Transcript Intracorneal Ring Segments (ICRS)

Intracorneal Ring Segments
(ICRS)
Alireza Baradaran-Rafii, MD
www.iranophthalex.com
• small pieces made of synthetic material that are implanted in
the deep corneal stroma with the aim of generating
modifications of corneal curvature and refractive changes.
• good outcomes with this kind of rings in low–moderate
myopic patients.
• In 2000, could reduce the corneal steepening and astigmatism
associated with keratoconus, being proposed as an additive
surgical procedure for keratoconus management.
• an interesting alternative aiming to delay if not to avoid
corneal grafting in ectatic corneal disease.
• Two main types of ICRS, different in
geometrical profile and diameter, Intacs and
Ferrara rings
Intacs segments
• a pair of semicircular pieces of polymethyl methacrylate
(PMMA), each one having a circumference arc length of 150°
and a hexagonal transverse shape
• an external diameter of 8.10 mm, an internal diameter of
6.77 mm and a variable thickness (0.25–0.45 mm, with 0.05mm increments)
• Intacs SK, with inner diameter of 6 mm, an oval cross-section
shape and two different thicknesses (400 mm for steep Kvalue of 57–62 D and cylinder <5 D; 450 mmfor steep K > 62 D
and cylinder >5 D)
Ferrara ring segments
• The cross section of this ICRS type is triangular with the aim of
inducing a prismatic effect leading to a reduction of photic
phenomena
KeraRings
• years later but specifically for keratoconus management
• These ring segments are mainly identical in design,
composition and thicknesses to Ferrara rings, but different
options of arc length are available in order to achieve a better
astigmatic control (90°, 120°, 160° and 210°).
• Each segment has an internal diameter of 4.40 mm and an
external diameter of 5.60 mm.
355 DEGREE KERARING
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• Settings for Intralase femtosecond laser
• IEK program
Pocket size: 8.5mm
Energy: 0.5
Spot/line separation: 3/3
Incision: 45 deg
• Femtosecond pocket should be made at a minimum of 300 microns (75%
of pachymetry)
• Indications:
Nipple keratoconus (central)
• Contra-indications:
• Corneal thickness less than 400 microns
• K readings higher than 70D
• Nomogram:
• 200µm thickness: for spherical equivalent < 6 D.
300µm thickness for spherical equivalent > 6 D.
• Minimum corneal thickness of 400 microns anywhere on the cornea
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• Important Information:
• The 5 degree break in the ring arc can be positioned along any axis but
recommendation is to position it along the incision axis.
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• 355 Keraring specifications
• Ring diameter is 5.7mm
• Available in 200 microns and 300 microns
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Bisantis segments
• The segment perioptic implants are four segments of 80° of
arc, with an oval cross-section, a vertical diameter of 250 mm
and a horizontal diameter of 200 mm.
• The only variable parameter is the amount of curvature of the
inserts to obtain optical zone parameters of 3.5, 4.0 and 4.5
mm.
Myoring
• a flexible, continuous, PMMA ring designed to correct
moderate and high myopia
• The diameter ranges from 5.0 to 8.0 mm, the thicknesses
from 150 to 350 mm and the width of the ring is 0.5 mm. The
anterior surface is convex and the posterior surface concave,
with a radius of curvature of 8.0 mm. The particular shape
and dimensions permit folding that makes implantation in a
pocket via a small incision tunnel possible
APPLICATION
• Keratoconus
• reducing corneal steepening and refractive errors in pellucid
marginal degeneration
• post-LASIK ectasia.
• Patients with contact lens intolerance are excellent candidates
for this surgery
• in post-penetrating keratoplasty corneas with recurrent
keratoconus
KCN
• better visual acuity, corneal topography quality and more
significant reduction in spherical equivalent after Intacs
implantation in less advanced keratoconus (relatively low
mean K 53 D and relatively low spherical equivalent) than in
advanced cases (mean K 55 D)
Indications
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Vision with H.C.L above 0.5 (functional visual acuity)
BCVA with spectacles above 0.3
K mean below 55 diopters
K max below 60 diopters
Corneal thickness above 400 microns at center
Transparent corneal center (4mm over the pupil)
Patients who cannot tolerate HCL (less than 8 hour use per day) or
tolerate HCL but wish to have better spectacles corrected vision
when not using lenses.
• Patient under 20 years of age who is a transplant candidate due to
keratoconus and has severe decrease in visual acuity, but because
of his young age CXL + corneal ring is performed and surgery is
postponed until the patient is older.
Nomograms
• Different approaches have been proposed for intacs
implantation in keratoconus, some of them based on spherical
equivalent refraction and others on topographic profile.
Number of segments
• one or two Intacs implanted according to corneal topographic
profile provided good keratometric and refractive results: one
inferior segment in inferior cones and two segments in central
cones.
• Sharma and Boxer Wachler established that single-segment
Intacs induced more physiological corneal shape changes and
better postoperative results in keratoconus and post-LASIK
ectasia than double-segment Intacs.
Surgical procedures
• mechanical and femtolaser-assisted
corneal incision
• there is no general agreement about which location is the
better option.
• Different reference points such as the temporal position, the
12 o’clock position (superior), on the axis of positive cylinder if
it was not 90° away from topographic axis, temporal location
and at the 1 o’clock position superior to the horizontal middle
meridian of the cornea and on the steepest topographic
meridian.
• Theoretically, the ideal position would be on
the steepest corneal meridian (most of the
surgeons)
channel size
• there is no uniform agreement
• There is an apparent trend about using Intacs with narrow
channels to provide better outcomes.
• However, Ertan et al. did not find differences in refractive
outcomes between keratoconus eyes implanted with Intacs
using wide (6.7 × 8.2 mm) and narrow (6.6 × 7.6
mm)channels.
• a regression of the achieved spherical correction was
observed in the medium–long term that implied that the
segments were useful for corneal remodelling, but not for
stopping cone progression.
• The ICRS implantation in keratoconus has been also
demonstrated to be useful for improving the contact lens
tolerance.
Intraoperative Complications
• Segment decentration, asymmetry of the
implants, inadequate depth of channel,
superficial channel dissection with anterior
Bowman’s layer perforation and anterior
chamber perforation.
Postoperative Complications
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ring segment extrusion
corneal neovascularization
infectious keratitis
mild channel deposits around Intacs
ring segment migration
epithelial plug at the incision site, corneal haze
around segments or at the incision site, corneal
melting, night halos, chronic pain, and focal
oedema around segments
Explantation
• Ring segment extrusion
• dissatisfaction with outcomes
Adjustment Surgery
• 10%
• often has a good outcome
• on rotation of one segment or explantation of
the superior segment.
intrastromal deposits
• accumulate in the lamellar channel after Implantation
• The incidence and density of these deposits increases with
segment thickness and duration of implantation and it
consists of intracellular lipids as cholesterol ester or
triglyceride.
Thank you for your attention!