Page 52 - NAME OF CONDITION: REFRACTIVE ERRORS

b) Investigations:

Microbiology: Since the patient has been referred for a potentially serious condition, a

comprehensive microbiological evaluation including additional culture, antibiotic
sensitivity testing and if necessary, a corneal biopsy should be performed. A repeat
smear examination should be ordered for and carefully looked for mixed organisms.
Routine culture examinations are useful for the following reasons
i. Gold standard that confirm gram stain microscopy (GSM)
ii. Provide sensitive data, including antibiotic sensitivity measurement to enable
modification of initial therapy
iii. It will serve as an useful tool to understand the causative organisms prevalent in the

region
The cultures should be selected to identify common organisms like fungi and bacteria. An
ideal minimal culture tests would use blood agar and Sabouraud’s dextrose agar. Special
culture medial such as non nutrient agar should be reserved for non responsive cases or
cases which show clinical suspicion of Acanthamoeba. Ocular bacterial cultures usually
grow within 48 hours while the fungi from the ocular specimens grow within 7 days.

Recommended Stains and Culture media for Microbial Keratitis

Suspected Organisms Stain Media

Aerobic bacteria Gram’s Blood agar
Chocolate agar
Thioglycollate broth

Anaerobic bacteria Gram’s Anaerobic blood agar
(Rarely involved) Thioglycollate broth

Mycobacteria Gram’s Blood agar
Acid fast Lowenstein – Jenson

Fungi 10 % KOH Blood agar
Gram’s Sabouraud’s dextrose agar
Calcofluorwhite Brain heart infusion

Acanthamoeba 10 % KOH ------
Gram’s
Giemsa Non-nutrient agar
Calcofluorwhite with E.coli

Note: Acridine orange – GMS – if facilities available, use it.

Corneal biopsy:
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