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Lasik flap folds can induce irregular astigmatism with optical
aberrations and loss of BCVA especially if they involve the visual
axis. ‘Macrofolds’ are easily seen by slitlamp exam and represent full
thickness flap tenting in a linear fashion. On the other hand,
‘microfolds’ within the flap itself may represent wrinkles in Bowman’s
layer or in the epithelial basement membrane. They are best seen as
negative staining lines with sodium fluorescein. The incidence of
folds requiring intervention ranges between 0.2% and 1.5%.
Flap folds result from uneven alignment of the flap edge and the
peripheral epithelial ring. This can occur with unequally hydrated
stromal bed prior to flap repositioning. Thinner and larger flaps tend
to shift more readily with resultant surface wrinkling. Uneven sponge
smoothing can result in radial (with centrifugal movement) or
circumferential folds (with centripetal movement). A higher incidence
of flap folds is usually found in higher myopes and is sometimes
unavoidable. This is due to the reduced central convexity and stromal
support resulting in flap redundancy that may be quite difficult to
flatten.
Management ranges from simple lifting and refloating of the flap to
placement of sutures to stretch the flap in position. Probst et al.
described a technique using the red reflex as a way to better detect
flap wrinkles during flattening procedures. Smoothing of the flap
should aim towards an even distribution of forces applied to the
surface. This can be performed with methylcellulose sponges or their
equivalent. Instruments such as the Pineda corneal LASIK iron can also
be used to flatten isolated flaps at the slit lamp or under the
operating microscope by gently pressing on them. Other reported
strategies include hydrating the flap with hypotonic saline (60-80%)
which may facilitate leveling of the flap surface.
Fixed folds are sometimes encountered and probably occur when
epithelial hyperplasia has time to form in the crevices formed by the
folds. Superficial epithelial incisions or frank epithelial debridement
over the wrinkled area may relieve contractures that occur secondary to
the presumed epithelial hyperplasia in these longer standing folds.
Recalcitrant wrinkling is reported to respond well to placement of
running torque-antitorque 10-0 or 11-0 nylon sutures.
Epithelial Ingrowth after Lasik
Epithelium in growth under the corneal flap can cause irregular astigmatism
and induced hyperopia secondary to stromal melting. A swift
intervention is sometimes needed to prevent these complications.
Once the epithelium is noted to progress towards the visual axis or
once a significant hyperopic shift or loss of BCVA is encountered,
lifting of the flap and scraping of the epithelium should be performed
promptly. This can be performed with a #69 blade or the equivalent. It
is important to remember to scrape both the stromal bed as well as the
stromal aspect of the flap. Flap folds connected to the peripheral
epithelial ring are a special source of concern as they provide a
conduit for epithelial cells infiltration. Similarly, an epithelial
defect adjacent to the edge of the flap should be followed closely due
to the presence of high epithelial mitotic activity.
Which epithelium is safe to leave? Small epithelial pearls are usually
self-limited and do not progress. Epithelial tongues connected to the
flap edge are more worrisome, they do not need to be scraped unless
they exhibit a quick rate of progression or if they already
involving/threatening the visual axis.
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