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Review
. 2019 Jul-Sep;33(3):268-276.
doi: 10.1016/j.sjopt.2019.09.002. Epub 2019 Sep 11.

Challenges in the diagnosis of microbial keratitis: A detailed review with update and general guidelines

Hind M Alkatan  1   2 , Rakan S Al-Essa  1
Affiliations
Review

Challenges in the diagnosis of microbial keratitis: A detailed review with update and general guidelines

Hind M Alkatan et al. Saudi J Ophthalmol. 2019 Jul-Sep.

Abstract

The incidence of microbial keratitis (MK) is variable worldwide with an estimated 1.5-2 million cases of corneal ulcers in developing countries. The complications of MK can be severe and vision threatening. Therefore, proper diagnosis of the causative organism is essential for early successful treatment. Accurate sampling of microbiological specimens in MK is an important step in identifying the infective organism. Corneal scrapping, tear samples and corneal biopsy are examples of specimens obtained for the investigative procedures in MK. Ophthalmologists especially in an emergency room setting should be aware of the proper sampling techniques based on their microbiology-related basic information for each category of MK. This review article briefly describes the clinical presentation and defines in details the best updated diagnostic methods used in different types of MK. It can be used as a guide for ophthalmology trainees and general ophthalmologists who may be handling such cases at initial presentation.

Keywords: Acanthamoeba; Aspergillus; Bacterial; Candida; Corneal abscess; Corneal ulcer; Fusarium; Herpes simplex virus; Infectious crystalline keratopathy; Keratitis; Microbial; Microsporidium; Mycotic; Polymerase chain reaction.

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Conflict of interest statement

The authors declared that there is no conflict of interest.

Figures

Fig. 1
Fig. 1
A: The clinical appearance of a typical dendritic ulcer in a case of herpetic keratitis (courtesy of Dr. Almulhim AK). B: Histopathologic appearance of lipid keratopathy as a sequela of microbial keratitis. B: The clinical appearance of disciform keratitis (Courtesy of Prof. Al Mezaine H).
Fig. 2
Fig. 2
A: The clinical appearance of a partially treted bacterial (polymicrobial) keratitis with significant hypopyon (Courtesy of Dr. Kalantan H). B: Corneal abscess in a case of Pseudomonas keratitis with marked ciliary injection (Courtesy of Dr. Alkheraiji N).
Fig. 3
Fig. 3
A: Histopathologic appearance of Gram-positive cocci (Original magnification ×1000-oil Gram). B: The appearance of Gram-negative bacilli within the corneal stroma (Original magnification ×1000-oil Gram stain).
Fig. 4
Fig. 4
A: The clinical appearance of a late stage refractory case of infectious crystalline keratopathy eventually necessitating therapeutic corneal graft (Courtesy of Dr. Kalantan H). B: Corneal specimen from therapeutic keratoplasty showing intact corneal epithelium, minimal inflammation, and anterior stromal pockets of organisms (Original magnification ×200 Hematoxylin and eosin). C: The gram stain of the same corneal button showing collection of Gram-positive cocci (Original magnification ×400 Gram stain).
Fig. 5
Fig. 5
A: The clinical appearance of fungal keratitis following complicated cataract surgery (Courtesy of Dr. Alfawaz A). B: The clinical appearance of candida infection affecting a corneal graft. C: Corneal biopsy in a case of candida keratitis showing yeast forms (Original magnification ×400 Periodic Acid Schiff). D: Higher power photo of the yeast forms (Original magnification ×1000-oil Gomori methenamine silver). E: Another case of fungal keratitis showing hyphae in histological sections with retro-corneal giant cells (Original magnification ×400 Periodic Acid Schiff). F: The fungal hyphae penetrating Descemet’s membrane (Original magnification ×1000-oil Gomori methenamine silver).
Fig. 6
Fig. 6
A: The clinical appearance of Acanthamoeba keratitis (courtesy of Dr. Almulhim AK). B: Histopathologic appearance of Acanthamoeba cysts within the corneal stroma with overlying evidence of ulceration and retro-corneal inflammatory cells (Original magnification ×200 Periodic Acid Schiff). C: Higher power of the Acanthamoeba cysts within the posterior stroma (Original magnification ×400 Periodic Acid Schiff).
Fig. 7
Fig. 7
A: The clinical appearance of ring infiltrate in Microsporidial keratitis. B: The typical appearance of the organisms with waist-band (Original magnification ×1000-oil Acid fast stain). C and D: The ultrastructural appearance of the organisms in the same case by electron microscopic examination (Original magnification ×12K). (Reproduced with permission from SJO (2012) 26, 199–203).
See this image and copyright information in PMC

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