Nine Days of Antibiotic Drops and a Branching Corneal Lesion
A 34-year-old man returns 9 days after an urgent-care visit for a 'red right eye.' He was started on gentamicin 0.3% every 2 hours while awake and told to come back if it didn't improve. Today: OD VA 20/60, ciliary flush, photophobia, tearing. With fluorescein and cobalt blue you see diffuse punctate staining plus a branching, linear epithelial defect with small terminal bulbs in the inferior cornea. Corneal sensation is reduced compared with the left eye. The anterior chamber shows 1+ cells. IOP is 14 mmHg. He mentions a 'cold sore' before a similar red eye 2 years ago. He asks whether he should just switch to the antibiotic drops his wife has left over.
1. Differentiate the competing explanations for this corneal picture and explain exactly which findings separate them.
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1. Herpes simplex epithelial keratitis (most likely here)
- True dendrite: linear branching with terminal bulbs and a central ulcerated channel that stains with fluorescein; rose bengal or lissamine green highlights the devitalized terminal cells.
- Reduced corneal sensation compared with the fellow eye - a discriminating sign.
- Unilateral, with 1+ anterior chamber reaction (HSV is not purely epithelial), and a history of a prior similar episode and a cold sore.
2. Aminoglycoside toxicity (the competing diagnosis, and a real contributor)
- Diffuse superficial punctate keratopathy, typically worse inferiorly, with a gritty foreign-body sensation; bilateral if both eyes are treated.
- Normal sensation, no terminal bulbs, no true branching; improves after the drop is stopped.
- Gentamicin at q2h for 9 days is a textbook setup for this - so both processes may coexist.
3. Healing abrasion / recurrent erosion - linear staining but no terminal bulbs, normal sensation, and a clear inciting event.
4. Contact-lens–related microbial keratitis - would show a focal infiltrate with overlying epithelial loss, marked AC reaction, and often pain out of proportion; not a branching pattern.
Conclusion to report: a dendriform lesion with bulbs plus reduced sensation in a unilateral, inflamed eye is herpes until proven otherwise; the diffuse staining is plausibly superimposed toxicity.
2. What must NOT happen at this visit, and what is your role as the technician?
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Must not happen:
- No topical steroid without antiviral coverage. A steroid alone in active HSV epithelial disease can convert a small dendrite into a geographic ulcer with stromal melting and perforation. This is the single highest-stakes error in the case.
- No patching of an eye with active epithelial infection.
- No use of the wife's leftover drops - unknown drug, possibly expired or contaminated, and if it is another aminoglycoside it worsens the toxicity.
- No 'reassurance diagnosis' to the patient (e.g., 'it's just the drops irritating you').
- No corneal wiping or vigorous manipulation of the lesion during staining.
Your role:
- Obtain and document VA, IOP, sensation comparison, lesion description (location, size, bulbs present), and AC reaction - objectively, without naming a diagnosis to the patient.
- Report the findings to the ophthalmologist today and arrange a slit-lamp examination; this is not a 'call back next week' problem.
- Take a targeted history: prior HSV episodes, immunosuppression, atopy/eczema, contact lens wear, current or recent steroid use, and whether drops are being shared.
- Prepare the room for the likely workup (fluorescein, rose bengal/lissamine green, antiviral supply) and hold or continue the aminoglycoside only on physician instruction.
Judgment: the technician's value here is recognizing the pattern and escalating fast - not in choosing the antiviral.
3. Which additional history or findings would change how urgently this patient is handled? Name at least four and explain why each raises the stakes.
Read the worked answer
- Contact lens wear - a dendrite look-alike with a focal infiltrate could be Pseudomonas keratitis, which can perforate in 24–48 hours; same-hour evaluation.
- Immunosuppression, chemotherapy, or chronic steroid use - HSV becomes bilateral and atypical, and progression to geographic ulcer or perforation is far faster.
- Atopic disease / eczema - eczematous blepharokeratoconjunctivitis masquerades as and coexists with HSV, and is steroid-responsive but slow; changes management.
- Prior HSV with known stromal involvement or prior steroid use - raises the risk that this is not purely epithelial and that steroid will eventually be needed with antiviral cover; a different decision pathway.
- Marked AC reaction, hypopyon, or IOP rise - suggests uveitis or trabeculitis, requiring more aggressive treatment and closer follow-up.
- Pain out of proportion to findings or a non-healing epithelial defect - neurotrophic or Acanthamoeba suspicion, both of which change the workup completely.
Why it matters for triage: the same dendritic picture in a contact lens wearer with an infiltrate versus an otherwise healthy patient with a cold sore is a same-day surgical emergency versus a routine same-week ophthalmology visit. The technician's history determines which slot the patient gets.