Assessment of infectious keratitis

Note: Infectious keratitis is a sight-threatening emergency. Urgent referral to an ophthalmologist is essential.

Infectious keratitis is a sight-threatening condition involving infection of the cornea. Causes include bacteria (eg Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa) and viruses such as herpes simplex virus (HSV) and varicella zoster virus (VZV) – see Comparative features and assessment of types of infectious keratitis for comparative features. Keratitis caused by fungi, mycobacteria or Acanthamoeba species is rarer and more difficult to treat.

Differentiation between types of keratitis is difficult and requires slit lamp examination, so prompt referral to an ophthalmologist for assessment is recommended.

Table 1. Comparative features and assessment of types of infectious keratitis
Nguyen, 2019 The Royal Victorian Eye and Ear Hospital (RVEEH), 2024 The Royal Victorian Eye and Ear Hospital (RVEEH), 2022 The Royal Victorian Eye and Ear Hospital (RVEEH), 2022 Watson, 2020

Printable table
Type of infectious keratitis	Presentation and risk factors	Investigations
Bacterial keratitis	Presentation: painful eye red eye watery eye mucous discharge reduced or blurred vision photophobia white spot usually seen on cornea Risk factors: contact lens wear eye trauma compromised ocular surface (eg following eye trauma)	prompt ophthalmology referral for consideration of a corneal scrape for culture and susceptibility testing for contact lens wearers, culture of swab samples from contact lenses and cases
Herpes simplex keratitis	Presentation: painful eye red eye watery eye reduced or blurred vision photophobia itching epithelial keratitis (dendritic ulcer) geographical ulcer stromal keratitis (stromal opacity, stromal ulceration, scarring) endothelial keratitis (stromal oedema, keratic precipitates) Risk factors: previous HSV infection active cold sores	prompt ophthalmology referral fluorescein staining of the cornea to facilitate diagnosis of epithelial keratitis – see Dendritic ulcer caused by herpes simplex virus antigen detection or NAAT (eg PCR) of a conjunctival swab consider optometry services to aid in diagnosis if ophthalmology review is likely to be delayed
Herpes zoster ophthalmicus	Presentation: painful eye red eye watery eye reduced or blurred vision photophobia can also cause epithelial keratitis and stromal keratitis Risk factors: shingles (herpes zoster), especially if rash involves tip of the nose (Hutchinson’s sign)	ophthalmology referral diagnosis is usually clinical if diagnosis uncertain, swab inflamed conjunctiva for NAAT (eg PCR)
Note: HSV = herpes simplex virus; NAAT = nucleic acid amplification testing; PCR = polymerase chain reaction

Figure 1. Dendritic ulcer caused by herpes simplex virus