Superficial Purulent Keratitis.
Keratitis is the inflammation of the cornea. Keratitis can be categorized clinically into: i.
- Superficial
- a. Purulent - Bacterial & Fungal
- b. Non-purulent - Viral & Allergic
- ii. Deep
Over 90% of all corneal inflammations are caused by bacteria (e.g. S. epidermidis, S. aureus, S. pneumoniae, Coliforms, Pseudomonas, Haemophilus).
Pathogenesis - host of bacteria may infect the cornea. Some are found on the lid margin as part of the normal flora. The conjunctiva and cornea are protected against infection by blinking, washing away of debris by the flow of tears, entrapment of foreign particles by mucus, antibacterial properties of the tears, the barrier function of the corneal epithelium (N. gonorrhoeae is the only organism that can penetrate the intact epithelium).
Predisposing causes of bacterial keratitis include keratoconjunctivitis sicca (dry eye), breach in the corneal epithelium (e.g. following surgery or trauma), contact lens wear, prolonged use of topical steroids.
Symptoms and signs -
- pain, usually severe unless the cornea is anaesthetic
- purulent discharge
- ciliary injection
- visual loss (severe if the visual axis is involved)
- photophobia
- hypopyon – sometimes (a mass of white cells collected in the anterior chamber) a white corneal opacity which can often be seen with the naked eye
Treatment - Scrapes are taken from the base of the ulcer for Gram staining and culture. The patient is then treated with intensive topical antibiotics, often with dual therapy using specially formulated, concentrated, combined preparations to cover most organisms (e.g. cefuroxime against Gram - positive bacteria and gentamicin for Gram - negative bacteria). The use of fluoroquinolones (e.g. ciprofloxacin, ofloxacin, available commercially) as a monotherapy is gaining popularity. The drops are given hourly, day and night, for the first couple of days and are reduced in frequency as clinical improvement occurs. In severe or unresponsive disease, the cornea may perforate. This can be treated initially with tissue adhesives (cyanoacrylate glue) and a subsequent corneal graft. A persistent scar may also require a corneal graft to restore vision.