A 29-year-old man comes to the urgent care clinic because of a 24-hour history of severe pain, redness, and a "white spot" in his left eye. He reports that his vision has become increasingly blurry. He has no history of trauma to the eye but mentions that he often wears his extended-wear contact lenses for several days at a time without removing them. On physical examination, there is significant conjunctival injection and a 2-mm, round, opaque white infiltrate on the central cornea. A small level of layering leukocytes is visible in the anterior chamber on slit lamp examination. Fluorescein staining shows a focal area of epithelial loss overlying the infiltrate.
Which of the following is the most likely diagnosis?
The correct answer is:
B) Bacterial keratitis
This patient is presenting with a corneal ulcer, specifically bacterial keratitis. The most significant risk factor for bacterial keratitis is contact lens wear, especially overnight or extended wear. The presentation of a painful, red eye with a visible white corneal infiltrate (an accumulation of inflammatory cells) and a hypopyon (layering leukocytes in the anterior chamber of the eye) is highly characteristic. Pseudomonas aeruginosa and Staphylococcus aureus are the most common causative organisms in contact lens wearers. This is an ocular emergency that requires prompt scraping for culture and intensive topical fortified antibiotics to prevent corneal perforation and permanent vision loss.
Answer choice A: Acanthamoeba keratitis, is incorrect. This is a rare but serious infection often associated with contaminated water or poor contact lens hygiene, such as using tap water for cleaning. While it is painful, it typically presents with a ring-shaped infiltrate rather than the focal, round infiltrate seen in this patient.
Answer choice C: Fungal keratitis, is incorrect. Fungal keratitis usually occurs after trauma involving vegetable matter, such as a branch hitting the eye, or in immunocompromised patients. It often presents with "feathery" borders and satellite lesions, which are not described here.
Answer choice D: Herpes simplex keratitis, is incorrect. Viral keratitis caused by herpes simplex virus (HSV) typically presents with a classic dendritic (branching) ulcer on fluorescein staining rather than a thick, round infiltrate with a hypopyon.
Answer choice E: Marginal keratitis, is incorrect. Marginal keratitis is a hypersensitivity reaction to staphylococcal antigens often seen in patients with chronic blepharitis. It presents with small, peripheral (marginal) infiltrates near the limbus, usually with a clear space between the infiltrate and the limbus, rather than a large central infiltrate with a hypopyon.
Key Learning Point
Bacterial keratitis (corneal ulcer) is a sight-threatening condition commonly associated with contact lens wear. It presents with a painful red eye, a focal white corneal infiltrate, and potentially a hypopyon. Management requires urgent ophthalmology referral for cultures and intensive topical antibiotics.
