Conic intrastomal relaxing incisions can correct difficult types of astigmatism
Conic intrastromal relaxing incisions (CIRI) for astigmatic correction, a new surgical procedure performed with the femtosecond laser, can correct different types of astigmatism that previously had been difficult to address, according to Dr Roberto Zaldivar, scientific director of the Instituto Zaldivar, Mendoza, Argentina.
The 6-month results indicated that the eyes were stable between the first and sixth postoperative months, with most eyes achieving improvements in the corrected distance visual acuity (VA) and none losing any corrected distance VA. Dr Zaldivar elaborated on his findings at the annual meeting of the American Society of Cataract and Refractive Surgery.
Different groups of patients have astigmatism that is not easy to resolve (i.e., those who have undergone cataract surgery or keratoplasty and those with dry eye) Dr Zaldivar commented. For example, after cataract surgery, which is now a refractive procedure treated with premium IOLs, there is a need for a less-invasive procedure to improve residual refractive errors and sensitive enough to correct small amounts of cylinder and sphere, he explained.
"Most complications in refractive surgery are due to problems that originate on the corneal surface," said Dr Zaldivar. "Because of this, we always aspire to perform an intrastromal corneal surgery."
Dr Zaldivar began to address these problems in a small study of 20 patients that he conducted in 2006. In this study, he used a femtosecond laser to make side cuts. The procedure resulted in more stable flaps and less strain on the cornea with use of an inverted bevel side cut at 120° compared with more vertical side cuts. This result was corroborated independently in 2007 by Dr John Marshall in a laboratory study.
Building on that previous research, Dr Zaldivar continued with the new CIRI procedure to refine the refractive process. Its advantages include an incision that is only intrastromal, with no damage to the epithelium; greater stability in the oblique incision; less denervation and, therefore, less dry eye; the ability to add more incisions; no intrusion into the optical zone; and it can be combined with intraocular procedures, such as implantation of an implantable collamer lens (ICL) and pseudophakic IOLs, Dr Zaldivar explained.
The CIRI procedure can be currently performed in patients with induced astigmatism after cataract surgery or implantation of an ICL and a low degree of mixed astigmatism as well as in eyes that have not undergone surgery and that have normal pachymetry and topography, those who underwent penetrating keratoplasty, those with asymmetrical astigmatism, those with pellucid dystrophy and keratoconus, and those who underwent other refractive procedures such as LASIK, PRK, RK, or a bioptic procedure.
He showed what the eyes look like immediately after surgery, at which time the gas bubbles could be seen. He pointed out that there are almost no data available regarding the intrastromal incisions and stability.