Infectious Keratitis

An overview to infectious keratitis: etiopathogenesis and clinical features.

1. INFECTIOUSKERATITIS ETIOLOGY, PATHOLOGY, CLASSIFICATION Ritika Mukhija 3 rd 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 C orneal ulcer Location Shape Margins size Epithelial defect Infiltration Corneal sensations Surrounding cornea Vascularisation Corneal thinning & perforation

9. Bacterial Keratitis

10. 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 .

11. Fungal organisms causing keratitis

12. Risk Factors Clinical Features

13. Viral Keratitis

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

15. Contact Lens Related Keratitis

16. 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