Paired placement of ring segments results in variable effect

Issue: November 25, 2012

Implantation of two intrastromal corneal ring segments has a variable effect related to alignment relative to steep and flat topographic meridians, according to a study.

“Irrespective of the location of preoperative steep and flat keratometric meridians, the maximum reduction in astigmatism occurred when the incision and the segments were placed along the flat topographic meridian,” the study authors said.

The comparative case series analyzed 40 eyes of 40 keratoconic patients implanted with two 0.3-mm Intacs (Addition Technology). The patients were retrospectively placed in one of three groups: meridional, in which the incision site was within 30° on either side of the steep meridian; perpendicular, in which the incision site was within 30° on either side of the flat meridian; or oblique, in which the incision was more than 30° away from either meridian.

At 4 months postop, each group demonstrated a significant reduction in keratometric power (P < .01) but not in refractive error. The perpendicular group showed the greatest reduction in keratometric astigmatism (–2.67 D), followed by the oblique group (–0.9 D) and the meridional group (–0.65 D).

“Placement of the incision used for [intrastromal corneal ring segments] in the flat topographic keratometric meridian may be associated with a reduction in astigmatism, which although limited, is greater than alternative placement options,” the authors said.

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Source:

J Cataract Refract Surg. 2012;38(8):1432-1439.