Diagnosis and Management of Acanthamoeba Keratitis: A Continental Approach

: Acanthamoeba keratitis (AK) is a potentially blinding infection caused by protozoa found worldwide. The topical application of biguanides and diamidines is the most common anti-amoebic treatment for AK. In this study, we hypothesized that geographical location and socioeconomic status inﬂuence the management and treatment of AK. To test this hypothesis, we analyzed case reports and series of Acanthamoeba eye infections from different geographic regions to evaluate the association between diagnosis, treatment, and outcome worldwide. This study looked speciﬁcally at case reports of patients with diagnosed AK using bibliographic databases such as PubMed, BioMed Central, and Google Scholar, which were searched between 30 April 1990 and 1 May 2022. The search identiﬁed 38 eligible studies that provided data for 60 clinical cases of AK. The results indicated that current standard treatments are effective if the infection is identiﬁed early and that delays can lead to clinical symptoms, including permanent visual opacities. There was evidence suggesting an association between the treatment regimen practiced in certain geographic regions and treatment outcome. Patient access to medical facilities and economic background also had an inﬂuence on the treatment and outcome of AK. Further analysis of more case reports can expand our understanding of the inﬂuence of speciﬁc demographic and individual patient characteristics on the effectiveness and accessibility of AK medicines. Additionally, using a living systematic review approach to incorporate emerging evidence will reveal the relative merits of different treatment regimens for AK and outcomes.


Introduction
Acanthamoeba spp. are single-celled free-living amoebae found in almost all terrestrial biomes, hot springs in the Antarctic, estuaries, beaches, ocean sediment, dust, air, and both fresh and saltwater ecosystems, as well as sewage and aquaria [1][2][3][4]. Transmission between humans has not yet been reported; however, there have been many incidences of infection in different animal species with potential impact on public health [5]. Acanthamoeba spp. can cause three main conditions: a disseminated infection, an infection of the brain and spinal cord known as granulomatous amoebic encephalitis (GAE), and Acanthamoeba keratitis (AK). Both GAE and disseminated infection are more prevalent in immunocompromised patients [6], whilst AK more commonly involves poor hygienic practices when using contact lenses [7,8], such as poor hand hygiene before handling contact lenses [9], non-adherence to rules labeled on packaging regarding storage, hygiene, disposal of lenses, frequency of contact lens replacement [10], swimming or showering while wearing contact lenses [11], and using tap water to clean contact lenses or storage cases [12]. All three clinical conditions can be life-altering, with the disseminated infection being fatal in about 85% of cases [13] and GAE being fatal in almost all cases if not timely diagnosed [14]. Although AK is not fatal, it is potentially blinding. ported in countries without universal healthcare due to accessibility issues, leaving keratitis untreated. Control of Acanthamoeba and other protozoan parasites for developing nations relies mostly on access to clean water. Populations living in countries undergoing conflict are at even higher risk of infection due to increased infrastructure damage. In addition, risk management under these circumstances is limited to projects and charities providing clean water sources. This emphasizes the importance for ophthalmologists to continue educating patients about the possible sources of Acanthamoeba and the importance of good personal hygiene practices to control infection [40].
Large-scale analysis of AK patient data reported in case reports from different geographical regions can help develop an understanding of the risk factors to look for in terms of Acanthamoeba infection. This information could be utilized to educate at-risk patients about how they could reduce the risk of infection. A geographical analysis of how cases occur, diagnosis of infection, treatment given, and outcome for different countries/continents would be beneficial in understanding how different management regimens practiced in individual countries can influence the treatment outcome of AK. Hence, we conducted this study to gain more insight into current management and treatment options for AK and to identify how these may differ depending on geographical regions. We also reviewed the literature and case reports to identify factors involving the clinical history and symptoms and to note the most common methods of AK diagnosis.

Literature Search Results
As shown in Figure 1, 874 abstracts were identified as potentially relevant for inclusion in the study from all databases searched (PubMed, 126; BioMed Central, 59; Google Scholar, 689). Screening through the title and abstracts while applying exclusion criteria (e.g., reports on veterinary cases, non-parasitic keratitis, other forms of infection [e.g., GAE or disseminated infection], lack of relevant information on individual patient history, clinical signs, diagnosis, treatment, or outcome) led to 24 papers being identified from Google Scholar. From PubMed, 32 papers were obtained, which were narrowed down to 12. Two case reports were gathered from BioMed Central. Duplicates were deleted using EndNote. We attempted to gather a representative sample of papers for each geographical region. This was made difficult by the lack of case reports with the desired inclusion criteria for Africa and South America, with only seven and three reports found, respectively. Initially, results were categorized into six groups, representing the relevant case reports through a strictly continental approach; however, six case reports were found from the Middle East, and this was added as an extra category as a subsection of Asia.
Parasitologia 2022, 2, FOR PEER REVIEW 3 underreported in countries without universal healthcare due to accessibility issues, leaving keratitis untreated. Control of Acanthamoeba and other protozoan parasites for developing nations relies mostly on access to clean water. Populations living in countries undergoing conflict are at even higher risk of infection due to increased infrastructure damage. In addition, risk management under these circumstances is limited to projects and charities providing clean water sources. This emphasizes the importance for ophthalmologists to continue educating patients about the possible sources of Acanthamoeba and the importance of good personal hygiene practices to control infection [40].
Large-scale analysis of AK patient data reported in case reports from different geographical regions can help develop an understanding of the risk factors to look for in terms of Acanthamoeba infection. This information could be utilized to educate at-risk patients about how they could reduce the risk of infection. A geographical analysis of how cases occur, diagnosis of infection, treatment given, and outcome for different countries/continents would be beneficial in understanding how different management regimens practiced in individual countries can influence the treatment outcome of AK. Hence, we conducted this study to gain more insight into current management and treatment options for AK and to identify how these may differ depending on geographical regions. We also reviewed the literature and case reports to identify factors involving the clinical history and symptoms and to note the most common methods of AK diagnosis.

Literature Search Results
As shown in Figure 1, 874 abstracts were identified as potentially relevant for inclusion in the study from all databases searched (PubMed, 126; BioMed Central, 59; Google Scholar, 689). Screening through the title and abstracts while applying exclusion criteria (e.g., reports on veterinary cases, non-parasitic keratitis, other forms of infection [e.g., GAE or disseminated infection], lack of relevant information on individual patient history, clinical signs, diagnosis, treatment, or outcome) led to 24 papers being identified from Google Scholar. From PubMed, 32 papers were obtained, which were narrowed down to 12. Two case reports were gathered from BioMed Central. Duplicates were deleted using EndNote. We attempted to gather a representative sample of papers for each geographical region. This was made difficult by the lack of case reports with the desired inclusion criteria for Africa and South America, with only seven and three reports found, respectively. Initially, results were categorized into six groups, representing the relevant case reports through a strictly continental approach; however, six case reports were found from the Middle East, and this was added as an extra category as a subsection of Asia.

Summary of AK Cases Reported Worldwide
The review identified 38 Figure A1). The global geographical distribution of all reported AK cases is shown in Figure 2. The largest number of cases was reported from North America (n = 13), followed by Asia (n = 11), Europe (n = 10), Australasia (n = 10), Africa (n = 7), and Middle East (n = 6), and the lowest number of cases was reported from South America (n = 3).

Summary of AK Cases Reported Worldwide
The review identified 38 Figure A1). The global geographical distribution of all reported AK cases is shown in Figure 2. The largest number of cases was reported from North America (n = 13), followed by Asia (n = 11), Europe (n = 10), Australasia (n = 10), Africa (n = 7), and Middle East (n = 6), and the lowest number of cases was reported from South America (n = 3).

Clinical History and Symptoms
In all geographical regions, hygiene issues regarding contact lens care and use were the most prevalent risk factor leading to AK; this included swimming with lenses, sharing lenses between people, and reusing old lenses. Access to treated water is important, as many cases developed from rinsing lenses in tap water. Another common patient history included working-class patients (manual laborers and fishermen) getting organic materials or water in their eyes during work and developing infections, which was most notable in the Asiatic region. Information about previous infection or misdiagnosis was observed throughout all regions, with initial diagnosis often misidentified as more frequent conditions such as bacterial, fungal, or viral keratitis. Most cases were not initially identified as Acanthamoeba-related, and positive diagnosis only occurred after ineffective treatment or progression of symptoms. Figure 3 summarizes the clinical symptoms extracted from all reports included in this review.

Clinical History and Symptoms
In all geographical regions, hygiene issues regarding contact lens care and use were the most prevalent risk factor leading to AK; this included swimming with lenses, sharing lenses between people, and reusing old lenses. Access to treated water is important, as many cases developed from rinsing lenses in tap water. Another common patient history included working-class patients (manual laborers and fishermen) getting organic materials or water in their eyes during work and developing infections, which was most notable in the Asiatic region. Information about previous infection or misdiagnosis was observed throughout all regions, with initial diagnosis often misidentified as more frequent conditions such as bacterial, fungal, or viral keratitis. Most cases were not initially identified as Acanthamoeba-related, and positive diagnosis only occurred after ineffective treatment or progression of symptoms. Figure 3 summarizes the clinical symptoms extracted from all reports included in this review.

Diagnostic Methods Used
From a global perspective, culture was the most utilized diagnostic method. Figure 4 identifies all the diagnostic methods reported to have been utilized from individual patient data. Combined diagnostic testing occurred in 42% (25/60) of identified cases. Parasitologia 2022, 2, FOR PEER REVIEW 5 Figure 3. The frequency of clinical symptoms reported from all AK cases. Decreased vision included blurry vision, decreased visual acuity, and loss of vision. Ocular infiltrates included corneal, stromal, and other precipitates.

Diagnostic Methods Used
From a global perspective, culture was the most utilized diagnostic method. Figure  4 identifies all the diagnostic methods reported to have been utilized from individual patient data. Combined diagnostic testing occurred in 42% (25/60) of identified cases.

Alternative Treatment Methods
For cases where drug therapy proved ineffective or ocular damage was irreparable, PK, AMT, deep anterior lamellar keratoplasty (DALK), intraocular lens insertion, or corneal transplants were performed. Approximately 42% (25/60) of identified cases required surgery. The number of surgeries is represented in Figure 5. The non-surgical treatment approaches are shown in Figure 6. Prednisolone was used in the management of five cases from Australasia and one case from Europe.

Diagnostic Methods Used
From a global perspective, culture was the most utilized diagnostic method. Figure  4 identifies all the diagnostic methods reported to have been utilized from individual patient data. Combined diagnostic testing occurred in 42% (25/60) of identified cases.

Alternative Treatment Methods
For cases where drug therapy proved ineffective or ocular damage was irreparable, PK, AMT, deep anterior lamellar keratoplasty (DALK), intraocular lens insertion, or corneal transplants were performed. Approximately 42% (25/60) of identified cases required surgery. The number of surgeries is represented in Figure 5. The non-surgical treatment approaches are shown in Figure 6. Prednisolone was used in the management of five cases from Australasia and one case from Europe.

Alternative Treatment Methods
For cases where drug therapy proved ineffective or ocular damage was irreparable, PK, AMT, deep anterior lamellar keratoplasty (DALK), intraocular lens insertion, or corneal transplants were performed. Approximately 42% (25/60) of identified cases required surgery. The number of surgeries is represented in Figure 5. The non-surgical treatment approaches are shown in Figure 6. Prednisolone was used in the management of five cases from Australasia and one case from Europe. Parasitologia 2022, 2, FOR PEER REVIEW 6

AK Cases in Africa
A total of seven cases were reported from Africa. The age range of AK patients was 17-55 years old (M = 29.14, S.D. = 12.41). Contact lenses were utilized in five cases (71%). The most common diagnostic method used was culture, utilized in five cases (71%). Combined diagnostic efforts were used in three cases (43%). There was one case series with three cases reported. Combined drug therapy was used in six cases (86%). The percentages of drugs used in the treatment of AK are shown in Figure 7. Additional information about the management of AK in Africa is presented in Table A1. The outcome of all cases showed general improvement of clinical signs with no recurrence of the infection. Remaining corneal opacities or decreased visual acuity were present in five cases (71%).

AK Cases in Africa
A total of seven cases were reported from Africa. The age range of AK patients was 17-55 years old (M = 29.14, S.D. = 12.41). Contact lenses were utilized in five cases (71%). The most common diagnostic method used was culture, utilized in five cases (71%). Combined diagnostic efforts were used in three cases (43%). There was one case series with three cases reported. Combined drug therapy was used in six cases (86%). The percentages of drugs used in the treatment of AK are shown in Figure 7. Additional information about the management of AK in Africa is presented in Table A1. The outcome of all cases showed general improvement of clinical signs with no recurrence of the infection. Remaining corneal opacities or decreased visual acuity were present in five cases (71%).  (1)). Biguanides were used in 14% of identified cases (PHMB (1)). Antifungals were used in 71% of identified cases (econazole (1), amphotericin B (1), ketoconazole (2), fluconazole (1)). Antiseptics were used in 57% of identified cases (hexamidine (4), chlorhexidine (1)).

AK Cases in the Middle East
A total of six cases were reported from the Middle East. The age range of AK patients was 5-44 years old (M = 29.67, S.D. = 13.81). Contact lenses were utilized in four (66.7%) of the cases. The most common diagnostic method used was confocal microscopy, utilized in four (66.7%) cases. Combined diagnostic efforts were used in three (50%) cases. There was one case series involving two cases. The percentages of drugs used in the treatment of AK are shown in Figure 8. Additional information about the management of AK is presented in Table A2. Combined drug therapy was used in six (100%) of the cases. Deterioration of cases with subsequent improvement after undergoing PK was detected in two cases (33%). Another two (33%) of the cases showed gradual improvement with remaining clinical symptoms, including corneal opacity and decreased visual acuity. Complete recovery with no visual loss occurred in one case (17%), and one case (17%) did not have a clear outcome. In case 1 (Table A2), medicine was not available in that specific region and had to be ordered, delaying treatment. In case 3 (Table A2) original Acanthamoeba treatment was not successful and thus required altering the therapeutic regimen used.  (1)). Biguanides were used in 14% of identified cases (PHMB (1)). Antifungals were used in 71% of identified cases (econazole (1), amphotericin B (1), ketoconazole (2), fluconazole (1)). Antiseptics were used in 57% of identified cases (hexamidine (4), chlorhexidine (1)).

AK Cases in the Middle East
A total of six cases were reported from the Middle East. The age range of AK patients was 5-44 years old (M = 29.67, S.D. = 13.81). Contact lenses were utilized in four (66.7%) of the cases. The most common diagnostic method used was confocal microscopy, utilized in four (66.7%) cases. Combined diagnostic efforts were used in three (50%) cases. There was one case series involving two cases. The percentages of drugs used in the treatment of AK are shown in Figure 8. Additional information about the management of AK is presented in Table A2. Combined drug therapy was used in six (100%) of the cases. Deterioration of cases with subsequent improvement after undergoing PK was detected in two cases (33%). Another two (33%) of the cases showed gradual improvement with remaining clinical symptoms, including corneal opacity and decreased visual acuity. Complete recovery with no visual loss occurred in one case (17%), and one case (17%) did not have a clear outcome. In case 1 (Table A2), medicine was not available in that specific region and had to be ordered, delaying treatment. In case 3 (Table A2) original Acanthamoeba treatment was not successful and thus required altering the therapeutic regimen used.

AK Cases in Australasia
A total of 10 cases were reported from Australasia. The age range of AK patients was 17-50 years (M = 34.3, S.D. = 10.36). Contact lenses were utilized in 10 cases (100%). The most common diagnostic method used was culture, utilized in nine (90%) of the cases. Combined diagnostic efforts were used in two cases (20%). There was one case series involving seven cases. The percentages of drugs used in the treatment of AK are shown in Figure 9. Additional information about the management of AK is presented in Table A3. Combined drug therapy was used in nine cases (90%). Certain initial standard treatment options appeared to be ineffective in over half of the cases (see Table A3). Out of the reported cases, three cases (30%) underwent PK, and two cases (20%) underwent epithelial debridement as symptoms worsened. Optic atrophy was attributed to potential neurotoxicity from overuse of medication (see case 4). In case 6, PHMB resistance was noted, and therapy was adjusted. rioration of cases with subsequent improvement after undergoing PK was detected in two cases (33%). Another two (33%) of the cases showed gradual improvement with remaining clinical symptoms, including corneal opacity and decreased visual acuity. Complete recovery with no visual loss occurred in one case (17%), and one case (17%) did not have a clear outcome. In case 1 (Table A2), medicine was not available in that specific region and had to be ordered, delaying treatment. In case 3 (Table A2) original Acanthamoeba treatment was not successful and thus required altering the therapeutic regimen used.  (1)). Biguanides were used in 67% of identified cases (PHMB (4)). Antifungals were used in 50% of identified cases (ketoconazole (1), fluconazole (1), itraconazole (1)). Antiseptics were used in 100% of identified cases (chlorhexidine (3), propamidine isethionate (4)).

AK Cases in Australasia
A total of 10 cases were reported from Australasia. The age range of AK patients was 17-50 years (M = 34.3, S.D. = 10.36). Contact lenses were utilized in 10 cases (100%). The most common diagnostic method used was culture, utilized in nine (90%) of the cases. Combined diagnostic efforts were used in two cases (20%). There was one case series involving seven cases. The percentages of drugs used in the treatment of AK are shown in Figure 9. Additional information about the management of AK is presented in Table A3. Combined drug therapy was used in nine cases (90%). Certain initial standard treatment options appeared to be ineffective in over half of the cases (see Table A3). Out of the reported cases, three cases (30%) underwent PK, and two cases (20%) underwent epithelial debridement as symptoms worsened. Optic atrophy was attributed to potential neurotoxicity from overuse of medication (see case 4). In case 6, PHMB resistance was noted, and therapy was adjusted.  (1)). Biguanides were used in 80% of cases of identified cases (PHMB (8)). Antifungals were used in 40% of identified cases (itraconazole (4), miconazole (4)). Antiseptics were used in 80% of identified cases (propamidine isethionate (8), chlorhexidine (2)).

AK Cases in Europe
A total of 10 cases were reported from Europe. The age range of AK patients was 9-73 (M = 36.1, S.D. = 20.84). Contact lenses were utilized in eight cases (80%). The most common diagnostic method used was culture, utilized in eight cases (80%). Combined diagnostic efforts were used in four cases (40%). Four cases came from two case series, each with two cases. The percentages of drugs used in the treatment of AK are shown in Figure 10. Additional information about the management of AK is presented in Table A4. Combined drug therapy was used in 10 cases (100%). Of all cases reported, two cases (20%) underwent PK, with one case requiring enucleation. Corneal transplant occurred in one case (10%). Seven cases (70%) showed amelioration through drug therapy without surgical intervention showing improvement in visual acuity, with some cases reporting scarring and corneal opacities. In two (20%) of the cases, the required medication was not on hand, delaying treatment.  (1)). Biguanides were used in 80% of cases of identified cases (PHMB (8)). Antifungals were used in 40% of identified cases (itraconazole (4), miconazole (4)). Antiseptics were used in 80% of identified cases (propamidine isethionate (8), chlorhexidine (2)).

AK Cases in Europe
A total of 10 cases were reported from Europe. The age range of AK patients was 9-73 (M = 36.1, S.D. = 20.84). Contact lenses were utilized in eight cases (80%). The most common diagnostic method used was culture, utilized in eight cases (80%). Combined diagnostic efforts were used in four cases (40%). Four cases came from two case series, each with two cases. The percentages of drugs used in the treatment of AK are shown in Figure 10. Additional information about the management of AK is presented in Table A4. Combined drug therapy was used in 10 cases (100%). Of all cases reported, two cases (20%) underwent PK, with one case requiring enucleation. Corneal transplant occurred in one case (10%). Seven cases (70%) showed amelioration through drug therapy without surgical intervention showing improvement in visual acuity, with some cases reporting scarring and corneal opacities. In two (20%) of the cases, the required medication was not on hand, delaying treatment.

AK Cases in North America
A total of 13 cases were reported from North America. The age range of AK patients was 18-71 (M = 44.1, S.D. = 15.03). Contact lenses were utilized in 13 (100%) of the cases. The most common diagnostic method used was culture, utilized in nine cases (69%). Combined diagnostic efforts were used in six (46%) of the cases. Four case series included three, two, two, and three cases, respectively. The percentages of drugs used in the treatment of AK are shown in Figure 11. Additional information about the management of AK is presented in Table A5. Combined drug therapy was used in 13 (100%) of the cases. Seven cases (54%) underwent PK or DALK, two cases (15%) underwent corneal debridement, and one case (7%) received AMT. Out of all patients, three cases (23%) improved with drug therapy without additional therapy. UV therapy was used in three cases (23%) where standard treatment was found to be ineffective.  (1)). Antifungals were used in 30% of identified cases (itraconazole (2), ketoconazole (1)). Biguanides were used in 50% of identified cases (PHMB (5)). Antiseptics were used in 80% of identified cases (propamidine isethionate (8), chlorhexidine (2)).

AK Cases in North America
A total of 13 cases were reported from North America. The age range of AK patients was 18-71 (M = 44.1, S.D. = 15.03). Contact lenses were utilized in 13 (100%) of the cases. The most common diagnostic method used was culture, utilized in nine cases (69%). Combined diagnostic efforts were used in six (46%) of the cases. Four case series included three, two, two, and three cases, respectively. The percentages of drugs used in the treatment of AK are shown in Figure 11. Additional information about the management of AK is presented in Table A5. Combined drug therapy was used in 13 (100%) of the cases. Seven cases (54%) underwent PK or DALK, two cases (15%) underwent corneal debridement, and one case (7%) received AMT. Out of all patients, three cases (23%) improved with drug therapy without additional therapy. UV therapy was used in three cases (23%) where standard treatment was found to be ineffective.

AK Cases in South America
Three cases were reported from South America. The age range of AK patients was 19-28 (M = 24.33, S.D. = 4.93). Contact lenses were utilized in three cases (100%). The most common diagnostic methods used were culture and PCR, both being utilized in two cases (66.7%). Combined diagnostic efforts were used in two cases (66.7%). All the cases were derived from individual reports (i.e., no case series). The percentages of drugs used in the treatment of AK are shown in Figure 12. Additional information about the management of AK is presented in Table A6. Combined drug therapy was used in three (100%) of the cases. Out of all cases, one case (33%) underwent PK, and the other two cases (66%) underwent corneal transplants. No recurrence and general improvement after surgeries for cases 2 and 3. Case 1 underwent complications and was lost to follow-up. ment of AK are shown in Figure 11. Additional information about the management of AK is presented in Table A5. Combined drug therapy was used in 13 (100%) of the cases Seven cases (54%) underwent PK or DALK, two cases (15%) underwent corneal debride ment, and one case (7%) received AMT. Out of all patients, three cases (23%) improved with drug therapy without additional therapy. UV therapy was used in three cases (23% where standard treatment was found to be ineffective.  (1)). Antifungals were used in 46% of identified cases (itraconazole (1), fluconazole (1), voriconazole (5)). Biguanides were used in 69% of identified cases (PHMB (9)). Antiseptics were used in 77% of identified cases (propamidine isethionate (3), hexamidine (1), chlorhexidine (9), pentamidine (1)). Antimicrobials were used in 23% of identified cases (miltefosine (3)). UV therapy was used in 23% of identified cases (UVA and B2 (3)).

AK Cases in South America
Three cases were reported from South America. The age range of AK patients wa 19-28 (M = 24.33, S.D. = 4.93). Contact lenses were utilized in three cases (100%). The mos common diagnostic methods used were culture and PCR, both being utilized in two case (66.7%). Combined diagnostic efforts were used in two cases (66.7%). All the cases wer derived from individual reports (i.e., no case series). The percentages of drugs used in th treatment of AK are shown in Figure 12. Additional information about the managemen of AK is presented in Table A6. Combined drug therapy was used in three (100%) of th cases. Out of all cases, one case (33%) underwent PK, and the other two cases (66%) un derwent corneal transplants. No recurrence and general improvement after surgeries fo cases 2 and 3. Case 1 underwent complications and was lost to follow-up.  (3)). Antifungals were used in 33% of identified cases (ketoconazole (1)). Antiseptics wer used in 100% of identified cases (propamidine isethionate (3), chlorhexidine (1)).

AK Cases in Asia
A total of 11 cases were reported from Asia. The age range of AK patients was 9-4 (M = 28.27, S.D. = 13.07). Contact lenses were utilized in six cases (55%). The most common diagnostic method used was culture, utilized in eight cases (73%). Combined diagnosti efforts were used in five cases (45%). Two case series included two and four cases, respec tively. The percentages of drugs used in the treatment of AK are shown in Figure 13. Ad ditional information about the management of AK is presented in Table A7. Combined  (3)). Antifungals were used in 33% of identified cases (ketoconazole (1)). Antiseptics were used in 100% of identified cases (propamidine isethionate (3), chlorhexidine (1)).

AK Cases in Asia
A total of 11 cases were reported from Asia. The age range of AK patients was 9-47 (M = 28.27, S.D. = 13.07). Contact lenses were utilized in six cases (55%). The most common diagnostic method used was culture, utilized in eight cases (73%). Combined diagnostic efforts were used in five cases (45%). Two case series included two and four cases, respectively. The percentages of drugs used in the treatment of AK are shown in Figure 13. Additional information about the management of AK is presented in Table A7. Combined drug therapy was used in 11 cases (100%). Out of the cases reported, six (55%) of identified cases showed improvement without surgical intervention. Case 2 was advised PK but refused, leading to a deterioration of symptoms. One case received AMT. Two cases were lost to follow-up.

Discussion
We assessed current evidence regarding whether different geographic regions with varying socioeconomic resources have different treatment outcomes of AK based on th type of treatment intervention. AK causes grave consequences for those infected, and cer tain populations are at higher risk, specifically for those unable to receive prompt treat ment [17]. Looking at all 60 identified AK cases gathered in this review, 49 cases (81.67% ( Figure A2) were confirmed contact lens wearers, highlighting a higher prevalence of in fection for those utilizing lenses, which is a risk factor that has been frequently identified [29][30][31]. Other research indicates that contact lens use may not be as significant as previ ously thought [33].
Findings from this review showed infections were prevalent in all age groups with seemingly no correlation between age and infection; however, other research has identi fied some associations [31]. It was found that many cases had concurrent infections or pre existing conditions, which affected how rapidly treatment was administered. Patients suf fered for longer when misdiagnosed, and outcomes were less favorable [16,17]. Combined drug treatment was used in 97% of identified cases ( Figure A3), highlighting how the cur rent treatment procedure involves the use of many different drugs with no globally stand ardized therapeutic plan. UVA and B2 therapy were reported as potentially effective treat ments [41]. A total of 8% of the cases had issues with obtaining drugs due to location o lack of knowledge about Acanthamoeba, leading to an unprepared treatment approach.
It should be noted that the results presented in this paper are not conclusive; how ever, the study findings have implications for clinicians and researchers. The three mos significant clinical symptoms reported in AK cases that clinicians should recognize ar Figure 13. The percentages of drug classes used for the treatment of AK in Asia. Antibiotics were used in 64% of identified cases (neomycin (7), polymyxin B (7), bacitracin (6), gramicidin (1), gentamicin (1)). Antifungals were used in 55% of identified cases (miconazole (3), metronidazole (3), ketoconazole (3)). Biguanides were used in 18% of identified cases (PHMB (2)). Antiseptics were used in 55% of identified cases (propamidine isethionate (3), chlorhexidine (3)).

Discussion
We assessed current evidence regarding whether different geographic regions with varying socioeconomic resources have different treatment outcomes of AK based on the type of treatment intervention. AK causes grave consequences for those infected, and certain populations are at higher risk, specifically for those unable to receive prompt treatment [17]. Looking at all 60 identified AK cases gathered in this review, 49 cases (81.67%) ( Figure A2) were confirmed contact lens wearers, highlighting a higher prevalence of infection for those utilizing lenses, which is a risk factor that has been frequently identified [29][30][31]. Other research indicates that contact lens use may not be as significant as previously thought [33].
Findings from this review showed infections were prevalent in all age groups with seemingly no correlation between age and infection; however, other research has identified some associations [31]. It was found that many cases had concurrent infections or pre-existing conditions, which affected how rapidly treatment was administered. Patients suffered for longer when misdiagnosed, and outcomes were less favorable [16,17]. Combined drug treatment was used in 97% of identified cases ( Figure A3), highlighting how the current treatment procedure involves the use of many different drugs with no globally standardized therapeutic plan. UVA and B2 therapy were reported as potentially effective treatments [41]. A total of 8% of the cases had issues with obtaining drugs due to location or lack of knowledge about Acanthamoeba, leading to an unprepared treatment approach.
It should be noted that the results presented in this paper are not conclusive; however, the study findings have implications for clinicians and researchers. The three most significant clinical symptoms reported in AK cases that clinicians should recognize are pain, decreased vision, and ocular infiltrates (Figure 3). The initial misdiagnosis issues could be attributed to how uncommon AK is, thus leading to longer response times for administering treatment. Misdiagnosis was common in all regions, with AK mostly initially diagnosed as herpetic keratitis [42]; research shows that coinfection can also occur [43]. Culture using NNA seeded with E. coli was universally and regionally identified as the most utilized diagnostic tool and was present in 73% of all cases reported (Figure 4). Cultures are currently regarded as the "gold standard" [44], but sensitivity is often limited. Contamination of culture occurred in 5% of the cases, signifying the reason why multiple diagnostic tests should be performed. The proportions of the diagnostic tests used in all AK cases are shown in Figure A4. The current surgical options that were most utilized were PK or corneal transplants, with generally good outcomes ( Figure 5).
To our knowledge, there are few reviews using individual patient data reported in case reports to consider the associations of population and geographic factors with treatment outcomes across different treatment regimens of AK. However, case reports are often not standardized in terms of the information they contain, hindering deeper analysis and direct comparisons. Also, papers in languages apart from English and French were excluded, leading to potential bias in terms of reviewing case reports. Papers with more than one clinical case were noted as having an increased bias as most cases would have been treated in the same or similar manner.

Identification and Selection of Studies
In this review, the online bibliographic databases PubMed, BioMed Central, and Google Scholar were searched from 30 April 1990 to 1 May 2022. The following search terms were used: Acanthamoeba, Acanthamoeba keratitis, AK, case report(s), amoebic keratitis. Papers were limited to English and French.

Eligibility Criteria
Inclusion criteria included studies on clinical cases of AK from different regions around the world. Studies were excluded if they reported on veterinary cases, other forms of infection (e.g., GAE or disseminated infection), or if they lacked information on patient history, clinical signs, diagnosis, treatment, or outcome. Papers were also eligible if they contained more than one case report and included the above information but excluded if they did not show individual treatment and outcome. Studies involving "possible" cases of AK were excluded if not diagnosed as Acanthamoeba-related via confocal microscopy, culture, PCR, or other specified methods. Papers with concurrent diseases were included if there was a diagnosis, treatment, and outcome of AK.

Information Sources
One researcher reviewed all publications included in this review, screening through relevant abstracts until the paper was deemed eligible for the review. The full text was then read and analyzed, with the data being placed into different tables. An objective was made to gain a sample of papers for each geographic region to gather evidence to either support or disprove the hypothesis.

Data Charting Process
Data were extracted from each case report and key information, including year of publication, patient age, gender, wearing contact lenses, clinical symptoms, how Acanthamoeba was diagnosed, how Acanthamoeba was treated, and outcomes were all tabulated. The information gathered was specifically related to Acanthamoeba and not towards treatment or outcome of any other concurrent conditions to ensure that only information relevant to AK management was recorded. Extracted information was condensed into a more legible format, and data in the table was ordered from oldest to newest.
The diagnostic approaches recorded in the table were simplified to culture, direct examination, PCR, and confocal microscopy. The unspecified tests were also noted. Culture involved using NNA seeded with E. coli. Different types of culture media were utilized in some cases, but the majority was NNA. Direct examination involved directly looking at corneal scrapings, contact lenses, lens storage cases, and lens fluid under a microscope or using a slit lamp to examine the eye. PCR involved DNA amplification in identifying infection as Acanthamoeba. Confocal microscopy involved using a microscope as a noninvasive technique to observe and analyze ocular tissue.

Conclusions
The findings of this review of individual patient data suggest that there are differences when it comes to medical approaches for the treatment of AK. These can be linked to medical resources available, remoteness of patients, and higher exposure to parasites due to labor or lifestyles. In several cases, specific medications or diagnostic methods were not accessible in the regions that patients inhabited. This meant that either medication had to be ordered, delaying treatment, or patients attempted to seek treatment abroad, with this issue being identified in both developed and developing nations. It was also noted that diagnosis became limited when there was a lack of NNA seeded with E. coli because this method can confirm the presence of Acanthamoeba. A combined diagnostic approach should be utilized in all suspected cases of AK. Awareness of economic advantages in developed countries and how these can affect treatment outcomes are shown in the cases of North America. These cases often received surgery if treatment was ineffective due to facilities being more readily available compared to developing nations. Furthermore, countries may follow different legislations about novel treatments and alternate drug regulations, dictating what medication is available. Evidence suggests that antiseptics were the most utilized treatment, but it is the combination of drug use that appears to be the solution, possibly because no single drug has yet been developed to successfully eradicate Acanthamoeba infection. However, combinations vary by region, potentially affecting efficacy and outcome for cases. Taken together, these findings indicate that geographical location has an impact on the availability of adequate treatment and associated outcomes.

Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.

Conflicts of Interest:
The authors declare no conflict of interest. Figure A1. Gender ratio of all AK cases reported regionally and globally. Figure A2. Global and regional percentages of infected patients who wore contact lenses, wore no lenses, or had no specified lens use. Figure A1. Gender ratio of all AK cases reported regionally and globally. Figure A2. Global and regional percentages of infected patients who wore contact lenses, wore no lenses, or had no specified lens use. Parasitologia 2022, 2, FOR PEER REVIEW 15 Figure A3. Percentages of all cases utilizing combined diagnostic methods and combined treatment regimens. Figure A4. Percentages of different diagnostic tests utilized across different geographic regions. Figure A3. Percentages of all cases utilizing combined diagnostic methods and combined treatment regimens.   Moderate improvement of all clinical signs within 2 weeks. After 12 weeks, epithelial defect closed with no staining, leaving opacified cornea, which decreased visual acuity to hand motion.

A2
All medication continued. Follow-up 2 weeks later showed recurrence of symptoms. Advised to undergo therapeutic penetrating keratoplasty in India. Following graft cornea was clean with no pain and post-operatively treated with 0.1% propamidine isethionate, 0.5% moxifloxacin, and 0.1% dexamethasone eye drops.
[50] sleeping. Treatment altered to q4h for 1 week and tapered off to q6h for 1 month.
Gradual improvement over a 6-month period with no recurrence after treatment stopped.
No Acanthamoeba growth detected 2 months after treatment, but outcome not specified.
Symptoms improved after PHMB treatment, but cataract began swelling, which was treated using posterior chamber intraocular lens insertion and phacoemulsification. Treatment tapered off after 2 months with no recurrence. Visual acuity showed no improvement. [   All antibacterial therapy stopped after day 10; after day 21, amoebic treatment reduced to 5× per day with slight visual improvement. Pain medication stopped after 3 months. Gradual improvement over 12 months with no cysts present at 18 months. Central subepithelial scar present with best corrected visual acuity 6/6 + 1.
[58]      After day 40, symptoms improved, and patient was advised keratoplasty but refused. Returned later with worsened symptoms with no more specified outcome.  After 2 months, symptoms improved, with corrected vision being 20/20. Slight corneal opacity noted, and medication discontinued with no recurrence after 7 months. [80]