Mycotic keratitis — an underestimated mycosis

Pathogenesis of microbial keratitis

“…In case of filamentous fungal keratitis, clinical manifestations include sudden onset of pain along with photophobia, discharge with reduced vision and opacity on the surface of the cornea suggestive of an ulcer [7]. It may involve any part of the cornea and show firm, sometimes dry elevated slough, hyphate lines extending into the normal cornea beyond the edge of the ulcers, multifocal granular or feathery grey-white satellite stromal infiltrates, immune ring, Descemet's fold and mild iritis [163,178,194,196]. Although each fungal keratitis exhibits these basic features, they may vary depending on the etiological agent.…”

Fungal infections of the cornea

“…As far as possible, the lens should be left undisturbed to prevent spread of the infection to the posterior segment; however, where the lens is already exposed preoperatively because of a large perforation, lens extraction should be performed through the trephination wound. 1,2,13 Fungal malignant glaucoma 16 may occur in a small percentage of patients with mycotic keratitis, especially those with Fusarium infections; this complication is recognised by the occurrence of elevated intraocular tension, uniform shallowing of the anterior chamber, and a fungus-exudate-iris mass covering the pupillary area. Keratoplasty, with a good anterior and posterior chamber wash, an extracapsular lens extraction and postoperative systemic antifungal therapy, is recommended for management, and full dilatation of pupils early in the course of the disease is recommended as prophylaxis; a more invasive procedure, including anterior vitrectomy, may be unnecessary.…”

“…17 The outcome of mycotic keratitis ultimately depends on the interplay of agent (invasiveness, toxigenicity, resistance to drugs), host (inflammatory response, hypersensitivity reactions), and predisposing factors. 1 It has been hypothesised that rapid progression of mycotic keratitis in the early phases is mainly by agent factors, such as a large fungal inoculum and penetration deep into the corneal stroma, while progression in the later phases involves a combination of agent and host factors and resistance to antifungals. 17 Invasiveness of fungi in corneal tissue may be aided by formation of intrahyphal hyphae, 57,58 or by liberation of fungal proteinases 59 or toxins.…”

“…5,[10][11][12] It is not known whether the use of traditional eye medicines specifically predisposes to filamentous fungal keratitis. 1 Conversely, in keratitis due to Candida albicans and related fungi, there is usually some pre-existing ocular (eg insufficient tear secretion, defective eyelid closure) or systemic (eg diabetes mellitus, immunosuppression) condition; this type of keratitis may also supervene on a pre-existing epithelial defect because of herpes keratitis or abrasions caused by contaminated contact lenses. 5,13 Gopinathan et al 14 recently reviewed the epidemiological features of 1352 patients with culture-proven mycotic keratitis seen over a period of 10 years at a tertiary care eye hospital in southern India; keratitis due to yeast-like fungi occurred in only nine (0.7%) patients, hence the observations made relate overwhelmingly to filamentous fungal keratitis.…”

“…In filamentous fungal keratitis, which may involve any part of the cornea, firm (sometimes dry) elevated slough, 'hyphate' lines extending beyond the ulcer edge into the normal cornea, multifocal granular (or feathery) greywhite 'satellite' stromal infiltrates, 'immune ring', Descemet's folds, and mild iritis may be seen 1,10 ( Figures 1 and 2). An endothelial plaque and hypopyon may occur after the first week.…”