Food and Drug Administration clinical trials provided the most complete outcome analysis of Intacs for myopia. A total of 452 patients enrolled in these trials. Patients received 0.25-, 0.30-, or 0.35-mm ring segments to correct an average preoperative mean spherical equivalent of –2.240 D (range, –0.750 to –4.125 D). At 12 months postoperatively, 97% of treated eyes had 20/40 or better uncorrected vision and 74% had achieved 20/20 or better. In addition, 69% and 92% of eyes were within ±0.50 and 1.00 D of emmetropia, respectively. These clinical outcomes were similar to early results with photorefractive keratectomy (PRK) and LASIK, although excimer laser studies generally treated a broader range of preoperative myopia.
Figure 4-4 Rendering of the Intacs dissector tool as it is being rotated to create the intrastromal channel.
(Courtesy of Addition Technology.)
Additional FDA approval was later granted to include intermediate segment sizes of 0.275 and 0.325 mm. Internationally, CE (Conformité Européene) marking status (similar in concept to US FDA approval) was extended to thicker segment sizes. In 2000, Colin found that Intacs implantation compared favorably with PRK for treating low myopia, although it induced greater astigmatism.
The removal or exchange rate varies between 3% and 15%. A common reason for a ring segment exchange is residual myopia. Ring segment removal is most often performed because of disabling vision symptoms such as glare, double vision, and photophobia. Few complications are associated with ring segment removal. In a series of 684 eyes that received Intacs, 46 (6.7%) underwent their removal. Most patients returned to their original preoperative myopia by 3 months postremoval (73% returned to within 0.50 D of preoperative mean spherical equivalent). No patient had a loss of BCVA of more than 2 lines. However, up to 15% of patients reported new or worsening symptoms after removal.
Excerpted from BCSC 2020-2021 series: Section 13 - Refractive Surgery. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.