Summary

Microbial Keratitis is an inflammation of the cornea secondary to infection. In this article, we will discuss the various forms of microbial keratitis, including their presenting features and management.

Bacterial Keratitis

Aetiology

In most cases, bacterial keratitis only occurs where the ocular defences have been compromised, for example following an abrasion. It is typically common for this reason in contact lens wearers, particularly those who use soft lenses. The most common pathogens include:

• Pseudomonas aeruginosa
• Staphylococcus aureus

Some bacteria however are able to penetrate through the intact corneal epithelium, without there being a prior abrasion or defect. A nice way to remember this is the organisms that can create a “CNHL”

• Corynebacterium
• Haemophilus
• Neisseria species (gonorrhoea and meningitis
• Listeria

Bacterial keratitis seldom occurs in healthy, normal eyes. Risk factors include:

• Contact lens wear
• Trauma
• Ocular surface disease: e.g. dry eye, chronic blepharitis, trichiasis, entropion, exposure, severe allergic eye disease, corneal anaesthesia
• Vitamin A deficiency and immunosuppression