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Anterior Segment Cornea
Regarding the status of endothelial cells after LASIK, in a five-year Conclusion
outcome study there was a statistically significant decrease in In conclusion, corneal wound healing following laser refractive
endothelial cell density – 1.2% over five years – which is likely to be surgery follows a pattern of:
within the range of physiological, age-related loss.
30
However, there is
documentation of endothelial cell loss one and three months after epithelial changes (mostly hypertrophy);
PRK with 0.02% concentration applied for 30 seconds.
31
keratocyte apoptosis, activation and differentiation into
myofibroblasts;
Matrix metalloproteinases (MMPs), of which there are at least 20 recruitment of fibroblasts;
types in humans, are a family of proteolytic enzymes that are the absorption, remodelling and deposition of a new extracellular
principal mediators of tissue remodelling in physiology and pathology. matrix; and
They have been found in corneas following major and minor LASIK formation of both hypercellular and hypocellular stromal scarring.
complications. MMPs degrade components of the extracellular matrix
and basement membrane. In order to avoid uncontrolled and The same elements of wound healing follow other types of corneal
excessive tissue destruction, their expression is tightly regulated; they surgery (intrastromal corneal ring segments) as well as trauma.
are typically secreted in a latent form that undergoes internal Elucidation of the signalling components remains an important area
cleavage to be activated. They may perform a surveillance role in the of research. It is remarkable that despite biological variability in the
normal cornea, catalysing degradation of collagen molecules that millions of individuals worldwide who have undergone LASIK or PRK
occasionally become damaged.
1
surgery, the pattern of wound healing is conserved and
keratorefractive surgery enjoys excellent results in general. n
In a study of LASIK corneas with minor flap complications, MMPs
when present were localised exclusively at the flap margin and their
Irene C Kuo is an Associate Professor of Ophthalmology
presence was correlated with specific histopathological findings at
at the Wilmer Eye Institute. A corneal specialist and board-
the wound margin.
32
MMP-9, a gelatinase, stained most strongly in the certified ophthalmologist, Dr Kuo has clinical expertise in
largest number of corneas. Experimental models have demonstrated
refractive surgery, corneal disease and surgery. She is a
Diplomate of the American Board of Ophthalmology, a
a causal relationship between overexpression of MMP-9 in the
Fellow of the American Academy of Ophthalmology (AAO)
corneal epithelium leading to basement membrane dissolution and/or and a Member of the Cornea Society. Dr Kuo received her
failure to heal.
33,34
The presence of MMP-9 in association with a
bachelor’s degree from the Massachusetts Institute of
Technology. She completed her medical training at the
disrupted basement membrane around an area of epithelial ingrowth
University of California at San Francisco, her residency at the University of Southern
suggests chronic, ongoing tissue remodelling. This might explain the California—Doheny Eye Institute and her fellowship in cornea, refractive surgery and
finding that the weakest wound margin scars are those associated
uveitis at the University of California at San Francisco and the Proctor Foundation.
with epithelial ingrowth.
27
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66 EUROPEAN OPHTHALMIC REVIEW
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