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 0.05-mm increments)

• Intacs SK, with inner diameter of 6 mm, an oval cross-section shape and two different thicknesses (400 mm for steep K-value 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•

• Settings for Intralase femtosecond laser• IEK program

Pocket size: 8.5mmEnergy: 0.5Spot/line separation: 3/3Incision: 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• • • 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.• • • 355 Keraring specifications• Ring diameter is 5.7mm• Available in 200 microns and 300 microns•

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• 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

• 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!