BACTERIAL CORNEAL ULCER.

PATHOGENESIS

PATHOLOGY.

CLINICAL FEATURES.

BY:-DR.AYESHA SARWAR.

CORNEAL ULCER:-CORNEAL ULCER MAY BE DEFINED AS A DISCONTINUATION IN THE NORMAL EPITHELIAL SURFACE OF THE COREA ASSOCIATED WITH NECROSIS OF THE SURROUNDING CORNEAL TISSUE.

CHARACTERISED BY EDEMA & CELLULAR INFILTRATION.

BEING THE MOST ANTERIOR PART OF THE EYEBALL, THE CORNEA IS EXPOSED TO ATMOSPHERE AND HENCE PRONE TO GET INFECTED EASILY.

AT THE SAME TIME CORNEA IS PROTECTED FROM DAY-TO-DAY MINOR INFECTIONS BY NORMAL DEFENCE MECHANISMS PRESENT IN THE TEARS (Present in the form of lysozyme and other proteins)

THERFORE, INFECTIVE BACTERIAL ULCER MAY DEVELOP WHEN:-Either the local defence mechanism is jeopardised.Presence of local ocular predisposing disease.Host’s immunity is compromised.The causative organism is very virulent.

ETIOLOGY OF BACTERIAL CORNEAL ULCER:

THERE ARE 2 MAJOR FACTORS IN THE PRODUCTION OF A PURULENT ULCER:-

A]CORNEAL EPITHELIAL

DAMAGE

B]INFECTION OF THE ERODED AREA

HOWEVER, THE FOLLOWING 3 ORGANISMS CAN INVADE AN INTACT CORNEAL EPITHELIUM AND PRODUCE ULCERATION....

Neisseria gonorrhoeaN.meingitidisCorynebacterium diptheriae.

CORNEAL EPITHELIAL DAMAGE:

PREREQUISITE TO PRODUCE CORNEAL ULCERATION & MAY OCCUR IN THE FOLLOWING CONDITIONS:-

1.CORNEAL ABRASION: Foriegn body, misdirected cilia, concretions and trivial trauma.

2.EPITHELIAL DRYING: Xerosis & exposure keratitis.

3.NECROSIS OF EPITHELIUM: Keratomalacia.

4.DESQUAMATION OF EPITHELIUM: corneal edema in bullous keratopathy.

5.EPITHELIAL DAMAGE DUE TO TROPHIC CHANGES: Neuroparalytic keratitis.

CORNEAL ABRASION.

SOURCE OF INFECTION

1] EXOGENOUS INFECTION:- Conjuctival sac, lacrimal sac, infected foriegn bodies, water or air borne infections.

2] FROM THE OCULAR TISSUE: Owing to the direct anatomical continuity diseases spread from...•Conjuctiva to the corneal epithelium.•Sclera to stroma•Uveal tract to endothelium of cornea.

3] ENDOGENOUS INFECTION: Rare

CAUSATIVE ORGANISMS:

STAHYLOCOCCUS AUREUSPSEUDOONNAS PYOCYANEASTREPTOCOCCUS PNEUMONIAEE.COLIPROTEUSKLEBSIELLAN.GONORRHOEAN.MENINGITIDISC.DIPTHERIAE

PATHOGENESIS:ONCE THE CORNEAL EPITHELIUM IS INVADED BY THE OFFENDING AGENTS, THE SEQUENCE OF CHANGES OCCURING IN THE DEVELOPMENT OF A ULCER CAN BE DESCRIBED UNDER 4 STAGES:-1. STAGE OF INFILTRATION2. STAGE OF ACTIVE ULCERATION3. STAGE OF REGRESSION4. STAGE OF CICATRIZATION.

DEPENDING UPON THE CIRCUMSTANCES, THE COURSE OF THE BACTERIAL ULCER MAY TAKE ONE OF THE 3 FORMS:-

A. ULCER MAY HEAL & BECOME LOCALIZED.B. PENETRATE DEEP LEADING TO CORNEAL PERFORATION.C. SPREAD FAST IN THE WHOLE COREA AS A SLOUGHING

CORNEAL ULCER.

PATHOGENESIS.....

PATHOLOGY OF BACTERIAL CORNEAL ULCER.....

1]STAGE OF PROGRESSIVE INFILTRATION:

CHARACTERIZED BY INFILTRATION F LYMPHOCYTES INTO THE EPITHELIUM FROM THE PERIPHERAL CIRCULATION & THE UNDERLYING STROMA.

SUBSEQUENTLY, NECROSIS OF THE INVOLVED TISSUE MAY OCCUR.

2]STAGE OF ACTIVE ULCERATION:

ACTIVE ULCERATION RESULTS FROM NECROSIS & SLOUGHING OF THE EPITHELIUM, BOWMAN’S MEMBRANE & THE INVOLVED STROMA.

THE WALLS OF THE ULCER PROJECT OWING TO SWELLING OF THE LAMELLAE BY IMBIBITION OF FLUID & PACKING OF MASSES OF LEUCOCYTES BETWEEN THEM.

HYPEREMIA OF CIRCUMCORNEAL VESSELS RESULTING IN ACCUMULATION OF PURULENT EXUDATES O THE CORNEA.

EXUDATION INTO THE ANTERIOR CHAMBER FROM VESSELS OF IRIS & CILIARY BODY LEAD TO HYPOPYON FORMATION.

ULCER MAY FURTHER PROGRESS AS FOLLOWS:By lateral extension resulting in diffuse superficial ulcerationOr it may progress by deeper penetration leading to decemetocoele fomation & a possible corneal perforation.

3]STAGE OF REGRESSION:-

INDUCED BY NATURAL HOST DEFENCE MECHANISMS & TREATMENT THAT AUGMENTS THE NORMAL HOST RESPONSE.

A LINE OF DEMARCATION DEVELOPS AROUND THE ULCER WHICH CONSISTS OF LEUCOCYTES THAT PHAGOCYTOSE THE OFFENDING AGENTS.

THE DIGESTION OF NECROTIC DEBRI MAY RESULT IN INITIAL ENLARGEMENT OF THE ULCER.

THIS PROCESS MAY BE ACCOMPANIED BY VASCULARIZATION THAT INCREASES THE IMMUNE RESPONSE.

THE ULCER NOW BEGINS TO HEAL & EPITHELIUM BEGINS TO GROW OVER THE EDGES.

4]STAGE OF CICATRIZATION:-IN THIS STAGE, HEALING CONTINUES BY PROGRESSIVE EPITHELIZATION WHICH FORMS A PERMANENT COVERING.

BENEATH THE EPITHELIUM, FIBROUS TISSUE IS LAID DOWN, PARTLY BY THE CORNEAL FIBROBLASTS & PARTLY BY THE ENDOTHELIUM OF NEW VESSELS.

THE STROMA THUS THICKENS, PUSHING THE EPITHELIAL SURFACE ANTERIORLY.

THE DEGREE OF SCARRING FROM HEALING VARIES:-If the ulcer was very superficial involving only the epithelium, it heals without scar .When the ulcer involves Bowman’s membrane, the ulcer is called a NEBULA.MACULA results from ulcers involving 1/3rd of corneal stroma.LEUCOMA results from ulcers involving more than 1/3rd of the stroma.

MACULA OF THE CORNEA VS NEBULA & LEUKOMA

The 3 words - all from latin- NEBULA, MACULA & LEUKOMA, are the words used to describe the appearance of a corneal scar.

NEBULA (fog/mist) describes a hard to see corneal scar- one where slit lamp detection is required.

MACULA (stain/spot) is typified by the scar in the photo... It can be seen by proper illumination.

LEUKOMA (white) is a white scar that is easily seen just by looking at the eye.

LEUKOMATOUS CORNEAL ULCERATION WITH FATTY INFILTRATION

ON PRESENTATION- Eye highly inflamed with circum corneal congestion as well as a large nebula macular grade central corneal opacity.

Stages of corneal ulceration..

Regressive

Progressive

Cicatrization

Leucocytic infiltration

PMN leucocytic infiltration

vascularisation

Active Ulceration

CLINICAL PICTURE (SIGNS AND SYMPTOMS)....

A 50year OLD MAN COMES WITH A HISTORY OF........

PAIN AND FOREIGN BODY SENSATIONWATERING FROM THE EYEPHOTOPHOBIABLURRED VISIONREDNESS OF EYES.SWOLLEN LIDS.MARKED BLEPHAROSPASM.CHEMOSED CONJUCTIVA.

A WELL ESTABLISHED CORNEAL ULCER (characteried by):-Yellowish white area of ulcer...may be oval/irregular.Margins of ulcer oval and overhanging.Floor of the ulcer covered by necrotic material.Stromal oedema present surrounding the ulcer area.

INFILTRATEEPITHELIAL DEFECT

HYPOPYONCORNEAL CONGESTION

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