INTACS
(intra-corneal rings) are polymethylmethacrylate
segments that are surgically fitted into the core
corneal stroma to even out
the central cornea. INTACS are currently manufactured
and marketed by Addition Technologies. More and
more eye specialists are choosing this optical
application for the treatment of various eye conditions
like keratoconus, “forme frusta” keratoconus
with mild myopia, post-LASIK ectasia, pellucid
marginal degeneration and cornea that is too fragile
for supplementary uplift after undergoing a LASIK
for myopia.
History of the development of INTACS
INTACS was initially manufactured by a company
named Keravision. It was originally designed
and approved by the FDA for the therapy of mild
myopia in the range of – 1 to – 3
Diopters. But with the invention of excimer
laser and laser-assisted subepithelial keratomileusis
(LASIK), INTACS became redundant. For LASIK proved
more accurate and easier to implement in various
refractive error conditions. Hence, Keravision
went kaput and INTACS were no more considered
a viable correction for myopia.
The use of INTACS for treatment of keratoconus
was pioneered by Dr Joseph Colin in France. In
2001, he released a one-year follow-up and recently
he came up with a five-year study on a selected
group of patients and both times he reported
effective results. Since his achievements, at
least five other research groups have successfully
proved the efficacy of INTACS for keratoconus
cure.
Recently, United States sanctioned the use of
INTACS for the treatment of keratoconus. However,
it comes under a human device exemption, which
permits its use only under the supervision of
a review group. Right now, 0.25, 0.275, 0.30,
0.325, and 0.35 mm segments of INTACS are manufactured
in the US. One can also get the.40 and 0.45 mm-sized
segments outside the US.
It has also been reported (at least 2 published
studies) that INTACS is an effective means to
correct astigmatism in patients with pellucid
marginal degeneration who have clear corneas
but are contact lens intolerant.
Latest developments in the implementation of
INTACS have suggested its potential use in performing
PRK on patients after an INTACS surgery on cases
with thick corneas and non-progressive type.
Symptoms and applications of INTACS
INTACS are applicable in the following conditions:
- Mild to moderate keratoconus with clear corneas
and contact lens intolerance
- INTACS is a desired
choice to penetrating or lamellar keratoplasty
for eyesight correction
- As a refractive remedy
on patients wearing either contact lenses
or spectacles. (However,
this is not permitted in the US since it
does not conform to the FDAs human device
exemption
approval)
- For treatment of forme fruste
keratoconus or patients with extremely fragile
corneas
whose
myopic error is less than 3D. In fact
it is a highly desired therapy since it is
safer when
compared to laser refractive surgery.
The surgical process
The surgical procedure consists of the following
pre and post-operative steps:
- INTACS selection
- Incision
- Surgery
- Post-operative care
INTACS selection
There are various sizes of INTACS available.
Hence, there are various possible permutations
and combinations of INTACS as well, for implantation
in the process of flattening of the core cornea
and astigmatism correction. What is best is that
whatever the combination used, there is always
some desired result.
Incision
There are a variety of theories and no standard
code regarding the place of the opening through
which the INTACS is inserted. A common recommendation
is to place the incision on the steepest axis.
Surgery
Originally the surgery was done using a mechanical
spreader, but now-a-days a femtosecond laser
(the Intralase) has come up as a close competitor.
The advantages of the femtosecond laser are:
- Enables easy
insertion of the INTACS
- Saves time
- Surgeon and patient friendly
- Ensures high
rate of certainty in INTACS placement, hence
deters superficial placement
and INTACS
wear and tear
- Allows easy reinsertion
of INTACS if the first attempts are disappointing
- Ensures speedier post-operative eyesight
recuperation
Post-operative care
The main issue in post-operative care is the
use of contact lenses and it is a highly challenging
and evolving process. Apart from a good surgeon,
one also needs a proficient contact lens provider
since lens intolerance is a major cause of going
for INTACS implants.
Right after the surgery a soft disposable contact
lens can be safely used. Usually a contact lens
of around 3D less than their preoperative spherical
equivalent is suggested. This ensures maximum
comfort and instant postoperative eyesight.
It is advised to use rigid contact lenses after
3 months, when the cornea is fairly settled,
the stitches have been removed and the wound
has healed. There have also been reports about
the effectiveness of customized lenses after
an INTACS surgery.
Disadvantages of INTACS
INTACS comes with its set of both intraoperative
and postoperative complications. Some of them
are:
- Puncture of the anterior segment and superficial
positioning of the INTACS
- Infection from
leaving the INTACS too near the edge of the
incision
- Erosion of the INTACS implant
since they keep hitting each other. This
results from
excess
rotation of the INTACS
- Halo and glare
in young patients
- Rare problems like constant
swelling, consistently unstable eyesight,
intraocular sensitivity,
photophobia, loss of UCVA, and loss
of BCVA.
