Medical interventions for acanthamoeba keratitis

  • Protocol
  • Intervention


  • Majed Alkharashi,

    Corresponding author
    1. Johns Hopkins University School of Medicine, Department of Ophthalmology, Baltimore, MD, USA
    • Majed Alkharashi, Department of Ophthalmology, Johns Hopkins University School of Medicine, 600 N. Wolfe St., Maumenee #317, Baltimore, MD, 21287, USA.

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  • Kristina Lindsley,

    1. Johns Hopkins Bloomberg School of Public Health, Department of Epidemiology, Baltimore, Maryland, USA
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  • Shameema Sikder

    1. Johns Hopkins University School of Medicine, Wilmer Ophthalmological Institute, Baltimore, Maryland, USA
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This is the protocol for a review and there is no abstract. The objectives are as follows:

The objective of this review is to evaluate the effectiveness and safety of medical therapy for the treatment of AK.


Description of the condition


Acanthamoeba, a genus containing at least 24 species of free-living amoebic protozoa (single-celled organisms), is ubiquitous in nature, existing both in soil and in nearly all water sources and supplies. Worldwide, Acanthamoeba has been found in seawater, lakes, rivers, and streams and is commonly found in water supplies, such as tap and bottled water, drinking fountains, eye wash stations, dental units, and dialysis machines. Acanthamoeba can be isolated from the upper respiratory tracts of humans, 50% to 100% of whom have antibodies to it (Alizadeh 2001). The life-cycle of Acanthamoeba is characterized by two stages: 1) a motile, feeding, and replicating trophozoite form, which is the most common form found in water, and 2) a double-walled dormant cyst (Park 2002). Trophozoites feed on a variety of organisms, including cyanobacteria, bacteria, fungi, and other protozoa. Trophozoite encystment allows the organism to survive adverse conditions such as nutrient deficient environments, extreme temperatures and pH, desiccation, and chemical exposure. In the resilient double-walled cyst form, Acanthamoeba can survive for years under such adverse conditions (Biddick 1984; Brandt 1989; Neff 1969). Trophozoites and cysts vary in size from 25 to 50 µm. Acanthamoeba reproduce by asexual binary fission.

Despite its near universal presence, Acanthamoeba infection in humans is relatively uncommon. The combination of corneal epithelium barrier disruption, whether from trauma or from contact lens wear, and exposure to a sufficient inoculum of Acanthamoeba substantially increases the risk of keratitis (inflammation of the cornea) (Garate 2006; Ibrahim 2007). There are a number of steps that take place after exposure, before keratitis results. First, a pathogenic trophozoite attaches to the outer corneal epithelial cells via binding proteins. The attached trophozoite then secretes an enzyme that desquamatizes (peels back) the corneal epithelial cells allowing the trophozoite to invade the middle stromal layers of the cornea. Once inside the stroma, the trophozoite secretes collagenolytic factors that dissolve the stromal matrix, mediating an inflammatory response. Corneal cell death and keratitis result from the inflammatory response (Alizadeh 2005). Acanthamoeba infection can result in the loss of the eye if unresolved. Acanthamoeba castellanii (T4 genotype) is the most common reported species to cause Acanthamoeba infection, accounting for 94.3% of keratitis cases and 79.3% of those with skin, lung, and/or brain infections (Awwad 2007; Walochnik 2000).


Acanthamoeba keratitis (AK) was first described in the early 1970s with a dramatic increase in observed cases occurring in the early to mid-1980s (Naginton 1974; Stehr-Green 1989). This rise was associated with the increasing use of contact lens wear. In 1985, the US Centers for Disease Control issued a report to alert ophthalmologists about the association between contact lens wear and this difficult infection (US DHHS 1986). The development of AK in contact lens users is much more strongly related to poor lens hygiene and contaminated water than is bacterial keratitis, for which the overnight wear of lenses remains the dominant risk factor (Dart 2008). Swimming in contact lenses, irregular or inadequate disinfection of contact lenses, cleaning the lens case with tap water, minor corneal trauma, and exposure to contaminated water are all additional risk factors for developing AK (Radford 2002; Stehr-Green 1987).

Contact lens wear remains the most common risk factor for development of AK. In recent case series, contact lens wear was reported in 80% to 86% of cases (Butler 2005; Claerhout 2004; Radford 2002). Generally, AK is a rare infection and comprises less than 5% of contact lens-related microbial keratitis (Butler 2005; Claerhout 2004). The incidence of AK is estimated at 0.33 to 1.0 per 10,000 hydrogel contact lens wearers per year (Seal 2003). Extended wear soft contact lenses (SCLs), which are worn overnight, and daily wear SCLs, which require daily cleaning and overnight storage, carry higher risks of infection than daily disposable lenses, which are not worn or stored overnight (Butler 2005). The incidence of AK in rigid contact lens wearers is 9.5 times lower than for SCL wearers (Seal 2003). Recently, however, patients using rigid contact lenses overnight for orthokeratology, a clinical technique to reshape the cornea to correct refractive errors, have displayed high rates of AK (Watt 2005).

Contact lens storage cases may be colonized with Acanthamoeba, regardless of whether the user develops infection. For example, studies examining contact lens cases from individuals in the UK asymptomatic for any ocular infection have shown that between 4% and 7% of lens storage cases were colonized with Acanthamoeba (Seal 1999). The unfortunate fact is that most commercially available contact lens disinfection solutions are ineffective against Acanthamoeba (Hiti 2005; Johnston 2009; Radford 2002). Further, contaminated contact lens disinfection solutions have been directly linked to outbreaks of Acanthamoeba infection among contact lens wearers (Acharya 2007; Stehr-Green 1987; Yoder 2012).

There is a 10 to 15 times higher rate of AK reported in the UK than that noted in the US: as few as 0.15 per million in the US (Stehr-Green 1989) to as high as 1.4 per million in the UK (Radford 2002; Seal 2003). Rates of AK in other countries fall somewhere between the US and UK rates, with diverse rates among geographic locations (Watson 2012). Additionally, certain regions of the US have higher rates of AK compared with other regions. Differences in national and regional rates have been attributed to water supply factors, including the colonization rate of pathogens in the domestic water supply, the higher prevalence of bacteria at the ends of the water distribution system, and the subsequent use of these waters to store SCLs and to prepare the home made lens care saline solutions (Gray 1995; Kilvington 2004; Lindsay 2007).

Presentation and diagnosis

The most common symptom of AK is severe pain, which is out of proportion to the clinical signs and associated with photophobia, blurry vision, and tearing. AK usually presents in one eye, although disease may be bilateral in contact lens wearers (Kim 2010). Absence of pain does not exclude diagnosis. Later, patients may develop ring infiltrates, hypopyon, and/or diffuse inflammation.

Diagnosis and treatment of Acanthamoeba are difficult. The most important step in diagnosing AK is to suspect it. Early diagnosis and prompt delivery of appropriate medical therapy is essential to secure a good prognosis. If effective therapy is delayed for three weeks or more the prognosis deteriorates (Claerhout 2004; Tu 2008). AK should be considered in any case of corneal trauma complicated by exposure to soil or contaminated water and in all contact lens wearers, especially in those with significant pain or poor response to first-line therapy for bacterial or herpes simplex virus (HSV) keratitis. Even when there has been a positive culture for another organism, Acanthamoeba may still be present since 10% to 23% of cases of AK may be polymicrobial or co-infected with HSV (Mathers 1997; Sun 2006).

Confirmation of infection, even when the diagnosis is suspected, is also challenging. Diagnosis is made much more easily when the disease is in its early stages and superficial in the cornea. Confocal microscopy is a noninvasive tool that allows visual confirmation of cysts in the eye and may aid in the diagnosis of Acanthamoeba. The cystic form of Acanthamoeba appears as a double-walled, hexagonal, hyperreflective structure that is 10 to 25 μm in diameter (Rezaei Kanavi 2012; Winchester 1995). The trophozoite form and surrounding swollen nerves also can be seen by confocal microscopy, but it may be difficult to differentiate the trophozoites from normal corneal keratocyte nuclei. The trophozoite form may appear as a pear-shaped structure 15 to 45 μm in diameter with a surrounding bright halo (Rezaei Kanavi 2012). Corneal scrapings also may demonstrate the cyst and trophozoite forms. Culturing the scrapings on non-nutrient agar overlaid with Escherichia coli may show characteristic trails (markings) as trophozoites move across the plate to feed on the bacteria (Borin 2013; Dart 2009; Winchester 1995). Corneal scrapings stained with Giemsa, periodic acid–Schiff (PAS), hematoxylin and eosin (H&E), calcofluor white, or acridine orange stains may be used to identify the cyst and trophozoite forms. Once deeper involvement of the stroma occurs, a corneal biopsy may be necessary.

The sensitivity and specificity of diagnosis using confocal microscopy compared with the conventional method of corneal scrapings has been reported to be as high as 88% and 91%, respectively (Vaddavalli 2011). Identification of Acanthamoeba by polymerase chain reaction (PCR) showed a sensitivity of 84% and a specificity of 100%; it was positive in 16 of 19 epithelial samples (84%) compared to 10 of 19 (53%) culture-positive (Lehmann 1998). Neither confocal microscopy nor PCR can be expected to distinguish between viable and nonviable Acanthamoeba cysts; this leaves culture of corneal scrapes or biopsies as the only certain way of identifying persistent culture-positive disease. Unfortunately, a negative culture result does not confirm that all the viable organisms have been eradicated unless a substantial corneal excision biopsy has been taken.

In non-contact lens wearers the diagnosis of AK is more difficult and often takes longer than in contact lens wearers as the suspicion for this infection is usually lower (Sharma 2000; Speer 2003), despite comprising 3% to 15% of AK cases in the UK and US (Stehr-Green 1989). Due to delays in diagnosis, non-contact lens wearers tend to have worse visual outcomes than those with contact lens-associated AK. AK in non-contact lens wearers is usually associated with trauma, exposure to contaminated water or soil, and agricultural work (Stehr-Green 1989; Sun 2006).

Description of the intervention

The goals of medical therapy in AK include the eradication of viable cysts and trophozoites along with rapid resolution of the associated inflammatory response. The first medical cure was noted in the mid-1980s through the use of topical propamidine and neomycin (Wright 1985). Propamidine, a diamidine anti-amoebic, is commonly administered as eyedrops (0.1%), but may also be applied as an ointment (0.15%). Hexamidine, usually administered as 0.1% eyedrops, is another type of diamidine anti-amoebic used for treating AK. Biguanides are another class of anti-amoebics that may be used. Two biguanides that are in use are polyhexamethylene biguanide (PHMB) 0.02% to 0.06% and chlorhexidine 0.02% to 0.2%. Other topical drugs that have been used for the treatment of AK include antibiotics (e.g., aminoglycoside, neomycin) and antifungals (e.g., azole, itraconazole, metronidazole, voriconazole). Oral itraconazole has been used in severe cases to prevent the potential spread of trophozoites into adjacent tissues (Sun 2006; Thebpatiphat 2007). There are currently no drugs licensed for the treatment of AK in the US. Brolene (propamidine isethionate 0.1%; Sanofi-Aventis, Australia) is licensed in Australia.

Although the current anti-amoebics show low or very low minimal cysticidal concentrations, the diamidines and biguanides are currently the most effective cysticidal anti-amoebics in vitro and their use is supported by multiple case series (Dart 2009). However, the clinicopathologic correlation between the in vitro sensitivities and the clinical outcome has been less than satisfactory, with treatment failing despite the use of topical preparations at 10 to 60 times the minimal cysticidal concentration for biguanides in vitro. Although the reasons for this difference are not well understood, it is possible that therapeutic intrastromal concentrations are not being achieved, that drugs may bind to tissue components or that they may be inactivated in vivo, or that organisms in vivo intrinsically are more resistant than in vitro. Repeated epithelium debridement is used in some centers to improve drug penetration (Pérez-Santonja 2003; Sun 2006).

The role of steroids in treating AK is controversial and unnecessary in most cases diagnosed early, as these cases usually respond rapidly to anti-amoebic drugs (Dart 2009). Further, steroids should not be started until most organisms have been killed by using anti-amoebic drugs for a few weeks. Steroids may be helpful in ameliorating persistent inflammation of the cornea, anterior chamber, or sclera. In cases where the inflammation has spread to the limbus (limbitis) or sclera (scleritis), oral nonsteroidal anti-inflammatory treatment (NSAIDs) or even oral steroid might be indicated (Dart 2009). Scleritis can be severe and result in scleral necrosis and uncontrollable pain in which enucleation is indicated.

In cases of corneal perforation or corneal abscess not responding to medical treatment, therapeutic keratoplasty (corneal transplantation) is indicated. Optical penetrating keratoplasty for the purposes of improving vision should be delayed until the infection has been treated and there is no evidence of recurrence for a few months after stopping the medication (Awwad 2007).

Cryotherapy can be used for refractory cases, but persistent corneal edema with endothelial failure may occur (Oh 2010). In vitro studies of AK have shown that cryotherapy kills trophozoites but not cysts unless combined with medical treatment (Matoba 1989).

How the intervention might work

When Acanthamoeba face environmental stress the trophozoites transform to thick-walled cysts. Thus, persistent or recurrent infection often is related to the presence of Acanthamoeba cysts (Pérez-Santonja 2003). Because of the transformation to cysts in the human body, effective medical treatment of Acanthamoeba infection demands cysticidal drugs (Hammersmith 2006; Hay 1994).

Cataract, iris atrophy, glaucoma, and peripheral ulcerative keratitis have all been reported as complications of severe and prolonged AK and have been attributed to toxicity from the use of topical biguanides, diamidines, or both (Herz 2008; Murthy 2002). Although a possibility, it is currently uncertain that anterior segment ocular complications are drug-induced. Investigators of several studies have reported using topical biguanides without any apparent ocular complications (Dart 2009). It may be likely that complications result more from immune reactions to the infection than from drug toxicity.

Why it is important to do this review

Our goal is to review and summarize the medical management of AK systematically. Medical management of AK includes a few classes of anti-amoeba agents, none of which are licensed for use in AK in the US. There are no formal guidelines or standard of care in treating this infection and most of the current treatment regimens are based on personal experience.


The objective of this review is to evaluate the effectiveness and safety of medical therapy for the treatment of AK.


Criteria for considering studies for this review

Types of studies

We will include randomized controlled trials (RCTs) of medical therapy for AK.

Types of participants

We will include RCTs that included people with AK regardless of the participants’ age or sex or etiology of disease.

Types of interventions

  1. We will include studies that compared medical anti-amoeba therapy (drugs used alone or in combination with other medical therapies) with no anti-amoeba therapy.

  2. We will include studies that compared one medical anti-amoeba therapy with another medical anti-amoeba therapy.

Types of outcome measures

Primary outcomes

The primary outcome of the review will be the proportion of participants in whom infection was resolved at six months follow-up. We will define resolution of infection as the absence of patient-reported symptoms, epithelial defects, corneal edema, and stromal infiltrates with no evidence of recurrence. Patient-reported symptoms may include, but will not be limited to, pain, foreign body sensation, photophobia, and blurry vision. The absence of epithelial defects, corneal edema, and stromal infiltrates will be determined clinically. We also will include studies that used other definitions of resolution and report how resolution was defined.

Secondary outcomes

Secondary outcomes will include:

  1. Resolution of infection

    1. The proportion of participants in whom infection was resolved at one year

    2. The mean time to resolution of infection

    3. The mean number of treatments administered

  2. Visual acuity

    1. The proportion of patients with 20/40 or better best-corrected visual acuity (BCVA) at one year

    2. The proportion of patients with worse than 20/40 but better than 20/200 BCVA at one year

    3. The proportion of patients with 20/200 or worse BCVA at one year

  3. Additional therapy

    1. The proportion of participants needing or who underwent therapeutic keratoplasty (for corneal perforation or infection not responding to topical treatment), optical keratoplasty (to restore vision), or cryotherapy at one year

    2. The proportion of participants who needed pain control medication either because of the infection itself or the pain associated with treatment at one year

    3. The proportion of participants who received immunosuppressive therapy at one year

    4. The proportion of participants who underwent enucleation/evisceration at one year

The categories for visual acuity are based on the US requirements for an unrestricted driver's license (BCVA 20/40 or better) and the common definition of legal blindness (BCVA 20/200 or worse).

We will also consider secondary outcomes at six months follow-up.

Adverse events

We will document adverse events related to medical therapies as reported in the included studies. Specific adverse events of interest include pain from drug toxicity, allergic reaction, superficial punctate keratopathy, persistent epithelial defect, scleritis, and extra corneal inflammation.

Search methods for identification of studies

Electronic searches

We will search the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library), MEDLINE (OVID), EMBASE, Latin American and Caribbean Health Sciences Literature Database (LILACS), PubMed, the metaRegister of Controlled Trials (mRCT) (, ( and the WHO International Clinical Trials Registry Platform (ICTRP) ( We will not use any date or language restrictions in the electronic searches for trials.

See: Appendices for details of search strategies for CENTRAL (Appendix 1), MEDLINE (Appendix 2), EMBASE (Appendix 3), LILACS ( Appendix 4), PubMED (Appendix 5), mRCT (Appendix 6), (Appendix 7) and the ICTRP (Appendix 8).

Searching other resources

We will search the reference lists of included studies and the Science Citation Index to identify potentially relevant studies that cited included studies. We will not search conferences proceedings, such as abstracts from the Association for Research in Vision and Ophthalmology (ARVO) or the American Academy of Ophthalmology (AAO) meetings, for the specific purposes of this review as RCTs presented at these meetings are routinely searched by the Cochrane Eyes and Vision Group and included in CENTRAL.

Data collection and analysis

Selection of studies

Two authors independently will assess the eligibility of search results using a two-staged approach. First, each author will assess the title and abstract of each record identified by the searches and classify it as (1) definitely include, (2) unsure, or (3) definitely exclude according to the 'Criteria for considering studies for this review'. Next, we will obtain full-text copies of each record classified by at least one review author as either (1) definitely include or (2) unsure. We will map each record to its study, thereby making the unit for the second stage study-based rather than record-based. In the second stage, two authors independently will assess the full-text report(s) of studies and classify each study as (a) include, (b) unclear, or (c) exclude. We will document all studies excluded at the second stage and the reasons for exclusion. We will contact study investigators for studies classified as unclear for additional information to determine eligibility. If no response is received after four weeks, we will classify the reference based on the information available. We will resolve discrepancies at each stage by consensus. For articles written in languages not read by the review authors, we will identify colleagues to assist with assessing the studies for eligibility and, if included, translate the study information.

Data extraction and management

Two authors independently will extract data using data extraction forms developed by the Cochrane Eyes and Vision Group and modified for the specific purposes of this review. We will extract data for each included study regarding study characteristics, such as methods, participants, interventions, outcomes, and funding sources. One review author will enter the data into Review Manager (Review Manager 2012) and a second review author will verify the data entered. We will resolve discrepancies by discussion. We will contact primary investigators to request missing data. If no response is received after four weeks, we will document that data were not reported and report available information.

Assessment of risk of bias in included studies

Two review authors independently will assess the risks of bias in studies according to the methods described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Disagreements between authors will be resolved through discussion.

We will consider the following parameters when assessing risk of bias: (a) selection bias (random sequence generation, adequacy of allocation concealment); (b) performance bias (masking of participants and study personnel); (c) detection bias (masking of outcome assessors and data analyzers); (d) attrition bias (completeness of follow-up, reasons for missing data, intention-to-treat (ITT) analysis); (e) reporting bias (selective outcome reporting); and (f) other potential sources of bias (such as funding source).

We will assess each included study for each parameter as having a 'low risk of bias', a 'high risk of bias', or an 'unclear risk of bias' (insufficient information to permit judgment of low or high risk). We will contact the primary investigators of studies when the study methods are unclear or additional information would facilitate making an assessment. If no response is received after four weeks, we will assess the risk of bias based on the information available.

Measures of treatment effect

The primary outcome for this review, the proportion of participants in whom infection was resolved at six months follow-up, is a dichotomous outcome. We will report the measure of effect as a risk ratio with a 95% confidence interval. We will report dichotomous secondary outcomes in the same way. We also will report adverse events as risk ratios with 95% confidence intervals when data are available.

We will report continuous outcomes, including the mean number of treatments administered, as mean differences between groups with 95% confidence intervals. When distributions are skewed, we will report the median and interquartile ranges whenever sufficient data are available. We will use survival analysis to report the time to resolution of infection as hazard ratios with 95% confidence intervals when data are available.

Unit of analysis issues

The unit of analysis will be the eye. For studies in which both eyes of a single participant were included and analyzed separately, we will report whether or not adjustments for intra-person correlation of outcomes were made.

Dealing with missing data

When data are missing or incomplete, we will contact study authors for additional information. If no response is received after four weeks, we will use the information available and document missing data.

Assessment of heterogeneity

We will assess statistical and clinical heterogeneity among included studies. We will use the I2 statistic to examine statistical heterogeneity. We will consider an I2 value greater than 60% as denoting substantial statistical heterogeneity. We will assess clinical heterogeneity based on the characteristics of the participants, interventions, and outcomes of the included studies. If substantial statistical or clinical heterogeneity is present, we will not combine data in meta-analysis. Rather, we will report the study results independently.

Assessment of reporting biases

We will examine reporting biases at the individual study level (selective outcome reporting bias) and review level (publication bias). As described above, we will assess selective outcome reporting bias for each included study by comparing stated study outcomes (e.g., outcomes from study protocol, clinical trial registration, or methods section) with those that were reported. We will examine publication bias based on the symmetry of funnel plots when 10 or more studies are included in meta-analysis.

Data synthesis

When no substantial statistical or clinical heterogeneity is detected, we will combine results in meta-analysis. We will use a random-effects model for meta-analyses including three or more studies. When fewer than three studies are meta-analyzed, we will use a fixed-effect model. We will calculate the summary risk ratio with 95% confidence intervals for dichotomous outcomes and the summary mean difference between groups with 95% confidence intervals for continuous outcomes. We will document study results that are not included in meta-analysis as narrative summaries.

Subgroup analysis and investigation of heterogeneity

When sufficient data are available, we will perform subgroup analyses to evaluate potential effect modifiers and investigate heterogeneity. We will consider the following subgroup analyses:

  1. Use of contact lenses prior to infection

  2. Geographical region of study

  3. Length of delay in starting treatment (less than three weeks versus three weeks or more)

  4. Concomitant ocular surface disease

We will include the use of contact lenses and geographical region as subgroups as they are factors associated with differing rates of infection (Butler 2005; Seal 2003). The reason for looking at the time when anti-amoeba treatment was initiated is because some studies have found that when effective therapy is delayed for three weeks or more the prognosis deteriorates (Claerhout 2004; Tu 2008). We also will evaluate subgroups based on whether concomitant ocular surface disease was present as it may relate to risk factors as well as prognosis (Tu 2008).

Sensitivity analysis

When sufficient data are available, we will conduct sensitivity analyses to examine the impact of excluding unpublished studies, industry-funded studies, and studies assessed as having a high risk of bias for any risk of bias parameter.


We acknowledge the Cochrane Eyes and Vision Group (CEVG) Trials Search Co-ordinator for developing the search strategy for this review. We thank Stephanie Watson, Barbara Hawkins, David Lloyd, and the CEVG editorial base for providing comments on the protocol.

Richard Wormald (Co-ordinating Editor for CEVG) acknowledges financial support for his CEVG research sessions from the Department of Health through the award made by the National Institute for Health Research to Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology for a Specialist Biomedical Research Centre for Ophthalmology.

The views expressed in this publication are those of the authors and not necessarily those of the NIHR, NHS or the Department of Health.


Appendix 1. CENTRAL search strategy

#1 MeSH descriptor: [Acanthamoeba Keratitis] explode all trees
#2 MeSH descriptor: [Keratitis] explode all trees
#3 Keratiti* or cornea* or ocular or eye*
#4 #2 or #3
#5 MeSH descriptor: [Acanthamoeba] explode all trees
#6 MeSH descriptor: [Amoeba] explode all trees
#7 (Acanthamoeb* or amoeb* or Amebia* or Amebic* or Amebom* or ameba* or microbial)
#8 #5 or #6 or #7
#9 #4 and #8
#10 MeSH descriptor: [Keratitis] explode all trees
#11 #10 from 1975 to 1989
#12 #1 or #9 or #11

Appendix 2. MEDLINE (OvidSP) search strategy

1. Randomized Controlled
2. Controlled Clinical
3. (randomized or randomised).ab,ti.
4. placebo.ab,ti.
5. drug therapy.fs.
6. randomly.ab,ti.
7. trial.ab,ti.
8. groups.ab,ti.
9. 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8
10. exp animals/ not
11. 9 not 10
12. exp Acanthamoeba Keratitis/
13. exp Keratitis/
14. (Keratiti* or cornea* or ocular or eye*).tw.
15. 13 or 14
16. exp Acanthamoeba/
17. exp Amoeba/
18. (Acanthamoeb* or amoeb* or Amebia* or Amebic* or Amebom* or ameba* or microbial).tw.
19. 16 or 17 or 18
20. 15 and 19
21. exp Keratitis/
22. limit 21 to yr="1975 - 1989"
23. 12 or 20 or 22
24. 11 and 23

The search filter for trials at the beginning of the MEDLINE strategy is from the published paper by Glanville et al (Glanville 2006).

Appendix 3. search strategy

1. 'randomized controlled trial'/exp
2. 'randomization'/exp
3. 'double blind procedure'/exp
4. 'single blind procedure'/exp
5. random*:ab,ti
6. 1 OR 2 OR 3 OR 4 OR 5
7. 'animal'/exp OR 'animal experiment'/exp
8. 'human'/exp
9. 7 AND 8
10. 7 NOT 9
11. 6 NOT 10
12. 'clinical trial'/exp
13. (clin* NEAR/3 trial*):ab,ti
14. ((singl* OR doubl* OR trebl* OR tripl*) NEAR/3 (blind* OR mask*)):ab,ti
15. 'placebo'/exp
16. placebo*:ab,ti
17. random*:ab,ti
18. 'experimental design'/exp
19. 'crossover procedure'/exp
20. 'control group'/exp
21. 'latin square design'/exp
22. 12 OR 13 OR 14 OR 15 OR 16 OR 17 OR 18 OR 19 OR 20 OR 21
23. 22 NOT 10
24. 23 NOT 11
25. 'comparative study'/exp
26. 'evaluation'/exp
27. 'prospective study'/exp
28. control*:ab,ti OR prospectiv*:ab,ti OR volunteer*:ab,ti
29. 25 OR 26 OR 27 OR 28
30. 29 NOT 10
31. 30 NOT (11 OR 23)
32. 11 OR 24 OR 31
33. 'acanthamoeba keratitis'/exp
34. 'keratitis'/exp
35. keratiti*:ab,ti OR cornea*:ab,ti OR ocular:ab,ti OR eye*:ab,ti
36. 34 OR 35
37. 'acanthamoeba'/exp
38. 'acanthamoeba infection'/exp
39. 'amebic infection'/exp
40. acanthamoeb*:ab,ti OR amoeb*:ab,ti OR amebia*:ab,ti OR amebic*:ab,ti OR amebom*:ab,ti OR ameba*:ab,ti OR microbial:ab,ti
41. 37 OR 38 OR 39 OR 40
42. 36 AND 41
43. 'keratitis'/exp AND [1974-2000]/py
44. 33 OR 42 OR 43
45. 32 and 44

Appendix 4. LILACS search strategy

"Acanthamoeba Keratitis" OR "Queratitis por Acanthamoeba"  OR "Ceratite por Acanthamoeba" OR MH: C03.300.125$ OR MH:C03.752.049.203$ OR MH:C11.204.564.112$ OR MH:C11.294.725.125$ OR ((Keratiti$ OR Queratitis OR Ceratite OR MH:C11.204.564$ OR cornea$ OR ocular OR Eye$ OR Ojo OR Olho) AND (Acanthamoeb$ OR MH:B01.046.500.100.075.080$ OR Amoeb$ OR MH:B01.046.500.100.700.089$ OR MH:SP4.$ OR Amebia$ OR Amebic$ OR Amebom$ OR ameba$ OR microbial))

Appendix 5. PubMed search strategy

#1 ((randomized controlled trial[pt]) OR (controlled clinical trial[pt]) OR (randomised[tiab] OR randomized[tiab]) OR (placebo[tiab]) OR (drug therapy[sh]) OR (randomly[tiab]) OR (trial[tiab]) OR (groups[tiab])) NOT (animals[mh] NOT humans[mh])
#2 (Keratiti*[tiab] OR cornea*[tiab] OR ocular[tiab] or eye*[tiab]) NOT MEDLINE[sb]
#3 (Acanthamoeb*[tiab] OR amoeb*[tiab] OR Amebia*[tiab] OR Amebic*[tiab] OR Amebom*[tiab] OR ameba*[tiab] OR microbial[tiab]) NOT MEDLINE[sb]
#4 #1 AND #2 AND #3

Appendix 6. metaRegister of Controlled Trials search strategy

(acanthamoeba OR amoeba OR amebiasis OR amebiases OR amoebiasis OR amoebiases OR amebia OR amebic OR ameboma) AND (keratitis OR cornea OR ocular OR eye)

Appendix 7. search strategy

Condition: (acanthamoeba OR amoeba OR amebiasis OR amebiases OR amoebiasis OR amoebiases OR amebia OR amebic OR ameboma) AND (keratitis OR cornea OR ocular OR eye)

Appendix 8. ICTRP search strategy

Condition: (acanthamoeba OR amoeba OR amebiasis OR amebiases OR amoebiasis OR amoebiases OR amebia OR amebic OR ameboma) AND (keratitis OR cornea OR ocular OR eye)

Contributions of authors

MA designed and wrote the protocol. KL assisted with writing the protocol. SS conceived the review and provided substantive comments and edits to the protocol.

Declarations of interest

None known.

Sources of support

Internal sources

  • No sources of support supplied

External sources

  • Grant 1 U01 EY020522-01, National Eye Institute, National Institutes of Health, USA.