Ophthalmology · Corneal Infections
The facts most likely to be tested
Contact lens wear is the most significant risk factor for Pseudomonas aeruginosa keratitis, which presents as a rapidly progressive corneal ulcer.
Herpes simplex keratitis classically presents with a dendritic ulcer on the cornea that stains brightly with fluorescein dye.
Bacterial keratitis is characterized by a hazy cornea, purulent discharge, and a white corneal infiltrate on slit-lamp examination.
Fungal keratitis should be suspected in patients with a history of vegetative trauma or exposure to organic matter.
Acanthamoeba keratitis is associated with improper contact lens hygiene, such as using tap water or swimming while wearing lenses, and presents with severe pain out of proportion to clinical findings.
Topical corticosteroids are strictly contraindicated in suspected infectious keratitis as they can worsen the infection and lead to corneal perforation.
Urgent ophthalmology referral is mandatory for all cases of suspected infectious keratitis to prevent permanent vision loss and corneal scarring.
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A 24-year-old graduate student presents to the urgent care clinic with a 2-day history of severe eye pain, photophobia, and blurred vision in the right eye. She admits to wearing her soft contact lenses for several days at a time, including while sleeping. On physical examination, there is conjunctival injection and a central white corneal infiltrate with an overlying epithelial defect. The anterior chamber shows a small hypopyon.
What is the most likely diagnosis and the most appropriate initial management?
Bacterial keratitis (likely Pseudomonas); urgent ophthalmology referral for topical antibiotic therapy.
The patient's history of contact lens wear and the presence of a central corneal infiltrate are classic for bacterial keratitis, which requires immediate specialist evaluation to prevent vision-threatening complications.
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High yield triage
Etiology / Epidemiology
Primary risk factor is contact lens wear (especially overnight). Bacterial, viral, and fungal pathogens cause corneal inflammation.
Clinical Manifestations
Presents with pain, photophobia, and decreased vision. Look for a corneal ulcer and hypopyon.
Diagnosis
Slit-lamp examination with fluorescein staining is the gold standard. Culture is required for large or central ulcers.
Treatment
Bacterial: Fluoroquinolones (e.g., moxifloxacin). Do not patch the eye as this promotes bacterial growth.
Prognosis
Risk of corneal perforation and permanent vision loss. Requires urgent ophthalmology referral.
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Epidemiology & Etiology
Contact lens wearers are at highest risk due to biofilm formation and hypoxia. Other risks include ocular trauma, dry eye, and topical corticosteroid use. Bacterial causes include *Pseudomonas* (contact lenses) and *Staphylococcus* species.
Pertinent Anatomy
The cornea is an avascular, transparent structure. It relies on tear film for oxygenation and nutrition. Disruption of the epithelium allows pathogens to penetrate the stroma.
Pathophysiology
Epithelial defect allows microbial invasion of the corneal stroma. This triggers an inflammatory cascade leading to leukocyte infiltration, known as a hypopyon. If untreated, proteolytic enzymes cause stromal melting and potential perforation.
Clinical Manifestations
Patients report a foreign body sensation, intense pain, and tearing. Examination reveals a white corneal infiltrate (ulcer) with overlying epithelial defect. Red flags include severe pain, vision loss, and a visible hypopyon (pus in the anterior chamber).
Diagnosis
Slit-lamp examination with fluorescein staining reveals the epithelial defect. Corneal scrapings for culture are indicated for ulcers >2mm or those involving the visual axis. Gram stain provides rapid identification of bacterial morphology.
Treatment
Bacterial keratitis requires Fluoroquinolones (e.g., moxifloxacin or gatifloxacin) drops. Do not patch the eye as it creates a warm, dark environment for bacterial proliferation. Avoid topical corticosteroids as they can worsen fungal or viral infections.
Prognosis
Prompt treatment prevents corneal scarring and permanent visual impairment. Complications include corneal perforation and endophthalmitis. Patients require daily follow-up until the ulcer shows signs of healing.
Differential Diagnosis
Herpes Simplex Keratitis: Dendritic ulcer on fluorescein staining
Fungal Keratitis: Feathery borders and satellite lesions
Acanthamoeba Keratitis: Severe pain out of proportion to exam; history of water exposure
Chemical Burn: History of exposure; requires immediate irrigation
Acute Angle-Closure Glaucoma: Mid-dilated fixed pupil and steamy cornea