Atypical presentation of Acanthamoeba keratitis

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.

Lately Diagnosed Acanthamoeba Keratitis Manifesting as an Intrastromal Corneal Abscess: A Case Report

ABSTRACT

A 42-year-old female contact lens wearer presented to a local emergency department with a 3-day history of decreased vision and ocular discomfort in her right eye. She was started on topical fluorometholone and oral acyclovir with initial diagnosis of herpes simplex keratitis. After 3 weeks of worsening symptoms, she was diagnosed with bacterial corneal ulcer and treated with levofloxacin eye drops every 2 hr. After 14 days of no improvement, she was referred to our clinic for further workup. Slitlamp examination demonstrated a solitary dense 3×3-mm infiltration involving anterior and central corneal stroma. The overlying epithelium was intact, and there was no subepithelial infiltration, radial perineuritis, keratic precipitates, or anterior chamber reaction. Corneal sensation was normal. Confocal microscopy and corneal biopsy were definitive for Acanthamoeba infection. The patient received polyhexamethylene biguanide 0.02% every 2 hr and oral ketoconazole 200 mg twice a day, which resulted in improvement in her signs and symptoms within 10 days. The medications were gradually tapered off over 5 months per clinical response. At the 9-month follow-up visit, the best-corrected visual acuity was 5/10 with a superficial central stromal scar at slitlamp examination. Acanthamoeba infection should be considered in contact lens wearers who present with intrastromal corneal abscess.

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.

Atypical presentation of acanthamoeba keratitis resembling central toxic keratopathy

PURPOSE

To describe an atypical case of acanthamoeba keratitis with positive in vivo confocal microscopy in a non-contact lens user who presented with signs and symptoms suggestive of central toxic keratopathy.

OBSERVATIONS

The patient presented with bilateral, though sequential, decreased visual acuity with mild pain. Examination showed stromal haze with corneal flattening and thinning without epithelial defects. Optical coherence tonometry of the right eye revealed an inverse dome-shaped appearance of the opacity and in-vivo confocal imaging showed double-walled cysts consistent with acanthamoeba. Corneal haze, stromal loss, resolved and visual acuity improved over time.

CONCLUSION AND IMPORTANCE

Acanthamoeba is a rare cause of infectious keratitis that is most often associated with contact lens wear in developed countries. Typically, it presents with a unilateral decrease in visual acuity, photophobia, watering, and pain that is out of proportion to slit lamp examination findings. However, many atypical presentations have been reported in the literature. Consequently, it may be misdiagnosed, especially early in the course of the disease. This delay in diagnosis can lead to progressive ulceration and visual impairment. In addition, cyst formation can make eradication with anti-amoebic treatment especially difficult.Central toxic keratopathy is a non-inflammatory clinical syndrome of unknown etiology that is most often associated with excimer laser ablation, though other associated causes have been reported. It is characterized by a central or paracentral opacity with corneal stromal loss and resultant hyperopic shift. The opacification and stromal loss mostly resolve over the course of months with an improvement in visual acuity. This report may help physicians broaden their differential and correctly diagnose atypical presentations of amoebic infection.

Clinical aspects and prognosis of polymicrobial keratitis caused by different microbial combinations: a retrospective comparative case study

PURPOSE

The purpose of this study is to compare the predisposing factors, clinical findings, treatment results, and prognosis for polymicrobial keratitis.

METHODS

In this retrospective comparative case study, we identified the cases of polymicrobial keratitis from the microbiological records (n = 649) at Balcalı Hospital, Çukurova University (Adana, Turkey; October 2010-2018). We included all the cases of infectious keratitis with two different types of microbial agents and grouped them as follows: group 1 (n = 25), bacterium-fungus coexistence; group 2 (n = 12), herpes simplex virus (HSV) or Acanthamoeba with bacterial infection; and group 3 (n = 7), HSV or Acanthamoeba with fungal infection. We compared the clinical and microbiological characteristics, and treatment outcomes among the groups.

RESULTS

In our study, we found that 44 infectious keratitis cases (6.7%) were of polymicrobial nature. The mean follow-up period was 11.4 ± 17.8 months. In total, 17 different bacteria along with 3 different fungi, HSV, and Acanthamoeba were isolated. The most common bacterium was Staphylococcus epidermidis (25%). Most of the fungal pathogens were filamentous. Patients with initial treatment failure and requiring surgical intervention had larger infiltrates (p = 0.023, p = 0.003, respectively) than other patients. Older age was associated with delayed recovery and poor visual prognosis.

CONCLUSIONS

Bacterial-fungus coexistence is the most common combination among patients, but other combinations should also be considered for suspected polymicrobial etiology. The corneal infiltrate size may be an important indicator of the course of disease and response to treatment. A closer and longer follow-up period should be planned for older patients.

The impact of triathlon training and racing on athletes' general health

Although the sport of triathlon provides an opportunity to research the effect of multi-disciplinary exercise on health across the lifespan, much remains to be done. The literature has failed to consistently or adequately report subject age group, sex, ability level, and/or event-distance specialization. The demands of training and racing are relatively unquantified. Multiple definitions and reporting methods for injury and illness have been implemented. In general, risk factors for maladaptation have not been well-described. The data thus far collected indicate that the sport of triathlon is relatively safe for the well-prepared, well-supplied athlete. Most injuries 'causing cessation or reduction of training or seeking of medical aid' are not serious. However, as the extent to which they recur may be high and is undocumented, injury outcome is unclear. The sudden death rate for competition is 1.5 (0.9-2.5) [mostly swim-related] occurrences for every 100,000 participations. The sudden death rate is unknown for training, although stroke risk may be increased, in the long-term, in genetically susceptible athletes. During heavy training and up to 5 days post-competition, host protection against pathogens may also be compromised. The incidence of illness seems low, but its outcome is unclear. More prospective investigation of the immunological, oxidative stress-related and cardiovascular effects of triathlon training and competition is warranted. Training diaries may prove to be a promising method of monitoring negative adaptation and its potential risk factors. More longitudinal, medical-tent-based studies of the aetiology and treatment demands of race-related injury and illness are needed.

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.

Clinical and histologic evaluations of experimental Acanthamoeba keratitis

Amoebic keratitis, a sight-threatening, progressive corneal disease, is commonly caused by ubiquitous, pathogenic, free-living Acanthamoeba spp., which are widely distributed in the environment. We investigated clinical findings and histology of Acanthamoeba keratitis in a rat cornea model. Experimental Acanthamoeba keratitis was induced in Wistar rats by intrastromal inoculation of Acanthamoeba castellanii trophozoites. The clinic features of Acanthamoeba keratitis by day 70 are observed. All rats inoculated with Acanthamoeba developed keratitis. Histologically, the eyes displayed blood vessels, edema, and amoebae in stroma. A mixed cellular response, including neutrophils, mononuclear cells, and spindle-shaped cells, was seen. In conclusion, progressive, suppurative Acanthamoeba keratitis can be induced in the rat cornea model. This rat cornea model assists researchers who study the pathogenesis of Acanthamoeba keratitis and devise treatment for this difficult condition.

Updates in Acanthamoeba Keratitis

PURPOSE

Acanthamoeba keratitis is a potentially blinding microbial disease that has been increasing in incidence during the past two decades. Prognosis of this serious disease had been dismal, but improvement in diagnosis, a better understanding of the natural course of the disease, and recent introduction of multiple and effective therapeutic agents have resulted in improvement of visual outcomes.

METHODS

A review of literature pertaining to Acanthamoeba keratitis.

RESULTS

Contact lens wear and exposure to contaminated water sources remain the most important risk factors; however, in vivo confocal microscopy and improved biomicroscopic screening have proven instrumental in accurate early diagnosis. Complications of Acanthamoeba keratitis include dacryoadenitis, corneal melting and scarring, severe secondary glaucoma, cataract, and chronic anterior segment inflammation that can rarely lead to reactive blinding retinal ischemia. Combination chemotherapeutic agents have been shown to be more effective than monotherapy, whereas rehabilitative surgery such as penetrating keratoplasty is best performed on a quiet eye free of ocular inflammation and with no residual amoebae.

CONCLUSIONS

Increased suspicion by clinicians for Acanthamoeba and confocal microscopy have allowed more rapid and accurate diagnosis; treatment with multiple antiamoeba drugs is essential to disease resolution. Provided there are no residual amoebae after treatment, penetrating keratoplasty has been successful in visual rehabilitation. Secondary glaucoma occurs frequently and may require drainage procedures for control of intraocular pressure. Posterior complications are rare but may lead to ischemic retinitis.

Unusual Case of Acanthamoeba Keratitis in a Contact Lens Wearer

PURPOSE

To present an atypical case of acanthamoeba keratitis in a soft contact lens wearer.

METHODS

A case report of a 28-year-old female soft contact lens wearer with a 6-day history of redness and blurred vision in her right eye. Examination showed stromal keratitis that did not respond to therapy for herpes simplex virus. Four weeks later, the patient had increased stromal infiltration, an endothelial plaque, and a hypopyon. She did not complain of pain apart from mild discomfort. Corneal smears and anterior chamber tap were negative for bacteria, fungi, acanthamoeba, and herpes simplex virus, and the patient was prescribed fortified antibiotics. One week later, a large epithelial defect with a surrounding ring infiltrate was apparent. Corneal biopsy showed acanthamoeba.

RESULTS

The acanthamoeba keratitis resolved with successful treatment. One year later, the patient had a residual visual deficit secondary to stromal scarring and her best-corrected visual acuity was 20/29.

CONCLUSIONS

This case emphasizes the importance of considering acanthamoeba species in the differential diagnosis of keratitis, even without the classic symptom of severe pain. A high degree of suspicion with rapid and appropriate treatment may result in improved recovery of vision.

[Acanthamoeba stromal keratitis: epidemiology and prognosis factors]

PURPOSE

Early treatment of amebic stromal keratitis can change patients' final visual and esthetic prognosis. The aim of this study was to review all proven Acanthamoeba stromal keratitis cases presenting at our ophthalmology emergency department over the past 3 years, in order to delineate the incidence and the factors still leading to this serious complication.

PATIENTS

and methods: All cases of Acanthamoeba stromal keratitis confirmed with a parasitology examination and treated between January 2000 and December 2002 were recorded. During this period of time, eight patients were identified with this condition. Their charts, as well as biomicroscopic, therapeutic, and outcome data were analyzed.

RESULTS

All patients were referred in a second or third intention. Only one patient did not usually wear contact lenses. Six patients had an associated bacterial abscess. The typical amebic annular infiltrate was only observed in one patient. Three patients received an effective antiamebic treatment in the 15 days following the first symptoms and five patients 1 month or more after. An emergency keratoplasty was carried out in one patient. Finally, visual acuity was lower than 5/10 in all cases. The patients treated in the first 15 days had the best final visual acuity.

DISCUSSION

Soft contact lenses are still responsible for the majority of serious amebic corneal complications. Late diagnosis remains the main cause of Acanthamoeba stromal keratitis development, particularly in the absence of contact lens history, because of the delay in treatment.

CONCLUSION

The catastrophic consequences of this complication justify a systematic treatment against ameba in each case of suspected diagnosis. An early and effective treatment of the stromal amebic keratitis can increase the final visual prognosis.