In Vivo Confocal Microscopy Morphologic Features and Cyst Density in Acanthamoeba Keratitis

The Orphan Drug for Acanthamoeba Keratitis (ODAK) Trial: PHMB 0.08% (Polihexanide) and Placebo versus PHMB 0.02% and Propamidine 0.1

PURPOSE

To compare topical PHMB (polihexanide) 0.02% (0.2 mg/ml)+ propamidine 0.1% (1 mg/ml) with PHMB 0.08% (0.8 mg/ml)+ placebo (PHMB 0.08%) for Acanthamoeba keratitis (AK) treatment.

DESIGN

Prospective, randomized, double-masked, active-controlled, multicenter phase 3 study (ClinicalTrials.gov identifier, NCT03274895).

PARTICIPANTS

One hundred thirty-five patients treated at 6 European centers.

METHODS

Principal inclusion criteria were 12 years of age or older and in vivo confocal microscopy with clinical findings consistent with AK. Also included were participants with concurrent bacterial keratitis who were using topical steroids and antiviral and antifungal drugs before randomization. Principal exclusion criteria were concurrent herpes or fungal keratitis and use of antiamebic therapy (AAT). Patients were randomized 1:1 using a computer-generated block size of 4. This was a superiority trial having a predefined noninferiority margin. The sample size of 130 participants gave approximately 80% power to detect 20-percentage point superiority for PHMB 0.08% for the primary outcome of the medical cure rate (MCR; without surgery or change of AAT) within 12 months, cure defined by clinical criteria 90 days after discontinuing anti-inflammatory agents and AAT. A prespecified multivariable analysis adjusted for baseline imbalances in risk factors affecting outcomes.

MAIN OUTCOME MEASURES

The main outcome measure was MCR within 12 months, with secondary outcomes including best-corrected visual acuity and treatment failure rates. Safety outcomes included adverse event rates.

RESULTS

One hundred thirty-five participants were randomized, providing 127 in the full-analysis subset (61 receiving PHMB 0.02%+ propamidine and 66 receiving PHMB 0.08%) and 134 in the safety analysis subset. The adjusted MCR within 12 months was 86.6% (unadjusted, 88.5%) for PHMB 0.02%+ propamidine and 86.7% (unadjusted, 84.9%) for PHMB 0.08%; the noninferiority requirement for PHMB 0.08% was met (adjusted difference, 0.1 percentage points; lower one-sided 95% confidence limit, -8.3 percentage points). Secondary outcomes were similar for both treatments and were not analyzed statistically: median best-corrected visual acuity of 20/20 and an overall treatment failure rate of 17 of 127 patients (13.4%), of whom 8 of 127 patients (6.3%) required therapeutic keratoplasty. No serious drug-related adverse events occurred.

CONCLUSIONS

PHMB 0.08% monotherapy may be as effective (or at worse only 8 percentage points less effective) as dual therapy with PHMB 0.02%+ propamidine (a widely used therapy) with medical cure rates of more than 86%, when used with the trial treatment delivery protocol in populations with AK with similar disease severity.

FINANCIAL DISCLOSURE(S)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Diagnosing and monitoring the characteristics of Acanthamoeba keratitis using slit scanning and laser scanning in vivo confocal microscopy

INTRODUCTION

Acanthamoeba keratitis (AK) is a serious and potentially blinding ocular infection caused by the free-living amoeba, Acanthamoeba. In vivo confocal microscopy (IVCM) is a non-invasive device which has been proven of great use to diagnose Acanthamoeba infections immediately. The aim of this review was to establish different patterns and signs of AK that appear on the IVCM both before and after treatment.

METHODS

A systematic review of the literature from 1974 until September 2021 was performed using Embase and PubMed, following The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

Twenty different signs of AK were observed using IVCM. The included studies used vastly different criteria to diagnose infections, ranging from just 1 to 13 of the signs, demonstrating the current lack of a standardised diagnosis of this infection using the IVCM. The appearance of double wall cysts, trophozoites, signet rings, target signs and clusters were shown to be pathognomonic to AK infections. Bright spots located in the corneal epithelium were demonstrated as non-reliable predictors of AK. The presence of cysts in clusters and single file can predict the need for corneal transplantation. The morphological changes in cysts using the IVCM following treatment were described as breaking down to hollow forms and occasionally surrounded by black cavities. Using this information, a visual guideline for identifying AK signs in diagnosis and follow-up using IVCM was created.

CONCLUSION

Increased awareness of the different signs and patterns of AK that appear on the IVCM is crucial in order to correctly identify an infection and increase the potential of this device. Our guidelines presented here can be used, but further studies are needed in order to determine the relationship and aetiology of these signs and cellular changes on the IVCM both before and after anti-amoeba treatment.

Correlation of ex vivo and in vivo confocal microscopy imaging of Acanthamoeba

BACKGROUND/AIMS

The aim of this study was to correlate the various forms of Acanthamoeba on ex vivo confocal microscopy (EVCM) with in vivo confocal microscopy (IVCM) and findings from cultured positive cases of Acanthamoeba keratitis.

METHODS

Acanthamoeba live, dead and empty cysts, and live trophozoites were prepared in vitro and inoculated into porcine cornea using a sterile 26-gauge needle and examined ex vivo using the Heidelberg Retina Tomograph II/Rostock Corneal Module. IVCM images from 12 cultured positive Acanthamoeba cases, obtained using the same instrument, were compared with EVCM findings. Phase contrast images were also obtained to compare with both EVCM and IVCM findings. The change in cyst morphology with depth was evaluated by imaging the same cysts over a defined cornea depth measurement.

RESULTS

EVCM morphologies for live cysts included four main types-hyper-reflective central dot with hyper-reflective outer ring, hyper-reflective central dot with hyporeflective outer region, stellate shaped hyper-reflective centre with hyporeflective outer region and hyper-reflective round/polygonal shaped cyst; one main type for dead cysts-hyper-reflective central dot with hyporeflective outer region; two main types for empty cysts- hyper-reflective central dot with hyper-reflective outer ring/hyporeflective outer region; and one main type for trophozoites-large coarse speckled area of heterogeneous hyper-reflective material. Matching IVCM images show good correlation with EVCM. Cyst morphology altered when imaged at different depths.

CONCLUSION

EVCM demonstrated the various forms of Acanthamoeba cyst and trophozoites can be used as a reference to identify similar structures on IVCM.

Diagnosis and treatment of Acanthamoeba Keratitis: A scoping review demonstrating unfavorable outcomes

Acanthamoeba spp. are pathogens that cause Acanthamoeba keratitis (AK), a serious cornea inflammation that can lead to gradual loss of vision, permanent blindness, and keratoplasty. The efficacy of AK treatment depends on the drug's ability to reach the target tissue by escaping the protective eye barrier. No single drug can eradicate the living forms of the amoeba and be non-toxic to the cornea tissue. The treatment aims to eradicate both forms of protozoan life but is hampered by the resistance of the cysts to the most available drugs, leading to prolonged infection and relapses. Drug therapy is currently performed mainly using diamidines and biguanides, as they are more effective against cysts. However, they are cytotoxic to corneal cells. Drugs are applied topically, and hourly. Over time, the frequency of administration decreases, but the treatment time varies from month to years. This study aims to obtain an up-to-date summary of the literature since 2010, allowing us to identify the trends and gaps and address future research involving new alternatives for treating AK. The results were divided into three phases, pre-treatment, empirical treatment, and the treatment after diagnosis confirmation. The drugs prescribed were stratified into antiamoebic, antibiotic, antifungal, antivirals, and steroids. It was possible to observe the transition in drug prescription during three different stages until the diagnosis was confirmed. There were more indications for antibiotic, antifungal, and antiviral drugs in the early stages of the disease. The antiamoebic drugs were only prescribed after exhausting other treatments. This can be directly involved in developing complications and no responsiveness to medical treatment.

The global epidemiology and clinical diagnosis of Acanthamoeba keratitis

Acanthamoeba keratitis is a rare parasitic infection of the cornea that can lead to permanent blindness if not diagnosed and treated promptly. We collected data on the incidences of Acanthamoeba keratitis from 20 countries and calculated an annual incidence of 23,561 cases, with the lowest rates in Tunisia and Belgium, and the highest in India. We analyzed 3755 Acanthamoeba sequences from the GenBank database across Asia, Europe, North America, South America, and Oceania and genotyped them into T1, T2, T3, T4, T5, T10, T11, T12, and T15. Many genotypes possess different characteristics, yet T4 is the most prevalent genotype. As efficient treatment against Acanthamoeba remains lacking, prevention from early diagnosis via staining, PCR, or in vivo confocal microscopy (IVCM) becomes significant for the condition's prognosis. IVCM is the most recommended approach for the early detection of Acanthamoeba. If IVCM is unavailable, PCR should be used as an alternative.

Recovery of Corneal Innervation after Treatment in Dry Eye Disease: A Confocal Microscopy Study

PURPOSE

To analyze the changes in corneal innervation by means of in vivo corneal confocal microscopy (IVCM) in patients diagnosed with Evaporative (EDE) and Aqueous Deficient Dry Eye (ADDE) and treated with a standard treatment for Dry Eye Disease (DED) in combination with Plasma Rich in Growth Factors (PRGF).

METHODS

Eighty-three patients diagnosed with DED were enrolled in this study and included in the EDE or ADDE subtype. The primary variables analyzed were the length, density and number of nerve branches, and the secondary variables were those related to the quantity and stability of the tear film and the subjective response of the patients measured with psychometric questionnaires.

RESULTS

The combined treatment therapy with PRGF outperforms the standard treatment therapy in terms of subbasal nerve plexus regeneration, significantly increasing length, number of branches and nerve density, as well as significantly improving the stability of the tear film (p < 0.05 for all of them), and the most significant changes were located in the ADDE subtype.

CONCLUSIONS

the corneal reinnervation process responds in a different way depending on the treatment prescribed and the subtype of dry eye disease. In vivo confocal microscopy is presented as a powerful technique in the diagnosis and management of neurosensory abnormalities in DED.

Update on Corneal Confocal Microscopy Imaging

In vivo corneal confocal microscopy (IVCM) is a non-invasive ophthalmic imaging technique that provides images of the cornea at the cellular level. Despite the uses in ocular surface pathologies, in the last decades IVCM has been used to provide more knowledge in refractive surgery wound healing, in neuropathies diagnosis, etc. The observation of the corneal cells, both normal and inflammatory, and the possibility of quantification of the corneal nerve density with manual or automated tools, makes IVCM have a significant potential to improve the diagnosis and prognosis in several systemic and corneal conditions.

Amoebicidal effect of Allium cepa against Allovahlkampfia spelaea: A keratitis model

Allovahlkampfia spelaea (A. spelaea) is a free-living amoeba, proved to cause Acanthamoeba-like keratitis with quite difficult treatment. This study aimed to evaluate the amoebicidal effect of Allium cepa (A. cepa) on A. spelaea trophozoites and cysts both in vitro and in vivo using Chinchilla rabbits as an experimental model of this type of keratitis. Chemical constituents of the aqueous extract of A. cepa were identified using Liquid Chromatography-mass Spectrometry (LC-MS). In vitro, A. cepa showed a significant inhibitory effect on trophozoites and cysts compared to the reference drug, chlorhexidine (CHX) as well as the non-treated control (P < 0.05) with statistically different effectiveness in terms of treatment durations and concentrations. No cytotoxic effect of A. cepa on corneal cell line was found even at high concentrations (32 mg/ml) using agar diffusion method. The in vivo results confirmed the efficacy of A. cepa where the extract enhanced keratitis healing with complete resolution of corneal ulcers in 80% of the infected animals by day 14 (post infection)pi compared to 70% recovery with CHX after 20 treatment days. The therapeutic effect was also approved at histological, immune-histochemical, and parasitological levels. Our findings support the potential use of A. cepa as an effective agent against A. spelaea keratitis.

Applications of in vivo confocal microscopy in the management of infectious keratitis in veterinary ophthalmology

In vivo confocal microscopy (IVCM) is a relatively new ocular imaging technique that permits morphological and quantitative assessment of the living cornea on the cellular level. The applications for IVCM in clinical ophthalmology are numerous and diverse. There are several advantages inherent to IVCM over standard diagnostic techniques currently used to confirm a diagnosis of infectious keratitis in veterinary ophthalmology. With IVCM, images can be viewed in real-time providing immediate diagnostic information. Traumatic corneal sampling techniques are avoided, and the procedure can be repeated as frequently as is clinically indicated without risk of corneal tissue damage. Both superficial and deep corneal lesions can be evaluated by IVCM in an atraumatic fashion. Microorganism viability is not required for their detection and specialized diagnostic laboratory assay procedures are not necessary. Many larger infectious agents can be directly identified within corneal lesions by IVCM, including fungi and parasites such as Acanthamoeba spp. In other situations, such as bacterial infectious crystalline keratopathy, the biological systems associated with the microorganism can be detected within the cornea. The current resolution of IVCM is inadequate to directly visualize some corneal infectious agents, such as herpesviruses, but host responses and virus-infected epithelial cells can be identified. This review summarizes the current knowledge and applications of IVCM in the management of infectious keratitis in veterinary ophthalmology, including its use in animals with bacterial, fungal, parasitic, and viral keratitis.

Optical coherence tomography in the 2020s-outside the eye clinic

Optical coherence tomography (OCT) is a paragon of success in the translation of biophotonics science to clinical practice. OCT systems have become ubiquitous in eye clinics but access beyond this is limited by their cost, size and the skill required to operate the devices. Remarkable progress has been made in the development of OCT technology to improve the speed of acquisition, the quality of images and into functional extensions of OCT such as OCT angiography. However, more needs to be done to radically improve the access to OCT by addressing its limitations and enable penetration outside of typical clinical settings and into underserved populations. Beyond high-income countries, there are 6.5 billion people with similar eye-care needs, which cannot be met by the current generation of bulky, expensive and complex OCT systems. In addition, advancing the portability of this technology to address opportunities in point-of-care diagnostics, telemedicine and remote monitoring may aid development of personalised medicine. In this review, we discuss the major milestones in OCT hardware development to reach those beyond the eye clinic.

Drug Discovery against Acanthamoeba Infections: Present Knowledge and Unmet Needs

Although major strides have been made in developing and testing various anti-acanthamoebic drugs, recurrent infections, inadequate treatment outcomes, health complications, and side effects associated with the use of currently available drugs necessitate the development of more effective and safe therapeutic regimens. For any new anti-acanthamoebic drugs to be more effective, they must have either superior potency and safety or at least comparable potency and an improved safety profile compared to the existing drugs. The development of the so-called 'next-generation' anti-acanthamoebic agents to address this challenge is an active area of research. Here, we review the current status of anti-acanthamoebic drugs and discuss recent progress in identifying novel pharmacological targets and new approaches, such as drug repurposing, development of small interfering RNA (siRNA)-based therapies and testing natural products and their derivatives. Some of the discussed approaches have the potential to change the therapeutic landscape of Acanthamoeba infections.