## Diagnosis of Viral Keratitis: Investigation of Choice ### Clinical Context The patient presents with classic features of **herpes simplex virus (HSV) keratitis**: - Dendritic ulcers with terminal bulbs (pathognomonic) - Unilateral presentation - Anterior uveitis - Photophobia and pain ### Investigation Comparison | Investigation | Sensitivity | Specificity | Speed | Clinical Use | |---|---|---|---|---| | **PCR of corneal scrapings** | 95–98% | >95% | 2–4 hours | **Gold standard** | | Viral culture | 60–80% | 100% | 5–7 days | Slow; requires viable virus | | Confocal microscopy | Variable | Variable | Real-time | Morphological; not confirmatory | | Fluorescein angiography | N/A | N/A | N/A | Assesses retinal perfusion; not diagnostic | ### Key Point: **PCR of corneal scrapings is the investigation of choice** for confirming HSV keratitis. It detects viral DNA with high sensitivity and specificity and provides rapid results, enabling early antiviral therapy initiation. ### High-Yield: PCR is superior to viral culture because: 1. Detects non-viable virus 2. Results available within hours (vs. days) 3. Higher sensitivity in epithelial disease 4. Allows typing (HSV-1 vs. HSV-2) ### Clinical Pearl: While **clinical diagnosis** of dendritic keratitis is often sufficient to start topical acyclovir, **PCR confirmation** is essential in: - Atypical presentations - Recurrent episodes (to exclude bacterial superinfection) - Research or medicolegal settings - Immunocompromised patients ### Warning: ~~Viral culture~~ is no longer the standard because it is slow and requires viable virus; many specimens are culture-negative despite active infection. 
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