Decreased corneal sensation as an initial feature 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.

Acanthamoeba Keratitis, Pathology, Diagnosis and Treatment

Acanthamoeba keratitis is an unusual corneal infection that is recently increasing in frequency and is often contracted by contact lens wearers, someone who experienced recent eye trauma, or someone exposed to contaminated waters. Acanthamoeba survive in air, soil, dust, and water. Therefore, eye trauma and poor contact lens hygiene practices lead to the entrapment of debris and thus infection. Acanthamoeba keratitis results in severe eye pain, inflammation, and defects of the epithelium and stroma that can potentially result in vision loss if not diagnosed early and treated promptly. The disease can be diagnosed using corneal scrape/biopsy, polymerase chain reactions, impression cytology, or in vivo confocal microscopy. Once diagnosed, it is usually treated with an antimicrobial combination therapy of biguanide and aromatic diadine eye drops for several months. Advanced stages of the disease result in vision loss and the need for corneal transplants. Avoiding the risk factors and diagnosing the disease early are the most effective ways to combat Acanthamoeba keratitis.

Acanthamoeba keratitis - Clinical signs, differential diagnosis and treatment

PURPOSE

To summarize actual literature data on clinical signs, differential diagnosis, and treatment of acanthamoeba keratitis.

METHODS

Review of literature.

RESULTS

Clinical signs of acanthamoeba keratitis are in early stages grey-dirty epithelium, pseudodendritiformic epitheliopathy, perineuritis, multifocal stromal infiltrates, ring infiltrate and in later stages scleritis, iris atrophy, anterior synechiae, secondary glaucoma, mature cataract, and chorioretinitis. As conservative treatment, we use up to one year triple-topical therapy (polyhexamethylene-biguanide, propamidine-isethionate, neomycin). In therapy resistant cases, surgical treatment options such as corneal cryotherapy, amniotic membrane transplantation, riboflavin-UVA cross-linking, and penetrating keratoplasty are applied.

CONCLUSION

With early diagnosis and conservative or surgical treatment, acanthamoeba keratitis heals in most cases.

Total necrosis of cornea, iris and crystalline lens with exposure of vitreous hyaloid face in the context of recalcitrant acanthamoeba keratitis

PURPOSE

To report a rare and complicated case of acanthamoeba keratitis (AK) presented with total necrosis and dislodgment of cornea, iris, and crystalline lens with exposure of vitreous hyaloids face.

METHODS

Case report of 28-year-old female referred to the Farabi Eye Hospital with a history of known left eye AK since 4 months earlier. She also had a history of soft contact lens wear for two years and topical steroid use before proper diagnosis. Slit-lamp examination of the left eye revealed ring infiltration and stromal edema with haziness. The patient was prescribed anti-acanthamoeba treatment. She returned after 2 weeks with increasing ring infiltration and slight vision loss. Slit-lamp examination showed spontaneous total necrosis of cornea, iris, and crystalline lens with vitreous exposure to the air.

RESULTS

The patient underwent an urgent operation consisting of total debridement of necrotic tissues including a 1 mm rim of the sclera, anterior vitrectomy, tectonic penetrating keratoplasty, and amniotic membrane transplantation (AMT) with temporary lateral tarsorrhaphy. The graft was clear within the 4 years of follow-up. At the last examination, the left eye was pthysic due to ciliary shut down and visual acuity remained light perception.

CONCLUSION

Early suspicion to AK, especially in contact lens wearers, and applying diagnostic modalities like confocal microscopy and early appropriate management with cysticide agents such as polyhexamethylene biguanide may prevent these untoward complications.

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.

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.

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.

Arthrographis Keratitis Mimicking Acanthamoeba Keratitis

OBJECTIVE

To describe a case of keratomycosis caused by Arthrographis kalrae, mimicking Acanthamoeba keratitis.

METHODS

Case report.

RESULTS

A 23-year-old female contact lens wearer developed dendritic keratitis in her amblyopic eye (OD). Baseline vision was 20/50. Treatment with trifluridine 1% resulted in resolution of the dendrite, but an area of stromal haze developed, spreading to a discontinuous ring shape, and the vision dropped to 20/200. Photophobia was intense, and pain was out of proportion to the examination. Cultures were sent, and empiric treatment of Acanthamoeba was begun, without subsequent improvement. After 4 weeks, cultures were positive for a fungal species. Amphotericin 0.5% drops were begun, with moderately rapid resolution of the active keratitis. At last follow-up, best-corrected vision was 20/100. Review of the culture showed the organism to be Arthrographis kalrae.

CONCLUSION

Arthrographis kalrae has been reported only once before as an ocular pathogen. As in the previously reported case of Arthrographis, our patient's presentation was strongly suggestive of Acanthamoeba keratitis.

Corneal esthesiometry in the healthy horse

OBJECTIVE

To determine corneal sensitivity in healthy adult horses in order to establish reference values.

ANIMALS STUDIED

One hundred eyes of 50 healthy adult horses.

PROCEDURE

Corneal sensitivity was determined by evaluating the corneal touch threshold (CTT) in five different corneal regions using a Cochet-Bonnet esthesiometer.

RESULTS

Comparing CTT values (in mm filament length) of the five prescribed corneal regions revealed regional variations in corneal sensitivity, with the central region (21.15 +/- 6.23 mm) being the most sensitive, followed by the nasal (20.75 +/- 5.14 mm), temporal (20.70 +/- 5.37 mm), ventral (20.15 +/- 5.88 mm) and dorsal (15.85 +/- 3.70 mm) region. However, differences between the central, nasal, temporal and ventral regions were not statistically significant, whereas the dorsal region was significantly (P < 0.0001) less sensitive compared to the other regions. Division of the horses into three age groups revealed an insignificant decrease in corneal sensitivity with age in the nasal, temporal, ventral and central region, and an insignificant increase with age in the dorsal region. Correlation of corneal sensitivity with age was statistically significant in the central, ventral and temporal region. No statistically significant difference in the CTT was found between left and right eyes and between males and females.

CONCLUSIONS

CTT values in 100 eyes of 50 healthy adult horses evaluated with a Cochet-Bonnet esthesiometer generated reference values. Reference values are necessary to determine alterations of corneal sensation accompanying various eye diseases or systemic diseases.

Acanthamoeba keratitis

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. The first cases were recognized in 1973, but the disease remained very rare until the 1980s, when an increase in incidence mainly associated with contact lens wear was reported. There is an increased risk when contact lens rinsing and soaking solutions are prepared with nonsterile water and salt tablets. The clinical picture is often characterized by severe pain with an early superficial keratitis that is often treated as herpes simplex infection. Subsequently a characteristic radial perineural infiltration may be seen, and ring infiltration is common. Limbitis and scleritis are frequent. Laboratory diagnosis is primarily by culture of epithelial samples inoculated onto agar plates spread with bacteria. Direct microscopy of samples using stains for the cyst wall or immunostaining may also be employed. A variety of topically applied therapeutic agents are thought to be effective, including propamidine isethionate, clotrimazole, polyhexamethylene biguanide, and chlorhexidine. Various combinations of these and other agents have been employed, often resulting in medical cure, especially if treatment is commenced early in the course of the disease. Penetrating keratoplasty is preferably avoided in inflamed eyes, but may be necessary in severe cases to preserve the globe or, when the infection has resolved, to restore corneal clarity for optical reasons.