Keratitis and Corneal Ulcers

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Mechanism: Keratitis and corneal ulcers represent a sight-threatening emergency characterized by severe inflammation and infection of the cornea.
• The Breakdown: The process typically begins when the protective corneal epithelium is breached—often due to microtrauma from contact lens overwear. Once the barrier is broken, virulent pathogens invade the normally clear and avascular corneal stroma (External Knowledge).
• The Pathogens: The most common bacterial culprits are Staphylococcus, Streptococcus, and Pseudomonas. Pseudomonas is particularly virulent and is highly associated with contact lens use.
• The Clinical Result: The infection triggers a massive leukocytic infiltration and edema, physically manifesting as a "scooped out" epithelial defect surrounded by a characteristic white "cloudiness" in the otherwise clear corneal tissue.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Immediate Stabilization: While not life-threatening, this is a profound vision-threatening emergency. The mandatory first bedside action is to assess and document the patient's visual acuity using a Snellen chart with visual correction.
• First-Line Interventions:
• Culture: The emergency physician should facilitate culturing of the cornea.
• Medication: Administer potent topical antibiotics in the ED; specifically, topical ciprofloxacin eye drops are indicated to provide critical Pseudomonas coverage.
• Analgesia: Treat the associated pain aggressively; topical therapies (like cycloplegics (External Knowledge)) are useful in the management of pain due to inflammatory keratitis.
• Consultation & Disposition: Urgent ophthalmology consultation in the ED is strictly required for bacterial keratitis. The emergency physician must consider inpatient admission for these patients.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

Top "Can't-Miss" Differentials:
The diagnostic algorithm for a red and painful eye requires differentiating keratitis from other "Critical" and "Emergent" diagnoses. You must rule out:

• Acute Angle-Closure Glaucoma: A "Critical" diagnosis requiring immediate IOP lowering, presenting with headache, nausea, and a fixed pupil.
• Endophthalmitis: Deep intraocular infection often following recent eye surgery or trauma.
• Anterior Uveitis / Iritis: Intraocular inflammation that may present with a hypopyon.
• Ruptured Globe: Occurs in the setting of trauma, presenting with a misshapen cornea or globe.

Prioritized Diagnostic Workup:

• Visual Acuity: The absolute first step to assess the baseline functional deficit.
• Slit-Lamp Examination: Utilize a thin, bright light beam to systematically examine the tear film, corneal epithelium, corneal stroma, and endothelium.
• Fluorescein Staining: Perform a fluorescein dye test to identify the exact location and size of the epithelial breakdown.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• The Slit-Lamp Checklist:
• Locate the structural damage on the cornea. The classic visual finding is a "scooped out" epithelium representing the ulcer crater.
• Look closely at the surrounding corneal stroma; you will see edema appearing as a dense white "cloudiness" in the normally clear tissue, known as a corneal infiltrate.
• Fluorescein Overlay: When illuminated with a cobalt blue light, the "scooped out" ulceration will rapidly pool the glowing green fluorescein dye .
• POCUS View : While Point-of-Care Ultrasound is highly sensitive for retinal detachment, it is generally not the primary imaging modality for superficial corneal ulcers, as the slit lamp provides superior macroscopic visualization of the stroma.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• ED Triage Algorithm: According to the diagnostic algorithm for red and painful eyes, the presence of severe pain, foreign body sensation, or limbal injection automatically categorizes the patient out of the "Non-Urgent" pathways and into the "Emergent" pathway (Diagnosis #19: Keratitis).
• Disposition Criteria: Keratitis and corneal ulcers are designated as sight-threatening emergencies. They definitively require:

1. Urgent ophthalmology consultation in the ED.
2. Consideration for inpatient admission to ensure aggressive, round-the-clock topical antibiotic therapy.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The Eye Patching Trap: A deadly cognitive error is applying an eye patch to a patient with a suspected corneal ulcer or abrasion. Eye patches are strictly not recommended because they can mask a worsening infection and create a dark, warm environment for bacteria to rapidly multiply.
• The "Simple Abrasion" Trap: Prematurely closing the diagnosis as a simple corneal abrasion in a contact lens wearer without inspecting for the white stromal cloudiness (infiltrate). Simple abrasions heal in 1-2 days; ulcers destroy the eye.
• The Pseudomonas Pitfall: Failing to cover for Pseudomonas in patients who wear contact lenses. Contact lens overwear is a major risk factor for keratitis, and Pseudomonas coverage (e.g., with topical ciprofloxacin) is mandatory.

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzwords: "Scooped out epithelium", "white cloudiness in clear tissue", "contact lens wearer".
• Most Common Pathogen Trap: If the question stem features a contact lens wearer with a new corneal ulcer, the most highly tested causative organism is Pseudomonas.
• Distractor Options: A question will describe a painful red eye with a white corneal spot and ask for the next best step. Options will include "Apply a pressure patch" or "Discharge with follow-up in 3 days." These are dangerous distractors. The correct answer is "Urgent ophthalmology consultation and culture" or "Avoid eye patching".

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

"This patient presents with a painful red eye and photophobia. My mandatory first step is to document baseline visual acuity. On slit-lamp examination with fluorescein, I observe a 'scooped out' epithelial defect that is surrounded by a dense, white stromal cloudiness, which is the classic presentation of a corneal ulcer. Because the patient is a contact lens wearer, I am highly suspicious of a virulent Pseudomonas bacterial keratitis. This is a sight-threatening emergent diagnosis. My critical actions include withholding any eye patching, culturing the cornea, administering topical ciprofloxacin eye drops, and obtaining an urgent, STAT ophthalmology consultation in the ED for definitive management and possible inpatient admission."