Collagen Cross-Linking with Photoactivated Riboflavin (PACK-CXL) for the Treatment of Advanced Infectious Keratitis with Corneal Melting

Biomechanical and histological changes associated with riboflavin ultraviolet-A-induced CXL with different irradiances in young human corneal stroma

Keratoconus (KC) is a degenerative condition affecting the cornea, characterized by progressive thinning and bulging, which can ultimately result in serious visual impairment. The onset and progression of KC are closely tied to the gradual weakening of the cornea's biomechanical properties. KC progression can be prevented with corneal cross-linking (CXL), but this treatment has shortcomings, and evaluating its tissue stiffening effect is important for determining its efficacy. In this field, the shortage of human corneas has made it necessary for most previous studies to rely on animal corneas, which have different microstructure and may be affected differently from human corneas. In this research, we have used the lenticules obtained through small incision lenticule extraction (SMILE) surgeries as a source of human tissue to assess CXL. And to further improve the results' reliability, we used inflation testing, personalized finite element modeling, numerical optimization and histology microstructure analysis. These methods enabled determining the biomechanical and histological effects of CXL protocols involving different irradiation intensities of 3, 9, 18, and 30 mW/cm2, all delivering the same total energy dose of 5.4 J/cm2. The results showed that the CXL effect did not vary significantly with protocols using 3-18 mW/cm2 irradiance, but there was a significant efficacy drop with 30 mW/cm2 irradiance. This study validated the updated algorithm and provided guidance for corneal lenticule reuse and the effects of different CXL protocols on the biomechanical properties of the human corneal stroma.

A double-masked, sham-controlled trial of rose bengal photodynamic therapy for the treatment of fungal and acanthameoba keratitis: Rose Bengal Electromagnetic Activation with Green Light for Infection Reduction (REAGIR) Study

Background

Infectious keratitis secondary to fungus or acanthamoeba often has a poor outcome despite receiving the best available medical therapy. In vitro Rose Bengal Photodynamic therapy (RB-PDT) appears to be effective against fungal and acanthamoeba isolates.22,23 In one published series RB-PDT reduced the need for therapeutic penetrating keratoplasty in severe bacterial, fungal, and acanthameoba keratitis not responsive to medical therapy.

Methods

This international, randomized, sham and placebo controlled 2-arm clinical trial, randomizes patients with smear positive fungal and acanthameoba and smear negative corneal ulcers in a 1:1 fashion to one of two treatment arms: 1) Topical antimicrobial plus sham RB-PDT or 2) Topical antimicrobial plus RB-PDT.

Discussion

We anticipate that RB-PDT will improve best spectacle corrected visual acuity and also reduce complications such as corneal perforation and the need for therapeutic penetrating keratoplasty. This study will comply with the NIH Data Sharing Policy and Policy on the Dissemination of NIH-Funded Clinical Trial Information and the Clinical Trials Registration and Results Information Submission rule. Our results will be disseminated via clinicaltrials.gov website, meetings, and journal publications. Our data will also be available upon reasonable request.

Trial Registration

NCT, NCT05110001, Registered November 5, 2021. https://www.clinicaltrials.gov/study/NCT05110001.

Fungal Keratitis: Diagnosis, Management, and Recent Advances

Fungal keratitis is one of the major causes of microbial keratitis that may lead to corneal blindness. Many problems related to diagnosis and therapy are encountered in fungal keratitis, including difficulty in obtaining laboratory diagnoses and the availability and efficacy of antifungal medications. Intensive and prolonged use of antifungal topical preparations may not be enough. The use of antifungal medications is considered the main treatment for fungal keratitis. It is recommended to start antifungal therapy after confirmation of the clinical diagnosis with a smear or positive cultures. Topical application of antifungal medications is a mainstay for the treatment of fungal keratitis; however, systemic, intra-stromal, or intra-cameral routes may be used. Therapeutic keratoplasty is the main surgical procedure approved for the management of fungal keratitis with good success rate. Intrastromal corneal injection of antifungal medications may result in steady-state drug levels within the corneal tissue and prevent intervals of decreased antifungal drug concentration below its therapeutic level. In cases of severe fungal keratitis with deep stromal infiltration not responding to treatment, intracameral injection of antifungal agents may be effective. Collagen cross-linking has been proposed to be beneficial for cases of fungal keratitis as a stand-alone therapy or as an adjunct to antifungal medications. Although collagen cross-linking has been extensively studied in the past few years, its protocol still needs many modifications to optimize UV fluence levels, irradiation time, and concentration of riboflavin to achieve 100% microbial killing.

Human corneal epithelial cell and fibroblast migration and growth factor secretion after rose bengal photodynamic therapy (RB-PDT) and the effect of conditioned medium

PURPOSE

To investigate human corneal epithelial cell and fibroblast migration and growth factor secretion after rose bengal photodynamic therapy (RB-PDT) and the effect of conditioned medium (CM).

METHODS

A human corneal epithelial cell line (HCE-T), human corneal fibroblasts (HCF) and keratoconus fibroblasts (KC-HCF) have been used. Twenty-four hours after RB-PDT (0.001% RB concentration, 565 nm wavelength illumination, 0.17 J/cm2 fluence) cell migration rate using scratch assay and growth factor concentrations in the cell culture supernatant using ELISA have been determined. In addition, the effect of CM has been observed.

RESULTS

RB-PDT significantly reduced migration rate in all cell types, compared to controls (p≤0.02). Migration rate of HCE-T cultures without RB-PDT (untreated) was significantly higher using HCF CM after RB-PDT, than using HCF CM without RB-PDT (p<0.01). Similarly, untreated HCF displayed a significantly increased migration rate with HCE-T CM after RB-PDT, compared to HCE-T CM without treatment (p<0.01). Furthermore, illumination alone and RB-PDT significantly decreased keratinocyte growth factor (KGF) concentration in HCF and KC-HCF supernatant, and RB-PDT significantly decreased soluble N-Cadherin (SN-Cad) concentration in HCF supernatant, compared to controls (p<0.01 for all). In HCE-T CM, RB-PDT increased hepatocyte growth factor (HGF) and basic fibroblast growth factor (FGFb) concentration (p≤0.02), while decreasing transforming growth factor β (TGF-β) concentration (p<0.01). FGFb concentration increased (p<0.0001) and TGF-β concentration decreased (p<0.0001) in HCF CM, by RB-PDT. Epidermal growth factor (EGF), HGF, and TGF-β concentration decreased (p≤0.03) and FGFb concentration increased (p<0.01) in KC-HCF CM, using RB-PDT.

CONCLUSIONS

HCE-T, HCF and KC-HCF migration rate is reduced 24 hours after RB-PDT. In contrast, HCE-T migration is enhanced using HCF CM after RB-PDT, and HCF migration rate is increased through HCE-T CM following RB-PDT. Modulation of EGF, KGF, HGF, FGFb, TGF-β and N-Cadherin secretion through RB-PDT may play an important role in corneal wound healing.

Photoactivated chromophore-corneal cross-linking accelerates corneal healing in fungal keratitis: an updated meta-analysis

AIM

To determine the effectiveness and safety of photoactivated chromophore-corneal cross-linking (PACK-CXL) adjuvant in infectious keratitis by April 5, 2022.

METHODS

We searched randomized controlled trials (RCTs) comparing standard antibiotic treatment (SAT) plus PACK-CXL to SAT in infectious keratitis in Embase, MEDLINE with PubMed, Web of Science, and Cochrane Library. We independently screened and extracted data using predesigned tables. Cochrane's risk-of-bias tool was utilized to examine the quality of RCTs. A random-effects model was employed to determine the overall effect size of the meta-analyses. Grading of Recommendations, and Assessment, Development and Evaluations (GRADE) was also performed to examine the quality of evidence.

RESULTS

Seven eligible RCTs with 283 patients were acquired. Adjuvant PACK-CXL reduced the time needed to perform corneal healing in fungal keratitis (- 1.33 months; 95% CI, - 1.83 to - 0.42, I2 = 0%, P < 0.05) as compared to SAT alone. The risks of adverse events were not significantly different both in fungal and bacterial keratitis. Due to the substantial heterogeneity among studies, such as population, the type and severity of infectious keratitis, drug regimens of SAT, PACK-CXL protocol, and the judgment of subjective outcomes, the evidence grade was low.

CONCLUSION

Adjuvant PACK-CXL accelerates fungal keratitis healing as compared to SAT alone. But more rigorous RCTs are required to determine the clinical effectiveness and safety.

High-Fluence Accelerated PACK-CXL for Bacterial Keratitis Using Riboflavin/UV-A or Rose Bengal/Green in the Ex Vivo Porcine Cornea

Purpose

To investigate and compare the efficacy of high-fluence accelerated photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) using either riboflavin/ultraviolet (UV)-A light or rose bengal/green light to treat Staphylococcus aureus or Pseudomonas aeruginosa infections in an ex vivo porcine cornea model.

Methods

One hundred and seventeen ex vivo porcine corneas were injected with clinical isolates of S. aureus or P. aeruginosa, divided into eight groups, and cultured for 24 hours. Then, either riboflavin with UV-A light irradiation (30 mW/cm2; 8 minutes, 20 seconds; 15 J/cm2) or rose bengal with green light irradiation (15 mW/cm2, 16 minutes, 40 seconds; 15 J/cm2) was applied; unirradiated infected groups served as controls. All corneas were incubated for another 24 hours. Next, corneal buttons were obtained and vortexed to release the bacterial cells. The irradiated and unirradiated solutions were then plated and incubated on agar plates. The amount of colony-forming units was quantified and the bacterial killing ratios (BKRs) resulting from different PACK-CXL protocols relative to non-treated controls were calculated.

Results

Riboflavin/UV-A light PACK-CXL resulted in median BKRs of 52.8% and 45.8% in S. aureus and P. aeruginosa, respectively, whereas rose bengal/green light PACK-CXL resulted in significantly greater BKRs of 76.7% and 81.0%, respectively (both P < 0.01).

Conclusions

Both accelerated PACK-CXL protocols significantly decreased S. aureus and P. aeruginosa bacterial loads. Comparing the riboflavin/UV-A light and rose bengal/green light PACK-CXL approaches in the same experimental setup may help develop strain-specific and depth-dependent PACK-CXL approaches that could be used alongside the current standard of care.

Translational Relevance

Our study used an animal model to gain insight into the efficacy of high-fluence accelerated PACK-CXL using either riboflavin/UV-A light or rose bengal/green light to treat Staphylococcus aureus or Pseudomonas aeruginosa infections.

Use of corneal cross-linking beyond keratoconus: a systemic literature review

PURPOSE

The success of corneal collagen cross-linking in altering keratoconus' clinical course has driven a search for further uses of this procedure. This literature review aims to analyze the scientific evidence available for the benefit of cross-linking in the management of ophthalmic diseases other than progressive keratoconus or ectasia induced by corneal refractive procedures.

METHODS

A systemic literature review.

RESULTS

We reviewed 97 studies. We found that collagen cross-linking can limit the progression of several other corneal ectasias, thus reducing and limiting the need for keratoplasty. Collagen cross-linking also can reduce the refractive power of the cornea and can be considered for a moderate degree of bacterial keratitis or when the organism is unidentified, which is refractive to antibiotics alone. However, the comparative rarity of these procedures has limited the extent of evidence. In fungal, Acanthamoeba, and herpes virus keratitis, the evidence is inconclusive of the safety and efficacy of cross-linking.

CONCLUSION

Current clinical data is limited, and laboratory data has not fully correlated with published clinical data.

The novel role of lymphatic vessels in the pathogenesis of ocular diseases

Historically, the eye has been considered as an organ free of lymphatic vessels. In recent years, however, it became evident, that lymphatic vessels or lymphatic-like vessels contribute to several ocular pathologies at various peri- and intraocular locations. The aim of this review is to outline the pathogenetic role of ocular lymphatics, the respective molecular mechanisms and to discuss current and future therapeutic options based thereon. We will give an overview on the vascular anatomy of the healthy ocular surface and the molecular mechanisms contributing to corneal (lymph)angiogenic privilege. In addition, we present (i) current insights into the cellular and molecular mechanisms occurring during pathological neovascularization of the cornea triggered e.g. by inflammation or trauma, (ii) the role of lymphatic vessels in different ocular surface pathologies such as dry eye disease, corneal graft rejection, ocular graft versus host disease, allergy, and pterygium, (iii) the involvement of lymphatic vessels in ocular tumors and metastasis, and (iv) the novel role of the lymphatic-like structure of Schlemm's canal in glaucoma. Identification of the underlying molecular mechanisms and of novel modulators of lymphangiogenesis will contribute to the development of new therapeutic targets for the treatment of ocular diseases associated with pathological lymphangiogenesis in the future. The preclinical data presented here outline novel therapeutic concepts for promoting transplant survival, inhibiting metastasis of ocular tumors, reducing inflammation of the ocular surface, and treating glaucoma. Initial data from clinical trials suggest first success of novel treatment strategies to promote transplant survival based on pretransplant corneal lymphangioregression.

Therapeutic non-ectasia applications of cornea cross-linking

Corneal cross-linking is a photopolymerization technique traditionally used to strengthen corneal tissue. Corneal cross-linking utilizes riboflavin (vitamin B2) as a photosensitizer and ultraviolet-A light (UVA) to create strong covalent bonds within the corneal stroma, increasing tissue stiffness. Multiple studies have demonstrated corneal cross-linking's effectiveness in treating corneal ectasia, a progressive, degenerative, and non-inflammatory thinning disorder, as quantified by key tomographic, refractive, and visual parameters. Since its introduction two decades ago, corneal cross-linking has surpassed its original application in halting corneal ectatic disease and its application has expanded into several other areas. Corneal cross-linking also possesses antibacterial, antienzymolytic and antioedematous properties, and has since become a tool in treating microbial keratitis, correcting refractive error, preventing iatrogenic ectasia, stabilising bullous keratopathy and controlling post keratoplasty ametropia. This review provides an overview of the current evidence base for the therapeutic non-ectasia applications of cornea cross-linking and looks at future developments in the field.

Surgical management of infectious keratitis

The successful management of infectious keratitis is usually achieved with a combination of tools for accurate diagnosis and targeted timely antimicrobial therapy. An armamentarium of surgical interventions is available in the acute stage which can be resorted to in a step wise manner or in combination guided by the response to treatment. Simple surgical modalities can facilitate accurate diagnosis e.g. corneal biopsy and alcohol delamination. Surgery to promote epithelial healing can vary from tarsorrhaphy, amniotic membrane transplantation or conjunctival flaps depending on the extent of infection, visual prognosis, availability of tissue and surgeon's experience. Collagen crosslinking has been increasingly utilized with successful results to strengthen the cornea and reduce the infective load consequently the need for further elaborate surgical interventions. It has shown encouraging results specially in superficial bacterial and fungal keratitis but for deeper infections, viral and acanthamoeba keratitis, its use remains questionable. When globe integrity is compromised, corneal gluing is the most commonly used procedure to seal small perforations. In larger perforations/fulminant infections a tectonic/therapeutic graft is advisable. Partial thickness grafts are increasingly popular to treat superficial infection or internally tamponade perforations. Peripheral therapeutic grafts face challenges with potential requirement for a manually fashioned graft, and increased risk of rejection due to proximity to the limbal vessels. Late stage visual rehabilitation is likely to require further surgical interventions after complete resolution of infection and inflammation. A preliminary assessment of corneal sensation and integrity of the ocular surface are key for any successful surgical intervention to restore vision.

Urgent unmet needs in the care of bacterial keratitis: An evidence-based synthesis

Bacterial corneal infections, or bacterial keratitis (BK), are ophthalmic emergencies that frequently lead to irreversible visual impairment. Though increasingly recognized as a major cause of global blindness, modern paradigms of evidence-based care in BK have remained at a diagnostic and therapeutic impasse for over half a century. Current standards of management - based on the collection of corneal cultures and the application of broad-spectrum topical antibiotics - are beset by important yet widely underrecognized limitations, including approximately 30% of all patients who will develop moderate to severe vision loss in the affected eye. Though recent advances have involved a more clearly defined role for adjunctive topical corticosteroids, and novel therapies such as corneal crosslinking, overall progress to improve patient and population-based outcomes remains incommensurate to the chronic morbidity caused by this disease. Recognizing that the care of BK is guided by the clinical axiom, "time equals vision", this chapter offers an evidence-based synthesis for the clinical management of these infections, underscoring critical unmet needs in disease prevention, diagnosis, and treatment.

Photoactivated Chromophore Corneal Collagen Cross-Linking for Infectious Keratitis (PACK-CXL)-A Comprehensive Review of Diagnostic and Prognostic Factors Involved in Therapeutic Indications and Contraindications

Infectious keratitis is a severe infection of the eye, which requires urgent care in order to prevent permanent complications. Typical cases are usually diagnosed clinically, whereas severe cases also require additional tools, such as direct microscopy, corneal cultures, molecular techniques, or ophthalmic imaging. The initial treatment is empirical, based on the suspected etiology, and is later adjusted as needed. It ranges from topical administration of active substances to oral drugs, or to complex surgeries in advanced situations. A novel alternative is represented by Photoactivated Chromophore Corneal Collagen Cross-Linking (PACK-CXL), which is widely known as a minimally invasive therapy for corneal degenerations. The purpose of this review is to identify the main diagnostic and prognostic factors which further outline the indications and contraindications of PACK-CXL in infectious keratitis. Given the predominantly positive outcomes in the medical literature, we ponder whether this is a promising treatment modality, which should be further evaluated in a systematic, evidence-based manner in order to develop a clear treatment protocol for successful future results, especially in carefully selected cases.

Photo-oxidative stress response and virulence traits are co-regulated in E. faecalis after antimicrobial photodynamic therapy

Knowledge of photo-oxidative stress responses in bacteria that survive antimicrobial photodynamic therapy (aPDT) is scarce. Whereas aPDT is attracting growing clinical interest, subsequent stress responses are crucial to evaluate as they may lead to the up-regulation of pathogenic traits. Here, we aimed to assess transcriptional responses to sublethal aPDT-stress and identify potential connections with virulence-related genes. Six Enterococcus faecalis strains were investigated; ATCC 29212, three dental root-canal isolates labelled UmID1, UmID2 and UmID3 and two vancomycin-resistant isolates labelled A1 and A2. TMPyP was employed as a photosensitiser. A viability dose-response curve to increasing concentrations of TMPyP was determined by culture plating. Differential expression of genes involved in oxidative stress responses (dps and hypR), general stress responses (dnaK, sigma-factor^V and relA), virulence-related genes (ace, fsrC and gelE) and vancomycin-resistance (vanA) was assessed by reverse-transcription qPCR. TMPyP-mediated aPDT inactivated all strains with comparable efficiencies. TMPyP at 0.015 μM was selected to induce sublethal photo-oxidative stress. Despite heterogeneities in gene expression between strains, transcriptional profiles revealed up-regulations of transcripts dps, hypR as well as dnaK and sigma factor^V after exposure to TMPyP alone and to light-irradiated TMPyP. Specifically, the alternative sigma factor^V reached up to 39 ± 113-fold (median ± IQR) (p = 0.0369) in strain A2. Up-regulation of the quorum sensing operon, fsr, and its downstream virulence-related gelatinase gelE were also observed in strains ATCC-29212, A1, A2 and UmID3. Finally, photo-oxidative stress induced vanA-type vancomycin-resistance gene in both carrier isolates, reaching up to 3.3 ± 17-fold in strain A2 (p = 0.015). These findings indicate that, while aPDT successfully inactivates vancomycin-resistant and naïve strains of E. faecalis, subpopulations of surviving cells respond by co-ordinately up-regulating a network of genes involved in stress survival and virulence. This includes the induction of vancomycin-resistance genes in carrier isolates. These data may provide the mechanistic basis to circumvent bacterial responses and improve future clinical protocols.

The bactericidal effect of two photoactivated chromophore for keratitis-corneal crosslinking protocols (standard vs. accelerated) on bacterial isolates associated with infectious keratitis in companion animals

Background

Bacterial corneal infections are common and potentially blinding diseases in all species. As antibiotic resistance is a growing concern, alternative treatment methods are an important focus of research. Photoactivated chromophore for keratitis-corneal crosslinking (PACK-CXL) is a promising oxygen radical-mediated alternative to antibiotic treatment. The main goal of this study was to assess the anti-bactericidal efficacy on clinical bacterial isolates of the current standard and an accelerated PACK-CXL treatment protocol delivering the same energy dose (5.4 J/cm²).

Methods

Clinical bacterial isolates from 11 dogs, five horses, one cat and one guinea pig were cultured, brought into suspension with 0.1% riboflavin and subsequently irradiated. Irradiation was performed with a 365 nm UVA light source for 30 min at 3mW/cm² (standard protocol) or for 5 min at 18mW/cm² (accelerated protocol), respectively. After treatment, the samples were cultured and colony forming units (CFU’s) were counted and the weighted average mean of CFU’s per μl was calculated. Results were statistically compared between treated and control samples using a linear mixed effects model.

Results

Both PACK-CXL protocols demonstrated a significant bactericidal effect on all tested isolates when compared to untreated controls. No efficacy difference between the two PACK-CXL protocols was observed.

Conclusion

The accelerated PACK-CXL protocol can be recommended for empirical use in the treatment of bacterial corneal infections in veterinary patients while awaiting culture results. This will facilitate immediate treatment, the delivery of higher fluence PACK-CXL treatment within a reasonable time, and minimize the required anesthetic time or even obviate the need for general anesthesia.

Rose Bengal Photodynamic Antimicrobial Therapy: A review of the intermediate term clinical and surgical outcomes

PURPOSE

To evaluate the intermediate term clinical outcomes of Rose Bengal Photodynamic Antimicrobial Therapy (RB-PDAT) for infectious keratitis. Secondarily, to evaluate the surgical outcomes of individuals that underwent optical keratoplasty after RB-PDAT.

DESIGN

Retrospective cohort study.

METHODS

Retrospective chart review of 31 eyes from 30 consecutive individuals with infectious keratitis refractory to standard medical therapy who underwent RB-PDAT at the Bascom Palmer Eye Institute between January 2016 and July 2020. Data collected included demographics, risk factors for infectious keratitis, microbiological diagnosis, Best Spectacle-Corrected Visual Acuity (BCVA), clinical outcomes after RB-PDAT and complication rates post-keratoplasty. RB-PDAT was performed as described in previous studies. Graft survival was evaluated using Kaplan Meier curves with log-ranks in individuals that underwent keratoplasty after RB-PDAT.

RESULTS

Mean age of the study population was 53±18.0 years. 70% were female; 53.3% self-identified as non-Hispanic White; 43.3% as Hispanic. Mean follow-up time was 28.0±14.4 months. Risk factors included contact lens use (80.6%), history of infectious keratitis (19.3%), and ocular surface disease (16.1%). Cultures were positive for Acanthamoeba (51.6%), Fusarium (12.9%), and Pseudomonas (6.5%). 22.5% of individuals with Acanthamoeba infection were treated with concomitant Miltefosine. Clinical resolution was achieved in 77.4% of individuals on average 2.72±1.85 months after RB-PDAT with 22.5% requiring therapeutic penetrating keratoplasties and 54.8% subsequently requiring optical penetrating keratoplasties. At 2 years, the overall probability of graft survival was 78.7% and the graft failure rate was 21.3%.

CONCLUSION

RB-PDAT is a potential adjunct therapy for infectious keratitis that may reduce the need for a therapeutic penetrating keratoplasty. Cases that undergo keratoplasty after RB-PDAT may have a higher probability of graft survival at one year postoperatively.

Review of the literature on the currently available evidence for the management of infectious keratitis with PACK-CXL

Infectious keratitis (IK) is one of the most common causes of monocular blindness worldwide, especially in developing countries and may account for 5.1%-32.3% of all indications for penetrating keratoplasty (PK). However, performing a therapeutic PK on a "hot eye" is associated with a higher incidence of IK recurrence and graft rejection. Standard treatment includes antimicrobials (ATM) and, once the causative pathogen has been identified, must be continued with targeted treatment, depending on antibiogram sensitivity. However, appearance of multiresistant strains to ATM is progressively increasing at an alarming rate. Besides that, the diversity of the causative microorganisms (bacteria, fungi, parasites, viruses) may hinder the clinical diagnosis and secondarily the proper treatment from the beginning. It is estimated that only 50% of eyes will have a good visual result if the correct therapy is delayed. All these factors make the identification of alternatives to ATM treatment of paramount importance. Due to the ATM properties of photoactivated chromophore (riboflavin, RB) and ultraviolet (UV) light of wavelength (λ) 200-400 nanometers (nm), used in multiple medical and non-medical applications for disinfection, photoactivated chromophore for corneal cross-linking (CXL) of IK (PACK-CXL), as an addition to the therapeutic arsenal for the management of IK has been proposed. It must be differentiated from CXL used for the management of progressive keratoconus (KC). The objective of this review is to update the available evidence on the efficacy and safety of PACK-CXL in IKs.

Comparison of Corneal Collagen Cross-Linking and Voriconazole Treatments in Experimental Fungal Keratitis for Aspergillus fumigatus

Aims

To compare the antifungal efficacy of corneal cross-linking (CXL) and voriconazole in experimental Aspergillus keratitis models.

Methods

Thirty-nine New Zealand rabbits were divided into three groups: a control group, a voriconazole group (M group), and a voriconazole combined with CXL group (CXL-M group). The ulcer area was measured via slit lamp imaging, the corneal and corneal epithelial thickness, and ulcer depth was measured via anterior segment optical coherence tomography (AS-OCT). The existence time of the hyphae was observed via in vivo confocal microscopy (IVCM), and the cornea was taken for pathological examination after modeling and at the end of the study to determine the hyphae and corneal repair. The observation times were as follows: at successful modeling and at 1, 4, 7, 14, 21, and 28 days after intervention.

Results

In the CXL-M group, ulcer area and depth decreased continuously from Day 4 to Day 28 after CXL (all P &lt; 0.05). In the CXL-M group, ulcer area and depth were smaller than those in the other two groups from Day 4 to Day 21 after CXL (all P &lt; 0.05, except ulcer area in the CXL-M vs. M group on Day 21). The duration of hyphae in the CXL-M group was significantly shorter than in the other two groups (P = 0.025). On Day 28, in CXL-M group, corneal thickness was thicker than baseline (P &lt; 0.05). Meanwhile, in CXL-M group, corneal and corneal epithelial thickness were significantly thinner than in the other two groups (P &lt; 0.001). The CXL-M group had no complications, such as corneal perforation, at the end of the study.

Conclusions

Voriconazole combined with CXL is effective in treating Aspergillus-infected keratitis. Combined therapy could effectively inhibit Aspergillus, accelerate corneal repair, and shorten the course of the disease.

Corneal Collagen Cross-Linking Inhibits Corneal Blood and Lymphatic Vessels Temporarily in Alkali-Burned Rabbits

PURPOSE

This study aimed to explore whether corneal cross-linking (CXL) could regress corneal blood vessels (CBV) and corneal lymphatic vessels (CLV) in alkali-burned rabbits.

METHODS

A total of 80 rabbits 2-3 months old weighing 1.5-2.0 kg were randomly divided into four groups: CXL7 group; CTL7 group; CXL14 group; and CTL14 group. Then, 3% sodium pentobarbital 1 ml/kg and tetracaine eye drop 5 g/L were administered before surgery. NaOH 2 mol/L was topically applied to the central cornea to establish the alkali burning model. Then CXL was administered within 2 h in groups CXL7 and CXL14. Corneal opacity and edema, CBV and CLV volume, cluster differentiation 31 (CD31), and lymphatic vessel endothelial receptor 1 (LYVE-1) expression levels were analyzed on days 7 and 14.

RESULTS

CXL reduced cornea opacity, CNV, and CLV volumes on day 7 in alkali-burned rabbits. However, CNV and CLV volumes were increased on day 14. CXL also showed down- and upregulation of CD31 and LYVE-1 expression levels on days 7 and 14, respectively.

CONCLUSIONS

CXL effectively regulated CBV and CLV in alkali-burned rabbits. The transient angioregression and lymphangioregression induced by CXL may be potentially helpful in vascularized high-risk eyes.

Is Corneal Collagen Cross-Linking Beneficial as an Adjunct to the Conventional Treatment of Bacterial Keratitis?

Background:

To evaluate the therapeutic effects of corneal collagen cross-linking CXL as an adjuvant to standard antimicrobial agents in the treatment of bacterial keratitis when compared to treatment with antimicrobial agents alone.

Methods:

This prospective comparative interventional study included 20 eyes of 20 patients with clinical and laboratory evidence of bacterial keratitis who attended the Outpatient Cornea Unit, Ophthalmology Department, Faculty of Medicine in Assiut University Hospital, Assiut, between January 2019 and December 2020.Patients were divided into two groups: group A, treated with CXL using the Dresden Protocol at the EL-Nour Eye Centre, and group B treated with antibiotics alone.

Results:

Group A had ten patients in the age range of 20-80 years (mean age 49.2 years), while that of group B (ten patients) was 19 -70 years (mean age 47.3 years).

The ulcer sizes started to decrease significantly from week 2 in group A to week 3 in group B. The epithelization time was significantly different between the two treatment groups as reepithelization in 60% of group A cases started at week two, while it began at week three in group B. There was no significant difference in the V/A between the two groups after treatment.

Conclusion:

CXL as an adjunct to topical antimicrobial treatment was more effective in treating bacterial keratitis than conventional antimicrobial therapy alone, as it led to shorter recovery times due to more rapid ulcer healing, resolution of infiltration, and faster symptomatic relief in patients. Despite CXL promoted the ulcer to heal quickly, there was no significant change in V/A before and after CXL or between the CXL with antimicrobial or antimicrobial therapy alone .

Clinical outcomes of Rose Bengal mediated Photodynamic Antimicrobial Therapy on Fungal Keratitis with their microbiological and pathological correlation

PURPOSE

To report the clinical outcome of Photodynamic Antimicrobial Therapy (PDAT) with Rose Bengal (RB) used as an early adjuvant therapy in patients with fungal keratitis and their microbiological and pathological correlation.

METHODS

Patients with microbiologically confirmed fungal keratitis underwent PDAT-RB along with topical natamycin 5% drops hourly and oral ketoconazole 200 mg twice a day. This was performed by applying rose bengal (0.1%) to the de-epithelialized cornea for 30 minutes, followed by irradiation with a 6 mW/cm² custom-made green LED source for 15 minutes (5.4 J/cm²). The corresponding fungal isolates were tested in vitro using PDAT-RB and corneal buttons were evaluated for correlation.

RESULTS

Following informed consent, seven patients (male-5, female-2, mean age 47.7 years) with fungal keratitis were recruited. There were 3 cases each of Fusarium and Aspergillus flavus and 1 case of Acremonium sp. The average vertical and horizontal diameters of the corneal infiltrate were 4.12+/- 0.55 and 3.99+/- 1.19 mm, respectively. The average depth of corneal involvement was 283 +/- 75.27μ as measured by anterior segment OCT. Clinical resolution was achieved in the cases with Fusarium keratitis with an average time of 39 days. Three cases of A. flavus and a single patient with Acremonium keratitis worsened and needed therapeutic keratoplasty (TPK) for resolution. Post-TPK, the corneal tissues grew Aspergillus flavus in one out of three cases and Acremonium sp. in one case. In vitro PDAT-RB experiment was performed on the corresponding fungal isolates grown from the corneal scraping. PDAT-RB produced clear inhibition of Fusarium and Acremonium sp. with no effect on the growth of A. flavus. Histopathologically, 2 out of 4 (50%) corneal buttons showed fungal filaments.

CONCLUSION

While the in vitro and in vivo results of PDAT-RB matched for Fusarium species and Aspergillus flavus keratitis being favourable in the former and non-favourable in the latter, these results were discrepant in Acremonium sp.

PACK-CXL vs. antimicrobial therapy for bacterial, fungal, and mixed infectious keratitis: a prospective randomized phase 3 trial

BACKGROUND

Infectious keratitis is a major cause of global blindness. We tested whether standalone photoactivated chromophore corneal cross-linking (PACK-CXL) may be an effective first-line treatment in early to moderate infectious keratitis, compared with standard antimicrobial treatment.

METHODS

This is a randomized, controlled, multinational phase 3 clinical trial. Participants in five centers in Egypt, India, Iran, Israel, and China, aged ≥ 18 years, with infectious keratitis of presumed bacterial, fungal, or mixed origin, were randomly assigned (1:1) to PACK-CXL, or antimicrobial therapy. Outcomes measures included healing, defined as time to re-epithelialization of the corneal epithelial defect in the absence of inflammatory activity in the anterior chamber and clearance of stromal infiltrates. Treatment success was defined as the complete resolution of signs of infection.

RESULTS

Between July 21, 2016, and March 4, 2020, participants were randomly assigned to receive PACK-CXL (n = 18) or antimicrobial therapy per American Academy of Ophthalmology (AAO) guidelines (n = 21). No participants were lost to follow-up. Four eyes were excluded from the epithelialization time analysis due to treatment failure: two in the antimicrobial therapy group, and two in the PACK-CXL group. Success rates were 88.9% (16/18 patients) in the PACK-CXL group and 90.5% (19/21 patients) in the medication group. There was no significant difference in time to complete corneal re-epithelialization (P = 0.828) between both treatment groups.

CONCLUSIONS

PACK-CXL may be an alternative to antimicrobial drugs for first-line and standalone treatment of early to moderate infectious keratitis of bacterial or fungal origin. Trial registration This trial is registered at ClinicalTrials.gov, trial registration number: NCT02717871.

Bacterial keratitis: identifying the areas of clinical uncertainty

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

Double-masked, sham and placebo-controlled trial of corneal cross-linking and topical difluprednate in the treatment of bacterial keratitis: Steroids and Cross-linking for Ulcer Treatment Trial (SCUT II) study protocol

INTRODUCTION

Although antibiotics are successful at achieving microbiological cure in infectious keratitis, outcomes are often poor due to corneal scarring. Ideal treatment of corneal ulcers would address both the infection and the inflammation. Adjunctive topical steroid treatment may improve outcomes by reducing inflammation. Corneal cross-linking (CXL) is a novel prospective therapy that may simultaneously reduce both inflammatory cells and bacterial pathogens. The purpose of this study is to determine differences in 6-month visual acuity between standard medical therapy with antibiotics versus antibiotics with adjunctive early topical steroid therapy versus antibiotic treatment plus CXL and early topical steroids.

METHODS AND ANALYSIS

This international, randomised, sham and placebo-controlled, three-arm clinical trial randomises patients with smear positive bacterial ulcers in a 1:1:1 fashion to one of three treatment arms: (1) topical 0.5% moxifloxacin plus topical placebo plus sham CXL; (2) topical 0.5% moxifloxacin plus difluprednate 0.05% plus sham CXL; or (3) the CXL group: topical 0.5% moxifloxacin plus difluprednate 0.05% plus CXL.

ETHICS AND DISSEMINATION

We anticipate that both adjunctive topical steroids and CXL will improved best spectacle corrected visual acuity and also reduce complications such as corneal perforation and the need for therapeutic penetrating keratoplasty. This study will comply with the NIH Data Sharing Policy and Policy on the Dissemination of NIH-Funded Clinical Trial Information and the Clinical Trials Registration and Results Information Submission rule. Our results will be disseminated via ClinicalTrials.gov website, meetings and journal publications. Our data will also be available on reasonable request.

TRIAL REGISTRATION NUMBER

NCT04097730.

Recent Advances in Photodynamic Therapy against Fungal Keratitis

Fungal keratitis is a serious clinical infection on the cornea caused by fungi and is one of the leading causes of blindness in Asian countries. The treatment options are currently limited to a few antifungal agents. With the increasing incidence of drug-resistant infections, many patients fail to respond to antibiotics. Riboflavin-mediated corneal crosslinking (similar to photodynamic therapy (PDT)) for corneal ectasia was approved in the US in the early 2000s. Current evidence suggests that PDT could have the potential to inhibit fungal biofilm formation and overcome drug resistance by using riboflavin and rose bengal as photosensitizers. However, only a few clinical trials have been initiated in anti-fungal keratitis PDT treatment. Moreover, the removal of the corneal epithelium and repeated application of riboflavin and rose bengal are required to improve drug penetration before and during PDT. Thus, an improvement in trans-corneal drug delivery is mandatory for a successful and efficient treatment. In this article, we review the studies published to date using PDT against fungal keratitis and aim to enhance the understanding and awareness of this research area. The potential of modifying photosensitizers using nanotechnology to improve the efficacy of PDT on fungal keratitis is also briefly reviewed.

Fusarium Keratitis-Review of Current Treatment Possibilities

In many parts of the world, fungi are the predominant cause of infectious keratitis; among which, Fusarium is the most commonly isolated pathogen. The clinical management of this ophthalmic emergency is challenging. Due to the retardation of the first symptoms from an injury and the inability to differentiate fungal from bacterial infections based on clinical symptoms and difficult microbial diagnostics, proper treatment, in many cases, is postponed. Moreover, therapeutical options of Fusarium keratitis remain limited. This paper summarizes the available treatment modalities of Fusarium keratitis, including antifungals and their routes of administration, antiseptics, and surgical interventions.

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

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

Photodynamic Therapy for Infectious Keratitis

Infectious keratitis is a sight-threatening microbial infection. The prevalence of antimicrobial resistance in cases of infectious keratitis has increased the demand for fortified compounded antimicrobial drops. Even with proper medical management, severe cases of infectious keratitis can further evolve into corneal perforation, requiring surgical intervention in the form of keratoplasty to control the infectious process. Due to the invasive nature of the procedure and the shortage of available donor tissue around the world, alternative treatments are needed for the management of progressive infectious keratitis. In ophthalmology, photodynamic therapy (PDT) has been used for numerous applications. PDT with Rose Bengal as a photosensitizer combined with green light optical irradiation (RB-PDAT) is a novel treatment with dual purpose: to arrest the infection from progressing and strengthen the collagen of the cornea. RB-PDAT may be considered as an adjunct therapy in severe cases of infectious keratitis to minimize the need for a therapeutic keratoplasty.

The promise of endogenous and exogenous riboflavin in anti-infection

To resolve the growing problem of drug resistance in the treatment of bacterial and fungal pathogens, specific cellular targets and pathways can be used as targets for new antimicrobial agents. Endogenous riboflavin biosynthesis is a conserved pathway that exists in most bacteria and fungi. In this review, the roles of endogenous and exogenous riboflavin in infectious disease as well as several antibacterial agents, which act as analogues of the riboflavin biosynthesis pathway, are summarized. In addition, the effects of exogenous riboflavin on immune cells, cytokines, and heat shock proteins are described. Moreover, the immune response of endogenous riboflavin metabolites in infectious diseases, recognized by MHC-related protein-1, and then presented to mucosal associated invariant T cells, is highlighted. This information will provide a strategy to identify novel drug targets as well as highlight the possible clinical use of riboflavin.

Can microorganisms develop resistance against light based anti-infective agents?

Recently, there have been increasing numbers of publications illustrating the potential of light-based antimicrobial therapies to combat antimicrobial resistance. Several modalities, in particular, which have proven antimicrobial efficacy against a wide range of pathogenic microbes include: photodynamic therapy (PDT), ultraviolet light (UVA, UVB and UVC), and antimicrobial blue light (aBL). Using these techniques, microbial cells can be inactivated rapidly, either by inducing reactive oxygen species that are deleterious to the microbial cells (PDT, aBL and UVA) or by causing irreversible DNA damage via direct absorption (UVB and UVC). Given the multi-targeted nature of light-based antimicrobial modalities, it has been hypothesised that resistance development to these approaches is highly unlikely. Furthermore, with the exception of a small number of studies, it has been found that resistance to light based anti-infective agents appears unlikely, irrespective of the modality in question. The concurrent literature however stipulates, that further studies should incorporate standardised microbial tolerance assessments for light-based therapies to better assess the reproducibility of these observations.

Adjunctive Green Thermal Laser Photocoagulation for Treatment of Resistant Infectious Keratitis

Purpose

To investigate the safety and efficacy of green thermal laser as an adjunctive therapy for the treatment of resistant infectious keratitis (IK) in the Delta region of Egypt.

Methods

A retrospective case series of 150 patients, within a 4 year duration, with resistant IK, who failed to respond to specific medical treatment alone for 7 days, were included. They all received green thermal laser photocoagulation treatment to the cornea as an adjunctive to medical treatment.

Results

Forty-eight women and 102 men were included in this study with a mean age of 46.2 ± 7.7 years. Common risk factors associated with IK included trauma by material of plant origin and contact lens wear. The mean duration of healing was 2.87 ± 0.7 weeks. A single session of green thermal laser application was adequate in 138 IK cases (92%), while 12 cases (8%) required an additional session a week later. Supplementary amniotic membrane transplantation (AMT) was required in 26 cases (17.3%). Two patients (1.3%) required tectonic keratoplasty for corneal perforation. The final corrected distance visual acuity (CDVA) was counting fingers (CF) or better in 78 patients (52%). No decrease of CDVA was reported throughout the study.

Conclusion

Green thermal laser is a safe and effective adjunctive therapy for the treatment of resistant infectious keratitis.

Molecular characteristics of the photosensitizer TONS504: Comparison of its singlet oxygen quantum yields and photodynamic antimicrobial effect with those of methylene blue

TONS504 (C51H58O5I2) is a chlorin derivative that exhibits a photodynamic antimicrobial effect (PAE) on various infectious keratitis pathogens. However, the molecular characteristics of TONS504 are not well understood. This study aimed to investigate the molecular characteristics of TONS504 by comparing its singlet oxygen (¹O₂) quantum yields and PAE with those of methylene blue (MB). To measure the ¹O₂ quantum yields, TONS504 and MB were dissolved in phosphate-buffered saline and phosphate-buffered saline containing 1% Triton X-100. The solutions were then activated by a Nd:YAG laser with an average output power of 8 mW. Near-infrared ¹O₂ luminescence was detected as an indicator of the ¹O₂ quantum yields. To evaluate the PAE, TONS504 and MB were activated by a light-emitting diode with a total light energy of 30 J/cm². We compared the minimum molar concentration of each photosensitizer to show apparent PAEs on Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. TONS504 exhibited higher ¹O₂ quantum yields than MB in PBS/Triton X-100 but not in PBS. S. aureus and C. albicans were reduced by TONS504 at lower concentrations than by MB, but this was not the case for P. aeruginosa. Our results provide insight on the molecular characteristics of TONS504 and suggest that TONS504 has excellent ¹O₂ quantum yields and PAE. Compared with MB, TONS504 in PBS has stronger efficacy toward some infectious keratitis pathogens but not others.

High Fluence Increases the Antibacterial Efficacy of PACK Cross-Linking

PURPOSE

Photoactivated chromophore for keratitis cross-linking (PACK-CXL) is used as an adjunct therapy to antibiotic medication in infectious keratitis. This experimental study aimed at quantifying the PACK-CXL efficacy as a function of UV fluence using several bacterial strains and irradiated volumes.

METHODS

Six distinct bacterial strains, including standardized strains and clinically isolated strains from patients with keratitis, were analyzed. Bacterial concentrations between 10 and 10 cells/mL were used (simulating small corneal ulcers). Volumes of either 11 μL (≈285 μm stromal thickness) or 40 μL (≈1000 μm stromal thickness) were irradiated within a microtiter plate at different fluences (5.4-27 J/cm) and irradiances (3, 9 and 18 mW/cm). The ratio of bacterial killing (B†) was determined to evaluate the antimicrobial efficacy of PACK-CXL.

RESULTS

B† was similar (51 ± 11%) in bacterial concentrations between 10 and 10 per ml. In 11 μL volume, Staphylococcus aureus (SA) 8325-4 ATCC 29213, Bacillus subtilis (BS) 212901, and Pseudomonas aeruginosa (PA) 2016-866624 were most sensitive to PACK-CXL at 5.4 J/cm (on average B† = 49 ± 8%), whereas Klebsiella oxytoca (KO) 2016-86624 (B† = 25%) was least sensitive. When irradiating a larger volume, B† was on average lower in 40 μL (19 ± 18%), compared with 11 μL (45 ± 17%, P < 0.001). By contrast, applying a higher UV fluence increased B† of SA ATCC 29213, from 50% at 5.4 J/cm to 92% at 10.8 J/cm, to 100% at 16.2 J/cm and above.

CONCLUSIONS

Applying higher UV fluences substantially increases the bacterial killing rates. Safety limits for clinical application require further investigation.

Comparison of modified corneal cross-linking with intrastromal voriconazole for the treatment of fungal corneal ulcer

The present study aimed to evaluate the efficacy of modified corneal cross-linking (CXL) for the treatment of fungal corneal ulcers compared with that following intrastromal voriconazole injection. In total, 31 patients with fungal corneal ulcers treated at The General Hospital of Northern Theater Command between October 2017 and October 2019 were enrolled. Among them, 10 eyes were treated with ultraviolet A (UV-A)/riboflavin CXL (CXL group), whilst 21 eyes were treated with debridement combined with intrastromal voriconazole (stromal injection group). Preoperative microbiological examination was performed in both groups, and evaluated using Fisher's exact test. Postoperatively, infection control and total efficacy rates, localized lesion, ulcer healing rate 1 week after surgery, visual acuity and complications were evaluated using Fisher's exact test, however visual acuity was analyzed by mixed-model ANOVA. The results showed that the pre-operative species distribution between the CXL and stromal injection groups did not significantly differ. The infection control rate in the CXL group was notably higher compared with that in the stromal injection group (P=0.04). Furthermore, the total efficacy rate in the CXL group was also markedly higher compared with that in the stromal injection group, though no statistically significant differences were observed. Localized lesions were observed in nine eyes (90.0%) in the CXL group and nine eyes (42.9%) in the stromal injection group (P=0.02). However, the rate of ulcer healing at 1 week postoperatively and the logarithm of the minimum angle of resolution (logMAR) of visual acuity were not found to be significantly different between the two groups. In terms of complications, with the exception of one patient in the CXL group exhibiting loss of corneal transparency and one patient in the stromal injection group presenting with partial corneal thinning, no other forms of complications were observed. In conclusion, the present study suggested that CXL could have a beneficial impact for treating fungal corneal ulcers in the aspects of infection control, localized lesions and accelerated epithelialization. In addition, except the loss of corneal transparency, this treatment approach could be applied with reduced risks of adverse events.

Accelerated corneal collagen cross-linking in clinical management of infectious keratitis

Objective

To evaluate the clinical efficacy of corneal collagen cross-linking (CXL) in the treatment of infectious corneal diseases.

Methods

This study retrospectively analyzed the clinical efficacy of CXL in 65 eyes with infectious keratitis in Jinan Second People’s Hospital from December 2016 to June 2018. During 6 months of follow-up after CXL treatment, the results of confocal microscopy and anterior segment optical coherence tomography, as well as visual acuity and corneal biomechanical parameters, were recorded in detail.

Results

In general, the overall cure rate was 93.85%; no corneal endothelial dysfunction was encountered in any patients. After 6 months of follow-up, the visual acuity of cured patients was significantly enhanced, while corneal thickness was significantly reduced. Hyphae growth of patients with fungal keratitis was completely inhibited at 1 month postoperatively. Furthermore, corneal biomechanical parameters (i.e., central corneal thickness, deformation amplitude, and pachymetry intraocular pressure) were significantly improved after surgery, compared with baseline measurements.

Conclusion

Accelerated CXL may be an effective adjuvant treatment for infectious keratitis.

Alternative Indications for Corneal Crosslinking

ABSTRACT

Corneal crosslinking (CXL) is the current mainstay treatment for progressive keratoconus. In the past 15 years, a variety of other indications have been tested. A systematic review was conducted to examine these alternative indications for CXL. In total, of 143 papers on crosslinking as a treatment for infectious keratitis, bullous keratopathy, pellucid marginal degeneration, post- laser in situ keratomileusis (LASIK) ectasia, and as a way to improve vision either on its own or in combination with other interventions were included. Post-LASIK ectasia is a definite indication for crosslinking. Surprisingly, only limited research has been performed on pellucid marginal degeneration, with no randomized trials available to date. Other interesting applications are the combined use of refractive lasers and crosslinking for suspicious or ectatic corneas and crosslinking as a standalone intervention for minor refractive errors. CXL might offer a solution for refractory bacterial keratitis. In bullous keratopathy, it seems to offer only a transient benefit.

Infectious keratitis: an update on epidemiology, causative microorganisms, risk factors, and antimicrobial resistance

Corneal opacity is the 5th leading cause of blindness and visual impairment globally, affecting ~6 million of the world population. In addition, it is responsible for 1.5-2.0 million new cases of monocular blindness per year, highlighting an ongoing uncurbed burden on human health. Among all aetiologies such as infection, trauma, inflammation, degeneration and nutritional deficiency, infectious keratitis (IK) represents the leading cause of corneal blindness in both developed and developing countries, with an estimated incidence ranging from 2.5 to 799 per 100,000 population-year. IK can be caused by a wide range of microorganisms, including bacteria, fungi, virus, parasites and polymicrobial infection. Subject to the geographical and temporal variations, bacteria and fungi have been shown to be the most common causative microorganisms for corneal infection. Although viral and Acanthamoeba keratitis are less common, they represent important causes for corneal blindness in the developed countries. Contact lens wear, trauma, ocular surface diseases, lid diseases, and post-ocular surgery have been shown to be the major risk factors for IK. Broad-spectrum topical antimicrobial treatment is the current mainstay of treatment for IK, though its effectiveness is being challenged by the emergence of antimicrobial resistance, including multidrug resistance, in some parts of the world. In this review, we aim to provide an updated review on IK, encompassing the epidemiology, causative microorganisms, major risk factors and the impact of antimicrobial resistance.

Safety and efficacy of UV application for superficial infections in humans: A systematic review and meta-analysis

BACKGROUND

Ultraviolet (UV) light is naturally antimicrobial, but risks associated with UV overexposure have limited its clinical application. This systematic review evaluates the safety and efficacy of UV light treatment of superficial human infections.

METHODS

MEDLINE, Embase, Cochrane CENTRAL, ANZCTR and US National Library of Medicine were searched (March 25, 2020). Clinical studies applying UV light (200-400 nm) for superficial infections and non-clinical studies evaluating the antimicrobial effects of UV light on human samples were included. Randomised controlled trials (RCTs) and non- RCTs were appraised using the Cochrane risk of bias and the ROBINS-I tools, respectively.

RESULTS

Eleven RCTs, seven non-RCTs, 24 case studies, and 11 in vitro studies were included. Most clinical studies (34/42) evaluated UVA treatment for microbial keratitis (MK) using cross-linking (UVA-CXL) methods. Six clinical studies assessed UVC; one, UVB; and one, broadband UV for chronic skin infections. Pooled data analysis showed no difference in the time to wound resolution with UVA-CXL relative to standard treatment (mean difference [MD]: -18.20 [95% CI: -39.04 to 2.65] days; p = 0.09). Adverse event incidence was similar to control for UVA-CXL in MK (RR: 0.70 [95%CI: 0.32-1.79]; 5 RCTs) and UVC in skin infections (RR: 0.63 [95%CI: 0.25-1.54]; 2 RCTs).

CONCLUSION

Alone or as an adjunct to standard therapy, UV light shows promise as a safe and effective treatment for a wide range of infections. Applications of UV light as an anti-infective agent are deserving of further evaluation, especially in the context of growing antibiotic resistance.

REGISTRATION

PROSPERO registration number CRD42020176510.

Current understanding and therapeutic management of contact lens associated sterile corneal infiltrates and microbial keratitis

Contact lenses are widely prescribed in clinical practice with multiple applications and advantages. However, contact lenses can be associated with various complications which range from innocuous to severe. Clinicians thus not only need to possess the ability to prescribe the most appropriate contact lenses for each individual patient but also be able to recognise and manage any associated complications. This review examines the existing literature on the management of corneal infiltrative events associated with soft contact lenses, including microbial keratitis, particularly in the context of practising in Australia. The definitions and diagnosis of corneal infiltrative events, as well as the current understanding of their aetiologies, will be explored. The various aspects of a successful management will be discussed, including the applications of therapeutic agents such as antimicrobial and anti-inflammatory agents, the role of microbiological investigations, and strategies to improve long-term prognosis. The currently available evidence supporting management options will be presented, highlighting the relative abundance of high-level evidence on management protocols, antimicrobial selection and treatment duration for microbial keratitis; and the relative paucity of studies and trials for sterile corneal infiltrative events, despite this condition being much more commonly encountered in clinical practice.

Repeated Corneal Cross-linking (CXL) in Keratoconus Progression After Primary Treatment: Updated Perspectives

Background: Corneal collagen cross-linking (CXL) has recently become the preferred practice in the management of progressive keratoconus and other corneal ectasias as it has been proven to be successful in halting progression of the disease with an excellent safety and efficacy profile. However, there is a known variation regarding the response to CXL, depending on several parameters related either to the treatment protocol, patient characteristics, or corneal biomechanical properties. In fact, continuing progression of keratoconus has been noted in some cases despite prior treatment with CXL.Methods: The aim of this article is to provide an updated review of all published results on repeated-CXL, focusing on the indications and the efficacy of repeated treatment and highlighting possible explanations of progression after primary CXL. Conclusions: The diagnosis of primary treatment failure should always be made based on specific clinical and imaging criteria, with repeated and consistent measurements, in order to exclude pseudoprogression. In cases of confirmed progression, physicians need to decide whether repeating CXL could be an option to enhance corneal stability without any complications.

Accelerated vs. conventional collagen cross-linking for infectious keratitis

Infectious keratitis represents a serious concern for ophthalmologists, with a progressively growing incidence in the last few years. In this prospective comparative study, we evaluated two groups of patients with infectious keratitis or corneal ulcer resistant to antimicrobial and antifungal therapy, treated respectively with conventional and accelerated photoactivated chromophore collagen cross-linking. Eight patients were assigned to each group and they were monitored for 12 months. We investigated the differences between groups, comparing on one side the mean of the quantitative variables using the t-test and on the other side the frequencies of qualitative variables using the Fisher exact test. The time to healing for the group treated with conventional cross-linking was 2 days longer than for the group undergoing accelerated cross-linking (34.9±11.4 vs. 32.9±9.4 days), a difference that did not reach statistical significance (P=0.708). We conclude that the accelerated protocol is as safe and efficient as the classic procedure. The accelerated protocol has an important advantage, both for the doctor and the patient, of being time sparing (the time for accelerated cross-linking is 3 times shorter than in the case of the conventional protocol).

Accelerated Corneal Cross-linking as an Adjunct Therapy in the Management of Presumed Bacterial Keratitis: A Cohort Study

PURPOSE

To compare the outcomes of accelerated photoactivated chromophore for keratitis corneal cross-linking (PACK-CXL) as an adjunct treatment for bacterial keratitis (PACK-CXL plus standard antibiotic therapy) for patients receiving only standard antibiotic therapy.

METHODS

Retrospective cohort study of outcomes of patients with moderate infectious presumed bacterial keratitis (ulcer diameter 2 to 7 mm and stromal depth < 300 µm) were compared before and after initiation of a new treatment protocol of PACK-CXL in addition to standard antibiotic treatment.

RESULTS

A total of 70 eyes of 70 patients were included: 39 eyes in the PACK-CXL plus antibiotic (PACK-ABX) group and 31 eyes in the antibiotic only (ABX) control group. The PACK-ABX group showed shorter times to complete reepithelialization (9.3 ± 6.0 vs 16.0 ± 12.7 days, P = .01) and did not require tectonic emergency keratoplasty (0% versus 19.4%, P = .006). The PACK-ABX group also showed a higher percentage of eyes with complete reepithelialization in 6 days or less (46.2% vs 6.5%, P < .001) and a trend for shorter hospitalizations (6.3 ± 5.0 vs 8.5 ± 4.5 days, P = .06). A multivariate analysis controlling for age showed that PACK-ABX treatment remained significantly associated with early ulcer reepithelialization (odds ratio = 0.09, 95% confidence interval = 0.02 to 0.48, P = .005).

CONCLUSIONS

This study validates previous findings regarding the use of accelerated PACK-CXL in the treatment of bacterial keratitis. Adding PACK-CXL improved clinical outcomes (reducing healing time) when compared to antibiotics alone. [J Refract Surg. 2020;36(4):258-264.].

Photoactivated Chromophore for Keratitis-Corneal Collagen Cross-Linking (PACK-CXL) Improves Outcomes of Treatment-Resistant Infectious Keratitis

Purpose

To investigate the efficacy of photoactivated chromophore corneal collagen cross-linking (PACK)-CXL in the management of treatment-resistant infectious keratitis.

Design

Observational cohort study.

Participants

Forty-two eyes from 41 patients with treatment-resistant infectious keratitis.

Methods

Eyes underwent PACK-CXL treatment with the Dresden modified protocol in addition to standard antimicrobial therapy. The primary endpoint was the size of the corneal ulcer. Descriptive statistics, Wilcoxon rank test, McNemar test and Spearman correlation coefficient were used for statistical analysis, and p values lower than 0.05 were considered statistically significant.

Results

Success rate at third postoperative month was of 90.5%. Statistical analyses showed a significant effect of (PACK)‑CXL with standard antimicrobial therapy to reduce corneal ulcer size (p=0.031).

Conclusion

As adjuvant therapy to standard antimicrobial treatment, PACK-CXL improves the outcomes in patients with treatment-resistant corneal ulcers.

Tissue Inhibitor of Metalloproteinase (TIMP) Peptidomimetic as an Adjunctive Therapy for Infectious Keratitis

Matrix metalloproteinase 9 (MMP-9) has a key role in many biological processes, and while it is crucial for a normal immune response, excessive release of this enzyme can lead to severe tissue damage, as evidenced by proteolytic digestion and perforation of the cornea during infectious keratitis. Current medical management strategies for keratitis mostly focus on antibacterial effects, but largely neglect the role of excess MMP activity. Here, a cyclic tissue inhibitor of metalloproteinase (TIMP) peptidomimetic, which downregulated MMP-9 expression both at the mRNA and protein levels as well as MMP-9 activity in THP-1-derived macrophages, is reported. A similar downregulating effect could also be observed on α smooth muscle actin (α-SMA) expression in fibroblasts. Furthermore, the TIMP peptidomimetic reduced Pseudomonas aeruginosa-induced MMP-9 activity in an ex vivo porcine infectious keratitis model and histological examinations demonstrated that a decrease of corneal thickness, associated with keratitis progression, was inhibited upon peptidomimetic treatment. The presented approach to reduce MMP-9 activity thus holds great potential to decrease corneal tissue damage and improve the clinical success of current treatment strategies for infectious keratitis.

Cross-Linking Assisted Infection Reduction (CLAIR): A Randomized Clinical Trial Evaluating the Effect of Adjuvant Cross-Linking on Bacterial Keratitis

PURPOSE

To determine whether there is a benefit to adjuvant corneal cross-linking (CXL) for bacterial keratitis.

METHODS

This is an outcome-masked, randomized controlled clinical trial. Consecutive patients presenting with a smear-positive bacterial ulcer at Aravind Eye Hospitals at Madurai, Pondicherry, and Coimbatore in India were enrolled. Study eyes were randomized to topical moxifloxacin 0.5% or topical moxifloxacin 0.5% plus CXL. The primary outcome of the trial was microbiological cure at 24 hours on repeat culture. Secondary outcomes included best spectacle corrected visual acuity at 3 weeks and 3 months, percentage of study participants with epithelial healing at 3 weeks and 3 months, infiltrate and/or scar size at 3 weeks and 3 months, 3-day smear and culture, and adverse events.

RESULTS

Those randomized to CXL had 0.60 decreased odds of culture positivity at 24 hours (95% confidence interval [CI]: 0.10-3.50; P = 0.65), 0.9 logarithm of the minimum angle of resolution lines worse visual acuity (95% CI: -2.8 to 4.6; P = 0.63), and 0.41-mm larger scar size (95% CI: -0.48 to 1.30; P = 0.38) at 3 months. We note fewer corneal perforations or need for therapeutic penetrating keratoplasty in the CXL group.

CONCLUSIONS

We were unable to confirm a benefit to adjuvant CXL in the primary treatment of moderate bacterial keratitis. However, CXL may reduce culture positivity and complication rates; therefore, a larger trial to fully evaluate this is warranted.

TRIAL REGISTRATION

NCT02570321.

Surgical alternatives to keratoplasty in microbial keratitis

Penetrating keratoplasty is often required in microbial keratitis not responding to the standard treatments available or the development of complications like corneal perforation. Performing keratoplasty in microbial keratitis has several challenges, the major ones being the availability of donor corneal tissue and the poor success of the corneal graft performed in such a setting. For overcoming these challenges, several alternatives to keratoplasty have been described. Broadly, these options could be categorized into autologous tissues such as conjunctival and tenon tissue, synthetic products like tissue adhesives and therapeutic contact lenses, or biological tissues like amniotic membrane graft. These alternative modalities are not universal. They have their specific indications in microbial keratitis. Most of these alternatives are useful only for small corneal perforations. While autologous tissues are cost-effective and readily available, lack of tectonic support is a significant limitation. Tissue adhesives are excellent alternatives in terms of tectonic support, but surface irregularity and tissue reaction are their potential limitations. The amniotic membrane is useful for small corneal perforations, but availability, cost, and poor tectonic support restrict its use. Herein, we discuss these various alternatives to keratoplasty in microbial keratitis, their indications, advantages, disadvantages, and the various techniques of performing these procedures.

[Clinical results of modified crosslinking in the treatment of purulent keratitis and corneal ulcers]

PURPOSE

To evaluate the efficiency of modified crosslinking (M-CXL) in the treatment of purulent keratitis (PK) and corneal ulcers, including ulcers of mixed etiology.

MATERIAL AND METHODS

M-CXL method involves simultaneous performance of CXL and frequent instillations of anti-infective agents (one drop every 5 minutes for 1 hour). The study included 39 patients (41 eyes) with purulent corneal ulcers (PCU) of various origin. The main group consisted of 26 patients (27 eyes) who were treated with M-CXL in combination with active conservative therapy. In the control group (13 patients, 14 eyes) only active conservative management was used.

RESULTS

Complete suppression of the purulent process in the main group was achieved in 21 (77.8%) eyes after 32.6±10.66 days, in the control group - in 9 (64.3%) eyes in 52.4±16.6 days. Complete suppression of purulent keratitis was achieved in 100% of cases with bacterial keratitis, 83% of cases with fungal keratitis and 70.5% of cases with mixed keratitis. When purulent infiltration occupied the entire depth of the stroma but was limited in area (less than 6 mm), the efficiency of M-CXL decreased to 66.6%. The clinical effect of M-CXL was absent or insufficient when PK extended to the Descemet's membrane with an area of more than 7 mm.

CONCLUSION

In 77.8% of cases, modified crosslinking has showed pronounced therapeutic effect - complete arrest of purulent corneal infiltration. Recovery time in the main group was 1.6 times shorter than in the control group (p<0.05). Resorption of the purulent infiltration occupying all layers of the stroma up to the Descemet's membrane with extensive areas was not achieved, however the corneal melting and keratitis progression were stopped, which allowed planned therapeutic penetrating keratoplasty with a graft of smaller diameter to be performed.