|
Treatment
There are no drugs known to
reverse or prevent
keratoconus, but patients
may be able to slow its
progression by refraining
from rubbing their eyes.
When spectacles or contacts
are no longer effective,
there are several surgical
options, including the
following:
Penetrating keratoplasty.
Full-thickness penetrating
keratoplasty (PK) is the
treatment most commonly
offered. Nearly 95 percent
of these procedures maintain
a clear and functioning
graft at five years. The
rejection rate appears to be
lower than that seen in
patients undergoing PK for
other indications. In spite
of successful surgery,
residual corneal astigmatism
and refractive error often
limits the corrective power
of spectacles and usually
requires additional
correction with a contact
lens. In addition to
irregular astigmatism,
complications after PK can
include allograft rejection,
a fixed, dilated pupil and,
on occasion, recurrence of
keratoconus. What causes
recurrence is unclear; it
may represent underlying
disease in the donor or
possibly progression of
disease.
Lamellar keratoplasty.
For patients who have
moderate keratoconus without
significant scarring, there
is renewed interest in
lamellar keratoplasty,
especially with the
precision, predictability
and convenience of the
femtosecond laser for these
cases.
Corneal ring segments.
Corneal stromal ring
segments (Intacs, Addition
Technology) are also an
option, particularly if the
patient demonstrates disease
progression with apical
displacement. These ring
segments consist of two
150-degree PMMA arcs that
are inserted surgically into
the cornea through a small
1.8- to 2-mm radial incision
created in the steep axis.
Adding ring segment
thickness to the
midperipheral corneal stroma
produces an “arc
shortening,” effectively
flattening the central
cornea. This results from
the corneal lamellae
extending from limbus to
limbus in a continuous
fashion with a new
alteration in corneal
curvature that is in
proportion to the ring
thickness. The thin,
ectatic, keratoconic cornea
is particularly amenable to
this effect.
Complications have primarily
been associated with the
insertion technique, but
technique has improved
greatly due to the use of
new equipment designed to
reduce the risk of poor ring
placement. Although the ring
segments lack great
predictability, most
properly selected patients
experience some improvement
in their uncorrected vision
and may regain contact lens
tolerance due to improved
corneal topography.
Recent studies have shown
that Intacs corneal ring
segment implantation is a
safe and effective treatment
for keratoconus, with
significant and sustained
improvements in vision as
well as improved contact
lens tolerance.2 Studies
have also compared placement
of single-ring with
double-ring segments. In
some cases, the single-ring
segment offers improved
astigmatic correction, but
the evidence is not
conclusive.3 Studies are
also under way examining the
combination of ring segments
with collagen cross-linking
using riboflavin activated
by ultraviolet irradiation.
Contraindicated
surgeries. LASIK remains
contraindicated in patients
with keratoconus due to the
possible risk of
accelerating the ectasia.
Surface ablation
photorefractive keratectomy
procedures are also
considered contraindicated
in patients with known
keratoconus; however, this
surgery is currently under
study in patients with early
disease that is considered
stable or slowly
progressive.
|
