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A corneal
abrasion is an injury to the epithelium that is
superficial enough not to involve the basement membrane. It is due
to mechanical trauma. The defect is seen as superficial on slit
lamp and takes up fluorescein, shining green upon illumination
with cobalt blue light.
Treatment is usually prophylactic antibiotics with pressure
patching over 24 hours to decrease the mechanical movement of the
blinking lid and moving globe, which disrupt the epithelial
network trying to heal the defect. Antibiotics are usually broad
spectrum eye drops or ointments, like erythromicin, fucithalmic,
polymixin/sulfacetamide. If the foreign object causing the
abrasion is wood, twig, and so on, the use of polymixin/trimethoprim
is more judicious to cover fungi as well.
Note that corneal abrasions
generally do not cause scarring upon healing because the
Bowman’s membrane is not violated.
Corneal ulcer is
a defect that involve the stroma, past Bowman’s membrane. It is
usually infected (with few exceptions, like the sterile ulcers
seen in Vernal Catarrh due to releases of toxic inflammatory
mediators), and leaves a scar upon healing. It shows as a more or
less deep corneal defect with infiltrates in the ulcer bed as well
as around it, with sometimes pus and tissue melting. It surely
takes up fluorescein. Cultures should be taken from the ulcer
prior to initiating treatment, which include specially prepared
fortified doses of antibiotics eye drops, like Tobramicin and
Kefzole together, or Amikacin and Vancomycin, to be used as
frequently as Q1/2 hr to 1 hr, awaiting for the cultures to be
out. Microorganisms recovered are Staph and Strep, Pseudomonas
(especially in contact lens wearers and ICU patients), fungi (amphotericin
eye drops hance to be used), or acanthameoba. An ulcer is NEVER
patched, unlike an abrasion. If an ulcer is axial, the final
outcome after healing could be poor vision because of scarring,
necessitating corneal transplant (Penetrating Keratoplasty ). The
use of topical steroids in conjunction to antibiotics once the
ulcer approaches healing is beneficial to decrease scarring from
the inflammatory reaction elicited and hence reach better visual
outcome.
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