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Describe corneal ulcer with its aetiology, clinical features, investigation and management.

Ophthalmology · 3rd Professional

A corneal ulcer (infective keratitis) is a discontinuity of the corneal epithelium with necrosis and inflammatory infiltration of the underlying stroma.
It is the leading cause of monocular blindness in India, and is overwhelmingly a disease of the rural working population.
The essential precondition is a breach in the epithelium, since the intact epithelium is an effective barrier. Hence the importance of the small number of organisms that can penetrate an intact epithelium: neisseria gonorrhoeae and N. Meningitidis, corynebacterium diphtheriae, haemophilus (Koch-Weeks) and listeria

Group	Predisposing factors
Loss of the epithelial barrier	Trauma, especially with vegetable matter; a corneal foreign body; contact lens wear, particularly overnight; and corneal surgery
Loss of the tear film	Dry eye, xerophthalmia, and Sjogren syndrome
Failure of lid closure and protection	Lagophthalmos, seventh nerve palsy, proptosis, ectropion, and coma or sedation with the lids apart
Mechanical irritation	Trichiasis, entropion, and a misdirected lash
A reservoir of infection	Chronic dacryocystitis — a sac full of organisms draining onto the cornea, and the classical Indian antecedent of ulcus serpens. It must be looked for by regurgitation testing in every corneal ulcer
Loss of sensation	Herpetic disease, fifth nerve lesions, diabetes, and after refractive surgery — the eye does not know it is injured
Impaired host defence	Diabetes, malnutrition, vitamin A deficiency, alcoholism, HIV, and above all the use of topical steroids.

Symptoms — pain, which is severe and is what distinguishes keratitis from conjunctivitis; photophobia, lacrimation and blepharospasm — the classical triad of corneal irritation; blurred vision; and discharge
Signs — ciliary (circumcorneal) congestion; an epithelial defect staining with fluorescein; a stromal infiltrate beneath and around it, which is the essential sign of infection as opposed to a simple abrasion; surrounding corneal oedema; an anterior chamber reaction with cells and flare; and often a hypopyon
The four stages (sattler) — infiltration, active ulceration, regression, and cicatrisation

Organism	Characteristic picture
staphylococcus aureus and epidermidis	A well-defined, round or oval, white infiltrate with distinct borders and relatively little surrounding oedema; slowly progressive
streptococcus pneumoniae — ulcus serpens	The classical Indian ulcer. A greyish-yellow, disc-shaped central ulcer with one creeping, undermined, serpiginous advancing edge and a healing edge behind it; with an early and often large hypopyon. Follows minor trauma in an eye with chronic dacryocystitis — hence the need to check the sac
pseudomonas aeruginosa	The most fulminant. Associated with contact lens wear and contaminated solutions. Progresses within 24 to 48 hours, with a copious greenish mucopurulent discharge, marked stromal necrosis with a ground-glass appearance, a ring infiltrate, and perforation within days. Produces proteolytic enzymes that liquefy the stroma
moraxella	An indolent, oval ulcer of the lower cornea in debilitated, alcoholic or malnourished patients
neisseria, Corynebacterium, Haemophilus, Listeria	Penetrate an intact epithelium — the exception to the rule

Corneal scraping is the key investigation, and it must be taken before any antibiotic is started → Under topical anaesthesia at the slit lamp, using a KIMURA spatula or a sterile blade, scrape the advancing edge and the base of the ulcer — not the surface slough, which is sterile debris → smears — gram (bacteria), GIEMSA (Acanthamoeba cysts, chlamydia), 10% KOH wet mount and calcofluor white (fungal hyphae, which the KOH mount demonstrates within minutes and which is cheap and available anywhere) → culture — blood agar and chocolate agar (bacteria); sabouraud dextrose agar at 25 to 27°C (fungi); thioglycolate broth (anaerobes); and non-nutrient agar with an E.
Coli overlay for acanthamoeba → Material is plated directly onto the media in C-shaped streaks at the bedside, since transport reduces the yield → confocal microscopy where available demonstrates fungal hyphae and Acanthamoeba cysts in vivo, without waiting for culture
Treatment of bacterial keratitis — intensive topical antibiotic, hourly day and night for the first 48 hours. Either fortified preparations — cefazolin 5% with tobramycin 1.4% or gentamicin, which cover Gram-positive and Gram-negative organisms respectively — or monotherapy with a fourth-generation fluoroquinolone (moxifloxacin or gatifloxacin 0.5%).

Hypopyon is an accumulation of inflammatory cells in the anterior chamber, forming a white or yellow layer with a horizontal fluid level in the lower angle
The essential point is that a hypopyon in a corneal ulcer is sterile — a toxin-driven outpouring from the iris and ciliary body in response to the corneal infection, with an intact Descemet membrane keeping the organisms out. It settles as the ulcer settles and should not be drained
The exception — a hypopyon in fungal keratitis may contain organisms, since fungi penetrate Descemet; and a hypopyon after intraocular surgery or a penetrating injury means endophthalmitis and is an emergency

Feature	Sterile hypopyon of corneal ulcer	Endophthalmitis
Setting	An obvious corneal ulcer with an intact globe	After intraocular surgery, injection or a penetrating injury
Vitreous	Clear	Vitritis; loss of the red reflex
Pain	From the cornea	Deep, severe and increasing
Fundus view	Obtainable	Obscured; B-scan shows vitreous opacities
Management	Treat the ulcer; the hypopyon resolves with it	Urgent vitreous tap and intravitreal antibiotics

Complications — descemetocele, a clear bulge of Descemet membrane through the ulcer floor, which signals imminent perforation; perforation, often precipitated by coughing or straining, with iris prolapse and a flat anterior chamber; anterior staphyloma; secondary glaucoma; endophthalmitis and panophthalmitis; and, in every healed ulcer, a corneal scar whose density and position determine the visual outcome
Management of perforation — cyanoacrylate tissue adhesive with a bandage contact lens for a small perforation; a patch graft; or therapeutic (tectonic) keratoplasty for a large one, done to preserve the globe rather than for vision
Scrape before you treat; once antibiotics are started the yield falls sharply, and a patient who fails to respond then cannot be investigated

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