Surgically induced astigmatism after implantation of intacs intrastromal corneal ring segments

To analyze surgically induced astigmatism (SIA) after implantation of Intacs intrastromal corneal ring segments.

Multicenter clinical trials in the United States.

Data from 11 investigational sites involved in the Phase II and III trials of Intacs for the United States Food and Drug Administration were retrospectively analyzed. The distribution of Intacs thicknesses implanted in 449 eyes was 0.25 mm in 148 eyes, 0.30 mm in 151 eyes, and 0.35 mm in 150 eyes. Refractive astigmatism was measured by subjective manifest refraction preoperatively and 1 week and 1, 2, 3, 6, 9, and 12 months postoperatively. The mean simple change in astigmatism and the surgically induced refractive change were determined by vector analysis.

Mean induced astigmatism at 12 months was 0.13 diopter (D) +/- 0.52 (SD). Induced astigmatism was more frequently with the rule (44%) than against the rule (26%) or oblique (30%). Maximal mean astigmatism was 0.50 +/- 1.09 D and occurred at 7 days. Mean induced astigmatism increased with segment thickness (0.01 D, 0.17 D, and 0.21 D for the 0.25 mm, 0.30 mm, and 0.35 mm segments, respectively). Mean surgically induced refractive change in cylinder power in all eyes at 12 months by vector analysis was 0.17 D x 92.

Mean SIA was not clinically meaningful 12 months after Intacs implantation.