Inferior Intrastromal Corneal Ring Segments in Paracentral Keratoconus With No Coincident Topographic and Coma Axis

PURPOSE: To assess the visual and refractive outcomes of implantation of intrastromal corneal ring segments (ICRS) in keratoconic eyes with no coincident topographic and comatic axes. METHODS: Forty-one keratoconic eyes of 39 patients with no coincident topographic and comatic axes were implanted inferiorly with a Ferrara-type ICRS (Keraring SI6; Mediphacos Inc., Belo Horizonte, Brazil) of 150 degrees of arc with a thickness of 150, 200, and 250 mu m. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), corneal coma-like root mean square, and residual refractive errors analyzed using vector analysis were recorded before and 6 months after the ICRS implantation. RESULTS: Mean UDVA was 0.76 +/- 0.41 logMAR before and 0.53 +/- 0.46 logMAR after surgery (P = .0006). CDVA was 0.13 +/- 0.14 logMAR before and 0.07 +/- 0.09 logMAR after surgery (P = .0007). Two eyes (4.9%) lost two lines or more of CDVA, 3 eyes (7.32%) lost one line, 16 eyes (39.02%) had no change in CDVA, 9 eyes (21.95%) gained one line, and 11 eyes (26.83%) gained two lines or more of CDVA. The safety index was 1.10. Spherical equivalent was significantly reduced after ICRS implantation (P < .001). Corneal coma-like root mean square changed from 0.80 +/- 0.53 mu m before surgery to 0.61 +/- 0.59 mu m after surgery (P = .02) for 4.5 mm of pupil size. CONCLUSIONS: One Ferrara-type ICRS of 150 degrees of arc with a thickness of 150, 200, or 250 mu m implanted inferiorly may reduce both astigmatism and corneal coma-like aberrations in keratoconic eyes with no coincident topographic and comatic axes, providing an improvement of UDVA and CDVA values.