The original intrastromal corneal segment design (Intrastromal Corneal Ring, KeraVision, Inc, Fremont, CA) was a 360° ring composed of polymethylmethacrylate.1
This was reconfigured as two separate 150° Intacs segments due to wound healing complications at the incision site directly overlying the ring and for improved ease of surgical insertion.1
ICRS were originally designed as an additive approach to treat myopia through reduction of the central arc length, which in effect flattens the cornea. The same premise has been applied to ectatic diseases such as keratoconus, pellucid marginal degeneration, and post-LASIK ectasia.2
In a study of keratoconus using confocal microscopy, Hollingsworth and Efron concluded that the clinical sign of Vogt’s striae is indicative of collagen lamellae under stress.7
The authors have noted the same phenomenon on confocal microscopy of keratoconic corneas with stress lines intersecting at the center of the cone (). The depth of these tension lines explains why ICRS segments work best when they are implanted deep within the stroma. The relief of the posterior lamellae may also explain why ICRS have been shown to slow progression of ectasia.5
Confocal microscopy of keratoconus showing the deep stress lines in the posterior stroma.
By increasing both the thickness and arc length of ICRS, a greater degree of cornea flattening has been observed.8
Although not approved in the USA, newer modifications of ICRS have recently increased the arc length available. The use of single 210° intrastromal corneal rings (Ferrara Intrastromal Corneal Ring [Ferrara Ophthalmics, Belo Horizonte, Brazil] and Kerarings [Mediphacos Ltd, Belo Horizonte, Brazil]) for keratoconus9
and pellucid marginal degeneration10
showed improved visual outcomes and corneal flattening, with less unpredictable astigmatic induction. In keratconous patients, a flexible intracorneal continuous ring (MyoRing ICCR, Dioptex GmbH, Linz, Austria) implanted into an intrastromal corneal pocket allowed for recentering of the ring postoperatively, to further adjust refractive outcomes.11
No studies have directly compared outcomes of continuous rings with ring segments.
The described coupling technique is another option to not only cover an extended arc length but also create a “purse string” effect of enhanced structural support. This may provide further and more uniform reinforcement to help delay progressive ectasia and refractive changes. Several authors have reported success with asymmetric ring segments, especially in inferiorly displaced cones in which a thicker ICRS in placed inferiorly with a thinner ICRS placed superiorly.12
Such asymmetric ring segments could also be coupled with suture to enhance and prolong the desired effect. The suturing of the ring segments together can better secure the planned position of the ICRS, without the undesired effects of migration. This could also potentially decrease complications of extrusion.
Clinical studies are needed to validate the proposed enhancement of coupling Intacs segments. If explantation is needed, after removing the joining suture under the original radial incision site, the attached segments could be removed together through one side of the incision site. Possible complications include cheese wiring of the suture through the islets or suture loosening, which may reduce the coupling effect over time.
The management of corneal ectasia is evolving with multiple intermediate alternatives before penetrating keratoplasty. ICRS technology is readily available and the surgical technique is relatively uncomplicated. The modification proposed here does not add significantly to the complexity of the technique. Further studies evaluating the effect of ICRS coupling in the clinical setting are needed.