1. MICROBIAL KERATITIS
Sam Ath Huon
1st year resident

2. OUTLINE
• Bacterial keratitis
- risk factor
- cause
- pathogenesis
- clinical feature
- investigation
- management
• Fungal
- predisposing factors
- clinical features
- investigation
- management

3. BACTERIAL KERATITIS
Risk factors
• Trauma,
• Contact lens wear
• ocular medications (topical steroids) vs hypovitaminosis A
• Impaired defense mechanisms
• Altered structure of the corneal surface ( bullous
Keratophathy, exposure vs diminished corneal sensation).

4. Causes
• Common organisms
– St, aureus
– St, epidermidis
– Str, pneumoniae and other
strs
– Pseudomonas aeruginosa
(soft contact lens wearers)
– Enterobacteriaceae
(proteus, Enterobacter)
– Moraxella spp
• Uncommon organisms
– Neisseria spp
– Listeria
– Mycobacterium spp
– Nocardia spp
– Non-spore-forming
anaerobes
– Corynebacterium spp
– Haemophilus influenzea
– Chlamydia trachomatis

5. . The most common pathogens
- Pseudomonas aeruginosa
- Staphylococcus aureus
- Streptococci
. Intact coneal Keratitis
- N. gonorrhoeae
- N. meningitidis
- C. diphtheriae
- H. influenzae
- Shigella

6. • Staphylococcal ulcer:
– Well defined
– Gray-white stromal infiltrate
• Streptococcal
– Infiltrate purulent
– Severe anterior chamber reaction
– Hypopyon formation
• Pseudomonas
– Rapidly progressive,
– Suppurative
– Necrotic infiltrate
– Associated with a hypopyon and mucopurulent discharge

7. Pathogenesis
– bacterial and fungal co-infection
– Sta. aureus : adhesins to bind to collagen vs other
components of exposed Bowman vs stroma.
– Pseudomonas aeruginosa can bind to molecular receptors
exposed on injured epithelial cells.

8. • Cornea inflammation with local productions of cytokines vs
chemokines  diapedesis vs migration of neutrophils into
peripheral cornea from limbal vessels.
• microorganisms produce proteases  disrupt the
extracellular matrix.
• Enzymes released by neutrophils vs activation of corneal
matrix metalloproteinases  exacerbate inflammatory
necrosis.

9. • With antimicrobial control of bacteial replication  wound
healing processes  NV vs scarring.
• Progessive inflammation however may lead to corneal
perforation.

10. Clinical features
• Presentations:
– Rapid onset of pain
– Decreased vision
– Photophobia
– Discharge
– Eyelid edema

11. • Signs:
– Conjunctival injection
– White stromal infiltrate associated with an overlying
epithelial defect and secondary anterior uveitis
– Enlargement of stromal infiltration associated with stromal
oedema
– Severe infiltration and hypopyon formation
– Corneal perforation and endophthalmitis in neglected
cases

14. Investigations
+ Corneal scraping and culture
- Blood agar : most bacteria & fungi except Neisseria,
Hemophilus & Moraxella
- Chocolate agar : Neisseria, Hemophilus, Moraxella
- Sabouraud dextrose agar : fungi
- Non nutrient agar : Acanthamoeba
- Brain Heart Infusion : Streptococci and Meningococus
- Löwenstein-Jensen : Mycobacteria and Nocardia

15. Investigations
+ Staining
- Gram : Bacteria, fungi, Microsporidia
- Giemsa : Bacteria, fungi, Acanthamoeba, Microsporidia
- Calcofluor white : Acanthamoeba, fungi, Microsporidia
- Acid-fast stain : Mycobacterium, Nocardia

16. Investigations
+ Conjunctival swabs : Severe cases and corneal
scraping is negative
+ Contact lens cases
+ Sensitivity reports
- Susceptible
- Intermediate
- Resistant

17. Management
• Principles of Rx;
– Broad-spectrum topical antibiotics.
– Dual Rx; Combination 2 fortified antibiotic for Gram(-) vs
Gram (+)

18. Management
• Monotherapy;
– Fluoroquinolone (Ciprofloxacin 0.3% or ofloxacin 0.3%
– But may be corneal toxicity (white corneal precipitates)
• Topical antibiotics
– Initial instilation hourly intervals.
– If response favourable => reduced 2hourly during waking
hours.
– If progress => fortified drops changed to commercial
preparation with tapered vs discontinued.

19. Management
• Oral ciprofloxacin, 750mg b.id, when juxtalimbal ulcer, to
prevent spread to sclera.
• Atropine : prevent PS vs reduce pain from ciliary spasm.
• Steroid Rx; is controversial
– Benefits of steroid topical reducing stromal necrosis vs
scarring, but decreased fibroblast activity vs wound
healing  incraesed risk of perforation.

20. • When to change antibiotics?
– Resistant pathogen vs ulceration progressing.
– No need to change if induced favourable response, even
cultures show resistant organism.

21. Fungal Keratitis
• Less common than BK, 5%-10% of corneal infections, but may
devastating effects.
• Can severe stromal necrosis vs enter AC by penetrating intact
Descemet membrane, vs difficult control because poor
penetration of antimycotic agents.
• Filamentous fungal : Asprgillus vs Fasarium
• Non Filamentous or Yeast : Candida

22. Predisposing factors :
- chronic ocular surface disease
- long-term use of topical steroids
- contact lens wear
- systemic immunosuppression
- diabetes
- vegetable matter

23. Clinical features
• Presentation
– Gradual onset of FB sensation
– Photophobia
– Blurred vision
– Discharge

24. • Signs
– Filamentous keratitis
• Greyish-white infiltrate with indistinct feathery
margins.
• Often surrounded by finger-like satellite stromal
infiltrates
– Candida keratitis
• Yellow-white infiltrate
• dense suppuration
• similar to bacterial keratitis

26. Investigations
• Staining
- Gram and Giemsa staining
- Periodic acid-Schiff (PAS)
• Culture
- Sabouraud dextrose agar
- on blood agar or in enrichment media.
- contact lenses
• Corneal biopsy
- is indicated in the absence of clinical improvement after
3–4 days
- if no growth develops from scrapings after a week.

27. Management
• hospital admission
• Removal of the epithelium
• Topical treatment : hourly for 48 hours
- Candida : amphotericin B 0.15% or econazole 1%;
alternatives include natamycin 5%,
fluconazole 2%, and clotrimazole 1%
- Filamentous infection is treated with natamycin 5% or
econazole 1%; alternatives are amphotericin B 0.15% and
miconazole 1%.
• A broad-spectrum antibiotic
• Cycloplegia as for bacterial keratitis

28. • In servere case :
- Subconjunctival fluconazole
- Systemic antifungals lesions are near the limbus, or for
suspected endophthalmitis
• Superficial keratectomy
• Therapeutic keratoplasty

29. Thank you