Corneal Ulcer

Lutfi AbdallahMedical Student

Contents

• Applied anatomy of the cornea• Definition of corneal ulcer• Causes• Pathogenesis• Clinical presentation• Management• Complications

• The cornea is a transparent, avascular, watch-glass like structure. It forms anterior one-sixth of the outer fibrous coat of the eyeball.

Structure of the Cornea

Dimensions –

The anterior surface of cornea is elliptical with an average horizontal diameter of 11.7 mm and vertical diameter of 11 mm.

– The posterior surface of cornea is circular with an average diameter of 11.5 mm.

– Thickness of cornea in the centre is about 0.52 mm while at the periphery it is 0.7 mm.

– Radius of curvature. The central 5 mm area of the cornea forms the powerful refracting surface of the eye. The anterior and posterior radii of curvature of this central part of cornea are 7.8 mm and 6.5 mm, respectively.

– Refractive power of the cornea is about 45 dioptres, which is roughly three-fourth of the total refractive power of the eye (60 dioptres).

Histology

Layers of the Cornea1. Corneal epithelium2. Bowman’s layer3. Corneal stroma4. Dua’s layer - This layer's discovery was

reported in May 2013 5. Descemet’s membrane6. Corneal endothelium

Fig. Layers of the cornea

Fig. Microscopic structure of the cornea

Corneal Ulcer

• Corneal ulcer is the discontinuation of the normal epithelial surface of the cornea.

Causes of Corneal ulcerInfectious

Bacterial causes Viral causes Fungal causes Protozoal Chlamidial Spirochaetal

Noninfectious Allergic Trophic Traumatic Idiopathic Vitamin A deficiency Drug-Induced Epithelial Keratitis Keratoconjunctivitis Sicca (Sjögren's Syndrome)

Pathogenesis

• Once the damaged corneal epithelia is invaded by offending agent the sequence of pathological changes which occur during development of corneal ulcer can be described under four stages:

1. Progressive infiltration2. Active ulceration3. Regression4. Cicatrization

1) Stage of progressive infiltrationCharacterized by the infiltration of polymorphonuclear and/or lymphocytes into epithelium from the peripheral circulation supplemented by similar cells from the underlying stroma if this tissue is also affected.

2. Stage of Active ulcerationActive ulceration result from necrosis and sloughing of the epithelium. Bowman’s membrane and the involved stroma.

3. Stage of regression- Induced by the natural host defence mechanisms

(both humoral and cellular) and the treatment with auguments the normal host response.

- A line of dermacation develops around the ulcer, which consists of leucocytes that neutralize and eventually phagocytose the offending organisms and necrotic cellular debris.

- The ulcer now begins to heal and epithelium starts growing over the edges.

4. Stage of Cicatrization- Healing continues by progressive epithelization which forms a permanent covering.Beneath the epithelium, fibrous tissue is laid down partly by the corneal fibroblasts and partly by the endothelial cells of the new vessels thus the stroma thickens and fills in under the epithelium, pushing the epithelial surface anteriorly.

Pathology of corneal ulcer : A, stage of progressive infiltration; B, stage of active ulceration; C, stage of regression; D, stage of cicatrization.

Clinical Presentation

Symptoms:

Pain

Photophobia

Tearing

Redness of the eye

Blurry/or poor vision due to haze

Some discharge

Foreign body sensation

Signs: Lids are swollenMarked blepharospasmConjuctiva is Chemosed, hyperemic and ciliary

congested.Yellowish white area of ulcer which may be oval or

irregular in shape.Margins of the ulcer are swollen and overhangingFlow of the ulcer is covered by necrotic materialStromal edema is present surrounding the ulcer area

MANAGEMENTInvestigations:

Routine investigations:1. CBC2. ESR3. RBG4. Urinalysis and stool examination5. VDRL6. HIV Serology test

Microbial Investigations:

7. Doing a corneal scraping and examining under the microscope with stains like Gram's and 10% KOH preparation may reveal the bacteria and fungi respectively.

8. Microbiological culture tests may be necessary to isolate the causative organisms for some cases. - Culture on blood agar medium for aerobic organisms. - Culture on Sabouraud's dextrose agar medium for fungi.

* The use of fluorescein stain, which is taken up by exposed corneal stroma and appears green, helps in defining the margins of the corneal ulcer, and can reveal additional details of the surrounding epithelium

Treatment

Specific treatment1. Treatment depending on the causative agent2. Topical antibiotics: Initial therapy (before

results of culture and sensitivity are available) should be with combination therapy to cover both gram-negative and gram-positive organisms.

Non – Specific treatment1. Cycloplegic drugs. Preferably 1 percent atropine eye

ointment or drops should be used to reduce pain from ciliary spasm and to prevent the formation of posterior synechiae from secondary iridocyclitis. Atropine also increases the blood supply to anterior uvea by relieving pressure on the anterior ciliary arteries and so brings more antibodies in the aqueous humour.

2. Systemic analgesics and anti-inflammatory drugs such as paracetamol and ibuprofen relieve the pain and decrease oedema.

3. Vitamins (A, B-complex and C) help in early healing of ulcer.

Complications

1. Toxic iridocyclitis2. Descementocele/ Keratocele3. Perforation of the cornea which may lead to

Loss of acqueos Anterior synechiae Iris Prolapse Cataract/or lens extrusion Loss of vitreous Endophthalmitis Staphyloma

4. Secondary glaucoma5. Corneal scarring6. Blindness if the scar is centrally located.

References

- Comprehensive ophthalmology 4th edition, A K KHURANA et al

- General ophthalmology 17th edition , Vaughan, Asbury et al.