Intracorneal ring segments (ICRS) are arc-shaped stromal implants made of which material?

Polymethyl methacrylate ICRS are small arc-shaped polymethyl methacrylate implants placed in a stromal tunnel to flatten and regularize the cornea.

On which segment properties does the central flattening produced by intracorneal ring segments depend?

Thickness and arc length Segments add material to the mid-peripheral stroma and, by arc shortening, flatten the central cornea; the effect depends on segment thickness and arc length.

What minimum corneal thickness at the planned tunnel site is usually required for intracorneal ring segments?

About 450 micrometers Indications include adequate thickness along the planned tunnel, usually not less than about 450 micrometers.

Which keratoconus patient may be better served by keratoplasty than by intracorneal ring segments?

A central scar in the visual axis ICRS need a clear central cornea; central scars, a very thin cornea or severe disease may be better treated by keratoplasty.

Contact lens intolerance with a clear central cornea

Moderate keratometry with spectacle blur

An inferior cone with adequate thickness

Why are intracorneal ring segments often combined with corneal cross-linking in keratoconus?

Segments do not strengthen the cornea against progression ICRS reshape but do not strengthen the cornea, so disease can progress; adding cross-linking gives more stable flattening and less progression.

Cross-linking anchors segments to prevent migration

Cross-linking thickens the stroma before tunnel creation

Segments alone always cause overcorrection

At roughly what depth is the stromal tunnel created for intracorneal ring segment implantation?

About two thirds of corneal thickness Through a radial incision at the planned meridian, the tunnel is made at about two thirds of corneal thickness, by mechanical dissector or femtosecond laser.

Immediately anterior to Descemet membrane

How are asymmetric keratoconus cones, with the steep area off centre, treated with intracorneal ring segments?

Segments of different thickness above and below the apex Asymmetric cones receive segments of different thickness above and below the apex, chosen from a nomogram.

A single full ring centred on the pupil

Two identical segments placed symmetrically

Segments placed only in the central optical zone

Which intracorneal ring segment complication is especially likely when a segment is shallow or near the incision?

Segment migration or extrusion Migration or extrusion is listed as a complication, especially with shallow segments or those near the incision; infectious keratitis around the tunnel is rare but serious.

What usually happens to corneal shape when intracorneal ring segments are removed for a complication?

The cornea returns toward its previous shape Segments can be removed or exchanged after a complication, and the cornea usually returns toward its previous shape.

The cornea becomes permanently flatter

The cornea develops irreversible ectasia

The cornea needs immediate keratoplasty

What is the realistic counselling goal of intracorneal ring segments in keratoconus?

Better vision and lens tolerance, delaying a transplant Counselling should stress improving vision and contact lens tolerance and delaying or avoiding a corneal transplant, not restoring normal vision.

Restoring fully normal vision without correction

Halting progression permanently without other treatment

Replacing the need for any future monitoring

Intracorneal Ring Segments: Indications and Results

Intracorneal ring segments (ICRS) are small arc-shaped implants made of polymethyl methacrylate that are placed in a tunnel within the corneal stroma to flatten and regularize the cornea.

Clinicians use them in keratoconus and in ectasia after refractive surgery, mostly for patients who can no longer wear contact lenses comfortably.

They improve the shape of the cornea, but they do not stop progression on their own.

What Are Intracorneal Ring Segments?

The segments are placed in the mid-peripheral stroma, and they add material to the periphery of the cornea.

Also, by the principle of arc shortening, this flattens the central cornea, and the amount of flattening depends on the thickness and the arc length of the segments.

Several designs exist, including Intacs, Ferrara rings, and Keraring, with different cross-sections and arc lengths.

Asymmetric cones, with the steep area off center, are treated with segments of different thickness above and below the apex, according to a nomogram.

Clinicians create the tunnel with a mechanical dissector or with a femtosecond laser, which gives better depth control.

Indications of Intracorneal Ring Segments

Keratoconus with contact lens intolerance and spectacle blur
Clear central cornea without scarring in the visual axis
Adequate corneal thickness at the planned site of the tunnel, usually not less than about 450 micrometers
Moderate keratometry, since extremely steep corneas respond less predictably
Post-LASIK or post-PRK ectasia (see post-LASIK ectasia)
Pellucid marginal degeneration in selected cases (see pellucid marginal degeneration)

Patients with central scars, a very thin cornea, or severe disease may be better served by other treatments such as keratoplasty.

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Intracorneal Ring Segments: Combination With Cross-Linking

Because segments do not strengthen the cornea, the underlying disease can continue to progress.

Many surgeons therefore combine the implants with corneal cross-linking, either at the same time or sequentially (see corneal collagen cross-linking).

Studies suggest that the combination gives more stable flattening and a lower rate of progression than segments alone, although the best sequence and timing remain debated.

Expected Results

In published series, ICRS reduce the steepest keratometry by several diopters on average.

They improve uncorrected and best-corrected acuity in many patients.

The effect varies between eyes, and some patients gain a few lines while others have little change.

Contact lens tolerance often improves, and a patient who could not wear lenses may be able to do so again.

The improvement may continue to evolve for months as the cornea remodels.

Complications of Intracorneal Ring Segments

Segment migration or extrusion, especially if shallow or near the incision
Infectious keratitis around the tunnel, a rare but serious event
Corneal thinning, melting, and stromal deposits near the segments
Glare, halos, and induced astigmatism
Neovascularization and persistent discomfort
Poor centration and undercorrection or overcorrection

Segments can be removed or exchanged if there is a complication, and the cornea usually returns toward its previous shape.

Intracorneal Ring Segments: Indications and Results

Counselling

Explain that the aim is to improve vision and contact lens tolerance and to delay or avoid a corneal transplant, not to restore normal vision.

Make clear that a cross-linking procedure may also be needed to stabilize the disease.

Discuss the possible need for glasses or lenses after surgery, and the small risks of infection and migration.

Planning the Procedure

The surgeon uses topography and tomography to locate the cone, to measure the corneal thickness along the planned tunnel, and to choose segment thickness and arc length from a nomogram.

Patients with a cone in the inferior cornea and a symmetric bow tie may receive one or two segments, while those with a central or asymmetric cone may receive different configurations.

Consider the patient’s contact lens history, the stability of keratometry, and the status of the fellow eye.

The Procedure Itself

Clinicians perform the operation under topical anesthesia, with a marked center, a radial incision at the planned meridian, and creation of a tunnel at a depth of about two thirds of the thickness.

The segments are inserted and positioned, and the incision is closed with a suture in some techniques.

Postoperative care includes topical antibiotics and steroids for a short period, with review in a day, a week, and a month.

Long-Term Follow-Up

Examine the segments periodically for depth, deposits, and any thinning of the overlying stroma.

Obtain topography at intervals to document the effect and to see whether the disease is still progressing.

If progression continues despite segments, plan cross-linking or other treatment without delay.

Informed consent should cover the chance that the implants fail to improve vision, the possibility of removal, and the need for continued monitoring of the disease.

Give patients the contact details of the clinic for any redness or pain after the operation, since infection around the segments needs immediate treatment.

References

Piñero DP, Alio JL. Intracorneal ring segments in ectatic corneal disease: a review. Clin Exp Ophthalmol. 2010;38:154-167.
Colin J, Cochener B, Savary G, Malet F. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg. 2000;26:1117-1122.
Gomes JAP, Tan D, Rapuano CJ, et al. Global consensus on keratoconus and ectatic diseases. Cornea. 2015;34:359-369.
American Academy of Ophthalmology. Basic and Clinical Science Course, Section 8: External Disease and Cornea. AAO; current edition.

Test yourself

A few questions straight from this article.

1 / 10 0 correct

Intracorneal ring segments (ICRS) are arc-shaped stromal implants made of which material?
ICRS are small arc-shaped polymethyl methacrylate implants placed in a stromal tunnel to flatten and regularize the cornea.
On which segment properties does the central flattening produced by intracorneal ring segments depend?
Segments add material to the mid-peripheral stroma and, by arc shortening, flatten the central cornea; the effect depends on segment thickness and arc length.
What minimum corneal thickness at the planned tunnel site is usually required for intracorneal ring segments?
Indications include adequate thickness along the planned tunnel, usually not less than about 450 micrometers.
Which keratoconus patient may be better served by keratoplasty than by intracorneal ring segments?
ICRS need a clear central cornea; central scars, a very thin cornea or severe disease may be better treated by keratoplasty.
Why are intracorneal ring segments often combined with corneal cross-linking in keratoconus?
ICRS reshape but do not strengthen the cornea, so disease can progress; adding cross-linking gives more stable flattening and less progression.
At roughly what depth is the stromal tunnel created for intracorneal ring segment implantation?
Through a radial incision at the planned meridian, the tunnel is made at about two thirds of corneal thickness, by mechanical dissector or femtosecond laser.
How are asymmetric keratoconus cones, with the steep area off centre, treated with intracorneal ring segments?
Asymmetric cones receive segments of different thickness above and below the apex, chosen from a nomogram.
Which intracorneal ring segment complication is especially likely when a segment is shallow or near the incision?
Migration or extrusion is listed as a complication, especially with shallow segments or those near the incision; infectious keratitis around the tunnel is rare but serious.
What usually happens to corneal shape when intracorneal ring segments are removed for a complication?
Segments can be removed or exchanged after a complication, and the cornea usually returns toward its previous shape.
What is the realistic counselling goal of intracorneal ring segments in keratoconus?
Counselling should stress improving vision and contact lens tolerance and delaying or avoiding a corneal transplant, not restoring normal vision.

Ahmed Ophthalmologist

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