MYCOTIC CORNEAL ULCER

The incidence of suppurative corneal ulcers caused by fungi has increased in the recent years due to injudicious use of antibiotics and steroids.

Etiology
1. Causative fungi. The fungi which may cause corneal infections are :
i. Filamentous fungi e.g., Aspergillus, Fusarium, Alternaria, Cephalosporium, Curvularia and Penicillium.
ii. Yeasts e.g., Candida and Cryptococcus. (The fungi more commonly responsible for mycotic corneal ulcers are Aspergillus (most common), Candida and Fusarium).
2. Modes of infection
i. Injury by vegetative material such as crop leaf, branch of a
tree, straw, hay or decaying vegetable matter. Common sufferers are field workers especially during harvesting season.
ii. Injury by animal tail is another mode of infection.
iii. Secondary fungal ulcers are common in patients who are immunosuppressed systemically or locally such as patients suffering from dry eye, herpetic keratitis, bullous keratopathy or postoperative cases of keratoplasty.
3. Role of antibiotics and steroids. Antibiotics disturb the symbiosis between bacteria and fungi; and the steroids make the fungi facultative pathogens
which are otherwise symbiotic saprophytes. Therefore, excessive use of these drugs predisposes the patients to fungal infections.

Clinical features
Symptoms are similar to the central bacterial corneal
ulcer , but in general they are less marked
than the equal-sized bacterial ulcer and the overall
course is slow and torpid.

Signs. A typical fungal corneal ulcer has following
salient features (Fig. 1):

Fig. 1. Fungal corneal ulcer.

• Corneal ulcer is dry-looking, greyish white, with elevated rolled out margins.
• Delicate feathery finger-like extensions are present into the surrounding stroma under the intact epithelium.
• A sterile immune ring (yellow line of demarcation) may be present where fungal antigen and host antibodies meet.
• Multiple, small satellite lesions may be present around the ulcer.
• Usually a big hypopyon is present even if the ulcer is very small. Unlike bacterial ulcer, the hypopyon may not be sterile as the fungi can penetrate into the anterior chamber without perforation.
• Perforation in mycotic ulcer is rare but can occur.
• Corneal vascularization is conspicuously absent.

Diagnosis
1. Typical clinical manifestations associated with history of injury by vegetative material are diagnostic of a mycotic corneal ulcer.
2. Chronic ulcer worsening in spite of most efficient treatment should arouse suspicion of mycotic involvement.
3. Laboratory investigations required for confirmation, include examination of wet KOH, Calcofluor white, Gram's and Giemsa- stained films for fungal hyphae and culture on Sabouraud's agar medium.

Treatment
I. Specific treatment includes antifungal drugs:
1. Topical antifungal eye drops should be used
for a long period (6 to 8 weeks). These
include :

• Natamycin (5%) eye drops
• Fluconazol (0.2%) eye drops
• Nystatin (3.5%) eye ointment.

2. Systemic antifungal drugs may be required for
severe cases of fungal keratitis. Tablet
fluconazole or ketoconazole may be given for
2-3 weeks.

II. Non specific treatment. Non-specific treatment
and general measures are similar to that of bacterial
corneal ulcer .
III. Therapeutic penetrating keratoplasty may be
required for unresponsive cases.