-CRC). Fluorescein corneal staining was graded according to Brien Holden Vision Institute scales. Length of CL wear was reported by subjects and subjective dryness ratings were collected using the UCB-CRC Dry Eye Flow Chart (DEFC).

RESULTS

More Asian CL wearers exhibited corneal staining compared to non-Asians, and Asian CL wearers had a higher mean grade of corneal staining (p<0.001), as well as a higher mean DEFC classification (p<0.001). The difference between Asians and non-Asians in grades of corneal staining extent and depth were significant (p<0.001). Among non-Asian CL wearers, dryness symptoms decreased with more years of CL wear and increased in the presence of corneal staining, which was not the case for Asian CL wearers.

CONCLUSIONS

Asian soft CL wearers reported more severe dryness symptoms and demonstrated more severe corneal staining overall compared to non-Asians. Among non-Asians, dryness symptoms were less severe on average with increased years of CL wear and more severe in the presence of corneal staining. Dryness severity does not appear to be related to years of CL wear or corneal staining among Asians.

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

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

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Disruption of contact lens-associated Pseudomonas aeruginosa biofilms formed in the presence of neutrophils

PURPOSE

To evaluate the capacity of neutrophils to enhance biofilm formation on contact lenses by an infectious Pseudomonas aeruginosa (PA) corneal isolate. Agents that target F-actin and DNA were tested as a therapeutic strategy for disrupting biofilms formed in the setting of neutrophils in vitro and for limiting the infectious bioburden in vivo.

METHODS

Biofilm formation by infectious PA strain 6294 was assessed in the presence of neutrophils on a static biofilm plate and on unworn etafilcon A soft contact lenses. A d-isomer of poly(aspartic acid) was used alone and with DNase to reduce biofilm formation on test contact lenses. The gentamicin survival assay was used to determine the effectiveness of the test compound in reducing subsequent intracellular bacterial load in the corneal epithelium in a contact lens infection model in the rabbit.

RESULTS

In a static reactor and on hydrogel lenses, PA biofilm density was enhanced 30-fold at 24 hours in the presence of neutrophils (P < 0.0001). The combination of DNase and anionic poly(aspartic acid) reduced the PA biofilms formed in the presence of activated neutrophils by 79.2% on hydrogel contact lenses (P < 0.001). An identical treatment resulted in a 41% reduction in internalized PA in the rabbit corneal epithelium after 24 hours (P = 0.03).

CONCLUSIONS

These results demonstrate that PA can exploit the presence of neutrophils to form biofilm on contact lenses within a short time. Incorporation of F-actin and DNA represent a mechanism for neutrophil-induced biofilm enhancement and are targets for available agents to disrupt pathogenic biofilms formed on contact lenses and as a treatment for established corneal infections.

Castroviejo Lecture 2009: 40 years in search of the perfect contact lens

PURPOSE

To identify the pathophysiological changes produced by contact lens wear that predispose the cornea to infection and search for prospective modifiable risk factors that could reduce the incidence of this critical complication in millions of patients worldwide.

METHODS

Significant experimental and clinical publications are reviewed, and the results of ongoing studies are presented.

RESULTS

Pseudomonas aeruginosa (PA) is the most common pathogen causing lens-related infectious keratitis over 3 decades. Contact lens wear can increase the risk of infection by increasing surface cell PA binding, thereby promoting invasion between broken tight junctions and initiating direct intracellular invasion mediated by lens-induced membrane lipid rafts. Prevention of upregulation of specific surface-binding receptors for PA with concomitant increase in infection risk is a zero damage game where independent interactions among lens type, mode of wear, oxygen transmissibility, polymer, and toxic effects of associated care solutions ideally should collectively produce no increased ability for PA to attach and/or to invade, thus minimizing the risk for lens-associated infections. The specific hypothesis tested is, "no increased epithelial surface damage... no increased PA binding or invasion... no increased risk for infection." Testing of this new paradigm has been performed in vitro and in animal and human clinical trials and correlated clinically with relative risk results from robust current epidemiological studies. Results to date clearly support the use of lens-related increases in PA binding (bench) as a noninvasive clinical predictor of risk for lens-related infection in subsequent large-scale population studies (bedside). Currently, results suggest that use of common commercial multipurpose lens care solutions with soft lenses may alone significantly increase infection risk by enhancing lens-related PA binding as compared with use of nonpreserved solutions (hydrogen peroxide). Clinical testing also shows that only peroxide solutions show significant disinfection capability against amoebic cysts. Further case-control studies to examine relative risk for infection by lens type and lens care solution are urgently needed.

CONCLUSIONS

Millions of patients are dependent on contact lenses for vision worldwide; over 3 decades, lens use has increased, although risk for lens-related infection has remained stubbornly unchanged. Unfortunately, recent introduction of a new generation of hyper-oxygen transmissible lenses used with traditional multipurpose lens care solutions has not lowered overall risks for lens-related infections; however, similar lenses used with nonpreserved care solutions (peroxide) recently demonstrated no significant increases in PA binding in a 1-year clinical trial. Collectively, these findings along with the urgent need for amoebic cysticidal disinfection have led to a current recommendation to patients to use nonpreserved (hydrogen peroxide) care solutions in soft lens wear.

The effects of short-term lens wear and eye rubbing on the corneal epithelium

OBJECTIVES

To measure the effects of short-term high oxygen-transmissible (Dk) soft and rigid contact lens wear and eye rubbing on basal epithelial appearance and epithelial thickness.

METHODS

Ten subjects were enrolled in a randomized crossover study. The subjects' left eye was used as a control, and the right eye either wore a high Dk soft lens, high Dk parallel fitted rigid gas-permeable lens, or was rubbed on 3 separate days. Epithelial basal cell regularity and central and peripheral epithelial thickness were assessed before and after 6-hr soft or rigid lens wear or 10-min rubbing using in vivo confocal microscopy and modified optical pachometry.

RESULTS

Basal cell regularity was unaffected by short-term lens wear or eye rubbing (Friedman Test, P=0.11 and 0.37 in test and control eyes, respectively). The peripheral epithelium was thicker than the central epithelium (repeated-measures analysis of variance, P=0.03) but remained unaffected by short-term lens wear or eye rubbing (repeated-measures analysis of variance, P>0.05, power <0.08).

CONCLUSIONS

Corneal epithelial thickness and basal cell morphology were not affected by short-term lens wear or eye rubbing in this pilot study.

Remote-controlled scanning and automated confocal microscopy through focusing using a modified HRT rostock corneal module

PURPOSE

To modify the HRT-II Confocal Microscope with Rostock Corneal Module (HRT-RCM) to allow computerized control of the focal plane position (depth) within the cornea.

METHODS

A threaded housing on the HRT-RCM microscope is normally rotated by hand to change the focal plane position within the cornea. This piece was removed to allow the front housing of the microscope to move freely. A linear actuator (Oriel Encoder Mike) was then attached to the side of the microscope and coupled to a drive shaft that was connected to the front housing. The actuator was connected to an Oriel 18011 Encoder Mike controller, which was interfaced to a PC. Software was developed to allow control and display of the focal plane position using this PC, while image acquisition software was run on the HRT-RCM PC. The instrument was tested on one human volunteer.

RESULTS

The modified instrument successfully allowed computer-controlled focusing throughout the entire cornea. Through-focus sequences could be collected online and analyzed and reconstructed three dimensionally off-line using modified confocal microscopy through-focusing software.

CONCLUSIONS

Although this is only a prototype instrument, it significantly improves the examination procedure by allowing completely "hands-free" operation of the HRT-RCM microscope. The data also demonstrate the feasibility of performing quantitative z-axis scans through the full thickness of the cornea with the HRT-RCM. Given the higher contrast images and improved optical sectioning of the HRT-RCM as compared with other instruments, these capabilities could have widespread application.

Rat silicone hydrogel contact lens model: effects of high- versus low-Dk lens wear

OBJECTIVES

This study used a rat contact lens (CL) model to test if high- versus low-Dk lens wear caused changes in (1) conjunctival Langerhans cell (LC) number or location; (2) Bcl-2 expression; and (3) infection risk.

METHODS

Female, Lewis rats wore a high- or low-Dk CL continuously for 2 weeks. Afterward, corneas were harvested and processed for ADPase activity to identify LCs, for immunostaining and for real time-polymerase chain reaction. Contact lens-wearing rats also were challenged with Pseudomonas aeruginosa by placing a bacterial-soaked CL on the eye followed by topical delivery of bacteria. After 48 hrs, slit lamp examination and real time-polymerase chain reaction were used to evaluate the corneal response.

RESULTS

Conjunctival LC were significantly increased after low- versus high-Dk CL wear (P<0.0001). In contrast, conjunctival LC in non-lens wearing rats was not significantly different from the high-Dk lens wearing group. Bcl-2 mRNA levels were significantly decreased in low- versus high-Dk CL wearing rats, while Bax, FasL, caspase 3, and caspase 9 levels were unchanged. Immunostaining for Bcl-2 showed fewer positively stained epithelial cells in the low- versus high-Dk lens wearing group. After bacterial challenge, 30% of low- versus none of the high-Dk CL wearing corneas became infected and showed increased mRNA levels for several proinflammatory cytokines/chemokines, inducible nitric oxide synthase and matrix metalloproteinase-9.

CONCLUSION

Low- versus high-Dk or non-CL wear led to an increased number of conjunctival LC, decreased Bcl-2 levels, and increased the risk of bacterial infection.

Thickness mapping of the cornea and epithelium using optical coherence tomography

PURPOSE

To measure corneal and epithelial thickness across four meridians using Optical Coherence Tomography (OCT) and to compare these measurements between normal non-lens wearers (NLW), rigid gas permeable (RGP) lens wearers, and RGP-wearing keratoconics (KC).

METHODS

Both eyes of 60 subjects were measured (20 NLW, nine female:11 male, 27.6 +/- 5.9 years; 20 RGP, 20 female, 23.9 +/- 7.6 years; and 20 KC, seven female:13 male, 32.4 +/- 8.1 years). A customized fixation target employing LEDs in eight directions of gaze was attached to the OCT and corneal images obtained. Raw OCT scans were analyzed to yield values for corneal and epithelial thickness and color-coded maps were compiled.

RESULTS

Central corneal thickness (CCT) was thinnest in KC (447 +/- 68 microm) and similar between RGP (518 +/- 32 microm; pKC < 0.001) and NLW (517 +/- 21 microm) (p(KC) < 0.001 NLW pRGP > 0.05). Peripheral corneal thickness in NLW was thickest in the superior temporal and thinnest in the inferior (I) regions (superior temporal(thickest) vs. I(thinnest) p < 0.001). Central epithelial thickness was thinnest in KC (44 +/- 7 microm), followed by RGP (50 +/- 4 microm), then NLW (54 +/- 2 microm) (pKC < 0.001 NLW p(RGP) < 0.05). Central epithelial thickness in the KC group was significantly thinner than in the RGP group (p < 0.001). In the NLW group, peripheral epithelial thickness was thicker (63 +/- 5 microm) than central (p < 0.001) and was thickest in the superior (S) region and thinnest in the inferior (I) region (S(thickest) vs. I(thinnest) p < 0.001). KC epithelium was thinnest in the inferior temporal meridian (42 +/- 5 microm).

CONCLUSIONS

Thickness of the normal cornea and epithelium was greatest in the superior region. In all groups, the inferior cornea and epithelium was thinnest, and to a greater extent in the KC group.

The effect of long-term wear of soft lenses of low and high oxygen transmissibility on the corneal epithelium

PURPOSE

To measure the effects of long-term wear of soft lenses of low and high oxygen transmissibility (Dk) on basal epithelial appearance and epithelial thickness.

METHODS

Sixty-three subjects were enrolled in a cross-sectional study. Seventeen high Dk lens wearers and 24 low Dk lens wearers who had worn lenses on an extended wear basis for more than 3 years (range: 3-22) were compared to a group of 22 age-matched subjects who had never worn contact lenses. Cell regularity and the intensity of light backscattered by the basal epithelium were assessed using confocal microscopy. Epithelial thickness was measured at the centre and at four peripheral locations using modified optical pachometry.

RESULTS

Epithelial basal cells appeared less regular in low Dk lens wearers than high Dk wearers or controls (Mann-Whitney U-test, P=0.001). The intensity of backscattered light did not differ across groups (Kruskal-Wallis test, P=0.37). Low Dk wearers had the thinnest epithelium (46 (10) microm), followed by high Dk wearers (54 (14) microm) and controls (58 (9) microm; ANOVA, P<or=0.006). Topographical position did not affect epithelial thickness (ANOVA, P=0.10).

CONCLUSIONS

Visible alterations to the basal epithelial cells can only be detected in long-term extended wearers of low Dk soft lenses. Extended wear of high Dk soft lenses results in topographically uniform epithelial thinning that is significantly less than the thinning seen with low Dk lenses. Confirmation of these findings using groups with evenly matched duration of lens wear is required.

The Clinical and Cellular Basis of Contact Lens-related Corneal Infections: A Review

Microbial keratitis (MK) is the most visually devastating complication associated with contact lens wear. Pseudomonas aeruginosa (PA) is highly invasive in the corneal epithelium and is responsible for more than half of the reported cases of contact lens-related MK. To protect against Pseudomonas-mediated MK, the corneal epithelium has evolved overlapping defense mechanisms that function to protect the ocular surface from microbial invasion. Research has shown that contact lens wear disrupts these protective mechanisms through breakdown of normal homeostatic surface renewal as well as damaging the corneal surface, exposing underlying cell membrane receptors that bind and internalize PA through the formation of lipid rafts. Human clinical trials have shown that initial adherence of PA with resulting increased risk for microbial infection is mediated in part by contact lens oxygen transmissibility. Recently, chemical preserved multipurpose solutions (MPS) have been implicated in increasing PA adherence to corneal epithelial cells, in addition to inducing significant levels of toxic staining when used in conjunction with specific silicone hydrogel lenses. This review summarizes what is currently known about the relationship between contact lenses, the corneal epithelium, MPS, and infection.

The role of contact lens type, oxygen transmission, and care-related solutions in mediating epithelial homeostasis and pseudomonas binding to corneal cells: an overview

Despite the widespread acceptance of silicone hydrogel contact lenses, microbial keratitis remains the most significant complication associated with contact lens wear and Pseudomonas aeruginosa is still recognized as the leading causative organism. The purpose of this review is to summarize and update the current knowledge of the effects of lens type, oxygen transmissibility, wearing mode, and contact-lens care solutions on corneal epithelial biology and lens-induced P. aeruginosa binding from human and animal studies. The collective results of this work suggest that there is a net interactive effect on corneal epithelial cells among these risk factors. Significantly, hyper-oxygen-transmissible lenses in any wearing mode with non-preserved care solutions appear to offer the safest potential clinical choice for contact lens wear.