Bacterial keratitis is the most common form keratitis(corneal ulcer), although it may also be caused by viruses,parasites and fungi.
Etiology: Common bacteria associated with corneal
ulceration include S. aureus, Pseudomonas, Streptococcus
pneumoniae, Enterobacteriaceae and Neisseria
Transmission: Infection spreads to cornea either
—(1)endogenously from underlying infection of adjacent
structures—conjunctiva, eyelid or lacrimal gland; or
(2)exogenously from water or airborne infection
Invasion: The bacteria may invade corneal epithelium,
leading to formation of purulent corneal ulcer. Invasion
usually occurs through abraded cornea, except for
Neisseria and C. diphtheriae, which can invade the intact
Broadly bacterial corneal ulcers may manifest as:
Purulent corneal ulcer: Present with eye pain, foreign
body sensation, watering, photophobia, blurred
vision, redness of eyes. Corneal ulcers are observed on
examination as yellowish-white lesions, oval or irregular
in shape (Fig.A)
Pseudomonas: Produce an irregular sharp ulcer with thick greenish mucopurulent discharge, spreads rapidly and may cause perforation
Enterobacteriaceae (E. coli) usually produce a shallow ulcer with greyish white suppuration and ring-shaped corneal infiltrate (Fig. B).
Hypopyon corneal ulcer: Hypopyon (presence of pus in anterior chamber) is a typical feature of pneumococcal
keratitis; although it may also be associated in other bacterial corneal ulcers.