Corneal ulcer (microbial keratitis)
Microbial keratitis (infectious corneal ulcer) is the unifying vision-threatening syndrome of a painful red eye with a corneal infiltrate, produced by bacterial, viral, fungal, or amebic invasion of a breached corneal epithelium, managed by the same urgent pathway regardless of organism: emergent scraping for smear and culture before any drug is given, then broad empiric coverage narrowed once results return. Delay, misdiagnosis as simple conjunctivitis, or premature corticosteroid use converts a treatable ulcer into stromal melt, perforation, and permanent vision loss.
- Topic reviewThe full article, organized the way the exam asks it.
- ABIM-format MCQsVignettes with an explanation for every wrong answer.
- Key factsThe numbers and thresholds worth memorizing, up front.
- AI tutorMedBrain answers the question you're stuck on.
What this article covers
- Overview
A syndrome, not a single disease: a painful red eye with a corneal epithelial defect and stromal infiltrate, produced by several distinct organism classes; this article covers the unifying…
- Epidemiology
Contact lens wear is the dominant exposure across organisms: soft contact lens wear, particularly extended or overnight wear with poor hygiene, is the leading risk factor for the bacterial and amebic forms.
- Risk factors
Contact lens wear: especially soft lenses worn overnight, reused lens solution, or showering/swimming with lenses in; the single most consistently cited risk factor across the bacterial and amebic forms.
- Pathophysiology
Epithelial breach is the prerequisite step for every organism class: a defect from lens-related hypoxia/trauma, foreign body, surface disease, or viral reactivation is required before any organism can adhere and penetrate the stroma.
- Clinical features
Painful red eye with a corneal opacity is the shared hallmark: severe discomfort, difficulty keeping the eye open, and a corneal opacity or infiltrate seen as a white spot, common to bacterial, viral, fungal, and amebic keratitis.
- Differential diagnosis
Corneal abrasion: trauma history with fluorescein staining of an epithelial defect but no stromal infiltrate, purulent discharge, or hypopyon; see corneal-abrasion.
- Diagnosis
Confirmed by corneal scraping for smear and culture before treatment starts, not by appearance alone: obtained emergently, before the first antimicrobial dose whenever feasible; Gram stain and…
- Management
First, refer to ophthalmology emergently and stop contact lens wear immediately: remove the lens at the first visit, do not resume wear until the ulcer has fully resolved, and do not patch the eye…
- Complications
Corneal perforation: progressive stromal collagenolysis can thin the cornea to descemetocele formation and rupture, the most feared outcome across organism classes.
- Prognosis
Outcome depends on organism, ulcer size/location, and time to appropriate treatment: small peripheral ulcers treated promptly recover good vision, while large, central, or hypopyon-associated ulcers…
- Prevention
Contact lens hygiene counseling for every wearer: never sleep in daily-wear soft lenses, never reuse or top off lens solution, never rinse or store lenses in tap or non-sterile water, never shower or…
Read the whole article
Subscribing to Internal Medicine opens every article, the full question bank and MedBrain, on the web, iPhone and Android.
Related articles
- Bacterial keratitis
Bacterial keratitis is a corneal epithelial and stromal infection, most often Pseudomonas or Staphylococcus in soft contact lens wearers, that is a sight-threatening emergency treated with same-day corneal culture followed by hourly topical moxifloxacin 0.5% (small ulcer) or alternating fortified vancomycin and tobramycin (large or central ulcer). Delay or misdiagnosis as a benign red eye risks stromal melt, perforation, and permanent vision loss.
- Viral keratitis
Non-herpetic viral keratitis, overwhelmingly adenoviral, produces copious watery discharge, severe irritation, and preauricular lymphadenopathy that starts unilateral and spreads to the second eye. Management is supportive and infection-control focused; chronic subepithelial infiltrates are the vision-affecting sequela that sometimes needs ophthalmology-directed topical corticosteroid.
- Herpes simplex keratitis
Herpes simplex keratitis is reactivation of latent HSV along the trigeminal nerve causing a corneal dendritic ulcer with pain, photophobia, and decreased corneal sensation. Diagnosis is clinical on slit lamp with fluorescein staining; treatment is a topical or oral antiviral, and topical corticosteroids are contraindicated in active epithelial disease.
- Acanthamoeba keratitis
Acanthamoeba keratitis is a corneal infection by a free-living amoeba, strongly linked to soft contact lens wear combined with freshwater exposure, diagnosed by microscopic examination of corneal scrapings and treated with prolonged topical antiamoebic/antifungal therapy that often fails to prevent progressive corneal destruction. Any contact lens wearer with a painful, non-healing keratitis that is not responding to antibacterial therapy needs this diagnosis considered and an urgent corneal scraping sent.
- Corneal abrasion
A corneal abrasion is a traumatic or foreign-body-related defect of the corneal epithelium diagnosed by fluorescein uptake under cobalt-blue light. Uncomplicated cases heal in days with lubrication and pain control, but contact-lens wear mandates antipseudomonal coverage and any red flag (rust ring, infiltrate, Seidel sign, hypopyon) demands same-day ophthalmology referral.
- Conjunctivitis
Conjunctivitis is inflammation of the conjunctiva from viral, bacterial, or allergic causes presenting with red eye, discharge, and preserved vision, diagnosed clinically by discharge character and managed with supportive care, targeted topical antibiotics, or topical antihistamine/mast-cell-stabilizer therapy.
- Endophthalmitis
Endophthalmitis is a vision-threatening suppurative infection of the aqueous and vitreous humors, most often exogenous after cataract or other intraocular surgery and less often endogenous from hematogenous seeding during bacteremia or candidemia. Diagnosis is clinical, confirmed by vitreous/aqueous tap, and treatment is emergent intravitreal antibiotics or antifungals with vitrectomy for severe cases.
- Uveitis
Uveitis is inflammation of the uveal tract, classified by anatomic location as anterior, intermediate, posterior, or panuveitis and by systemic association such as HLA-B27 spondyloarthritis, sarcoidosis, or Behcet disease. Anterior uveitis presents with a painful red eye and photophobia diagnosed at the slit lamp, while posterior uveitis presents with painless floaters or vision loss, and treatment is topical corticosteroid for anterior disease escalating to systemic corticosteroid and steroid-sparing immunosuppression for recurrent, severe, or posterior-segment disease.
- Acute angle-closure glaucoma
Acute angle-closure glaucoma is a pupillary-block emergency in which sudden closure of the iridocorneal angle blocks aqueous outflow, causing severe eye pain, halos, and rapidly rising intraocular pressure that can blind the eye within hours if not treated. Diagnosis is clinical plus tonometry and gonioscopy; treatment is immediate topical and systemic IOP-lowering therapy followed by laser peripheral iridotomy.
- Orbital cellulitis
Orbital cellulitis is infection of the fat and muscle posterior to the orbital septum, most often from spreading sinusitis, that causes proptosis, painful ophthalmoplegia, and vision loss and can progress to cavernous sinus thrombosis. It is a vision- and life-threatening emergency treated with admission, blood and tissue culture, orbital/sinus CT or MRI, and immediate empiric IV vancomycin plus ceftriaxone with ophthalmology and ear, nose, and throat (ENT) involvement.