Acanthamoeba keratitis: risk factors and outcome

Perspectives on the Incidence of Acanthamoeba Keratitis: A Systematic Review and Meta-Analysis

TOPIC

To provide an overview on the incidence of Acanthamoeba keratitis (AK).

CLINICAL RELEVANCE

Although being a sight-threatening cause of infectious keratitis, a comprehensive assessment of the incidence of AK is lacking.

METHODS

Incidence of AK was computed as the number of eyes with AK per health care center, per year (annualized center incidence [ACI]). Two meta-analytical ratios also were calculated: (1) the ratio of eyes with AK to the count of eyes with nonviral microbial keratitis (MK) and (2) the ratio of eyes with AK to the overall population (i.e., the total number of people in a nation or region, as indicated by the authors in each study). Center was defined as the health care facility where the study took place. Actual and projected estimates of the number of eyes with AK in years were calculated multiplying the ratio of eyes with AK to the total population and the corresponding population estimates, sourced from the United Nations Population Prospects.

RESULTS

Overall, 105 articles were included, published between 1987 and 2022. The total number of eyes identified was 91 951, with 5660 eyes affected by AK and 86 291 eyes affected by nonviral MK. The median ACI was 1.9 eyes with AK per health care center per year (95% confidence interval [CI], 1.5-2.6 eyes), with no statistically significant differences among continents. The ratio of eyes with AK to the total number of eyes with MK was 1.52% (95% CI, 1.03%-2.22%), whereas the ratio of eyes with AK in relationship to the entire population was estimated at 2.34 eyes per 1 000 000 people (95% CI, 0.98-5.55 per 1 000 000 people). The projected increase in the numbers of eyes with AK indicated an increase of 18.5% (n = 15 355 eyes with AK) in 2053 and 25.5% (n = 16 253 eyes with AK) in 2073, compared with the baseline of 2023 (n = 12 953 eyes with AK).

DISCUSSION

Acanthamoeba keratitis emerged as a relatively low-incident disorder, and no significant differences in terms of its incidence were found among different continents.

FINANCIAL DISCLOSURE(S)

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

Understanding Acanthamoeba Keratitis: An In-Depth Review of a Sight-Threatening Eye Infection

Acanthamoeba keratitis (AK) is a rare but potentially sight-threatening corneal infection caused by the Acanthamoeba parasite. This microorganism is found ubiquitously in the environment, often in freshwater, soil, and other sources of moisture. Despite its low incidence, AK presents significant challenges due to delayed diagnosis and the complex nature of therapeutic management. Early recognition is crucial to prevent severe ocular complications, including corneal ulceration and vision loss. Diagnostic modalities and treatment strategies may vary greatly depending on the clinical manifestation and the available tools. With the growing reported cases of Acanthamoeba keratitis, it is essential for the ophthalmic community to thoroughly understand this condition for its effective management and improved outcomes. This review provides a comprehensive overview of AK, encompassing its epidemiology, risk factors, pathophysiology, clinical manifestations, diagnosis, and treatment.

Diagnosis of Acanthamoeba Keratitis: Past, Present and Future

Acanthamoeba keratitis (AK) is a painful and sight-threatening parasitic corneal infection. In recent years, the incidence of AK has increased. Timely and accurate diagnosis is crucial during the management of AK, as delayed diagnosis often results in poor clinical outcomes. Currently, AK diagnosis is primarily achieved through a combination of clinical suspicion, microbiological investigations and corneal imaging. Historically, corneal scraping for microbiological culture has been considered to be the gold standard. Despite its technical ease, accessibility and cost-effectiveness, the long diagnostic turnaround time and variably low sensitivity of microbiological culture limit its use as a sole diagnostic test for AK in clinical practice. In this review, we aim to provide a comprehensive overview of the diagnostic modalities that are currently used to diagnose AK, including microscopy with staining, culture, corneal biopsy, in vivo confocal microscopy, polymerase chain reaction and anterior segment optical coherence tomography. We also highlight emerging techniques, such as next-generation sequencing and artificial intelligence-assisted models, which have the potential to transform the diagnostic landscape of AK.

The role of the calcofluor white staining in the diagnosis of Acanthamoeba keratitis

PURPOSE

Acanthamoeba keratitis is often misdiagnosed at disease onset. This study presents data to confirm the diagnosis using calcofluor white (CFW) staining.

METHODS

Forty three patients were retrospectively included who presented to the Department of Ophthalmology at the University Hospital Ulm with keratitis between 2000 and 2022. Condition positive cases were diagnosed based on the typical clinical presentation of Acanthamoeba keratitis with a positive polymerase chain reaction (PCR). Condition negative were patients with ulcers due to other causing pathogens with a negative Acanthamoeba PCR result. The condition was compared with the CFW test results.

RESULTS

After symptom onset, time until presentation was 17 ± 12 days and until diagnosis 27 ± 13 days in the 15 condition positive patients. Among the 35 patients with additional CFW test, 7 patients were condition positive and 28 negative. 5 of the 7 patients were true positive, 2 were false negative. In the 28 condition negative patients, 1 was false positive. Sensitivity of CFW was 71% and specificity 96%. The positive PCR results were available 3.4 ± 2.3 days after corneal scraping, the positive CFW test results on the same day in each case.

CONCLUSION

Our data demonstrate that diagnosis of Acanthamoeba keratitis remains difficult and therapy is initiated late. A positive CFW test confirms the diagnosis as there are almost no false positive results and it was available faster than PCR. In case of a negative CFW test, Acanthamoeba keratitis cannot be ruled out because of a high false negative rate.

Epidemiological profile of microbial keratitis in Alexandria-Egypt a 5 years retrospective study

OBJECTIVE

To evaluate the epidemiologic profile of microbial keratitis in Alexandria- Egypt, with special emphasis on risk factors, visual outcome and microbiological results.

METHODS

This retrospective study reviewed files of patients treated for microbial keratitis during a period of 5 years at Alexandria Ophthalmology Hospital Cornea Clinic, Alexandria- Egypt, between February 2017 and June 2022. The patients were evaluated for the risk factors e.g., trauma, eyelid disorders, co-morbidities, and contact lens use. They were also evaluated for their clinical picture, the identified microorganisms, visual outcomes, and complications. Non-microbial keratitis and incomplete files were excluded from the study.

RESULTS

A total of 284 patients were diagnosed as microbial keratitis in our study. Viral keratitis was the most common cause of microbial keratitis (n = 118 (41.55%)), followed by bacterial keratitis (n = 77 (27.11%)), mixed keratitis (n = 51 (17.96%)), acanthamoeba keratitis (n = 22 (7.75%)) and the least cause was fungal keratitis (n = 16 (5.63%)). Trauma was the most common risk factor for microbial keratitis (29.2%). Fungal keratitis had a statistically significant association with trauma (p < 0.001), while the use of contact lenses had a statistically significant association with Acanthamoeba keratitis (p < 0.001). The percentage of culture-positive results in our study was 76.8%. Gram-positive bacteria were the most frequently isolated bacterial isolate (n = 25 (36.2%)), while filamentous fungi were the most frequently isolated fungi (n = 13(18.8%)). After treatment, there was a significant increase in the mean visual acuity among all groups; it was significantly higher in Acanthamoeba keratitis group with a mean difference of 0.262 ± 0.161 (p = 0.003).

CONCLUSION

Viral keratitis followed by bacterial keratitis were the most frequent etiologic agents causing microbial keratitis found in our study. Although trauma was the most frequent risk factor for microbial keratitis, contact lens wear was found an important preventable risk factor for microbial keratitis in young patients. Performing culture properly whenever indicated before starting antimicrobial treatment increased the cultures' positive results.

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.

Surgical management of acanthamoeba chorioretinitis

Purpose

Acanthamoeba chorioretinitis is a rare manifestation of the parasitic infection, and reported cases often result in enucleation. Surgical removal of Acanthamoeba chorioretinitis has not been previously described. We report a surgical case of Acanthamoeba chorioretinitis spread from keratitis that ultimately resulted in a disease-free outcome.

Observations

A healthy 80-year-old male with a history of keratoconus requiring a penetrating keratoplasty in the fellow eye presented with a severe corneal ulcer clinically consistent with Acanthamoeba keratitis. He ultimately required a penetrating keratoplasty and improved clinically until he developed vitritis on post-operative month 1 and was diagnosed with endophthalmitis. B-scan ultrasound demonstrated vitreous opacities and a large retinal mass that reduced in size following serial intravitreal injections of antibiotics, oral antibiotics, and a limited pars plana vitrectomy. He underwent a repeat pars plana vitrectomy 6 weeks later and a retinal mass in the mid-periphery with an associated tractional retinal detachment was noted. A localized retinectomy was performed around the lesion which was excised entirely, and silicone oil was instilled. Pathology of the lesion showed acute and chronic granulomatous necrotizing inflammation with the presence of several definitive amoebic organisms and numerous cells suspicious for amoebae. The patient was maintained on oral antibiotics by the Infectious Disease Service and was disease-free 1-year post-infection.

Conclusions and importance

Acanthamoeba chorioretinitis is a rare, devastating disease and often leads to enucleation. We present a surgical case showing control of the infection utilizing a surgical retinectomy. Aggressive local therapy and a multidisciplinary approach with the Infectious Disease Service may lead to a successful outcome.

Therapeutic Corneal Transplantation in Acanthamoeba Keratitis: Penetrating Versus Lamellar Keratoplasty

PURPOSE

The purpose of this article was to compare clinical outcomes between therapeutic penetrating keratoplasty (TPK), therapeutic deep anterior lamellar keratoplasty (TDALK), and optical penetrating keratoplasty (OPK) in Acanthamoeba keratitis.

METHODS

A literature search was conducted in online libraries from 1980 to 2021. The primary end points were best-corrected visual acuity (VA), graft survival, and infection recurrence. In addition, we enrolled 35 consecutive patients with AK from our practice evaluating best-corrected VA and high-order aberrations.

RESULTS

A total of 359 AK eyes from 33 published studies were retrieved from 175 publications screened. One hundred sixty-five eyes (73%) that underwent TPK and 39 eyes (84%) treated with TDALK had a clear graft at the last follow-up visit. Only the patients treated with OPK had 82 clear grafts (94%) during the follow-up period. Forty-seven (21%) of TPK patients reached VA ≥20/30, compared with 11 (25%) of TDALK patients and 35 (40%) of OPK patients. Acanthamoeba infection recurrence occurred in 38 eyes (16.8%) that underwent TPK, 9 (19%) that underwent TDALK, and 8 (9.5%) that underwent OPK. In our series, best-corrected visual acuity in nonsurgically treated patients was 1 ± 0.50 logMAR compared with 0 logMAR of surgically treated patients. High-order aberrations were significantly lower in surgically treated eyes after AK resolution, particularly in TDALK when compared with TPK patients. Best-corrected visual acuity was better in TDALK patients compared with TPK patients.

CONCLUSIONS

After AK resolution by 6 to 12 months of medical treatment, OPK seems to be the best surgical choice in patients with AK. If AK could not be eradicated by medical therapy, TDALK may be chosen in the early disease stage and TPK in later stages.

Acanthamoeba keratitis and contact lens wear

Acanthamoeba keratitis is a rare but serious complication of contact lens wear that may cause severe visual loss. The clinical picture is usually characterised by severe pain, sometimes disproportionate to the signs, with an early superficial keratitis that is often misdiagnosed as herpes simplex virus (HSV) keratitis. Advanced stages of the infection are usually characterised by central corneal epithelial loss and marked stromal opacification with subsequent loss of vision. In this paper, six cases of contact lens-related Acanthamoeba keratitis that occurred in Australia and New Zealand over a three-year period are described. Three of the patients were disposable soft lens wearers, two were hybrid lens wearers and one was a rigid gas permeable lens wearer. For all six cases, the risk factors for Acanthamoeba keratitis were contact lens wear with inappropriate or ineffective lens maintenance and exposure of the contact lenses to tap or other sources of water. All six patients responded well to medical therapy that involved topical use of appropriate therapeutic agents, most commonly polyhexamethylene biguanide and propamidine isethionate, although two of the patients also subsequently underwent deep lamellar keratoplasty due to residual corneal surface irregularity and stromal scarring. Despite the significant advances that have been made in the medical therapy of Acanthamoeba keratitis over the past 10 years, prevention remains the best treatment and patients who wear contact lenses must be thoroughly educated about the proper use and care of the lenses. In particular, exposure of the contact lenses to tap water or other sources of water should be avoided.

Acanthamoeba sclerokeratitis in a cat

CASE DESCRIPTION

A 12-year-old neutered male domestic shorthair cat with chronic anterior uveitis and secondary glaucoma of the right eye was examined for persistent blepharospasm 2 weeks after corneal debridement and grid keratotomy for nonhealing superficial ulcerative keratitis.

CLINICAL FINDINGS

Examination of the right eye revealed a central superficial corneal ulcer associated with corneal epithelial and subepithelial infiltrates and mild aqueous flare. Structures consistent with amoeboid cysts and trophozoites were detected in the cornea by in vivo confocal microscopy. Suppurative keratitis was identified cytologically. An Acanthamoeba spp was isolated through culture and identified by a PCR assay of corneal specimens.

TREATMENT AND OUTCOME

Symptomatic and antiamoebic (polyhexamethylene biguanide 0.02% ophthalmic solution) treatments were instituted. Over the following 6 weeks, the cat lost vision in the affected eye and lesions progressed to nonulcerative stromal keratitis associated with a dense paracentral corneal stroma ring infiltrate and anterior lens luxation. The globe was enucleated, and lymphoplasmacytic sclerokeratitis, anterior uveitis, and retinal detachment were noted. Acanthamoeba organisms were detected within the corneal stroma and anterior sclera with histologic and immunohistochemical stains. The amoebae were classified to the Acanthamoeba T4 genotype by DNA sequencing. The cat had no medical problems attributed to Acanthamoeba infection over 36 months after enucleation, until the cat was lost to follow-up.

CLINICAL RELEVANCE

Naturally acquired Acanthamoeba sclerokeratitis is described in a cat for the first time. Acanthamoeba infection should be considered for cats with superficial corneal disease refractory to appropriate treatments and especially occurring after ocular trauma, including keratotomy.

The impact of patient behaviour and care system compliance on reusable soft contact lens complications

Reusable soft daily wear contact lenses (CLs) remain popular and were fit to just over half of all wearers in the most recent international CL prescribing survey. Unlike daily disposable CLs, reusables require cleaning and disinfecting after every use, along with storage in a CL case. These additional requirements add a number of steps to the daily wear and care routine, increasing the opportunities for CL wearers to exhibit non-compliant behaviour. The impact of non-compliance ranges from poor lens comfort through to potentially sight-threatening infective keratitis. The coronavirus pandemic has refocused the profession on the importance of hand hygiene in particular, and the need for promoting safe CL wear in general. This review summarises typical non-compliant behaviour related to reusable CLs, and examines strategies and opportunities to better support wearers. Patient education has a central role in encouraging compliant behaviour, although patient recall of information is low, and personal belief systems may result in continuation of non-compliant behaviour despite awareness of the risks. CL care solutions are required for the daily disinfection of lenses, however misuse of multipurpose solutions (MPS) and hydrogen peroxide (H₂O₂)-based care systems can challenge their ability to be fully efficacious. Standard efficacy testing is reviewed, with consideration of how well current protocols model real-world use of CL solutions. Although some recommendations are in place for the inclusion of additional variables such as lens cases, CL materials, organic soil and efficacy against Acanthamoeba, opportunity still exists to reevaluate global standards to ensure consistency of testing in all markets. Finally, potential future innovations are discussed which may further support increased safety in reusable lens wear through novel antimicrobial additions to both CL materials and cases.

In vitro evaluation of commercial foam Belcils® on Acanthamoeba spp

Interest in periocular (eyelid and eyelashes margins) hygiene has attracted attention recently and a growing number of commercials eye cleanser and shampoos have been marketed. In the present study, a particular eye cleanser foam, Belcils® has been tested against trophozoites and cysts on the facultative pathogen Acanthamoeba. Viability was tested by the alamarBlue™ method and the foam was tested for the induction of programmed cell death in order to explore its mode of action. We found that a 1% solution of the foam eliminated both trophozoite and cyst stage of Acanthamoeba spp. After 90 min of incubation, Belcils® induced, DNA condensation, collapse in the mitochondrial membrane potential and reduction of the ATP level production in Acanthamoeba. We conclude that the foam destroys the cells by the induction of an apoptosis-like process. The current eye cleanser could be used as part of AK therapy protocol and as prevention from AK infections for contact lens users and post-ocular trauma patients.

Effectiveness and Safety of Topical Chlorhexidine and Vitamin E TPGS in the Treatment of Acanthamoeba Keratitis: A Survey on 29 Cases

This study aimed to test the effectiveness of a solution of chlorhexidine (CHX) and D-α-tocopheryl polyethylene glycol succinate (Vitamin E TPGS or TPGS) in the treatment of Acanthamoeba keratitis (AK) via a prospective, interventional case series study. Twenty-nine consecutive patients with AK were enrolled. At baseline, best-corrected visual acuity (BCVA), slit lamp examination, confocal microscopy, and polymerase chain reaction (PCR) were performed. Topical therapy with CHX 0.02% and VE-TPGS 0.2% was administered hourly/24 h for the first day, hourly in the daytime for the next three days, and finally, every two hours in the daytime up to one month. BCVA and ocular inflammation were recorded after two weeks, four weeks, and three months from baseline. Mean logMAR BCVA significantly improved at two weeks (0.78) compared to baseline (1.76), remaining stable over time (0.80 at four weeks, 0.77 at three months). Ocular inflammation improved in 14 eyes at 2 weeks, with further slow improvements in all cases. At three months, no patient had signs of corneal inflammation. The presence of corneal scars was first recorded at the two-week follow-up, with an enlargement at the four-week follow-up. At the three-month follow-up, 19 eyes still showed corneal opacities. In conclusion, the tested solution was shown to be effective for the treatment of AK. Furthermore, it might represent a good first-line treatment.

In Vitro Evaluation of Farnesyltransferase Inhibitor and its Effect in Combination with 3-Hydroxy-3-Methyl-Glutaryl-CoA Reductase Inhibitor against Naegleria fowleri

Free-living amoeba Naegleria fowleri causes a rapidly fatal infection primary amebic meningoencephalitis (PAM) in children. The drug of choice in treating PAM is amphotericin B, but very few patients treated with amphotericin B have survived PAM. Therefore, development of efficient drugs is a critical unmet need. We identified that the FDA-approved pitavastatin, an inhibitor of HMG Co-A reductase involved in the mevalonate pathway, was equipotent to amphotericin B against N. fowleri trophozoites. The genome of N. fowleri contains a gene encoding protein farnesyltransferase (FT), the last common enzyme for products derived from the mevalonate pathway. Here, we show that a clinically advanced FT inhibitor lonafarnib is active against different strains of N. fowleri with EC₅₀ ranging from 1.5 to 9.2 µM. A combination of lonafarnib and pitavastatin at different ratios led to 95% growth inhibition of trophozoites and the combination achieved a dose reduction of about 2- to 28-fold for lonafarnib and 5- to 30-fold for pitavastatin. No trophozoite with normal morphology was found when trophozoites were treated for 48 h with a combination of 1.7 µM each of lonafarnib and pitavastatin. Combination of lonafarnib and pitavastatin may contribute to the development of a new drug regimen for the treatment of PAM.

In Vitro Effect of Pitavastatin and Its Synergistic Activity with Isavuconazole against Acanthamoeba castellanii

Acanthamoeba keratitis (AK) can occur in healthy individuals wearing contact lenses and it is a painful, blinding infection of the cornea caused by a free-living ameba Acanthamoeba. Current treatment for AK relies on a combination of chlorhexidine, propamidine isethionate, and polyhexamethylene biguanide. However, the current regimen includes an aggressive disinfectant and in 10% of cases recurrent infection ensues. Therefore, development of efficient and safe drugs is a critical unmet need to avert blindness. Acanthamoeba sterol biosynthesis includes two essential enzymes HMG-CoA reductase (HMGR) and sterol 14-demethylase (CYP51), and we earlier identified a CYP51 inhibitor isavuconazole that demonstrated nanomolar potency against A. castellanii trophozoites. In this study, we investigated the effect of well-tolerated HMGR inhibitors and identified pitavastatin that is active against trophozoites of three different clinical strains of A.castellanii. Pitavastatin demonstrated an EC₅₀ of 0.5 to 1.9 µM, depending on strains. Combination of pitavastatin and isavuconazole is synergistic and led to 2- to 9-fold dose reduction for pitavastatin and 11- to 4000-fold dose reduction for isavuconazole to achieve 97% of growth inhibition. Pitavastatin, either alone or in combination with isavuconazole, may lead to repurposing for the treatment of Acanthamoeba keratitis.

Genotyping and phylogenic study of Acanthamoeba isolates from human keratitis and swimming pool water samples in Iran

Objective

Acanthamoeba keratitis cause severe corneal infection and lead to poor vision and blindness. This disease is caused by a unicellular amphizoic protozoon called Acanthamoeba spp. that present in different environments. This study aimed to represent the existence and genotyping of Acanthamoeba spp. in patients with keratitis and swimming pool water (SPW) in Tehran Province, Central Iran.

Methods

In this descriptive study, 56 clinical samples were collected from patients with keratitis and 30 water samples were collected from different swimming pools in Tehran Province. All samples were examined based on the morphological and molecular techniques. The genotypes were determined by sequencing the partial of 18S rRNA gene.

Results

Of 56 clinical (corneal) and 30 environmental (SPW) samples, 30.3% and 40.0% were positive for Acanthamoeba spp., respectively. According to sequencing analysis, 94.1% of amoebic keratitis isolates were belonged to T4 genotype and only one (5.8%) isolate was belonged to T11 genotype. All genotypes were detected from SPW samples were identified as T4 genotype.

Conclusion

According to our results, use of contact lens and swimming in pool poses the major risk factor for amoebic keratitis in the studied area (Tehran). Moreover, T4 genotype was the predominant genotype of human keratitis and swimming pool samples there. Consequently, essential and practical measures are urgently needed to prevent subjects against this ocular seriously disease.

Safety of intrastromal injection of polyhexamethylene biguanide and propamidine isethionate in a rabbit model

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Intrastromal Injection can be considered in deep Acanthamoeba keratitis (AK).

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Intrastromal injection of 0.01% PHMB or 0.05% propamidine isethionate is safe.

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This model system could help to determine the toxic effect of other agents.

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Further experiments may determine the toxicity of multiple intrastromal injection.

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AK animal model is required to evaluate the true effect of intrastromal injection.

Acanthamoeba keratitis (AK) is difficult to treat, especially when the corneal deep stroma is involved. Intrastromal injection of antimicrobial agents is an effective adjuvant therapy for deep recalcitrant microbial keratitis; however, it has not been used to treat AK due to suspected drug toxicity. The purpose of this study was to evaluate the toxicity of corneal intrastromal injection of polyhexamethylene biguanide (PHMB) and propamidine isethionate (Brolene®, Sanofi) in New Zealand white rabbits. We performed intrastromal injections of PHMB (0.02 or 0.01%) and propamidine isethionate (0.1 or 0.05%) into the rabbits’ right corneas. The left corneas were injected with phosphate-buffered saline as controls. The rabbits were sacrificed on the 7th day after injection, and the corneal buttons were harvested for further evaluation by slit lamp microscopy, specular microscopy, hematoxylin and eosin staining, scanning electron microscopy, terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling assays, and WST-1 assays. We found that intrastromal injection of 0.02% PHMB or 0.1% propamidine isethionate resulted in corneal epithelial erosion, corneal edema, and severe neovascularization. However, 0.01% PHMB or 0.05% propamidine isethionate did not induce obvious cornea toxicity. In conclusion, intrastromal injection of 0.01% PHMB or 0.05% propamidine isethionate may be promising adjunctive treatments for deep stromal AK.

Early Penetrating Keratoplasty À Chaud May Improve Outcome in Therapy-Resistant Acanthamoeba Keratitis

INTRODUCTION

Long-standing acanthamoeba keratitis (AK) may result in corneal neovascularization, extension of the infiltrate to the limbus or sclera, broad peripheral synechiae, mature cataract or ischemic posterior segment inflammation. We investigated the impact of early emergency penetrating keratoplasty (PKP) in therapy-resistant cases among the patients of a highly specialized tertiary care center.

METHODS

In this retrospective, observational cohort within a single institution, we collected data on best-corrected visual acuity (BCVA), epithelial wound healing, graft survival and secondary complications of AK patients who underwent PKP. A total of 23 eyes of 23 patients diagnosed with acute, therapy-resistant AK between 2006 and 2015 were enrolled. Postoperative combined topical treatment was tapered for 6-9 months.

RESULTS

Eyes were grouped based on preoperative disease duration as shorter (group 1) or longer (group 2) than the median. The median was 5.3 (0.66-36) months. The BCVA in group 1 (20/44 ± 20/18; 0.32 ± 0.18 logMAR) was significantly better than in group 2 (20/1200 ± 20/1133; 1.28 ± 0.89; logMAR); p = 0.015. Persisting epithelial defects occurred in 5 patients (50%) of group 1 and in 10 patients (77%) of group 2. In 5 eyes (group 2), no epithelial healing could be achieved. After 36 months, graft survival (Kaplan-Meier) was 78% (18 grafts) for all patients (90% in group 1 and 44% in group 2).

CONCLUSION

PKP à chaud within 5.3 months after first symptoms of therapy-resistant AK seems to result in better final BCVA than delayed graft surgery if the disease is resistant to a classical topical triple therapy. In addition, early PKP may have a favorable impact on epithelial healing and graft survival.

FUNDING

We thank the Alexander von Humboldt Foundation for supporting the work of Prof. N. Szentmáry at the Department of Ophthalmology of Saarland University Medical Center in Homburg/Saar, Germany. We thank the University of Saarland for funding the medical writing assistance and the Rapid Service Fees. The funding organisation had no role in the design or conduct of this research.

Corneal Endotheliitis as a Presentation of Acanthamoeba Keratitis

OBJECTIVE

To report 2 cases of Acanthamoeba keratitis (AK) presenting with corneal endotheliitis.

METHODS

Case report.

RESULTS

Two contact lens wearers, who had been diagnosed with herpes simplex virus (HSV) keratitis, predominantly manifested corneal endotheliitis composed of corneal edema, keratic precipitates, and anterior chamber reaction at referral. AK was confirmed using cultures or through polymerase chain reaction testing. The patients were started on polyhexamethylene biguanide and responded favorably to regain satisfactory visual acuity.

CONCLUSIONS

Corneal endotheliitis, although uncommon, may be a manifestation of AK. We must have high-index suspicion for AK in all contact lens users, particularly before making a diagnosis of HSV keratitis. Accurate diagnosis and prompt treatment can result in a favorable prognosis for AK.

High fluence PACK-CXL as adjuvant treatment for advanced Acanthamoeba keratitis

Purpose

To describe the outcome of adjuvant high fluence photoactivated chromophore for infectious keratitis cross-linking (PACK-CXL) used to treat an advanced form of refractory Acanthamoeba keratitis (AK) diagnosed several months after initial presentation.

Observations

An otherwise healthy 24-year old female presented with a severe unilateral keratitis. The diagnosis eluded clinicians for several months and when finally confirmed as AK, anti-amoebic therapy was instated and only appeared to be effective after addition of high fluence PACK-CXL.

Conclusion and importance

In this case of advanced AK, high fluence PACK-CXL treatment given adjuvant to pharmacologic anti-amoebic therapy resulted in lasting pain relief, re-epithelization and eradication of the Acanthamoeba parasite. Given adjuvant to anti-amoebic pharmacotherapy, high fluence PACK-CXL might be a useful method for treating typically refractory advanced AK.

Risk factors and clinical signs of severe Acanthamoeba keratitis

Purpose

To determine risk factors and clinical signs for severe Acanthamoeba keratitis (AK) by comparing severe cases with mild cases with good prognosis.

Patients and methods

We reviewed medical records of ten cases of AK (five males and five females) referred to our hospital and classified cases into two groups. One eye that required therapeutic keratoplasty and three eyes with a poor visual acuity (<0.2) on last visit were included in the severe group. Six eyes that had good prognosis with a visual acuity of 1.2 on last visit were classified as mild group. We compared patients’ age, the time required for diagnosis, visual acuity on first visit, the history of steroid eye drops use, and other clinical findings.

Results

The average age of the severe group was older than the mild group (P=0.04). The duration between onset and diagnosis of AK and visual acuity on first visit was not statistically different. A history of steroid eye drop use was found in four eyes of the severe group (100%) and four eyes of the mild group (67%). Keratoprecipitates were found in all severe group eyes and one mild group eye during follow-up (P=0.01). One case in the severe group was diagnosed with diabetes mellitus at initial examination. We detected Staphylococcus epidermis by palpebral conjunctival culture in one case of the severe group.

Conclusion

Aging may be a possible risk factor for severe AK. The presence of keratoprecipitates is a possible sign of severe AK. Attention is also required in patients with comorbidities such as diabetes mellitus and bacterial infection.

Effect of ethanol pretreatment in Acanthamoeba keratitis: a long-term follow-up study

Purpose

The aim of this study was to evaluate the long-term outcomes of ethanol pretreatment in Acanthamoeba keratitis (AK).

Patients and methods

This single-center, retrospective, interventional study included 22 patients (24 eyes) who developed AK and underwent ethanol pretreatment between 2009 and 2015. Samples for smears, polymerase chain reaction, and culture for evidence of Acanthamoeba were collected. After ethanol pretreatment, the patients were treated with corneal epithelial debridement, topical 0.02% polyhexamethylene biguanide, and 0.1% propamidine isethionate. The primary outcomes were a clinically stable ocular surface, complete recovery from corneal infection, and acceptable corneal haze. The secondary outcome measure was improvement in best-corrected visual acuity. Complications and predictors of the visual outcome were also recorded.

Results

Ethanol pretreatment was successful in 20 (83.3%) of the 24 eyes, and no further optical keratoplasty was required. Four eyes required rescue therapeutic keratoplasty because of rapid progression of AK. Patients in whom ethanol pretreatment was successful achieved good final visual outcomes regardless of sex, age, or causative Acanthamoeba species. Patients with worse initial best-corrected visual acuity and rigid gas permeable lens-related AK had better improvement in vision.

Conclusion

Ethanol as a pretreatment for AK is safe and effective. Combined with corneal epithelial debridement, ethanol pretreatment may preclude the need for optical and therapeutic keratoplasty. This technique is suitable for all stages of AK presenting within 3 weeks of symptom onset and achieves favorable results especially in early AK.

Acanthamoeba in the eye, can the parasite hide even more? Latest developments on the disease

Acanthamoeba spp. is a free living protozoan in the environment, but can cause serious diseases. Acanthamoeba keratitis (AK), a severe and painful eye infection, must be treated as soon as possible to prevent ulceration of the cornea, loss of visual acuity, and eventually blindness or enucleation. Although the disease affects principally contact lens (CLs) wearers, it is recognized nowadays as a cause of keratitis also in non-CLs wearers. Although the number of infections caused by these amoebae is low, AK is an emerging disease presenting an extended number of cases each year worldwide mostly due to the increasing use of CLs, but also to better diagnostic methods and awareness. There are two principal causes that lead to severe outcomes: misdiagnosis or late diagnosis of the causal agent, and lack of a fully effective therapy due to the existence of a highly resistant cyst stage of Acanthamoeba. Recent studies have reported different genotypes that have not been previously associated with this disease. In addition, Acanthamoeba can act as a reservoir for phylogenetically diverse microorganisms. In this regard, recently giant viruses called Pandoravirus have been found within genotypes producing keratitis. What potential risk this poses is not yet known. This review focuses on an overview of the present status and future prospects of this re-emerging pathology, including features of the parasite, epidemiology, clinical aspects, diagnosis, and treatment.

[The German Acanthamoeba keratitis register: Initial results of a multicenter study]

BACKGROUND AND PURPOSE

In September 2011 the cornea section of the German Ophthalmological Society (DOG) established the first German Acanthamoeba keratitis registry. The data of this multicenter survey are being collected, compiled and evaluated at the Department of Ophthalmology at the Saarland University. The aim of this article is to present an intermediate report.

PATIENTS AND METHODS

Data from 172 eyes with Acanthamoeba keratitis were collected during the last 10 years. For this interim report we actually evaluated 121 eyes (60.2 % female patients, average age 41.3 years) and collected the following data: date of onset of symptoms, date and method of diagnosis, initial diagnosis, anamnestic data, clinical symptoms and signs at diagnosis and during follow-up, conservative and surgical therapy. Criteria for inclusion in the Acanthamoeba registry was the established diagnosis of an Acanthamoeba keratitis with at least one of the methods described in this article.

RESULTS

Acanthamoeba keratitis could be histologically proven in 55.3 % of the cases, via PCR in 25.6 %, with confocal microscopy in 20.4 % and using in vitro cultivation in 15.5 %. Clinical symptoms and signs in Acanthamoeba keratitis were pain in 67.0 %, ring infiltrates in 53.4 %, pseudodendritiform epitheliopathy in 11.7 % and keratoneuritis in 5.8 %. In 47.6 % of the cases the initial diagnosis was herpes simplex virus keratitis followed by bacterial keratitis in 25.2 % and fungal keratitis in 3.9 %. Acanthamoeba keratitis was the correct initial diagnosis in only 23.2 % of cases. The average time period between first symptoms and diagnosis was 2.8 ± 4.0 months (range 0-23 months). A triple therapy with Brolene® Lavasept® and antibiotic eye drops at least 5 ×/day was used in 54.5 % of eyes (n = 66). Penetrating keratoplasty was performed in 40.4 %, in 18 cases in combination with cryotherapy of the cornea. The mean graft diameter was 7.9 ± 1.1 mm (range 3.5-11.0 mm). The final visual acuity (Snellen visual acuity chart at 5 m) was comparable in the two groups of eyes with (5/40 ± 5/25) and without (5/32 ± 5/25) keratoplasty.

CONCLUSION

Acanthamoeba keratitis is a rare and often very late diagnosed disease and two thirds of the cases were initially misdiagnosed. The early recognition of the typical symptoms is crucial for the prognosis of the disease. All ophthalmological departments in Germany are invited to submit further data of all confirmed cases (berthold.seitz@uks.eu), whether retrospectively or prospectively in order to generate an adequate standardized diagnostic and therapeutic approach for this potentially devastating disease.

Repertoire of free-living protozoa in contact lens solutions

Background

The repertoire of free-living protozoa in contact lens solutions is poorly known despite the fact that such protozoa may act as direct pathogens and may harbor intra-cellular pathogens.

Methods

Between 2009 and 2014, the contact lens solutions collected from patients presenting at our Ophthalmology Department for clinically suspected keratitis, were cultured on non-nutrient agar examined by microscope for the presence of free-living protozoa. All protozoa were identified by 18S rRNA gene sequencing.

Results

A total of 20 of 233 (8.6 %) contact lens solution specimens collected from 16 patients were cultured. Acanthamoeba amoeba in 16 solutions (80 %) collected from 12 patients and Colpoda steini, Cercozoa sp., Protostelium sp. and a eukaryotic more closely related to Vermamoeba sp., were each isolated in one solution. Cercozoa sp., Colpoda sp., Protostelium sp. and Vermamoeba sp. are reported for the first time as contaminating contact lens solutions.

Conclusion

The repertoire of protozoa in contact lens solutions is larger than previously known.

Acanthamoeba keratitis: improving the Scottish diagnostic service for the rapid molecular detection of Acanthamoeba species

Acanthamoeba species are responsible for causing the potentially sight-threatening condition, Acanthamoeba keratitis, which is commonly associated with contact lens use. In this report, we highlight the challenges faced using conventional laboratory identification methods to identify this often under-reported pathogen, and discuss the reasons for introducing the first national service in Scotland for the rapid and sensitive molecular identification of Acanthamoeba species. By comparing culture and molecular testing data from a total of 63 patients (n = 80 samples) throughout Scotland presenting with ocular eye disease, we describe the improvement in detection rates where an additional four positive cases were identified using a molecular assay versus culture. The testing of a further ten patients by confocal imaging is also presented. This report emphasizes the importance of continuing to improve clinical laboratory services to ensure a prompt, correct diagnosis and better prognosis, in addition to raising awareness of this potentially debilitating opportunistic pathogen.

IL-17A-mediated protection against Acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a very painful and vision-impairing infection of the cornea that is difficult to treat. Although past studies have indicated a critical role of neutrophils and macrophages in AK, the relative contribution of the proinflammatory cytokine, IL-17A, that is essential for migration, activation, and function of these cells into the cornea is poorly defined. Moreover, the role of the adaptive immune response, particularly the contribution of CD4(+) T cell subsets, Th17 and regulatory T cells , in AK is yet to be understood. In this report, using a mouse corneal intrastromal injection-induced AK model, we show that Acanthamoeba infection induces a strong CD4(+) T effector and regulatory T cell response in the cornea and local draining lymph nodes. We also demonstrate that corneal Acanthamoeba infection induces IL-17A expression and that IL-17A is critical for host protection against severe AK pathology. Accordingly, IL-17A neutralization in Acanthamoeba-infected wild-type mice or Acanthamoeba infection of mice lacking IL-17A resulted in a significantly increased corneal AK pathology, increased migration of inflammatory cells at the site of inflammation, and a significant increase in the effector CD4(+) T cell response in draining lymph nodes. Thus, in sharp contrast with other corneal infections such as herpes and Pseudomonas aeruginosa keratitis where IL-17A exacerbates corneal pathology and inflammation, the findings presented in this article suggest that IL-17A production after Acanthamoeba infection plays an important role in host protection against invading parasites.

The impact of topical corticosteroid use before diagnosis on the outcome of Acanthamoeba keratitis

OBJECTIVE

To examine the impact of topical corticosteroid use before the diagnosis of Acanthamoeba keratitis (AK) on final visual outcomes and to determine the prognostic factors predicting poorer outcomes.

DESIGN

Cohort study.

PARTICIPANTS

A total of 209 eyes of 196 patients with retrievable medical records, diagnosed with AK at Moorfields Eye Hospital, London, between January 1991 and April 2012. One eye was randomly excluded from analysis in the 13 cases of bilateral AK.

METHODS

Patient demographic, initial clinical examination findings, and management details were collected. The outcomes of patients treated with topical corticosteroids before diagnosis of AK were compared with those not treated with topical corticosteroids before diagnosis. A multivariable logistic model, optimized for prior corticosteroid use, was used to derive the odds ratios (ORs) of a suboptimal visual outcome.

MAIN OUTCOME MEASURES

Suboptimal visual outcome was defined as final visual acuity (VA) ≤ 20/80, corneal perforation, or need for keratoplasty.

RESULTS

Acanthamoeba keratitis was diagnosed on microbiological culture in 94 eyes (48.0%), on histopathologic examination in 27 eyes (13.8%), on confocal microscopy in 38 eyes (19.4%), and on the basis of a typical clinical course and response to treatment in 37 eyes (18.9%). Final VA and prior corticosteroid use data were available for 174 eyes (88.8%). In multivariable analysis, corticosteroid use before diagnosis was associated with suboptimal visual outcome (OR, 3.90; 95% confidence interval [CI], 1.78-8.55), as were disease stage 3 at presentation (OR, 5.62; 95% CI, 1.59-19.80) and older age (60+ years) at diagnosis (OR, 8.97; 95% CI, 2.13-37.79).

CONCLUSIONS

Corticosteroid use before diagnosis of AK is highly predictive of a poorer visual outcome. This is largely due to the initial misdiagnosis of AK as herpetic keratitis. It is important to include AK in the differential diagnosis of keratitis in all contact lens users with keratitis, particularly before making a diagnosis of herpes keratitis and before the use of topical corticosteroids in the therapy of any indolent keratitis.

Acanthamoeba, fungal, and bacterial keratitis: a comparison of risk factors and clinical features

PURPOSE

To determine risk factors and clinical signs that may differentiate between bacterial, fungal, and acanthamoeba keratitis among patients presenting with presumed infectious keratitis.

DESIGN

Hospital-based cross-sectional study.

METHODS

We examined the medical records of 115 patients with laboratory-proven bacterial keratitis, 115 patients with laboratory-proven fungal keratitis, and 115 patients with laboratory-proven acanthamoeba keratitis seen at Aravind Eye Hospital, Madurai, India, from 2006-2011. Risk factors and clinical features of the 3 organisms were compared using multinomial logistic regression.

RESULTS

Of 95 patients with bacterial keratitis, 103 patients with fungal keratitis, and 93 patients with acanthamoeba keratitis who had medical records available for review, 287 (99%) did not wear contact lenses. Differentiating features were more common for acanthamoeba keratitis than for bacterial or fungal keratitis. Compared to patients with bacterial or fungal keratitis, patients with acanthamoeba keratitis were more likely to be younger and to have a longer duration of symptoms, and to have a ring infiltrate or disease confined to the epithelium.

CONCLUSIONS

Risk factors and clinical examination findings can be useful for differentiating acanthamoeba keratitis from bacterial and fungal keratitis.

In vitro efficacy of corifungin against Acanthamoeba castellanii trophozoites and cysts

Painful blinding keratitis and fatal granulomatous amebic encephalitis are caused by the free-living amebae Acanthamoeba spp. Several prescription eye medications are used to treat Acanthamoeba keratitis, but the infection can be difficult to control because of recurrence of infection. For the treatment of encephalitis, no single drug was found useful, and in spite of the use of a combination of multiple drugs, the mortality rate remains high. Therefore, efficient, novel drugs are urgently needed for the treatment of amebic keratitis and granulomatous amebic encephalitis. In this study, we identified corifungin, a water-soluble polyene macrolide, as amebicidal. In vitro, it was effective against both the trophozoites and the cysts. Transmission electron microscopy of Acanthamoeba castellanii incubated with corifungin showed the presence of swollen mitochondria, electron-dense granules, degeneration of cytoplasm architecture, and loss of nuclear chromatin structure. These changes were followed by lysis of amebae. Corifungin also induced the encystment process of A. castellanii. There were alterations in the cyst cell wall followed by lysis of the cysts. Corifungin is a promising therapeutic option for keratitis and granulomatous amebic encephalitis.

Non-contact lens use-related Acanthamoeba keratitis in southern Turkey: evaluation of risk factors and clinical features

PURPOSE

To assess the diagnostic methods, risk factors, and clinical features of Acanthamoeba keratitis cases in patients who do not wear contact lenses.

METHODS

Medical records of 26 consecutive patients with non-contact lens-related Acanthamoeba keratitis, who were followed up at the tertiary eye care center between May 2010 and May 2012, were analyzed. Laboratory, demographic, and clinical findings were evaluated pertaining to the patients.

RESULTS

Twenty-six non-contact lens-related Acanthamoeba keratitis cases were included in the study. The main risk factors were trauma (group 1, n = 13 patients) and ocular surface disease (group 2, n = 12 patients). One patient had both of the risk factors mentioned above. Overall test results showed that Acanthamoeba positivity rates were 15.3% for direct microscopy, 46.1% for culture, 92.3% for conventional polymerase chain reaction (PCR), and 100% for real-time PCR. The rates of full-thickness corneal involvement and ring-shaped infiltrations were higher in group 2, whereas superficial keratitis and radial keratoneuritis were higher in group 1. The final visual acuities were significantly better in group 1 than group 2 (p<0.025).

CONCLUSIONS

This study is the first regional report from Turkey about Acanthamoeba keratitis in non-contact lens users. A majority of cases admitted to a tertiary eye care center were related to trauma or ocular surface disease. Physician suspicion is critically important for the timely diagnosis of these cases. At this point, molecular diagnostic tests (PCR or real-time PCR) seem to support the clinical diagnosis of Acanthamoeba keratitis with the help of fast and reliable results.

Reevaluating the role of Acanthamoeba proteases in tissue invasion: observation of cytopathogenic mechanisms on MDCK cell monolayers and hamster corneal cells

The morphological analysis of the cytopathic effect on MDCK cell monolayers and hamster cornea and qualitative and quantitative analyses of conditioned medium and proteases were evaluated and compared between two strains of Acanthamoeba genotype T4. Further than highlighting the biological differences found between both strains, the most important observation in this study was the fact that proteases both in total extracts and in conditioned medium are apparently not determinant in tissue destruction. An interestingly finding was that no lysis of corneal tissue was observed as it was previously suggested. These results, together with previous studies, allow us to conclude that the invasion and disruption of corneal tissue is performed by the penetration of the amoebae through cell junctions, either by the action of proteases promoting cellular separation but not by their destruction and/or a mechanical effect exerted by amoebae. Therefore, contact-dependent mechanisms in Acanthamoeba pathogenesis are more relevant than it has been previously considered. This is supported because the phagocytosis of recently detached cells as well as those attached to the corneal epithelium leads to the modification of the cellular architecture facilitating the migration and destruction of deeper layers of the corneal epithelium.

Comparison of UVA- and UVA/riboflavin-induced growth inhibition of Acanthamoeba castellanii

PURPOSE

To investigate whether ultraviolet light (UVA) at 365 nm can inhibit/eliminate Acanthamoeba growth and if riboflavin would potentiate such an association.

METHODS

Acanthamoeba castellanii in a fluid medium with a concentration of approximately 1.7 × 10(4) protozoa/ml were prepared with (0.01 %) and without riboflavin. Exposure of UVA (dose 5.475 J/cm(2)) took place twice, with each illumination period followed by culturing of 10 μl in peptone yeast-extract glucose (PYG) medium for 7 days. Every suspension prepared had a non-exposed control solution. Determination of Acanthamoeba was conducted daily, by count in Burker chamber days 4 through 7 after exposure. Statistical analysis was done by repeated-measurement ANOVA and post-hoc analysis for unpaired samples.

RESULTS

The exposure of ultraviolet light resulted in an inhibited growth of Acanthamoeba compared to the non-exposed solutions, with a statistically significant reduction over time (p = 0.0003). The addition of riboflavin did not amplify the effect, and there were no tendencies for an interaction effect between UVA and riboflavin.

CONCLUSIONS

The antiprotozoal effect of the UVA wavelength, utilized in CXL, is solely mediated by ultraviolet light, and riboflavin does not seem to amplify the antimicrobial efficacy.

Practice patterns and opinions in the treatment of acanthamoeba keratitis

PURPOSE

Management of acanthamoeba keratitis remains challenging for ophthalmologists. We conducted a survey of members of The Cornea Society to elicit expert opinions on the diagnosis and treatment of acanthamoeba keratitis.

METHODS

An online survey was sent to all subscribers of The Cornea Society via the kera-net listserv. Descriptive statistics were performed.

RESULTS

Eighty-two participants completed the online survey. Of the 82 respondents, 76.8% included the combination of clinical examination and culture in their diagnostic strategy and 43.9% used confocal microscopy. Most respondents (97.6%) had used combination therapy with multiple agents to treat acanthamoeba keratitis at some point in the past, whereas a smaller proportion (47.6%) had ever used monotherapy. Respondents most commonly chose polyhexamethylene biguanide as the ideal choice for monotherapy (51.4%), and dual therapy with a biguanide and diamidine as the ideal choice for combination therapy (37.5%). The majority of respondents (62.2%) reported using topical corticosteroids at least some of the time for acanthamoeba keratitis. Keratoplasty was an option considered by most respondents (75.6%), although most (85.5%) would only perform surgery after medical treatment failure.

CONCLUSIONS

There was a wide range of current practice patterns for the diagnosis and treatment of acanthamoeba keratitis. The lack of sufficiently powered comparative effectiveness studies and clinical trials makes evidence-based decision-making for this disease difficult.

Visual outcome in Japanese patients with Acanthamoeba keratitis

PURPOSE

To identify prognostic factors affecting visual outcome in Acanthamoeba keratitis (AK) treated with topical chlorhexidine gluconate (CHG).

METHODS

A total of 35 eyes in 34 patients with AK were treated with 0.02% topical CHG. Patients were divided into two groups according to the final visual outcome: Group 1, final visual acuity (VA) of 20/25 or greater (22 eyes); Group 2, less than 20/25 (13 eyes). We compared these groups and evaluated the effectiveness of topical CHG compared with outcomes in previous reports.

RESULTS

Ring infiltrate was observed more often in Group 2 (4.5% vs 61.5%, OR 33.6, 95% confidence interval (CI) 3.4-333.9, P<0.01). The duration between onset and diagnosis of AK was significantly longer (24.9 days vs 48.4 days, OR 1.03, 95% CI 1.00-1.06, P = 0.04) and VA at initial examination (log MAR) significantly lower (0.47 vs 1.59, OR 25.5, 95% CI 3.4-186.7, P<0.01) in Group 2 (visual outcome <20/25). Multivariate analysis revealed that only VA at initial examination was independently associated with worse visual outcome (adjusted OR 24.5, 95% CI 1.9-312.6, P=0.01). Seventeen (85.0%) of the 20 eyes diagnosed within 1 month and 24 (82.8%) of 29 eyes diagnosed within 2 months achieved a VA of 20/40 or greater.

CONCLUSION

VA at initial examination was the most predictive factors for final visual outcome in AK. Topical CHG was comparably effective to other treatments, including polyhexamethyl biguanide and propamidine isethionate.

Microbiological cure times in acanthamoeba keratitis

AIMS

The purpose of this study was to estimate the duration of treatment necessary for sequential acanthamoeba laboratory tests from corneal scrapings to become negative, and to assess predictors that affect this duration period.

METHODS

We included all patients with at least one positive acanthamoeba culture or Giemsa stain at the F.I. Proctor Foundation Microbiology Laboratory from 1996 to 2009. A parametric survival analysis was performed among patients with repeat cultures to assess significant predictors for extended clearance time. Simulations were performed to estimate clearance time in the entire patient population, assuming imperfect sensitivity.

RESULTS

Thirty-seven patients with laboratory evidence of acanthamoeba had testing at 69 time points. The median clearance time among eyes with repeat cultures was 42.5 days (interquartile range (IQR) 22.0-82.0 days; unadjusted parametric model). Initial visual acuity was the only predictor significantly associated with clearance time in univariate analyses (P<0.0001). Using initial visual acuity as a predictor for clearance time among the entire patient population, the estimated clearance time decreased to 38.7 days (95% confidence interval (CI) 27.9-53.5 days). When the imperfect sensitivity of the culture technique was also taken into account, the estimated clearance time was 44.1 days (95% CI 31.9-61.0 days).

CONCLUSION

The duration of infection with acanthamoeba keratitis undergoing treatment has not been well characterized. In this report we estimate a median clearance time of approximately 6 weeks, with an IQR of 22-82 days.

Penetrating keratoplasty in active Acanthamoeba keratitis

PURPOSE

To report the results of penetrating keratoplasty (PK) in active Acanthamoeba keratitis (AK).

METHODS

Nine patients with deep stromal infiltrates because of AK were treated with intensive antiamoebic medical therapy followed by PK during the acute infectious phase because of poor clinical response or poor compliance. Antiamoebic therapy was tapered after PK.

RESULTS

Visual acuity ranged from 20/15 to 20/50 after an average of 17 months after PK with no signs of recurrences. Patients had rapid resolution of symptoms.

CONCLUSION

PK is a viable option for active AK not responding to maximum medical treatment.

Pathogenesis of acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a serious infection of the cornea. At present, diagnosis of the disease is not straightforward and treatment is very demanding. While contact lens wear is the leading risk factor for A K, Acanthamoeba parasites are increasingly recognized as an important cause of keratitis in non-contact lens wearers. The first critical step in the pathogenesis of infection is the adhesion of the microbe to the surface of the host tissues. Acanthamoebae express a major virulence protein, the mannose-binding protein (MBP), which mediates the adhesion of amoebae to the surface of the cornea. The MBP is a transmembrane protein with characteristics of a typical cell surface receptor. Subsequent to the MBP-mediated adhesion to host cells, the amoebae produce a contact-dependent metalloproteinase and several contact-independent serine proteinases. These proteinases work in concert to produce a potent cytopathic effect (CPE ) involving killing of the host cells, degradation of epithelial basement membrane and underlying stromal matrix, and penetration into the deeper layers of the cornea. In the hamster animal model, oral immunization with the recombinant MBP protects against AK, and this protection is associated with an increased level of anti-MBP IgA in tears of protected animals. Normal human tear fluid contains IgA antibodies against Acanthamoeba MBP that is likely to provide protection by inhibiting the adhesion of parasites to host cells. Indeed, in in vitro CPE assays, even a low concentration of tears (10 microL of undiluted tears per milliliter of media) almost completely inhibits Acanthamoeba-induced CPE . In addition to adherence-inhibiting, IgA-mediated protection, human tears also contain IgA-independent factors that provide protection against Acanthamoeba-induced CPE by inhibiting the activity of cytotoxic proteinases. Characterization of the CPE-inhibitory factors of human tears should lead to a better understanding of the mechanism by which the tissues of the host resist the infection and also help decode circumstances that predispose to Acanthamoeba infections.

Resurgence of Acanthamoeba keratitis in Auckland, New Zealand: a 7-year review of presentation and outcomes

PURPOSE

To investigate the presentation, clinical characteristics and outcomes of Acanthamoeba keratitis (AK) in Auckland, New Zealand over a 7-year period.

METHODS

Retrospective analysis of all cases of AK treated by the tertiary corneal service at Auckland City Hospital/ University of Auckland Department of Ophthalmology (August 2001 to May 2008). Data were collected regarding age, gender, contact lens history, presenting signs and symptoms, diagnosis at first presentation, time to final diagnosis, identifiable risk factors, presenting and final visual acuity, results of microbiological testing, medical treatment, surgical interventions, recurrence of disease and length of follow up. All photographs and in vivo confocal microscopy images were reviewed.

RESULTS

Twenty-five eyes of 25 patients were identified with a diagnosis of AK (mean age 40 +/- 13 years). Ninety-six per cent were contact lens wearers. Mean time to diagnosis was 41 +/- 49 days (range 0-181 days, median 21 days). Fourteen patients (56%) had been treated with topical corticosteroids prior to the diagnosis. Early diagnosis of AK (<21 days) was associated with significantly better final visual acuity and did not require any surgical intervention compared with those diagnosed at a later stage. Six patients, all in the late diagnosis group, required surgical intervention.

CONCLUSIONS

AK has become significantly more common in New Zealand in the current decade. This study highlights the fundamental importance of early diagnosis and appropriate management in ensuring favourable outcomes. Practitioners should maintain a clinical suspicion of AK, especially as 96% of the subjects in this study were contact lens wearers.