Intracorneal ring segments: less is more

April 1, 2007

Intracorneal rings (Intacs, Addition Technology) to correct keratoconus appear to yield better results when only one ring segment is implanted inferiorly rather than two segments implanted, one superiorly and one inferiorly, explains Joaquim N. Murta, MD, PhD.

Intracorneal rings (Intacs, Addition Technology) to correct keratoconus appear to yield better results when only one ring segment is implanted inferiorly rather than two segments implanted, one superiorly and one inferiorly, explains Joaquim N. Murta, MD, PhD.

SPECIAL CONTRIBUTORJoaquim N. Murta, MD, Phd is a professor of Ophthalmology in the Department of Ophthalmology, University Hospital, Coimbra, Portugal. He has no financial interest in the technology cited in the article. He may be reached by E-mail: jmurta@netcabo.pt

"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. 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," he said. They 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. "With the vertical orientation, there can be a number of associated complications, one of which is intense neovascularization of the cornea. There was also a great deal of discussion surrounding the combination of the number of segments and the thickness of the segments to be implanted."

One ring versus two

Based on this, 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.

There were two study groups with 12 patients (12 eyes) in each. In Group 1, the eyes received two intracorneal rings, the thicker (0.45 mm) placed inferiorly and the thinner (0.25 mm) superiorly. In Group 2, the eyes received one 0.45 mm intracorneal ring inferiorly. The 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.

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.

One-ring group fared better

"In both groups, there was always a decrease in K readings from the preoperative to the postoperative period at 12 months," Dr Murta reported. There were some other major differences between the two groups, however. "There was an increase in vision in both groups until the six month time point and then stabilization of the vision after that. In Group 1, the vision went from 0.30 to 0.50 and 0.55 at six and 12 months, respectively, whilst in Group 2, it increased 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," Dr Murta explained.

The pre- and postoperative spherical equivalents were similar in the first group, as compared to the second group where there was a significant decrease. There was an increase in visual acuity (VA) 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 VA whereas 8% of patients in Group 1 had no increase in vision.

What's the conclusion?

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