Diagnosis of Acanthamoeba Keratitis: Past, Present and Future

Abstract

Acanthamoeba keratitis (AK) is a painful and sight-threatening parasitic corneal infection. In recent years, the incidence of AK has increased. Timely and accurate diagnosis is crucial during the management of AK, as delayed diagnosis often results in poor clinical outcomes. Currently, AK diagnosis is primarily achieved through a combination of clinical suspicion, microbiological investigations and corneal imaging. Historically, corneal scraping for microbiological culture has been considered to be the gold standard. Despite its technical ease, accessibility and cost-effectiveness, the long diagnostic turnaround time and variably low sensitivity of microbiological culture limit its use as a sole diagnostic test for AK in clinical practice. In this review, we aim to provide a comprehensive overview of the diagnostic modalities that are currently used to diagnose AK, including microscopy with staining, culture, corneal biopsy, in vivo confocal microscopy, polymerase chain reaction and anterior segment optical coherence tomography. We also highlight emerging techniques, such as next-generation sequencing and artificial intelligence-assisted models, which have the potential to transform the diagnostic landscape of AK.

Clinical Applications of Anterior Segment Optical Coherence Tomography: An Updated Review

“…Optical source Superluminescent diode [5] Superluminescent diode [5] Swept-source laser [5] Superluminescent diode [5] Wavelength 1 = 1310 2 = 1310 nm [5] 1 = 820 nm 2 = 840 nm 3 = 840 nm [5] 1 = 1310 nm 2 = 1310 nm [5] 3 = 1300 nm [15] 1 = 850 nm [16] Scan width 1 = 16 mm 2 = 15 mm [17][18][19] 1 = 6 mm 2 = 13 mm 3 = 6 mm [5] 1 = 16 mm 2 = 16 mm [5,20] 3 = 9 mm [15] 1 = 10 mm [16] Scan depth 1 = 6 mm 2 = 7 mm [17][18][19] 1 = 40,000 scans/s 2 = 80,000 scans/s 3 = 27,000 scans/s [5,21] 1 = 30,000 scans/s 2 = 100,000 scans/s [5] 3 = 16,640 scans/s [15] 1 = 52,000 scans/s [16] * Some measurements are specific to the posterior segment used and might vary for anterior segment OCT; ** not documented in the literature; *** technical specifications shown are for the 'Cornea Application'. This table was adapted from Azzopardi et al [23].…”

“…1 = 52,000 scans/s [16] * Some measurements are specific to the posterior segment used and might vary for anterior seg ment OCT; ** not documented in the literature; *** technical specifications shown are for the 'Corne Application'. This table was adapted from Azzopardi et al [23].…”

A detailed dissection of the expression, localization, structure, and diagnostic potential of cyst wall proteins of the eye pathogen Acanthamoeba

“…Acanthamoeba keratitis (AK), which leads to scarring and blindness, if not successfully treated, is caused by free-living amoebae, named for acanthopods (spikes) on the surface of trophozoites [1][2][3]. In immunocompromised patients, Acanthamoebae may cause encephalitis, which is frequently fatal [4].…”

“…The cyst wall also makes Acanthamoebae resistant to disinfectants used to clean surfaces, alcohol-based hand sanitizers, sterilizing agents in contact lens solutions, and/or antibiotics applied to the eye [23][24][25][26][27]. While trophozoites cause damage to corneal epithelial cells, AK is most often diagnosed by microscopic identification of cysts in corneal scrapings [1,2,28].…”

“…The cyst wall also makes Acanthamoebae resistant to disinfectants used to clean surfaces, alcohol-based hand sanitizers, sterilizing agents in contact lens solutions, and/or antibiotics applied to the eye [23–27]. While trophozoites cause damage to corneal epithelial cells, AK is most often diagnosed by microscopic identification of cysts in corneal scrapings [1, 2, 28]. Acanthamoeba cysts are detected using calcofluor white (CFW) or wheat germ agglutinin (WGA), which bind to cellulose and chitin, respectively, in their walls [29, 30].…”