Q2 LONG ANSWER 10M ★ High-yield

Describe fungal keratitis and Acanthamoeba keratitis.

Ophthalmology · 3rd Professional

Fungal keratitis (keratomycosis) is of exceptional importance in India, accounting for a third to a half of all corneal ulcers in some regions — among the highest proportions in the world — because of the combination of agricultural work, a hot humid climate and uncontrolled steroid use
Organisms — filamentous fungi predominate: aspergillus (the commonest in most Indian series) and fusarium, together with Curvularia and Alternaria; and yeasts — candida — which affect an already diseased or compromised cornea rather than a healthy one
Risk factors — trauma with vegetable matter, which is the classical history: a paddy stalk, sugarcane leaf, straw, twig or mud in the eye of an agricultural worker at harvest; topical steroid use, which permits proliferation; contact lens wear; chronic surface disease; and immunosuppression

Feature	Description
The general impression	Signs out OF proportion to symptoms — the ulcer looks far worse than the patient feels.
The infiltrate	Dry, greyish-white, rough and raised above the surface, with a texture likened to a dry plaque — quite unlike the wet, excavated bacterial ulcer
The margins	Feathery, hyphate, irregular and indistinct, with fine finger-like extensions into the surrounding stroma — the most characteristic single sign
Satellite lesions	Discrete infiltrates separated from the main lesion by clear cornea — highly suggestive
Immune (wessely) ring	A ring of infiltrate around the ulcer, from antigen-antibody precipitation
Endothelial plaque	A fibrinous plaque on the endothelium beneath the lesion, indicating deep penetration
Hypopyon	Often present, characteristically thick, viscous and immobile (it does not shift with head position), and it may contain fungal elements — unlike the mobile, sterile hypopyon of bacterial ulcer
Course	Slow and indolent over weeks; and fungi penetrate an intact descemet membrane, so endophthalmitis may occur without perforation

acanthamoeba is a free-living protozoan present in tap water, swimming pools, hot tubs, soil and dust, existing as a motile trophozoite and a highly resistant double-walled cyst which survives chlorination and most disinfectants
Risk factors — contact lens wear with rinsing in tap water, swimming or showering in lenses, and poor hygiene, which together account for most cases in developed countries; and, in India, trauma with soil or contaminated water in non-lens wearers
The hallmark IS pain out OF all proportion TO the signs, which is severe and unremitting and is the feature that should prompt the diagnosis

Feature	Bacterial	Fungal	Acanthamoeba	Herpetic
History	Trauma, lens wear, ocular surface disease	Vegetative trauma; steroid use	Lens wear with tap water; swimming	Previous attacks; fever or ultraviolet exposure
Pain	Marked	Less than the signs suggest	Out OF all proportion to the signs	Reduced, with corneal anaesthesia
Onset and course	Rapid, over days	Slow, over weeks	Slow, with early misdiagnosis	Recurrent
Margins of the lesion	Sharply defined, excavated, wet	Feathery, hyphate, dry and raised	Ring infiltrate; radial keratoneuritis	Dendritic with terminal bulbs
Satellite lesions	Absent	Present	Absent	Absent
Hypopyon	Mobile, sterile	Thick and immobile; may contain organisms	May occur late	Uncommon
Diagnostic test	Gram stain; blood agar	KOH mount; sabouraud at 25°C	Non-nutrient agar with E. Coli; confocal	Clinical; PCR
Treatment	Fortified antibiotics or a fluoroquinolone	Natamycin or voriconazole, for weeks	PHMB or chlorhexidine with a diamidine, for months	Topical aciclovir; steroid only for stromal disease
Steroid	Only once controlled	Never	Never, or with great caution	Never on epithelial disease; yes for disciform

Suspect fungus after vegetative trauma, and do a KOH mount before starting anything; the history alone should raise it in every Indian agricultural worker
Suspect Acanthamoeba when the pain exceeds the signs, and especially in a contact lens wearer who has been swimming or using tap water
Reconsider the diagnosis of herpes in any "dendritic" ulcer that fails to respond; pseudodendrites of Acanthamoeba are the classic mimic and weeks are lost
Never use a steroid in fungal or amoebic keratitis; it is the single commonest reason these eyes are lost
Continue antifungals for weeks after apparent improvement; relapse on premature withdrawal is the rule

All questions in Diseases of the Cornea