As a treatment for keratoconus, intracorneal ring segment implantation with Intacs (Addition Technology, Inc., Des Plaines, Illinois), Ferrara rings (AJL Ophthalmic, SA, Alava, Spain), or Kerarings (Mediphacos Ltd., Belo Horizonte, Brazil) has recently gained popularity in patients who are unhappy with their spectacle or contact lens corrected vision. Although Flemming et al¹ were the first to use Intacs for the correction of low myopia, Colin et al² pioneered its use in keratoconus.

Intracorneal ring segments flatten the conic cornea and shift the decentralized corneal apex more centrally. These segments may be implanted using mechanical microkeratomes, however, the advent of femtosecond laser now enables surgeons to create intracorneal ring segment tunnels using laser energy. Within seconds, any desired size and diameter tunnel can be created.

ADVANTAGES
The femtosecond laser has distinct advantages over mechanical microkeratomes. I prefer the IntraLase femtosecond laser (Advanced Medical Optics, Santa Ana, California).

Short time. The femtosecond laser creates a tunnel in a shorter time than a mechanical technique. What takes the mechanical microkeratome approximately 8 minutes may be accomplished with the femtosecond laser in approximately 8 seconds (Figure 1).

Less risks. Creating tunnels with the femtosecond laser means less (1) epithelial defect, (2) discomfort, and (3) risk of inflammation/infection. In a mechanical technique, the risk of epithelial defect—in turn causing discomfort, inflammation and/or infection—is much more than when a femtosecond laser is used. Rabinowitz et al³ studied the epithelial defects in two patient sets (ie, mechanical microkeratome vs femtosecond laser). On the first postoperative day, 50% and 15% of patients in the mechanical and femtosecond groups, respectively, had significant epithelial defects along with moderate-to-severe discomfort.

Uniform dissection up to 400 µm. Digitally changing the depth and the inner and outer diameters of the channel is easily viewed on the femtosecond laser screen. This may avoid the risk of perforation compared with mechanical microkeratomes. Using a mechanical technique, Kanellopoulos et al4 presented one case of anterior chamber perforation in 20 patients.

Good centralization. Another big advantage of the femtosecond laser for intracorneal ring segment implantation is its predictable centralization, which is important especially for rings with 5-mm optical zones (ie, Keraring, Ferrara ring). Centralization may be more easily achieved using a marker before applying the laser (Figure 2). After placing the vacuum ring and applanation to the cornea, we choose the central point at the exact place we want it. Some ring companies advise that the central point should be the anatomical limbus center; other companies advise the Purkinje reflex as the center. I, however, prefer somewhere in between the Purkinje reflex and pupil center.

Better symmetry. Better symmetry provides a better outcome. In a mechanical ring segment implantation method, if the vacuum is lost after the first tunnel creation, the second tunnel may be created at a different depth and location. Alternately, femtosecond laser tunnels are created simultaneously in 8 seconds, and the chance of loosing the vacuum is low.

Aseptic technique, low vacuum. The femtosecond laser gives a chance for aseptic surgery, because we have sterile disposable suction rings and cones for each eye. Additionally, the femtosecond laser also uses low vacuum. Approximately 35 mm Hg of vacuum is applied for 8 seconds, whereas in a mechanical technique, the vacuum pressure exceeds 50 mm Hg for a couple of minutes.

Customizing tunnel size. Customization of the tunnel is possible with a femtosecond laser. As previously mentioned, the depth of the channel as well as the inner and outer channel diameters is digitally changed with ease in femtosecond laser techniques. If we decrease the inner diameter of the channel after ring implantation, the ring pulls the channel distally. This effect may increase with narrower channels. Rabiniovitz et al³ showed that narrower ring segment channels produced a greater change in visual acuity and refraction.

We conducted a study with three groups according to inner and outer diameters.⁵ In group two, we made a narrower channel, and in group three, the channel width was same as group two, but the inner diameter was smaller. We found that a smaller inner diameter and narrower channel resulted in more effective results versus the other groups.

More effective. The femtosecond laser is more effective for intracorneal ring segment implantation than a mechanical technique. Several studies compared mechanical versus femtosecond laser techniques. Rabinowitz et al showed that with the exception of the change in surface regularity index, the laser group performed better in all parameters. When we compared our IntraLase results with mechanical spreader results at 1 year,^6,7 we concluded that results with the IntraLase were better.

OUR STUDY DESIGN
We presented a similar study at the recent 11th Annual European Society of Cataract and Refractive Surgeons (ESCRS) Winter Refractive Surgery meeting,⁸ in which 300 eyes (200 keratoconus patients ranging in age between 18 and 50 years) were included. The inclusion criteria were: keratoconus grades 1, 2, or 3; contact lens intolerance; and corneal thickness of at least 350 µm at the thinnest point and at least 450 µm at the incision site. Patients were excluded if the keratometer reading was higher than 65.3; the endothelial cell count was below 1,000 mm²; if the expectation for emmetropia was high; or if there was a presence of acute keratoconus, severe ectopia, corneal erosion syndrome, herpetic keratitis, corneal dystrophies, grade 4 keratoconus, hydrops, a BCVA of 0.05 or less, autoimmune diseases, and pregnant/breast feeding mothers.

Patients were followed postoperatively on days 1, 7, 30, 90 and then every 6 months. At each follow-up, the UCVA and BCVA levels were recorded. Topography with the Orbscan II (Bausch & Lomb, Rochester, New York) and ultrasound pachymetry were performed. All interventions were performed under topical anesthesia. The incision site was chosen as the steep topographic axis in all eyes. We measured the corneal thickness at the site of the incision and at several points on the circumference above the tunneling zone. Each incision length was 1 mm, and the depth was taken as 75% of the corneal thickness measured at 7 mm, where 400 µm was the maximum in all eyes. A femtosecond laser (IntraLase FS15-FS30) was used to make the corneal incision and segment channels.

The laser system was activated with previously loaded parameters for both tunnel and incision site. We did not wait for the bubbles to disappear before placing one 10-0 nylon suture—removed 1 month after surgery—toward the end of the procedure. I have found the U-suture technique to be effective at stopping segment migration (Figure 3). The surgery was terminated by placing a bandage contact lens, which was taken out the next day, over the eye.

OUTCOMES
In this study, more than 85% of eyes gained lines of UCVA, and more than 60% of eyes gained lines of BCVA. When we analyzed UCVA, there was a one- to two-line vision loss in 4.6% of eyes. Visual acuity remained unchanged in 9% of eyes, and 32% experienced a one- to two-line gain. Furthermore, 46% of eyes gained three to five lines, and 8% had a six-line or greater gain in vision.

A one- to two-line loss of BCVA occurred in 13.3% of the eyes, however, BCVA did not change in 25% of the eyes, and 32% experienced a one- to two-line gain. Twenty-six percent of patients gained three to five lines, and 2.6% experienced a six-line or greater gain.

The mean UCVA increased from 0.12 preoperatively to 0.38 postoperatively, and the mean BCVA increased from 0.42 postoperatively to 0.55 postoperatively. The mean spherical equivalent decreased from -6.50 D preoperatively to -2.02 D postoperatively.

Levinger et al⁹ reported that with the mechanical technique, the mean spherical equivalent improved from 3.88 ±1.64 preoperatively to -1.04 ±1.51 D postoperatively. In our study, the mean K-readings decreased from 48.7 preoperatively to 44.2 postoperatively. Colin et al¹⁰ showed that with a mechanical technique, the keratometer decreased by a mean of -4.30 ±-2.80 D from the preoperative readings.

COMPLICATIONS
Although we had no intraoperative complications in our series, a number of complications are associated with Intacs implantation. Migrations of the intracorneal ring segments (4.6%) (Figure 4), vascularization of the wound (1%) (Figure 5), and corneal melting/exposed segments (5.6%) (Figure 6) were the complications we encountered during follow-up. In 20 patients (6.6%), intracorneal ring segments had to be explanted.

Rabinowitz et al³ described an Intacs explantation in one patient who underwent implantation with a mechanical microkeratome. The segment extruded because it was placed too superficially, and the patient elected not to have it reinserted. In another patient who complained of continued visual fluction—persisting up to 1 year postoperatively—a penetrating keratoplasty was performed in both eyes. In the femtosecond laser group, one patient experienced loosening of the stitch on the second postoperative day. A gram-positive infection developed, and both segment edges were close to each other under the wound. The Intacs was removed.

CONCLUSION
Creating femtosecond channels for intracorneal ring segment implantation is a safe and effective treatment for keratoconus. We need more research to create nomograms on depth and size of the channels and ring selection to make this surgery safer and more effective.

Efekan Coskunseven, MD, is Director of Refractive Surgery Department, Dunya Eye Hospital, in Istanbul. Dr. Coskunseven states that he has no financial interest in the products or companies mentioned. He may be reached at +90 212 413 75 75 7201; efekan.coskunseven@dunyagoz.com.

1. Flemming JF, Reynolds AE, Kilmer L, et al. The intrastromal corneal ring: two cases in rabbits. J Refract Surg. 1987;3:227-232.
2. Colin J, Cochener B, Savary G, Malet F. Correcting keratoconus with intracorneal rings. J Cataract Refract Surg. 2000;26:1117-1122.
3. Rabinowitz YS, Li X, Ignacio TS, Maguen E. Intacs Inserts Using the Femtosecond Laser Compared to the Mechanical Spreader in the Treatment of Keratoconus. J Refract Surg. 2006;22:764-771.
4. Kanellopoulos AJ, Pe LH, Perry HD, Donnenfeld ED. Modified intracorneal ring segment implantations (Intacs) for the management of moderate to advanced keratoconus: efficacy and complications. Cornea. 2006;25:29-33.
5. Coskunseven E. Modification of the parameters in intralase to improve effect in keratoconus patients with Intacs. Paper presented at the XXIV Meeting of the European Society of Cataract and Refractive Surgeons; London; September 11, 2006.
6. Colin J, Cochener B, Savary G, et al. INTACS insert for treating keratoconus: one-year results.Ophthalmology. 2001;108:1409-1414.
7. Siganos CS, Kymionis GD, Kartakis N, et al. Management of keratoconus with Intacs. Am J Ophthalmol. 2003;135:64-70.
8. Coskunseven E. Results of IntraLase Intacs in 300 Keratoconus Eyes. Paper presented at the 11th Winter Refractive Surgery Meeting of the European Society of Cataract and Refractive Surgery; Athens, Greece; February 3, 2007.
9. Levinger S, Pokrov R. Keratoconus managed with intacs: one-year results. Arch Ophthalmol. 2005;123:1308-1314.
10. Colin J. European clinical evalution: use of intacs for the treatment of keratoconus. J Cataract Refract Surg. 2006;32:747-755.