Intracorneal ring segments: more is not always better

Coimbra, Portugal-Intracorneal rings (Intacs, Addition Technology) to correct keratoconus appear to produce better results when one ring segment is implanted inferiorly instead of having two segments implanted, one superiorly and one inferiorly, reported Joaquim N. Murta, MD, PhD.

"There are a number of approaches to treating keratoconus, such as contact lenses and various surgeries like intracorneal ring implantation, depending on the degree of the disease," said Dr. Murta, professor of ophthalmology, department of ophthalmology, University Hospital, Coimbra, Portugal. "The intracorneal rings were used first to treat patients with low myopia because the rings flattened the central cornea, the visual axis was untouched, and the procedure was reversible.

"Intracorneal rings were first used to treat keratoconus a few years ago, but there was a great deal of debate about the orientation of them and whether horizontal or vertical rings were more beneficial," Dr. Murta continued. "With the vertical orientation, there can be a number of associated complications, one of which is intense neovascularization of the cornea.

Dr. Murta and colleagues achieved good results in their early experience using different thicknesses of the segments in the inferior and superior portions of the cornea, namely, thinner segments superiorly and thicker segments inferiorly, which decreased the irregularity of the central cornea, he explained.

"However, we realized that in those early cases we improved the vision in patients when we removed the thinner superior ring segments," he said. "Moreover, in patients who experienced ectasia after LASIK, if we implanted just the thicker ring segment inferiorly, there was a great improvement in vision and in the regularity of the central cornea."

Based on this finding, he and his colleagues conducted a prospective study in which they evaluated the anatomic and functional results following the implantation of intracorneal rings (one versus two segments) in patients with keratoconus with clear central corneas and intolerance to contact lens wear.

Two study groups had 12 patients (12 eyes) in each. In the first group, the eyes received two intracorneal rings, the thicker (0.45 mm) placed inferiorly and the thinner (0.25 mm) superiorly. In the second group, the eyes received one 0.45-mm intracorneal ring segment inferiorly. Investigators evaluated the corneal topography, the uncorrected and the best-corrected visual acuity levels, the residual refractive errors, and the safety and the stability of the vision. All eyes had at least 12 months of follow-up, according to Dr. Murta.

The surgical technique was similar in both groups. The surgeon made a temporal incision (70% of the pachymetry) and dissected one or two intrastromal channels depending on the group. No intraoperative complications occurred.

"In both groups, there was always a decrease in K readings from the preoperative to the postoperative period at 12 months," he reported.

Differing results

Some major differences existed between the two groups, however.

"There was an increase in vision in both groups until the 6-month time point and then stabilization of the vision after that," Dr. Murta said. "In group 1, the vision went from 0.30 to 0.50 and 0.55 at 6 and 12 months respectively, and in group 2, from 0.42 to 0.72 and 0.75. In group 1 there were some patients who did not achieve an increase in vision over time."

The preoperative and postoperative spherical equivalents were similar in the first group. In the second group, there was a significant decrease in the spherical equivalent. There was an increase in visual acuity in both groups, but the increase in the second group was significantly higher than that in the first group. All patients in group 2 gained two or more lines of visual acuity. Eight percent of patients in group 1 had no increase in vision.

"Intracorneal ring segments significantly reduce the astigmatism from keratoconus," Dr. Murta concluded. "We believe that the use of one intracorneal ring implanted inferiorly appears to improve the visual, refractive, and topographic results when compared with patients who had two ring segments implanted."