Acanthamoeba keratitis. Potential role for topical clotrimazole in combination chemotherapy

Acanthamoeba Keratitis: an update on amebicidal and cysticidal drug screening methodologies and potential treatment with azole drugs

Introduction: Acanthamoeba encompasses several species of free-living ameba encountered commonly throughout the environment. Unfortunately, these species of ameba can cause opportunistic infections that result in Acanthamoeba keratitis, granulomatous amebic encephalitis, and occasionally systemic infection.Areas covered: This review discusses relevant literature found through PubMed and Google scholar published as of January 2021. The review summarizes current common Acanthamoeba keratitis treatments, drug discovery methodologies available for screening potential anti-Acanthamoeba compounds, and the anti-Acanthamoeba activity of various azole antifungal agents.Expert opinion: While several biguanide and diamidine antimicrobial agents are available to clinicians to effectively treat Acanthamoeba keratitis, no singular treatment can effectively treat every Acanthamoeba keratitis case.Efforts to identify new anti-Acanthamoeba agents include trophozoite cell viability assays, which are amenable to high-throughput screening. Cysticidal assays remain largely manual and would benefit from further automation development. Additionally, the existing literature on the effectiveness of various azole antifungal agents for treating Acanthamoeba keratitis is incomplete or contradictory, suggesting the need for a systematic review of all azoles against different pathogenic Acanthamoeba strains.

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.

Anti-amoebic potential of azole scaffolds and nanoparticles against pathogenic Acanthamoeba

Acanthamoeba spp. are free living amoeba (FLA) which are widely distributed in nature. They are opportunistic parasites and can cause severe infections to the eye, skin and central nervous system. The advances in drug discovery and modifications in the chemotherapeutic agents have shown little improvement in morbidity and mortality rates associated with Acanthamoeba infections. The mechanism-based process of drug discovery depends on the molecular drug targets present in the signaling pathways in the genome. Synthetic libraries provide a platform for broad spectrum of activities due to their desired structural modifications. Azoles, originally a class of synthetic anti-fungal drugs, disrupt the fungal cell membrane by inhibiting the biosynthesis of ergosterol through the inhibition of cytochrome P450 dependent 14α-lanosterol, a key step of the sterol pathway. Acanthamoeba and fungi share the presence of similar sterol intermediate, as ergosterol is also the major end-product in the sterol biosynthesis in Acanthamoeba. Sterols present in the eukaryotic cell membrane are one of the most essential lipids and exhibit important structural and signaling functions. Therefore, in this review we highlight the importance of specific targeting of ergosterol present in Acanthamoebic membrane by azole compounds for amoebicidal activity. Previously, azoles have also been repurposed to report antimicrobial, antiparasitic and antibacterial properties. Moreover, by loading the azoles into nanoparticles through advanced techniques in nanotechnology, such as physical encapsulation, adsorption, or chemical conjugation, the pharmacokinetics and therapeutic index of the drugs can be significantly improved. The current review proposes an important strategy to target Acanthamoeba using synthetic libraries of azoles and their conjugated nanoparticles for the first time.

Drug Discovery against Acanthamoeba Infections: Present Knowledge and Unmet Needs

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

The Development of Drugs against Acanthamoeba Infections

For the past several decades, there has been little improvement in the morbidity and mortality associated with Acanthamoeba keratitis and Acanthamoeba encephalitis, respectively. The discovery of a plethora of antiacanthamoebic compounds has not yielded effective marketed chemotherapeutics. The rate of development of novel antiacanthamoebic chemotherapies of translational value and the lack of interest of the pharmaceutical industry in developing such chemotherapies have been disappointing. On the other hand, the market for contact lenses/contact lens disinfectants is a multi-billion-dollar industry and has been successful and profitable. A better understanding of drugs, their targets, and mechanisms of action will facilitate the development of more-effective chemotherapies. Here, we review the progress toward phenotypic drug discovery, emphasizing the shortcomings of useable therapies.

Successful treatment of chronic stromal acanthamoeba keratitis with oral voriconazole monotherapy

PURPOSE

To describe the treatment of chronic stromal Acanthamoeba keratitis (AK) with oral voriconazole monotherapy.

METHODS

All cases of chronic stromal AK recalcitrant to traditional therapy subsequently treated with systemic voriconazole seen at the University of Illinois Eye and Ear Infirmary between June 2003 and July 2009 were reviewed for clinical presentation, clinical course, and outcome.

RESULTS

Three eyes of 2 patients were identified with culture-confirmed chronic stromal AK unresponsive to traditional antiacanthamoebal therapies, requiring topical corticosteroids to maintain corneal clarity. Oral voriconazole 200 mg twice daily achieved a rapid but transient reduction of inflammation and elimination of corticosteroid dependency but, in both patients, recrudesced approximately 6 weeks after its discontinuation. Subsequent repeated and/or extended use of oral voriconazole alone resulted in complete resolution ranging from 7 to 11 months off all medications with final best-corrected visual acuity ranging from 20/20 to 20/25.

CONCLUSIONS

Recalcitrant chronic Acanthamoeba stromal keratitis was successfully treated with extended systemic voriconazole administration with good preservation of vision. The clinical resolution of chronic stromal keratitis in our 2 cases suggests that voriconazole may have a larger role in the treatment of AK.

Medical treatment for combined Fusarium and Acanthamoeba keratitis

PURPOSE

Acanthamoeba and fungal keratitis are rare ocular infections. We report cases of combined Fusarium and Acanthamoeba keratitis and the clinical course of medical treatment.

METHODS

We reviewed the medical records of patients treated for culture-proven Acanthamoeba keratitis at a referral centre, during 2001-2006.

RESULTS

Eleven consecutive patients were treated for culture-proven Acanthamoeba keratitis during the 5 years, two of whom had combined fungal infections. A 29-year-old man presented with ground-glass corneal oedema and epitheliopathy caused by contact lens use. The other patient, a 7-year-old girl, had eye trauma that led to a feathery corneal infiltrate. Both cases were treated with topical 0.02% polyhexamethylene biguanide (PHMB), 0.1% propamidine, 1% clotrimazole and 5% natamycin. Therapeutic keratoplasty was not required in either case.

CONCLUSIONS

Timely identification of the pathogen, with repeated culture and smear if necessary, as well as adequate dosage to prevent recurrence is highly recommended in order to preclude the need for therapeutic penetrating keratoplasty.

Free-living, amphizoic and opportunistic amebas

Amebas belonging to the genera Naegleria, Acanthamoeba and Balamuthia are free-living, amphizoic and opportunistic protozoa that are ubiquitous in nature. These amebas are found in soil, water and air samples from all over the world. Human infection due to these amebas involving brain, skin, lung and eyes has increased significantly during the last 10 years. The epidemiology, immunology, protozoology, pathology, and clinical features of the infections produced by these protozoa differ strikingly. Infection by the pathogenic Naegleria fowleri is acquired by exposure to polluted water in ponds, swimming pools and man-made lakes. Raised temperatures during the hot summer months or warm water from power plants facilitate the growth of N. fowleri. N. fowleri is a thermophilic ameba that grows well in tropical and subtropical climates. The CNS infection, called Primary Amebic Meningoencephalitis (PAM), produced by N. fowleri is characterized by an acute fulminant meningoencephalitis leading to death 3-7 days after exposure. Victims are healthy, young individuals with a history of recent water-related sport activities. The portal of entry is the olfactory neuroepithelium. The pathologic changes are an acute hemorrhagic necrotizing meningoencephalitis with modest purulent exudate, mainly at the base of the brain, brain-stem and cerebellum. Trophozoites can be seen within the CNS lesions located mainly around blood vessels. Thus far 179 cases have been reported; 81 in the USA alone. Balamuthia mandrillaris and several species of Acanthamoeba are pathogenic "opportunistic" free-living amebas which cause Granulomatous Amebic Encephalitis (GAE) in humans and animals. GAE is an infection, usually seen in debilitated, malnourished individuals, in patients undergoing immunosuppressive therapy for organ transplants and in Acquired Immunodeficiency Syndrome (AIDS). The granulomatous component is negligible, particularly in immunocompromised individuals. Pathologically these amebas produce a patchy, chronic or subacute granulomatous encephalitis with the presence of trophozoites and cysts. The portal of entry is probably through the respiratory tract or an ulceration of the skin reaching the CNS by hematogenous spread. As of October 1, 1996, 166 cases (103 due to Acanthamoeba and 63 due to Balamuthia) of GAE have been reported from around the world. Of these 103 cases due to Acanthamoeba (72 have been reported in the USA alone, > 50 in AIDS). It is well known that several species of Acanthamoeba can also produce, chronic sight threatening ulceration of the cornea called Acanthamoeba keratitis (AK), mostly in contact lens wearers or in individuals with minor corneal abrasions. Hundreds of cases of AK have been documented world wide.

In vitro effectiveness of Thymus sipyleus subsp. sipyleus var. sipyleus on Acanthamoeba castellanii and its cytotoxic potential on corneal cells

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. Acanthamoeba keratitis is difficult to treat, without total efficacy in some patients because of cysts which is less susceptible than trophozoites to the usual treatments. We investigated here the in vitro amoebicidal activity of methanolic extract of Thymus sipyleus subsp. sipyleus var. sipyleus from Turkish flora against Acanthamoeba castellanii and also its cytotoxicity on corneal cells in vitro. Extract was evaluated for its amoebicidal activity using an inverted light microscope. The effect of the polar extract with the concentrations ranging from 1.0 to 32.0 mg/ml on the proliferation of A. castellanii trophozoites and cysts were examined in vitro. For the determination of cytotoxicity of the extract on corneal cells, agar diffusion tests were performed. According to results obtained from the tests, the extract evaluated here showed remarkable amoebicidal effect on A. castellanii. In the case of the cytotoxic activities, it showed no cytotoxicity for corneal cells in the concentration of 32 mg/ml. As a result, polar subfraction of the methanolic extract of Thymus sipyleus subsp. sipyleus var. sipyleus could be concluded as a new natural agent for the treatment of Acanthamoeba infections. On the other hand, it still needs to be further evaluated by in vivo test systems to confirm the efficiency of its biological effect.

Acanthamoeba sclerokeratitis: treatment with systemic immunosuppression

OBJECTIVE

This study describes the clinical features, management, and outcome of 19 patients who had severe Acanthamoeba sclerokeratitis (ASK) unresponsive to conventional management, requiring systemic immunosuppression to control disease.

DESIGN

Retrospective, non-comparative, interventional case series.

PARTICIPANTS

Records of all patients with Acanthamoeba keratitis treated at Moorfields Eye Hospital between 1989 and 2000 were reviewed. From more than 200 patients, 19 who developed ASK treated with systemic immunosuppression were identified.

MAIN OUTCOME MEASURES

Visual acuity, level of pain, and degree of inflammation were recorded after immunosuppressive treatment.

RESULTS

ASK requiring immunosuppression occurred in 20 eyes of 19 patients (11 males and 8 females). The mean age (mean +/- standard deviation) at onset was 38.6 +/- 13.2 years. On presentation, best-corrected visual acuity was counting fingers or worse in 11 eyes (55%), 6/18 to 6/60 in 5 eyes (25%), and 6/12 or better in 4 eyes (20%). The mean time between onset of initial symptoms of Acanthamoeba keratitis and commencement of systemic immunosuppression was 4.8 +/- 3.5 months. The mean duration of immunosuppression required to control inflammation was 7.2 +/- 3.9 months. Severe scleritic pain remained uncontrolled in two patients and resulted in enucleation. Best-corrected visual acuity at final follow-up was counting fingers or worse in eight eyes (40%), 6/18 to 6/60 in six eyes (30%), and 20/40 or better in six eyes (30%). The mean follow-up period after resolution of inflammation was 24.3 +/- 20.9 months (range, 0.2-59.7 months).

CONCLUSIONS

ASK is an uncommon complication of Acanthamoeba keratitis. The scleritis associated with this infection seems to be an immune-mediated response. After topical amebicidal treatment, systemic immunosuppression may be required to control the pain and tissue destruction associated with ASK.

Standardized method of measuring acanthamoeba antibodies in sera from healthy human subjects

Acanthamoeba species can cause serious, debilitating, and sometimes life-threatening infections. Three groups have been identified using morphological and immunological comparisons. Previous serological studies have utilized a variety of antigen preparations and assay methods and reported disparate (3 to 100%) results. This study was designed to (i) optimize an enzyme-linked immunosorbent assay for detecting serum antibodies to each of the Acanthamoeba serogroups and (ii) test 55 healthy individuals for specific immunoglobulin G reactivity. The highest signal-to-background ratio was found when 3,000 fixed, intact trophozoites per well were used with a 1:10 serum dilution. Sera yielding optical densities of <0.25 against all three Acanthamoeba serogroups were used to define the cutoff for positive results. The highest background reactivity with these sera was seen with Acanthamoeba polyphaga (serogroup 2), followed by Acanthamoeba culbertsoni (serogroup 3) and Acanthamoeba astronyxis (serogroup 1). Of 55 subjects tested, the highest number of positive results was seen with A. polyphaga (81.8%), followed by A. astronyxis (52.8%) and A. culbertsoni (40%). Seven serum samples (12.7%) were negative for all three Acanthamoeba serogroups, 16 (29.1%) were positive for one serogroup only, 16 were positive for two serogroups, and 16 reacted to all three serogroups. Further analysis showed no significant associations between serogroup reactivity and age or gender. However, some ethnic differences were noted, especially with A. polyphaga antigens. In that case, serum samples from Hispanic subjects were 14.5 times less likely to be positive (P = 0.0025) and had lower mean absorbance values (P = 0.047) than those from Caucasian subjects. Overall, these data suggest that Acanthamoeba colonization or infection is more common than previously thought. Mild or asymptomatic infections may contribute to the observed serum reactivities.

Advances in the management of keratomycosis and Acanthamoeba keratitis

PURPOSE

In the late 1960s, the management of fungal keratitis was a serious unresolved problem. Little was known of the epidemiology of the disease, and there were no antifungal agents formulated for use in the eye.

METHODS

A thorough review of the literature was done back to 1969 on clinical reports and experimental studies for keratomycosis and Acanthamoeba keratitis.

RESULTS

Since 1969, through basic and clinical research, the epidemiology of the disease worldwide is better understood. One new topical antifungal agent, natamycin, with efficacy against filamentous fungi has been developed and the pharmacokinetics of topically applied antifungal drops have been explored. Progress has been slow but the prognosis for keratomycosis has immeasurably improved over the period. Acanthamoeba was first recognized as an ocular pathogen in 1973 and was the cause of an epidemic in the 1980s caused by contaminated contact lens, although other risk factors were also identified. At the onset of the epidemic, there was no known treatment. but as a result of intense research efforts, within a few years a well-defined therapeutic approach had been developed that had a significant impact on the prognosis for this initially devastating infection. For both infections, the role of corticosteroids for controlling the inflammation remains controversial, but the place for keratoplasty is now well defined.

CONCLUSIONS

Although there has been steady progress in the management of both infections, continued research is the way to define more effective medical and surgical therapy.

Outcome of acanthamoeba keratitis treated with polyhexamethyl biguanide and propamidine

OBJECTIVE

This study investigates the clinical outcome of Acanthamoeba keratitis treated with polyhexamethyl biguanide (PHMB) and propamidine isethionate (Brolene).

DESIGN

A retrospective review of all patients treated for Acanthamoeba keratitis between September 1992 and February 1995 was carried out. All patients were treated with PHMB 0.02% and propamidine 0.1% hourly for 3 days, the frequency reduced to four to six times daily according to clinical response.

MAIN OUTCOME MEASURES

Age, gender, result of laboratory investigation, duration of disease before diagnosis, visual acuity (VA) pretreatment and post-treatment, need for keratoplasty, and presence of adverse reaction were measured.

RESULTS

One hundred eleven cases were identified in 105 patients (60 male, 45 female; mean age, 32). Ninety-two percent of infections were in contact lens wearers. The clinical diagnosis was confirmed by corneal culture or histopathology in 64 cases (57.7%). The diagnosis was made "early" (within 28 days) in 65 cases (58.6%). Twenty-one (18.9%) were "intermediate" (28 days-2 months) and 20 (18%) were "late" (> 2 months) diagnoses. Overall post-treatment VA was 6/12 or better in the majority (88/111, 79.3%) of cases, and 18 (16.2%) had VA of 6/36 or worse. The VA of > or = 6/12 was achieved by 90.8% of the early, 71.4% of the intermediate, and 65% of the late groups. Clinical relapses occurred in 19 patients on reducing the therapy. Treatment toxicity was never serious and consisted only of stinging or superficial punctate keratopathy. Keratoplasty was indicated in only ten patients, and disease activity was controlled adequately in all patients before grafting.

CONCLUSIONS

Combined treatment with PHMB and propamidine is well tolerated, nontoxic, and effective. Typically, visual outcome is favorable and the requirement for keratoplasty reduced markedly.

Amoebicidal efficiencies of various diamidines against two strains of Acanthamoeba polyphaga

The first medical cure of Acanthamoeba keratitis was obtained by use of propamidine isethionate. Since then, it has been the basic drug recommended for use in treatment. Because some Acanthamoeba strains have been reported to be resistant to propamidine and propamidine was found to be only weakly cysticidal, superior homologs such as butamidine, pentamidine, hexamidine, heptamidine, octamidine, and nonamidine were tested for their amoebicidal effects on two Acanthamoeba strains isolated from patients with keratitis. Trophozoicidal and cysticidal efficiencies were found to be increased from propamidine to nonamidine; i.e., when the alkyl chain connecting the two benzene rings in their molecular structures was elongated, in comparison with propamidine, hexamidine and octamidine were the most amoebicidal molecules. As a result of these data, a kinetic study carried out on propamidine, hexamidine, and octamidine demonstrated that the amoebicidal effects resulted from two events: the diffusion of molecules through the plasma membrane or the double wall of trophozoites or cysts, respectively, and the lethal effects of molecules on amoebic protoplasm. The diffusion kinetics were increased when the alkyl chain was elongated, i.e., with an increase in the lipophilic properties of molecules. In contrast, the lethal effect kinetics were found to be unchanged by this elongation, indicating that they originated from the cationic surface-active properties induced by the protonated amidine groups attached to each benzene ring, which themselves remained unchanged from one molecule to the other. These results strongly advocate the immediate replacement of propamidine by hexamidine in the medical treatment of Acanthamoeba keratitis; in France, 0.1% hexamidine eyedrops are available (Desomedine). The results also advocate clinical investigations on the efficiency and toxicity of octamidine, which appears to be the most amoebicidal diamidine in vitro.

Drug resistance and Acanthamoeba keratitis: the quest for alternative antiprotozoal chemotherapy

Trophozoites and cysts of 20 isolates of Acanthamoeba from the cornea and five from related samples were tested in vitro for sensitivity to ten drugs (three aromatic diamidines, two aminoglycosides, two macrolides, a polyene macrolide antibiotic, an organoarsenical and an antimetabolite) and two cationic antiseptics (chlorhexidine and polyhexamethylene biguanide, PHMB). Only chlorhexidine and PHMB showed uniform amoebacidal activity. Aromatic diamidines (pentamidine isethionate, propamidine isethionate and diminazene aceturate) generally proved effective against both forms of the amoeba; only pentamidine gave synergy with the biguanide while propamidine gave an additive effect. Other drugs tested proved erratic or ineffective against different isolates. Chlorhexidine alone, or together with propamidine, was subsequently used in two patients with proven Acanthamoeba keratitis; the causative isolates were sensitive to the individual compounds and to the combination in vitro. The treatment provided resolution of the clinical disease; amoebae were shown to be nonviable by histology and culture. The combination of chlorhexidine and propamidine is recommended for treatment of proven Acanthamoeba keratitis.

Acanthamoeba sclerokeratitis

We treated a healthy soft contact lens wearer who developed Acanthamoeba sclerokeratitis in the left eye. The patient had severe pain and ring-shaped subepithelial infiltrates. The keratitis progressed and scleral nodules developed despite aggressive treatment with topical clotrimazole, dibromopropamidine isethionate, and corticosteroids. Corneal transplantation and cryotherapy were performed. The corneal button demonstrated Acanthamoeba cysts. Cultures of biopsy specimens taken from two different scleral nodules at two separate times were positive for Acanthamoeba. The disease progressed despite a second corneal graft and the addition of polyhexamethylene biguanide eyedrops. Enucleation of the left eye was required. Histopathologic examination of the specimen documented an Acanthamoeba cyst associated with a granulomatous inflammatory response deep in the sclera. Acanthamoeba scleritis may be associated with a poor prognosis, even with intensive medical and surgical treatment.

Acanthamoeba keratitis: a sobering case and a promising new treatment

This case report describing Acanthamoeba keratitis in a 41-year-old male disposable contact lens wearer, adds some sobering and some encouraging information for the future management of this infection. Initial treatment with topical propamidine isethionate (Brolene) and polymyxin B/neomycin/gramicidin (Neosporin) led to an unsatisfactory clinical response. Topical miconazole 1%, prednisolone acetate 0.12% and oral itraconazole were then added to his treatment. This was later discontinued on noticing ipsilateral toxic cataract formation and an unresponsive pupil. The above medications were replaced with topical polyhexamethylene biguanide (PHMB) 0.02%, which we had shown to have superior in-vitro amoebicidal activity when compared to the other antiamoebic agents used in this case. Withdrawal of the multitreatment schedule and commencement of PHMB was associated with resolution of his keratitis, healing of a large epithelial defect and settling of severe conjunctivitis. The identical Acanthamoeba strain was isolated from the patient's contact lens storage case and cornea, possibly implicating the contaminated contact lens case in the aetiology of his keratitis. This is the first Australasian experience using PHMB to treat Acanthamoeba keratitis. It appears to be a promising new treatment for this infection.

Acanthamoeba keratitis. A masquerade of presentation in six cases

Acanthamoeba keratitis is an uncommon but devastating complication of contact lens wear causing significant ocular morbidity. Six consecutive cases occurring in Western Australia in an 18-month period are reported. In all cases either poor contact lens hygiene or an association with swimming pools and contact lens use is a feature. There is invariably a delay in making the diagnosis, with the appearance frequently mistaken for herpes simplex keratitis. In all cases corneal biopsy was required to confirm the diagnosis. Of the six patients, four responded to medical therapy alone, one required a corneal graft and one required enucleation. We suggest that earlier rather than later corneal biopsy is important in unresponsive cases of culture-negative keratitis, especially in contact lens wearers. We would agree that the treatment of choice is intensive topical propamidine and neosporin. Prevention by strict adherence to contact lens care and hygiene is urged.

Acanthamoeba keratitis. The value of early diagnosis

BACKGROUND

The treatment of Acanthamoeba keratitis has been increasingly successful as diagnoses are made earlier. The authors investigated features of the disease and prognosis in a consecutive series of 15 patients who were treated within 1 month of initial symptoms.

METHODS

A database of patients with Acanthamoeba infection presenting between March 1984 and March 1992 was analyzed. The recognition, presenting features, culture methods, results, and treatment of the early cases were reviewed to determine the reasons for a good outcome.

RESULTS

Recognition depended on perineural infiltrates (11/15), uveitis (10/15), limbitis (14/15), and infiltrated epithelium; 6 of 15 patients had epithelial defects, but only 3 of 15 had ring infiltrates or ulcers. Epithelial biopsy was culture-positive in 12 of 15 patients. Most (11/15) patients needed only two anti-amebal drugs. One patient only required penetrating keratoplasty for uncontrolled disease. The final visual acuity was at least 6/12 in all patients who had been treated within 1 month of first symptoms, whereas only 17 (53%) of 32 eyes of patients who presented after 1 month achieved a visual acuity of 6/12.

CONCLUSIONS

Subtle diagnostic signs, supported by comprehensive microbiologic investigation, justify the immediate instigation of specific antiamebal therapy. Treatment within 1 month of onset results in a lower morbidity and a good visual outcome.

Results of therapeutic penetrating keratoplasty

PURPOSE

To determine the anatomic and visual results of therapeutic penetrating keratoplasty (PK) and its role in the management of corneal disease.

METHODS

The authors reviewed the records of all of their patients who had undergone therapeutic PK over the past 9 years and evaluated each for the following criteria: cure of disease, graft clarity, and visual acuity. Patients were divided into seven categories: (1 and 2) bacterial and fungal keratitis, (3 and 4) herpetic keratitis, with and without inflammation, (5) acanthamoebic keratitis, (6) perforations due to keratoconjunctivitis sicca, and (7) other causes of perforation.

RESULTS

In microbial keratitis, therapeutic PK eradicated the disease in all cases. Seventy-three percent of grafts for bacterial keratitis and 60% for fungal keratitis remained clear. A higher percentage of clarity was achieved when grafts were 9.0 mm or less. Seven patients with secondary endophthalmitis were cured with a surgical approach including therapeutic PK. In herpetic keratitis with active inflammation, only 36% of grafts remained clear, and inflammation recurred in 36%. All perforations due to post-herpetic persistent epithelial defects in "quiet" eyes were grafted successfully. In patients with severe keratoconjunctivitis sicca, eyes were anatomically stabilized in 83%, but all grafts failed because of complications from ocular surface disease.

CONCLUSIONS

Therapeutic PK is valuable in the management of microbial keratitis that does not respond to antimicrobial therapy. Results are poorer for patients with herpetic keratitis, although selected patients respond to therapeutic PK when other methods of management have failed. Patients with perforations due to keratoconjunctivitis sicca have a uniformly poor prognosis for graft clarity.

Prognosis for keratoplasty in Acanthamoeba keratitis

STUDY

Penetrating keratoplasty (PK) was undertaken between 1985-1991 at Moorfields Eye Hospital in 13 eyes (19 PKs) of 11 patients who developed Acanthamoeba keratitis. Infection was ultimately controlled in all cases. Retrospective analysis was undertaken to establish risk factors for PK. Six eyes were quiet and 7 had uncontrolled infection at the time of keratoplasty. The outcome for these was compared.

COMPLICATIONS

Complications included cataract in 50% of quiet eyes and 100% of inflamed eyes. Intumescent cataract resulted in glaucoma requiring drainage surgery in 4 eyes. Graft rejection episodes occurred in 50% of quiet eyes, but were treated aggressively and did not cause graft failure.

RESULTS

Graft survival was excellent for quiet eyes, but was compromised by recurrent infection in inflamed eyes and 6 patients were regrafted. Survival compared poorly with grafting for active herpetic or bacterial keratitis, indicating that early diagnosis and treatment are essential for adequate control of this disease.

Enhanced killing of Acanthamoeba cysts in vitro using dimethylsulfoxide

PURPOSE

Acanthamoeba keratitis is difficult to treat and requires prolonged therapy despite the well-documented in vitro effectiveness of a variety of drugs. The authors propose that this may be due to the cysts formed by the organism in response to hostile conditions. Consequently, the study concentrates on increasing penetration of drugs effective against the parasite into the cysts using dimethylsulfoxide (DMSO).

METHODS

The organism is forced to encyst in vitro on solid media by nutrient deprivation. In the first set of experiments, serial dilutions of a standard treatment regimen are applied to the organisms, and these treated cysts are then subcultured onto nutrient-rich material and observed for growth. The experiments are then repeated with DMSO added to the serially diluted standards. In a second set of experiments, the effects of retreatment on a larger concentration of organisms is examined.

RESULTS

When applied to a cyst-only population of Acanthamoeba, none of three standard drugs, propamidine isethionate 0.1%, neomycin 1%, or miconazole 1%, was cysticidal. When combined with DMSO 30%, propamidine isethionate was clearly cysticidal even in low dilution. This was confirmed by the retreatment experiments using a larger, standardized cyst population.

CONCLUSION

The authors propose that DMSO is acting as a "carrier" for the propamidine isethionate and increases its penetration into the normally drug-resistant cyst form of the organism. Because DMSO has been used topically in the past and shown to be quite safe, this may be a viable new therapy for this difficult condition.

Effects of magainins on ameba and cyst stages of Acanthamoeba polyphaga

Amebic keratitis produced by Acanthamoeba spp. is an increasingly important ocular infection in extended-use contact lens wearers. Problems associated with the infection are compounded by the lack of effective and well-tolerated chemotherapeutic agents. The magainins, a group of naturally occurring and synthetic membrane-active peptide compounds, have been shown to be active in vitro against a clinical isolate of Acanthamoeba polyphaga. Two magainins tested extensively had minimal inhibitory and minimal amebicidal values of 20 and 25 micrograms/ml for magainin MSI-103 and 25 and 40 micrograms/ml for magainin MSI-94, respectively. Both amebastatic and amebicidal activities are enhanced by combining the magainins with silver nitrate (200 micrograms/ml) and/or other marginally effective antimicrobial agents. These combinations have activity against both trophic and cystic stages in the Acanthamoeba life cycle and have promise as antimicrobial agents in the treatment of amebic keratitis.

Treatment of Acanthamoeba keratitis with polyhexamethylene biguanide

Polyhexamethylene biguanide (PHMB) is a polymeric biguanide disinfectant that has not previously been used in the treatment of infection. Six patients with confirmed Acanthamoeba keratitis were treated with PHMB 0.02%. All patients had uncontrolled keratitis refractory to therapy with multiple conventional antiamebic agents. The rationale for use and the dose of PHMB was determined by in vitro sensitivity testing of the Acanthamoeba corneal isolates to the drugs available for use. Trophozoite forms were sensitive to most agents. Only PHMB was cysticidal at low concentrations in all cases. Sensitivity to the other drugs, including propamidine, showed wide variation. In 5 of 6 cases, complete resolution of inflammation followed the introduction of PHMB. Toxicity to the ocular surface was not evident with PHMB, unlike propamidine or neomycin. The reasons for the treatment failure in one case, despite cyst sensitivity to both PHMB and propamidine, are not clear. PHMB is a promising new treatment for this infection.

Use of corticosteroids in combination with antimicrobial drugs in the treatment of infectious corneal disease

The use of corticosteroids in the management of infectious eye disease is controversial. In this study, the authors attempt to analyze the goals and risks of the use of corticosteroids in the treatment of various forms of infectious keratitis with reference to generally recognized principles for the treatment of infectious diseases. Existing clinical and research data are reviewed in this context to make appropriate recommendations for the use of corticosteroids in the treatment of bacterial, fungal, and acanthamoeba keratitis. The authors conclude that corticosteroids are definitely contraindicated in the treatment of fungal keratitis, and relatively contraindicated in the treatment of Acanthamoeba keratitis. Topical corticosteroid therapy may have a role in the treatment of bacterial keratitis if appropriate guidelines are followed.

Graft failure after penetrating keratoplasty

Despite the improving results that have been noted with penetrating keratoplasty, graft failure remains a significant problem. The causes of graft failure are quite varied. Primary donor failure, surgical complications, intraocular lens complications, persistent epithelial defects, allograft rejection, infection, glaucoma, trauma, and recurrences of primary corneal dystrophies are common etiologies. In this article, a critical review of the available literature concerned with the factors influencing the many causes of graft failure and their management is provided.