What is a dendritic ulcer and what causes it?

A dendritic ulcer is a branching, tree-like epithelial defect on the cornea with characteristic terminal bulbs at the ends of each branch. It is pathognomonic (uniquely diagnostic) for herpes simplex virus (HSV) keratitis. The ulcer is best visualized with fluorescein staining under cobalt blue light. It represents active viral replication in the corneal epithelium.

Why is Pseudomonas particularly dangerous for contact lens wearers?

Pseudomonas aeruginosa thrives in moist environments and can colonize contact lens cases and solutions. Once it infects the cornea, it produces destructive enzymes that can rapidly destroy corneal tissue, potentially causing perforation within 24-48 hours. The bacteria's ability to form biofilms on contact lenses and its resistance to some antibiotics make it a particularly aggressive pathogen.

How do you prevent adenovirus spread in the office?

Adenovirus is extremely contagious and can survive on surfaces for weeks. Prevention measures include rigorous hand hygiene before and after every patient contact, disinfection of all equipment that contacts the patient (tonometer tips, slit lamp chin rests, trial frames), using disposable supplies when possible, isolating suspected cases in separate exam rooms, and potentially closing the office for deep cleaning if an outbreak occurs.

Common Ocular Pathogens: Bacteria, Viruses, and Other Organisms

Why Know Ocular Pathogens?

Recognizing the common organisms that cause eye infections helps ophthalmic professionals anticipate the clinical course, understand treatment choices, and communicate effectively with patients. Different pathogens produce characteristic presentations that, combined with the clinical history, guide initial treatment before culture results are available.

Bacterial Pathogens

Staphylococcus Species

Staphylococcus aureus and Staphylococcus epidermidis are among the most common ocular pathogens. They cause:

Bacterial conjunctivitis: Mucopurulent discharge, lid crusting, red eye
Blepharitis: Chronic lid margin inflammation with collarettes at the base of the lashes
Bacterial keratitis: Round, white/gray corneal infiltrate with surrounding edema
Endophthalmitis: S. epidermidis is the most common cause of post-cataract surgery endophthalmitis

Streptococcus Species

Streptococcus pneumoniae causes hyperacute conjunctivitis and aggressive corneal ulcers. Streptococcal infections tend to progress rapidly and may produce significant mucopurulent or purulent discharge.

Pseudomonas aeruginosa

Pseudomonas is a gram-negative bacterium that deserves special attention because of its aggressiveness:

Strongly associated with contact lens wear, especially with poor hygiene or extended wear
Produces a rapidly progressive, vision-threatening corneal ulcer
The ulcer often appears as a dense, gray-white infiltrate with significant surrounding stromal edema
May have a characteristic "ring" infiltrate or mucopurulent discharge with a greenish tinge
Can perforate the cornea within 24-48 hours if untreated

Delaying treatment of a suspected Pseudomonas corneal ulcer. Any contact lens wearer presenting with a rapidly worsening corneal infiltrate, significant pain, and discharge should be treated as a potential Pseudomonas infection requiring urgent, aggressive antibiotic therapy. Do not wait for culture results before starting treatment.

Viral Pathogens

Adenovirus

Adenovirus causes epidemic keratoconjunctivitis (EKC), one of the most contagious ocular infections:

Highly contagious for 10-14 days
Presents with watery discharge, follicular conjunctivitis, lid edema, and preauricular lymphadenopathy
May develop subepithelial infiltrates (SEIs): Small, gray-white spots beneath the corneal epithelium that can persist for months and reduce vision
No effective antiviral treatment; management is supportive
Strict infection control is critical to prevent outbreaks in the office

Herpes Simplex Virus (HSV)

HSV keratitis is one of the most important infections to recognize:

The hallmark is the dendritic ulcer: A branching, tree-like epithelial defect with terminal bulbs visible with fluorescein staining
Often unilateral and recurrent
Can involve the epithelium (dendritic keratitis), stroma (stromal keratitis), or endothelium (disciform keratitis)
Treated with antiviral agents (oral acyclovir/valacyclovir, topical ganciclovir)
Steroids are contraindicated for epithelial disease but may be used cautiously for stromal disease with antiviral coverage

The dendritic ulcer is pathognomonic (uniquely diagnostic) for HSV keratitis. If you see a branching epithelial defect on fluorescein staining, the diagnosis is HSV until proven otherwise. This finding should be reported to the doctor immediately.

Other Pathogens

Chlamydia trachomatis

Causes adult inclusion conjunctivitis: Chronic, follicular conjunctivitis that does not respond to standard antibiotic drops. Often associated with concurrent genital infection. Treated with oral azithromycin or doxycycline.

Acanthamoeba

A free-living amoeba that causes severe, painful Acanthamoeba keratitis:

Strongly associated with contact lens exposure to water (swimming, showering, tap water rinse)
Characterized by severe pain disproportionate to clinical findings
May show a ring-shaped corneal infiltrate
Difficult to treat; requires prolonged therapy with specialized agents (polyhexamethylene biguanide, chlorhexidine)

Key Takeaways

Staphylococcus species are the most common bacterial ocular pathogens, causing conjunctivitis, blepharitis, and keratitis
Pseudomonas causes rapidly progressive corneal ulcers in contact lens wearers requiring urgent treatment
Adenovirus causes highly contagious EKC with subepithelial infiltrates; strict infection control is essential
HSV keratitis presents with pathognomonic dendritic ulcers; steroids are contraindicated without antiviral coverage
Acanthamoeba keratitis is associated with contact lens water exposure and produces pain disproportionate to findings