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.

Depth, size of infiltrate, and the microbe - The trio that prognosticates the outcome of infective keratitis

PURPOSE

To analyze the influence of infiltrate size, depth, and organism on the outcome of microbial keratitis.

DESIGN

Retrospective comparative study.

METHODS

Medical records of patients with infective keratitis, who reported from January 2015 to December 2019 to a tertiary eye care center, were analyzed. Size and depth of ulcer at presentation were the factors used to group patients, and the influence on the outcome of the organism causing it was analyzed. Grouping was as follows: group A: ulcer size <6 mm/anterior to midstromal infiltrate, group B: ulcer < 6 mm/full-thickness infiltrate, group C: ulcer >6 mm/anterior to midstromal infiltrate, group D: ulcer > 6 mm/full-thickness infiltrate. Patients with viral keratitis or unidentified organism were excluded. Response to treatment and best-corrected visual acuity (BCVA) at the final follow-up were the outcome measures.

RESULTS

In the study, 1117/6276 patients were included, with 60.8% patients in group A. A significant improvement in visual acuity was noted in groups A/B compared to groups C/D. Group A had the best response to medical management, irrespective of the organism. Higher risk for surgery was noted in group C compared to group B, with group A as the reference. Overall resolution with medical treatment was noted in 70% miscellaneous keratitis, 64.8% bacterial keratitis, 64.3% mixed keratitis, 62.5% acanthamoeba keratitis, 52.6% fungal keratitis, and 12.1% Pythium keratitis. Bacteria and acanthamoeba responded better to medical management than fungal keratitis, whereas Pythium had the highest risk for surgery.

CONCLUSION

An interplay between virulence of the organism along with depth and size of the infiltrate determines the outcome of microbial keratitis.

Steroids in the Management of Infectious Keratitis

PURPOSE

To summarize the evidence base on the use of topical corticosteroids for infectious keratitis.

METHODS

Narrative review.

RESULTS

Infectious keratitis is a painful condition that often results in visually significant corneal stromal scarring, even when antimicrobial therapy is successful. Corticosteroids may reduce inflammation and subsequent scar formation and while relieving the acute ocular pain associated with a corneal ulcer. However, corticosteroids also reduce the host immune response, which could hinder the ability to clear infection. The safety and effectiveness of corticosteroids depends to a large part on the efficacy of the antimicrobials being used to treat the underlying infection. Randomized trials have found that corticosteroids are safe and effective for herpetic keratitis when used with appropriate antiviral therapy, and are safe for bacterial keratitis when used with broad spectrum topical antibiotics. The effectiveness of corticosteroids for bacterial keratitis has not been shown conclusively, although more advanced bacterial corneal ulcers may do better with corticosteroids. No randomized trials have assessed the safety and effectiveness of steroids for fungal or acanthamoeba keratitis. Animal studies suggest corticosteroids may be harmful in fungal keratitis, and observational human studies have found that steroids are harmful for fungal and acanthamoeba keratitis when started prior to anti-amoebics.

CONCLUSIONS

Topical corticosteroids, when used as an adjunct to antimicrobial therapy, may be beneficial if the antimicrobial being used can effectively clear or suppress the infection, such as in bacterial and herpetic keratitis. Randomized trials would be helpful to further delineate the role of corticosteroids for infectious keratitis.

Three Consecutive Cases of Ocular Polyhexamethylene Biguanide (PHMB) Toxicity Due to Compounding Error

Acanthamoeba keratitis is treated with long-term biguanide therapy, and the treatment itself can lead to ocular side effects. Knowledge of possible toxic complications can help in the better titration of the treatment regimen. Here, we describe the toxic side effects of polyhexamethylene biguanide (PHMB), which occurred in three consecutive patients treated with in-house compounded PHMB. There was an error in compounding the solution, with the resultant concentration of PHMB being around 0.2%. Patients developed ocular toxicity like conjunctival inflammation, persistent epithelial defect, and large pigment clumps on endothelium within six weeks of initiation of therapy. All of them developed rapidly progressive cataract and mydriatic pupil within three months. PHMB has the potential to cause irreversible damage to ocular structures, and the toxicity is time and concentration-dependent.

Atypical Presentation of Herpes Stromal Keratitis in a Contact Lens Wearer

This article describes the case of a 21-year-old female habitual contact lens wearer who complained of left eye pain, redness, and decreased vision for one week. When a ring-shaped corneal infiltration indicative of an Acanthamoeba infection was discovered, standard anti-amoebic topical therapy with polyhexamethylene biguanide and chlorhexidine was commenced. However, her keratitis worsened. At the same time, corneal scraping revealed no pathogens. An anterior chamber examination revealed a loss of corneal sensation, and a positive herpes simplex virus (HSV) immunoglobulin G serology test indicated HSV keratitis. She was eventually treated with oral anti-viral medication and recovered completely. Her case was unusual, as she had a history of contact lens use, painful corneal ulceration, and the development of Acanthamoeba keratitis-like corneal ring infiltration. This case also reinforces the various manifestations of HSV keratitis, which lead to delayed diagnosis and treatment.

Bacterial isolates and antimicrobial susceptibility pattern of ocular infection at a tertiary referral hospital in the South of Italy

PURPOSE

The present study aimed to determine the prevalence of bacterial and fungal infections of the eye and also to assess the antibiotic susceptibility pattern of bacterial isolates at a tertiary referral eye care hospital in Bari, Italy.

METHODS

Two hundred seventy three samples collected during a 2-year observation period. Culture, Gram's stain, potassium hydroxide mount and occasionally Giemsa staining was done for the clinical specimens. Antibiotic susceptibility testing was performed for bacterial growth.

RESULTS

Out of 273 samples processed, 236 (86.4%) yielded growth: of them, 183 (77,5%) were bacterial, 26 (11%) fungal, and 23 (9,7%) specimens showed the presence of Acanthamoeba. Among bacterial infections, 99 (54.5%) bacterial isolates were Gram-positives, and 82 (44.8%) were Gram-negatives. Among Gram positives, Tigecycline showed the greatest susceptibility (93.8%), followed by Linezolid (97%) and Daptomycin (95.18%). Gram negative bacteria strains were susceptible to Imipenem (95%), Meropenem (98,5%) and Amikacin (91%) Multidrug in vitro resistance (resistance >3 classes of antibiotics) was found in 45 Gram positive (63%). and 33 Gram negative (44%).

CONCLUSION

Conjunctival specimens yielded mainly bacterial growth with Staphylococcus species being the predominant isolate followed by Pseudomonas species. Findings from the current analysis evidence a substantial level of in vitro resistance to ≥3 antibiotics.

Topical Sustained Delivery of Miltefosine Via Drug-Eluting Contact Lenses to Treat Acanthamoeba Keratitis

This study aimed to develop a miltefosine-eluting contact lens (MLF-CL) device that would allow sustained and localized miltefosine release for the treatment of Acanthamoeba keratitis. MLF-CLs were produced in three different miltefosine doses by solvent-casting a thin miltefosine-polymer film around the periphery of a methafilcon hydrogel, which was then lathed into a contact lens. During seven days of in vitro testing, all three formulations demonstrated sustained release from the lens at theoretically therapeutic levels. Based on the physicochemical characterization of MLF-CLs, MLF-CL's physical properties are not significantly different from commercial contact lenses in terms of light transmittance, water content and wettability. MLF-CLs possessed a slight reduction in compression modulus that was attributed to the inclusion of polymer-drug films but still remain within the optimal range of soft contact lenses. In cytotoxicity studies, MLF-CL indicated up to 91% viability, which decreased proportionally as miltefosine loading increased. A three-day biocompatibility test on New Zealand White rabbits revealed no impact of MLF-CLs on the corneal tissue. The MLF-CLs provided sustained in vitro release of miltefosine for a week while maintaining comparable physical features to a commercial contact lens. MLF-CL has a promising potential to be used as a successful treatment method for Acanthamoeba keratitis.

[Confocal microscopy in the diagnosis of acanthamoeba keratitis]

Acanthamoeba keratitis (AK) is a dangerous disease of the cornea, its prevalence has increased significantly due to widespread usage of contact lenses. The similarity of the clinical manifestations of AK to other infectious keratitis (especially herpetic keratitis) requires introduction of a rapid diagnosis method into clinical practice.

PURPOSE

To evaluate the capabilities of corneal confocal microscopy (CCM) in the diagnosis of acanthamoeba keratitis.

MATERIAL AND METHODS

We examined 33 patients (35 eyes) with suspected acanthamoeba keratitis using light and laser confocal microscopy of the cornea (ConfoScan and HRT devices, respectively).

RESULTS

CCM was technically feasible in 23 of 35 cases (65.7%). Acanthamoeba cysts were detected in 16 cases (69.6%); trophozoites were visualized in 17.4% of cases; signs of keratoneuritis were detected in 12 eyes (52.2%); in 7 cases (30.4%), hyporeflective honeycomb-like cavities were observed in the stroma; deep stromal striae were observed in 9 cases (39.1%); activated keratocytes were detected in 11 patients (47.8%), and Langerhans cells were detected in 19 cases (82.6%).

CONCLUSIONS

The main diagnostic value of confocal microscopy is the detection of direct markers of AK - cysts and trophozoites of Acanthamoeba. Both light and laser CCM techniques are suitable for the diagnosis of AK, but the resolution of laser confocal microscopy is higher. The non-invasive nature of this method and the possibility of multiple subsequent examinations make it possible to verify the diagnosis of acanthamoeba keratitis and monitor the treatment.

Design, synthesis and antiamoebic activity of dysprosium-based nanoparticles using contact lenses as carriers against Acanthamoeba sp

PURPOSE

Contact lenses have direct contact with the corneal surface and can induce sight-threatening infection of the cornea known as Acanthamoeba keratitis. The objective of this study was to evaluate the dysprosium-based nanoparticles (Dy-based NPs), namely Fe₃ O₄ -PEG-Dy₂ O₃ nanocomposites and Dy(OH)₃ nanorods, as an active component against Acanthamoeba sp., as well as the possibility of their loading onto contact lenses as the drug administering vehicle to treat Acanthamoeba keratitis (AK).

METHODS

The Dy-based NPs were synthesized, and they were loaded onto commercial contact lenses. The loading content of the NPs and their release kinetics was determined based on the absorbance of their colloidal solution before and after soaking the contact lenses. The cytotoxicity of the NPs was evaluated, and the IC₅₀ values of their antiamoebic activity against Acanthamoeba sp. were determined by MTT colorimetric assay, followed by observation on the morphological changes by using light microscopy. The mechanism of action of the Dy-based NPs against Acanthamoeba sp. was evaluated by DNA laddering assays.

RESULTS

The loading efficiencies of the Dy-based NPs onto the contact lens were in the range of 30.6-36.1% with respect to their initial concentration (0.5 mg ml^-1 ). The Dy NPs were released with the flux approximately 5.5-11 μg cm^-2  hr^-1 , and the release was completed within 10 hr. The emission of the NPs consistently showed a peak at 575 nm due to Dy³⁺ ion, offering the possible monitoring and tracking of the NPs. The SEM images indicated the NPs are aggregated on the surface of the contact lenses. The DNA ladder assay suggested that the cells underwent DNA fragmentation, and the cell death was due most probably to necrosis, rather than apoptosis. The cytotoxicity assay of Acanthamoeba sp. suggested that Fe₃ O₄ -PEG, Fe₃ O₄ -PEG-Dy₂ O₃ , Dy(NO₃ )₃ .6H₂ O and Dy(OH)₃ NPs have an antiamoebic activity with the IC₅₀ value being 4.5, 5.0, 9.5 and 22.5 μg ml^-1 , respectively.

CONCLUSIONS

Overall findings in this study suggested that the Dy-based NPs can be considered as active antiamoebic agents and possess the potential as drugs against Acanthamoeba sp. The NPs could be loaded onto the contact lenses; thus, they can be potentially utilized to treat Acanthamoeba keratitis (AK).

Acanthamoeba Keratitis in Minors With Orthokeratology (OK) Lens Use: A Case Series

OBJECTIVES

Myopia progression is a significant public health issue. Methods to halt myopia progression in minors continue to gain momentum. Orthokeratology, with market penetrance estimates approximating 1%, is a corneal reshaping therapy and potential myopia progression treatment. Our objective was to explore whether orthokeratology may increase the frequency of Acanthamoeba keratitis compared with other lens modalities.

METHODS

Individuals less than 18 years diagnosed with Acanthamoeba keratitis (AK) at the University of Illinois at Chicago (UIC) Cornea Service between January 1st, 2003, and December 31st, 2016, were retrospectively reviewed. Subjects were grouped by lens modality (soft, rigid gas permeable [RGP], and orthokeratology), and all cases with orthokeratology lens use were reviewed. The primary outcome was a history of orthokeratology lens use in minors diagnosed with AK.

RESULTS

Forty-seven contact lens users less than 18 years were diagnosed with AK. The mean age was 15.0 years (range 12-17), 26 (55%) were women, and 4 (8.5%) had bilateral disease. Lens modality included 6 (13%) with orthokeratology, 39 (83%) with soft contact lenses, 0 with nonorthokeratology RGP (0%), and 2 (4%) unknown.

CONCLUSIONS

The proportion of orthokeratology cases among AK minors (13%) in our case series exceeds the expected proportion of orthokeratology cases expected based on orthokeratology market penetrance (1%). Results from this case series suggest a potential increased risk of AK in orthokeratology users compared with other lens modalities. In the context of the current myopia epidemic and concerns for halting myopia progression in minors, caution should be exercised when selecting appropriate treatment options to minimize the risk of AK.

Acanthamoeba keratitis challenges a case report

Acanthamoeba keratitis is a rare, chronic, mainly contact lens-related infection caused by a free-living amoeba found ubiquitously in water and soil. A case of a 9-year-old child, who presented to our clinic with painful, red left eye, associated with photophobia, and decreased visual acuity, wais reported. The clinical examination revealed a discoid opacity inferiorly bounded by a dense, gray infiltrate. The progressive nature of the corneal infiltrate, the epithelial defect, and the lack of response to treatment was highly suggestive for Acanthamoeba keratitis. The distinctiveness of this case was the presence of Acanthamoeba keratitis in a child without a history of trauma or contact lens usage, the lack of an appropriate diagnosis and management of this vision-threatening infection.

Medical interventions for acanthamoeba keratitis

BACKGROUND

Acanthamoeba are microscopic, free-living, single-celled organisms which can infect the eye and lead to Acanthamoeba keratitis (AK). AK can result in loss of vision in the infected eye or loss of eye itself; however, there are no formal guidelines or standards of care for the treatment of AK.

OBJECTIVES

To evaluate the relative effectiveness and safety of medical therapy for the treatment of AK.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (2015, Issue 1), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to January 2015), EMBASE (January 1980 to January 2015), PubMed (1948 to January 2015), Latin American and Caribbean Health Sciences Literature Database (LILACS) (1982 to January 2015), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic search for trials. We last searched the electronic databases on 9 January 2015.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of medical therapy for AK, regardless of the participants' age, sex, or etiology of disease. We included studies that compared either anti-amoeba therapy (drugs used alone or in combination with other medical therapies) with no anti-amoeba therapy or one anti-amoeba therapy with another anti-amoeba therapy.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results and full-text reports, assessed risk of bias, and abstracted data. We used standard methodological procedures as set forth by the Cochrane Collaboration.

MAIN RESULTS

We included one RCT (56 eyes of 55 participants) in this review. The study compared two types of topical biguanides for the treatment of AK: chlorhexidine 0.02% and polyhexamethylene biguanide (PHMB) 0.02%. All participants were contact lens wearers with a median age of 31 years. Treatment duration ranged from 51 to 145 days. The study, conducted in the UK, was well-designed and had low risk of bias overall.Outcome data were available for 51 (91%) of 56 eyes. Follow-up times for outcome measurements in the study were not reported. Resolution of infection, defined as control of ocular inflammation, relief of pain and photosensitivity, and recovery of vision, was 86% in the chlorhexidine group compared with 78% in the PHMB group (relative risk (RR) 1.10, 95% confidence intervals (CI) 0.84 to 1.42). In the chlorhexidine group, 20 of 28 eyes (71%) had better visual acuity compared with 13 of 23 eyes (57%) in the PHMB group at final follow-up (RR 1.26, 95% CI 0.82 to 1.94). Five participants required therapeutic keratoplasty: 2 in the chlorhexidine group compared with 3 in the PHMB group (RR 0.55, 95% CI 0.10 to 3.00). No serious adverse event related to drug toxicity was observed in the study.

AUTHORS' CONCLUSIONS

There is insufficient evidence to evaluate the relative effectiveness and safety of medical therapy for the treatment of AK. Results from the one included study yielded no difference with respect to outcomes reported between chlorhexidine and PHMB. However, the sample size was inadequate to detect clinically meaningful differences between the two groups as indicated by the wide confidence intervals of effect estimates.

[Purulent corneal ulcers: clinical presentation, diagnosis, and conservative treatment]

This is a detailed review of purulent corneal ulcer signs and symptoms, problems in diagnosis, and conservative treatment options.