Abstract
Purpose :
Acanthamoeba keratitis can be diagnosed using corneal scrape, polymerase chain reactions (PCR), confocal laser scanning microscopy (CLSM) or specific culture tests. As early signs may be mild and non-specific, diagnosis is often difficult and delayed. The aim of this study is to evaluate the presence of Acanthamoeba in suspected microbial keratoconjunctivitis (KC) with negative swab for bacteria and fungi and the effectiveness of SEM examination of conjunctival scraping in the identification of germs not detected with usual microbiological exams.
Methods :
104 eyes of 87 patients, affected by KC with negative culture test, underwent scraping of the superior tarsal conjunctiva and cytological evaluation in SEM. Exclusion criteria: age < 18 years, corneal abscess and ulcer >3 mm, clinical signs of herpetic infection, allergy or severe dry eye, antibiotic therapy in the last 2 weeks. In case of Acanthamoeba detection, CLSM and PCR were performed. SEM examination was repeated at negative corneal fluorescein staining (CFS) after antiamoebic therapy; in case of persistence of Acanthamoeba, further therapeutic cycles were carried out with subsequent microscopy check.
Results :
Pathogens were identified in 96/104 eyes (92%). In 22 of them (21%) Acanthamoeba was found: 7 presented only cysts, 11 trophozoites, and 4 mixed forms; in 5 of them (23%) other pathogens coexisted. CLSM highlighted the parasite in 13/22 eyes (59%): 4 cases of mixed forms, 8 of trophozoites, 1 of cysts. PCR testing for Acanthamoeba was positive in 16/22 cases (73%). The therapy was effective in all diagnosed cases with microbial eradication in 20- 56 days (average 34.8 ± 2.1).
Conclusions :
92% of KC negative at culture tests showed pathogens, with a high prevalence of Acanthamoeba, in an atypical, non-abscess clinical form. CLSM did not allow diagnostic confirmation in 41% of cases, presumably due to the absence of stromal invasion by the parasite; similarly PCR was positive only in 73% of cases, probably for the reduced microbial load in the sample. SEM method applied to conjunctival scraping, minimally invasive and well tolerated, allowed the etiological diagnosis of atypical or unusual KC and the resolution of the clinical picture even when PCR and CLSM were negative. Limits of this examination are the need for dedicated equipment and experienced operators in SEM evaluation.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.