Keratoconus is a bilateral, progressive,
non inflammatory, degenerative disease characterized
by paraxial stromal thinning and weakening
of cornea resulting in a change in shape
of cornea from normal round to a cone shape.
The cause is unknown, but the tendency to
develop keratoconus is probably present
from birth. The extensive research sources
suggest that keratoconus likely arises from
a number of different factors: genetic,
environmental or cellular, any of which
may form the trigger for the onset of the
disease.
Keratoconus is thought to involve a defect
in collagen, the tissue that makes up most
of the cornea. Whatever the pathogenetical
process, the damage caused by activity within
the cornea results in a reduction in its
thickness and biomechanical strength.
The earliest symptom is subtle blurring
of vision. The patient becomes myopic but
the error of refraction cannot be satisfactorily
corrected with ordinary glasses owing to
parabolic nature of the curvature which
leads to irregular astigmatism.
The classic symptom of keratoconus is the
perception of multiple 'ghost' images, known
as monocular polyopia. The effect can worsen
in low light conditions as the dark-adapted
pupil dilates to expose more of the irregular
surface of the cornea. This effect is most
clearly seen with a high contrast field,
such as a point of light on a dark background.
Instead of seeing just one point, a person
with keratoconus sees many images of the
point, spread out in a chaotic pattern.
Treatment
There are various modalities of treatment
currently advocated:
Contact lenses
In early stages of keratoconus, spectacles
or soft contact lenses can suffice to correct
for the mild astigmatism. But as the condition
progresses, rigid gas-permeable lenses are
required to attain satisfactory degree of
visual acuity. RGP lenses provide a good
level of visual correction, but do not arrest
progression of the condition.
Scleral and semi-scleral lenses are larger
diameter gas permeable (GP) lenses. The
edges of such lenses rests on the sclera
hence they are more comfortable.
Surgical options
Corneal collagen crosslinking with riboflavin
Corneal Collagen Crosslinking with Riboflavin
also known as CXL, CCR, CCL and KXL is a
treatment developed at the Technische Universität
Dresden the early results of which indicate
that it may be the first treatment available
to actually stabilize the keratoconic process.
The aims of the treatment are to increase
the mechanical stability of the cornea and
its resistance to enzymatic digestion, by
inducing cross linkage between the corneal
collagen fibres. Photochemical collagen
crosslinking by riboflavin/UVA appears to
provide a simple, safe and technically easy
to perform outpatient surgical procedure.
The technique is performed as an outpatient
procedure under topical anaesthesia (eye
drops). As riboflavin does not penetrate
the epithelium (corneal skin), this is removed
using a blunt spatula (although some surgeons
advocate the use of minor epithelial trauma
only, as sufficient to allow riboflavin
penetration into the corneal tissue. Riboflavin
eye drops 0.1% are applied to the corneal
surface five minutes prior to the procedure
and then every five minutes during the procedure,
which involves, exposing the corneal surface
to ultraviolet A radiation (370nm) at a
radiance of 3mW/ cm2 for 30 minutes. At
this low energy level, UV wavelength and
using this concentration of riboflavin,
the technique has been shown to be safe
with no endothelial damage provided the
cornea is thicker than 400µm, with no loss
of corneal transparency and no damage to
deeper ocular structures.
Corneal ring segment inserts
A recent surgical alternative to corneal
transplant is the insertion of intrastromal
corneal ring segments. A small incision
is made in the periphery of the cornea and
two thin arcs of polymethyl methacrylate
are slid between the layers of the stroma
on either side of the pupil before the incision
is closed. The segments push out against
the curvature of the cornea, flattening
the peak of the cone and returning it to
a more natural shape, thus reducing or eliminating
morphological irregularities and existing
myopia and astigmatism. The procedure, carried
out on an outpatient basis under local anaesthesia,
offers the benefit of being reversible and
even potentially exchangeable as it involves
no removal of eye tissue.
In some cases, crosslinking may also be
successfully combined with other treatment
methods such as corneal ring segment inserts
and Keraflex, a new refractive correction
procedure. Corrective lenses may still be
required after these treatments but with
more normal prescriptions possible now,
and these newer methods may have an important
role in limiting deterioration of vision,
increasing unaided/uncorrected vision and
reducing the case for corneal transplantation.
Implantable contact lens/ ICL
Implantable contact lens also called as
ICL is a type of Phakic Lens. Phakic intraocular
lenses are specialized lenses made of plastic
or silicone materials, which are implanted
into the eye permanently to reduce a person’s
dependence on glasses or contact lenses.
They are called as Phakic lenses as they
are implanted into the eye without removing
the eye’s natural lens. The phakic lens
is inserted through a small incision and
placed just in front of or just behind the
iris.
The lens is soft and tiny, much like the
natural lens, but does not replace it. The
ICL is specially shaped to correct myopia/
hypermetropia/ astigmatism. Toric ICL’s
correct the cylindrical errors also thus
providing a very sharp vision
Other Operative procedure
Few cases of keratoconus will progress to
a point where vision correction is no longer
possible. For such cases various surgical
procedures are employed like corneal transplantation
and DALK transplant.
Keratoconus services at our centre:
We, at our centre, provide all options of
contact lenses available for keratoconus
patients. C3R surgery with Phakic IOLs that
provides a definitive treatment for vision
improvement is also available at our centre
with excellent results. |
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