Ophthalmology Update - Cleveland Clinic

i n v e s t i g a t i O n s
For more information, contact
Steven E. Wilson, M.D., at
wilsons4@ccf.org.
Study Conclusively Links Haze After PRK
Continued from page 13
while ptK smoothing after the –9.0 d prK treatment
significantly reduced haze development, but did not
eliminate it.
“the failure of ptK smoothing to prevent haze after
the higher correction indicates that there must be additional
factors besides stromal irregularity that contribute
to haze development,” dr. Wilson notes.
the rabbit study also confirmed that myofibroblast
density was a key factor in producing corneal haze.
Use of alpha-smooth muscle actin staining to identify
myofibroblasts showed the density of those cells
in the anterior stroma corresponded to the severity
of haze.
“the relationship between haze severity and myofibroblast
density makes sense since myofibroblasts
are less transparent than keratocytes and also produce
collagen and other stromal matrix components
that are disorganized compared with components in
normal stroma,” dr. Wilson says.
Using high-power confocal microscopy and immunohistochemical
staining techniques to examine
the corneas in vitro at 4 weeks after prK when the
epithelium had healed, the researchers also identified
residual ultrastructural defects in the basement
membrane in eyes with surface irregularity and
grade 1 or greater haze, along with localization of
the myofibroblasts beneath those breaks in the
basement membrane.
“the finding of imperfect regeneration of the basement
membrane is perhaps the most important finding of
this study because it can be used to explain why higher
prK corrections are associated with more haze. Our
study suggests that phenomenon occurs because the
higher correction produces more surface irregularity
that translates into structural and /or functional basement
membrane anomalies and greater potential for
transforming growth factor-beta, and perhaps other
cytokines, to penetrate into the stroma from the overlying
epithelium to stimulate myofibroblast generation
from stromal fibroblasts,” dr. Wilson says.
the study also provided evidence that late apoptosis
of the myofibroblast cells may be a key mechanism
for the disappearance of post-prK haze over time.
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