A new double-arc intrastromal corneal ring segment may help to improve visual outcomes and rehabilitate the physiologic optical surface by remodelling the cornea
Take-home: A new double-arc intrastromal corneal ring segment may help to improve visual outcomes and rehabilitate the physiologic optical surface by remodelling the cornea
At a glance:
- ICRS help to decrease irregular astigmatism and corneal steepening
- ICRS also play an important role in regularising the corneal surface, thus rescuing optical function and enhancing uncorrected and best corrected visual acuity
- A new double-arc ICRS may be suitable for many types and severities of keratoconus; studies are been developed to define the ring parameters for best results in these cases
- Preliminary findings from a study with the second-generation Keraring show that the device reduced astigmatism and Kmax as early as 7 days postoperative
Keratoconus patients and their surgeons have several alternative treatments available to manage a condition that varies in severity, age incidence, presentation and evolution. Management options include special contact lens adaptation, collagen corneal crosslinking, intrastromal corneal ring segments (ICRS), toric phakic intraocular lenses and other techniques still under investigation. These treatments can be combined and tailored according to the patient’s individual needs.
ICRS improve visual acuity by decreasing irregular astigmatism and reducing corneal steepening. They represent a particularly appealing option for both surgeons and patients because the surgery involved is minimally invasive, and they can be removed or repositioned if necessary.1 The accuracy of the femtosecond laser provides the precision needed for the attempted tunnel depth, as well as the ring centration and location, which manual techniques could not give. Such technology represents an important landmark in ICRS implant surgery because it assures results as planned with a significant decrease in complication rates.
The second-generation ICRS
There are numerous ICRS available on the market, including Intacs (AJL Ophthalmic SA, Miñano, Spain), the Ferrara ring (Ferrara Ophthalmics, Belo Horizonte, Brazil) and the Keraring (Mediphacos Ltda, Belo Horizonte, Brazil). Many published studies describe outcomes with each ICRS; however, I believe that ICRS choice depends largely on the surgeon’s preference.
In my practice the Keraring is the ICRS of choice. There are several reasons why this is so. The Keraring is available in two models (SI-5 and SI-6) for implantation in 5.0, 5.5 and 6.0 mm optical zones and it has a unique prismatic shape that helps to reduce the incidence of postoperative glare and haloes. It also has a variety of arc lengths, including 340° and 355° arcs that are specifically designed for central and advanced paracentral keratoconus. Finally, surgeons can count on a large range of arc thicknesses (from 150 to 350 μm). Recently, Mediphacos assumed a pioneer position by developing a gradient-thickening ICRS (150/250 or 200/300 µm) for patients with regular but asymmetric keratoconus. Studies on this new model have started and the results will soon be available.
Now, there is the second-generation (SG) double-arc Keraring (Figures 1A, 1B and 1C).
This new arc reshapes the cornea, unlike the traditional single-arc Keraring. It may be thought of as a corneal endoskeleton with a known base curvature. The optical zone of 5 mm is bound to a surrounding arc of 8 mm that works as a pseudo corneal limbus.
[FIGURE 1A] The 330° second-generation Keraring.
[FIGURE 1B] The 330° second-generation Keraring in situ.
[FIGURE 1C] The 160° second-generation Keraring.
The first multicentre study on the SG Keraring is being conducted at the Federal University of São Paulo with co-partners at the Hospital Oftalmológico de Brasília.
I am currently undertaking two studies to investigate the SG Keraring. The first (Study 1) involves 40 eyes of 40 patients that were subdivided into two groups according to preoperative Kmax: <60 D or 61–75 D. A single 330° arc or two 160° arcs (depending on the amount of corneal astigmatism) were implanted. All arcs had 45 D curvature. In the second study (Study 2), only 330° arcs were implanted; 35 D or 45 D base-curve arcs were randomly assigned. One of the inclusion criteria in this second study was a minimum preoperative Kmax of 60 D.
[FIGURE 2] Implantation of the second-generation Keraring.
Preliminary findings from Study 1 (n=28) show that the SG Keraring improved corneal astigmatism and maximum curvature. Specifically, in the group of patients with a preoperative Kmax <60 D (n=15), mean Kmax was reduced from 59.55 D preoperatively to 57.94 D at 7 days postoperative, 57.48 D at 30 days postoperative and 58.88 D at 3 months postoperative. In the group of patients with a preoperative Kmax >60 D (n=13), mean Kmax was reduced from 63.84 D preoperatively to 63.02 D at 7 days postoperative and 62.20 D at 30 days postoperative. At 3 months postoperative, the mean Kmax was 64.32 D, perhaps because of the corneal remodelling effects.
There were significant reductions in corneal astigmatism as early as 7 days postoperative, by 57.1% (p=0.011) in patients with astigmatism >5 D and by 32.4% (p=0.027) in patients with astigmatism <5 D. In the group with astigmatism >5 D, mean astigmatism was reduced from 6.9 D (range 5.2–11.6 D) to 3.0 D at 7 days postoperative, 2.9 D at 30 days postoperative and 2.58 D at 3 months postoperative. In the group with astigmatism <5 D, mean astigmatism was reduced from 2.5 D (range 1.78–4.98 D) to 2.3 D at 7 days postoperative, 1.9 D at 30 days postoperative and 2.3 D at 3 months postoperative.
Overall preliminary findings show improvements in asphericity centration, significant astigmatism control and lowering of the myopic defocus following implantation of the SG Keraring.2
The ultimate aim of the current research involving the SG Keraring is to determine whether this ICRS can significantly enhance visual acuity with low rates of complications in all types and stages of keratoconus. We are now collecting the 1-year data and, although definitive statements on outcomes are difficult to make at this stage, on the basis of the preliminary data presented here I expect the 1-year analysis to corroborate the initial positive perceptions of this novel ICRS. It could be an effective treatment option for many keratoconus cases.
1. A.M. Gharaibeh et al., Cornea 2012; 31(2): 115-120.
2. Mediphacos Ltda. Data on file.
Dr Eliane Mayumi Nakano
Eliane Mayumi Nakano, MD, is head of the Refractive Surgery Division at Federal University of São Paulo, São Paulo, Brazil. Preliminary results of the study involving the SG Keraring were provided in collaboration with Dr Heitor Costa, Hospital Oftalmológico de Brasília, Brazil. Dr Nakano has no financial interests in Mediphacos Ltda.