Intrastromal corneal ring segment 355° arc length expands keratoconus options

April 1, 2015

Early experience with a new intrastromal corneal ring segment arc length appears to be a valuable addition to the keratoconus treatment armamentarium for one surgeon.


Take-home message: Early experience with a new intrastromal corneal ring segment arc length appears to be a valuable addition to the keratoconus treatment armamentarium for one surgeon.



By Luis Cadarso, MD, PhD, Special to Ophthalmology Times

Vigo, Spain-Thanks to developments in ophthalmic technology, patients with corneal ectatic conditions-including keratoconus, postLASIK ectasia, and pellucid marginal degeneration-are no longer limited to managing these disorders with glasses or rigid contact lenses.

Treatments, such as collagen crosslinking (CXL), toric phakic lenses, and topography-guided PRK, promise to help stabilize and regularize the cornea, and may even eliminate the need for keratoplasty.1,2

Intrastromal corneal ring segments

One of the most versatile treatment options for corneal ectasia is the use of intrastromal corneal ring segments (ICRS). These small arc-like implants reduce corneal steepening, improve uncorrected and best-corrected visual acuity, and reduce refractive errors. Implanting such a device may also help to stall or even circumvent the need for keratoplasty, thus also avoiding the numerous risks and complications associated with the procedure.3,4

An additional advantage of these implants is they can be explanted if either the patient or the surgeon is unhappy with the postoperative result. They may also be exchanged or repositioned, or combined with other treatment modalities, such as CXL, PRK, and phakic IOL implants, as required.5

At my center, a certain device (Keraring, Mediphacos Ltda.) typically is used. Although other corneal ring segments are available-(including Intacs, Addition Technology and the Ferrara Ring, Ferrara Ophthalmics)-this implant was specifically designed for the treatment of corneal ectatic disorders.

Additionally, the device is available in variable thicknesses (150 to 350 μm in 50-μm increments), arc lengths (90°, 120°, 1500, 160°, 210°, and 355°) and optical zones (5, 5.5, and 6 mm), which allows customized treatment according to patients’ needs. The implant has also a unique prismatic-design effect, which means light coming through the implant is reflected-reducing the incidence of optical disturbances, such as glare and halos.5

Expanded arc length

Until relatively recently, the device was available in arc lengths of 90°, 120°, 150°, 160°, and 210°. However, ophthalmic surgeons now have also access to a 355° arc length (Keraring 355°, Mediphacos). This arc length was designed specifically for the treatment of central nipple keratoconus by helping to improve central corneal flattening.

Available in thicknesses of 200 and 300 μm, the 355° implant has an optical zone of 5.5 mm and requires a minimum incision of 2 mm. Although manual implantation techniques may be used to implant other arc sizes, the 355° device requires use of a femtosecond laser to create the ring channel due to the required channel length.

Presuming correct parameters for the femtosecond laser are selected, implantation of the 355° device is straightforward-achieved by grasping the ring close to the incision and pushing little by little until it is completely inside the cornea and both ends are equidistant from the incision.

Several prerequisites exist for using the 355° device. Patients must have a central zone with low astigmatism, a Kmax of <70 D, and a central corneal thickness of >400 μm. The central zone of the cornea must also be transparent, i.e., 4 mm over the pupil.

For patients with a spherical equivalent of ≤6 D, I select the 200-μm segment, and for those with a SE ≥6 D, a thickness of 300 μm is used.

Early experience

Though it has become commercially available only recently, my experience with this new arc length is somewhat limited. However, outcomes in patients who have been implanted with the 355° arc length are promising.

Findings from a study conducted at my center-which included four eyes of four patients (aged 17 to 37 years) with central nipple keratoconus-showed that at the 1-month, follow-up visit, the mean uncorrected distance visual acuity (UDVA) had improved from 0.08 (preoperatively) to 0.19.

It was also found that that mean corrected visual acuity (CDVA) had improved from 0.4 to 0.55, and that the sphere and cylinder were reduced from –9.69 ± 5.7 to –4.88 ± 4.31, and from –2.38 ± 1.9 to –1 ± 1.41, respectively.

A significant corneal flattening effect also occurred, with a mean change in Kmax of -3.57 D at 1-month postoperative (Figure 1).

Thus far, no complications have occurred and patients are happy with their visual outcomes.

Additional findings

Other ophthalmic surgeons have also evaluated the efficacy of the 355° implant, although to date, few findings have been published.

Results from a case study of a 32-year-old-female patient with advanced central-nipple-type keratoconus-presented at the 2013 Congress of the European Society of Cataract and Refractive Surgeons (ESCRS) by Dominique Pietrini, MD-showed that the 355o arc length improved both UDVA and CDVA at 5 months postoperatively. Dr. Pietrini also reported that the patient had an 80-μm reduction in anterior elevation and considerable flattening of the cornea without inducing high amounts of astigmatism.6

Francisco Sánchez León, MD, an ophthalmologist based at the Centro Nacional para Corrección del Queratocono in Mexico, also has experience with the 355° device. Presented at the 2013 ESCRS meeting, data from his study that included 7 eyes of 4 patients with advanced central nipple keratoconus, showed that mean UCVA improved from 0.17 preoperatively to 0.5 at 6 months postoperatively. There was also an improvement in CDVA, i.e., from 0.47 to 0.65.

Dr. Sánchez León also reported that all eyes were within 1 D of the intended refraction. Additionally, the mean SE improved from –7.05 D (range, –4 to –8.25 D) to –0.59 D (range, –0.75 to +1 D) and there were no complications (unpublished data).

Clearly, more experience with this new arc length needs to be gained before definitive statements can be made regarding its efficacy and safety in the treatment of central nipple keratoconus.

However, findings from my own small study suggest that the 355° implant can help to improve visual acuity, reduce both myopic and astigmatic components, and flatten and regularize the central cornea. Certainly, this new arc length is a valuable addition to my keratoconus treatment armamentarium.



1. Corneal ectatic disorders (keratoconus and pellucid marginal degeneration). The Ophthalmic News & Education Network. Last accessed March 07, 2014.

2. Tan DT, Por YM. Current treatment options for corneal ectasia. Curr Opin Ophthalmol. 2007;18:284-289.

3. Tunc Z, Helvacioglu F, Sencan S. Evaluation of intrastromal corneal ring segments for treatment of keratoconus with a mechanical implantation technique. Indian J Ophthalmol. 2013;61:218–225.

4. Lovisolo CF, Calossi A, Ottone AC. Intrastromal inserts in keratoconus and ecstatic corneal conditions. In: Lovisolo CF, Fleming JF, Pesando PM, editors. Intrastromal Corneal Ring Segments. Canelli AT, Italy: Fabiano Editore; 2000. pp. 95–163.

5. Keraring intrastromal corneal ring. Mediphacos Last accessed, Aug. 11, 2014.

6. Pietrini D. Early experience with the new Keraring 355o. Presented the Congress of the European Society of Cataract and Refractive Surgeons, October 2013.


Luis Cadarso, MD, PhD


Dr. Cadarso is medical director at the Hospital Meixoeiro CHUVI, Clinica Cadarso, Vigo, Spain. Dr. Cadarso has no financial interests in Mediphacos Ltda.