It is fast becoming a more standard procedure for the surgical treatment of irregular astigmatism
Kerarings are currently available in 39 countries around the world, including Latin America, Europe, the Middle East and Asian countries. It gained the CE Mark in 2003, though has yet to gain FDA approval. The implant is approved for the treatment of keratoconus (stages I, II, III, IV) in contact lens intolerant patients or patients presenting with cone progression, pellucid marginal degeneration, corneal ectasia following LASIK, irregular astigmatism following radial keratotomy, irregular astigmatism following PK and corneal irregularity secondary to trauma.
The indications and limits of use for intracorneal rings has been evolving as experience of the technique grows. The mechanisms of action, improvements in the nomograms, surgical instruments and better use of the femtosecond laser have all led to refinements in the process.
As a result, it is now possible to implant Kerarings at a much earlier stage, in patients who are intolerant of contact lenses or for those whose keratometry (K) values continue to increase despite satisfactory contact lens fitting. In my experience, the best results in stabilizing ectasia and improving best correct visual acuity are obtained in patients with lower K values.
Managing the complications
In my experience the use of a femtosecond laser allows for a more precise, tight and uniform tunnel, achieving better reproducibility. However, there is a limit on the maximum tunnel depth that can be achieved with the femtosecond (400 μm), which could pose a problem in cases where a deeper channel is required. As with all techniques, there are some complications; the most common being the extrusion of one ring segment. When this happens, I recommend waiting for approximately 60 days before re-implantation. Infections can also occur and should be managed with the immediate removal of the ring and treated with the appropriate antibiotics. We have also witnessed rare cases of chronic epithelial defects, these must be handled adequately to avoid erosion and segment exposition.
Promise in astigmatism correction
The ideal technique is one in which the ring segments are implanted symmetrically, deep and far from the insertion incision. More recently we have been using the intracorneal rings to correct irregular astigmatisms after PK with very promising results. In this setting, we suggest using thinner segments to treat the superficial irregularity only, thereby preserving the refractive error and ensuring good final visual acuity.
The diversity of clinical applications, coupled with the safety, efficacy and reversibility of the technique and the combined use of the femtosecond laser, shows why intrastromal corneal ring segments have become a popular choice for ophthalmologists. It is also certainly true to say that it is fast becoming a more standard procedure for the surgical treatment of irregular astigmatisms for ophthalmologists around the world.
AUTHORLeon Grupenmacher, MD works at the Oftalmoplastica, Clinica de Olhos Curitiba, Brazil. He may be reached by E-mail: firstname.lastname@example.org