An overview to infectious keratitis: etiopathogenesis and clinical features.

1. INFECTIOUS
KERATITIS
ETIOLOGY, PATHOLOGY,
CLASSIFICATION
Ritika Mukhija
3rd Semester JR

2. Introduction: Barriers to
microbial infection
• Anatomical : bony orbital rim, eyelids,
cilia, intact epithelial surface of
conjunctiva and cornea
• Mechanical : tear film, blinking, punctal
drainage system
• Antimicrobial : Tear film constituents (like
mucus layer, IgA, complement proteins,
lactoferrin, lysozyme, β-lysin)and CALT
(conjunctiva associated lymphoid tissue)

3. Etiology

4. Pathogenesis
 Occurs due to host cellular and immunological
responses to offending agent
 Host responses are responsible for corneal
destruction and stromal melting
 Corneal insult  secretion of PMNs  secrete lytic
enzymes like collagenase, elastase, cathepsin 
destruction of cornea  reactive fibroblasts 
synthesize collagen  repair
 For reparative phase, interaction between
keratocytes and blood vessels is essential.

5. Stages of Corneal Ulcer
 Stage 1: Progressive Stage
 Saucer shaped ulcer, with gray zone of infiltrartion
 Microbes adhere to epithelium, release toxins
 Necrosis & sloughing of epithelium, Bowman’s membrane
& involved stroma
 Lateral extension or deeper penetration
 Stage 2: Regressive Stage
 Line of demarcation (consisting of leukocytes)
 Margin & floor of ulcer become smooth & transparent
 Superficial vascularization
 Stage 3: Healing Stage
 Epithelialization starts
 Keratocytes & histiocytes convert to fibroblasts
 Vascularization occurs towards ulcer site & promotes
healing
 Vessels eventually regress, may form ghost vessels
 Degree of scarring depends on depth of involvement

6. Sequelae and Complications
 Corneal opacification :Nebular, Macular
& Leukomatous
 Descematocoele
 Peforation
 Ectatic cicatrix
 Corneal fistula
 Hemorrhage
 Endophthalmitis

7. Clinical features:
 History and symptoms:
 Onset of disease & progression
 Pain
 Redness & photophobia
 Discharge
 Decreased visual acuity
 Signs and clinical examination:
 External ocular examination : Lids and lacrimal
system
 Slitlamp examination : Conjunctiva, cornea, iris,
anterior chamber, pupil and lens status
 Posterior segment evaluation
 Intraocular pressure

8. Corneal examination
 Corneal ulcer
 Location
 Shape
 Margins
 size
 Epithelial defect
 Infiltration
 Corneal sensations
 Surrounding cornea
 Vascularisation
 Corneal thinning & perforation

10. Bacterial Keratitis

11. Risk Factors
 Corneal trauma : Bacillus Cereus & non tuberculous
mycobacteria following FB injury, Anaerobic bacteria
after contamination with soil, Listeria in animal handlers
& farmers
 Eyelid disease : Pneumococcus ass with dacrocystitis
 Ocular surface disorder
 Tear film disorders : Staphylococcus
 Previously compromised local or systemic defense
mechanisms : Pesudomonas, Moraxella
 Contact lens use : Pseudomonas, Enterobacteriaceae
 Prior ocular surgery : M.chelonei particularly after LASIK
 Bacteria which can invade intact cornea: Neisseria,
Corynebacterium, Haemophilus, Shigella and Listeria.

12. Fungal organisms causing keratitis

13. Risk Factors Clinical Features

14. Viral Keratitis

16. Acanthamoeba Keratitis
 Predisposing factors:
mainly contact lens
use.
 Others: contaminated
solutions/water,
corneal trauma,
orthokeratology.

18. Contact Lens Related Keratitis

19. Infectious Crystalline Keratopathy
 Indolent corneal infection with needle-like
branching crystalline opacities
 Most common risk factor: prior ocular
surgery and steroid use
 Most frequently seen following
penetrating keratoplasty, although also
reported after epikeratoplasty, LASIK,
glaucoma filtering surgery with post-op
subconjuctival 5 FU