Antimicrobial management of presumed microbial keratitis: guidelines for treatment of central and peripheral ulcers

Abstract

Aims: To determine the quantitative relation between the major risk factors for microbial keratitis of previous ocular surface disease and contact lens wear and central and peripheral infiltration, often associated with ulceration, in order to establish a rational chemotherapeutic management algorithm.

Methods: Data from 55 patients were collected over a 10 month period. All cases of presumed microbial keratitis where corneal scrapes had been subjected to microbiological examination were included. Risk factor data and laboratory outcome were recorded. Antimicrobial regimens used to treat each patient were documented.

Results: 57 episodes of presumed microbial keratitis were identified from 55 patients, 24 male and 31 female. There were 30 central infiltrates and 27 peripheral infiltrates of which 28 were culture positive (73% of central infiltrates, 22% of peripheral infiltrates). 26 patients had worn contact lenses of whom 12 had culture positive scrapes (9/14 for central infiltrates, 3/12 for peripheral infiltrates). 31 patients had an ocular surface disease of whom five previous herpes simplex virus keratitis patients developed secondary bacterial infection. Anterior chamber activity and an infiltrate size > or = 4 mm2 were more common with culture positive central infiltrates than peripheral infiltrates (chi 2 test = 11.98, p < 0.001).

Conclusions: Predisposing factors for "presumed" microbial keratitis, either central or peripheral, were: ocular surface disease (26/57 = 45.6%), contact lens wear (26/57 = 45.6%), and previous trauma (5/57 = 8.8%). Larger ulceration (> or = 4 mm2) with inflammation was more often associated with positive culture results for central infiltration. None of these four variables (contact lens wear, ocular surface disease, ulcer size, anterior chamber activity) were of intrinsic value in predicting if a peripheral infiltrate would yield identifiable micro-organisms. Successful management of presumed microbial keratitis is aided by a logical approach to therapy, with the use of a defined algorithm of first and second line broad spectrum antimicrobials, for application at each stage of the investigative and treatment process considering central and peripheral infiltration separately.

Figure 1

(A) Clinical signs: predictors of a positive culture result. (B) Predisposing risk factors for microbial keratitis.*CI = central infiltration; PI = peripheral infiltration. OCD = ocular surface disease. **Excludes all patients with Acanthamoeba and Vahlkampfia keratitis (since no infiltrate ⩾4 mm²). (a) Three extended wear contact lenses (one congenital cataract, 0.05 years; one chronic allergic keratoconjunctivitis; one band-shaped keratopathy: former two, S pneumoniae, latter, S aureus). (b) Two presentations due to contact lens associated keratopathy (CLAK). (c) One extended wear contact lens (exposure keratopathy due to S aureus).

Figure 2

(a) Pseudomonas aeruginosa keratitis with central desmetocele. Infection from use of contaminated cosmetic eyedrops. (b) Sporotrichon keratitis in patient A, 4 months after penetrating keratoplasty. (c) Nocardia keratitis in patient with mild ocular cicatricial pemphigoid. (d) Modified Ziehl-Neelsen (left) and acridine orange (right) stains of corneal biopsy material from patient C showing presence of Nocardia species. (e) Staphylococcus aureus keratitis in patient C, 5 months after lamellar keratoplasty. (f) Acinetobacter haemolyticus keratitis in a patient with a history of severe herpes simplex keratitis and secondary corneal vascularisation. (g) Acanthamoeba keratitis in a soft contact lens wearer (FDA group 4) who used chlorine based disinfection and tap water for contact lens hygiene. (h) Contact lens associated keratitis (CLAK) in a soft contact lens wearer (FDA group 1) who used both hydrogen peroxide based disinfection and tap water for contact lens hygiene.

Figure 3

Chemotherapeutic algorithm for the management of presumed microbial keratitis.