Microbial keratitis is a sight-threatening ocular emergency. It is an infection of the cornea, most commonly caused by bacteria, although the causative organism can also be fungus or amoeba.

The commonest organisms are Staphylococci and Pseudomonas species, the latter being very common in contact lens wearers.

The symptoms of microbial keratitis include:

1. Significant eye pain
   
2. Photophobia
   
3. A red eye
   
4. Reduced vision
   
5. Acute and rapid progression of symptoms

Microbial keratitis requires urgent referral to an ophthalmologist. Delay in presentation (of as little as a few hours) can result in corneal perforation requiring surgical management. Advanced cases can also result in severe corneal scarring with loss of vision, and need for corneal transplantation.

The treating ophthalmologist will perform corneal sampling in rooms, for microscopy and culture. They will then commence intensive broad spectrum topical antibiotic therapy. Severe cases require admission to hospital, so antibiotic eye drops can be instilled every hour around the clock, and the patient monitored daily.

It is important to note that Chloramphenicol has no role in the management of microbial keratitis, as it is intrinsically bacteriostatic (rather than bactericidal), as well as being ineffective against Pseudomonas species, one of the commonest causative organisms.

Critically, the General Practitioner or Optometrist needs to have some tools for differentiating this important condition from more benign and common presentations of a red eye to general practice, and so the following should act as ‘red flag’ features, prompting urgent referral to an ophthalmologist:

1. Recent contact lens wear**
   
2. Recent ocular trauma
   
3. Reduced vision
   
4. Photophobia