Effect of intracorneal ring segment implantation on corneal asphericity

AIM: To evaluate the visual, refractive and corneal asphericity changes after intrastromal corneal ring segment（ICRS） implantation for visual rehabilitation of keratoconus.METHODS: A total of 42 eyes of 32 patients were included. After creation of intrastromal tunnels of 5.01±0.03 mm inner diameter, 5.71±0.03 mm outer diameter and at 384.21±34.12 μm depth, 1 or 2 ICRS of 150-300 μm thickness and 90°-210° arc length were implanted. Changes in uncorrected distance visual acuity（UDVA）, corrected distance visual acuity（CDVA）, refractive errors, mean simulated keratometry readings SimK;, anterior and posterior corneal asphericity values(Q;and Q;, respectively) measured with Scheimpflug topography were evaluated retrospectively. RESULTS: There was a significant improvement in UDVA and CDVA, along with a significant decrease in refractive spherical equivalent（SE）, cylinder and SimK;postoperatively（P<0.001 for all）. Mean Qant increased from-1.06±0.48 to-0.57±0.58 postoperatively（P<0.001）. Change in mean Qpost was insignificant（P=0.92）. Postoperative changes in UDVA and CDVA were not correlated with the postoperative changes in SE and cylinder（P>0.05 for all）; but were correlated with the preoperative SimK;and Q;values（P<0.001 for all）. CONCLUSION: ICRS implantation seems to approximate the anterior corneal asphericity of "advanced prolate" shape to "optimal prolate" shape and an "ideal Q value" of-0.46; which may have a role in improved UDVA and CDVA postoperatively, besides decreased refractive cylinder values.